Posts Tagged ‘aa4oo’
Begali Intrepid
May 11th, 2023 | 
Author: The Perfect Bug?
In the Western World we are consumers. Advertising drives us to think we'd be a bit happier if we had that new "thing", whatever the thing is. It drives much of our economies and unfortunately keeps many burdened in debt.
That's certainly a pessimistic way to begin this but let's be honest. No one needs a ~$580 morse code key. Most of us are handy enough to make a straight key out of stuff laying around the house for free. I have a number of very fine keys that I've purchased used. I've purchased most of them for well under $70, including my 1970s Standard Vibroplex Bug.
So... having a key that is easy to operate; a key that disappears under your hand is an enjoyable thing.
Operating a Bug correctly, or more precisely in a manner that is pleasing to the person copying your code is more difficult than operating paddles with an electronic keyer. When the bug was invented it was a tool used by professional telegraphers. There were no electronic keyers, and having a tool that allowed them to send good code for hours on end with less mechanical stress on their bodies than a straight key was important, and they sought the best tool they could afford to allow them to do their work.
But no one reading this is a professional telegrapher, because that ship has sailed.
For those of us that choose to use a Bug, we do so for different reasons. For me, I enjoy the control I have in forming my characters, as well as the extra level of difficulty in sending good code. Why would I want it to be more difficult? Well, why do we do anything that is challenging. Being challenged is fun. It drives me to improve. It takes my mind off of things that might otherwise crowd my thoughts if I were not doing something challenging that is also fun.
I have operated a bunch of different bugs at my club gettogethers, from different makers. They all have a different feel. They all intrigue or annoy their user. I have two Vibroplex Bugs at my station. I've previously written about them. They each have advantages and challenges but they share the same design and they have more in common than they do differences.
A New Design
Fortunately for amateur radio operators there are still new keys being developed, and in this case a new design for a semi-automatic key that has a markedly different design from most of the bugs that came before.
The Begali Intrepid is distinctive in a few ways:
- The pendulum hinge is at the rear of the key rather than the middle
- The adjustments are all based on magnets rather than springs
- The dwell for the dits has a real control, rather than using various pieces of foam, string or clips to change dwell time
- The dit contact is a sprung plunger that always remains centered on the contact rather than brushing against it at various angles
- The split lever mechanism operates at the center of the key placing the DAH and DIT contacts much closer to one another than a traditional bug
- There is less mass in the pendulum itself than a Vibroplex Bug
- It has a sprung, nylon wheel damper that doesn't clatter
- It weighs a TON (well about 6 lbs) and feels welded to the desk without having to use non-slip material or using spit to semi glue them in place (yech, yes I use spit to hold my keys to my desk)
I've not had the chance to try the GHD fully automatic bugs, nor their bugs that use optical contacts. That would be interesting, but they still fundamentally follow the Vibroplex model.
You'll notice there are spare holes. I assume they are to allow the frame to be used for left handed operation.
Preparing for Use
The Intrepid ships with a cable but there's nothing to plug it into on the key. It's up to the owner to solder the connections. I understand that some transceivers require different plug wiring but in general they are fairly common. Be prepared to spend some time soldering under the key to wire it up.
I had some spare 1/8" plugs for projects, and with some heat shrink tubing and a couple pieces of wire I created a tidy connector for the male to male cable shipped with the key.
In Use
I spent about 2 hours practice sending into the practice oscillator that I built. I had a Vibroplex Deluxe Bug next to it that I alternated with. The range of DIT speeds on the Intrepid is impressive. Other makers like Vizkey have created bugs with a similar range of adjustment, and the Deluxe Bug I use has a Vari-Speed that can match the Intrepids speed range, bu the Intrepid is easier to quickly adjust and more importantly can be done one-handed. It will comfortably go from about 15 wpm up to 35 wpm and with the dwell adjustment makes changing speeds and keeping the DIT dwell correct, is singular. I don't think any bug can match it in that respect.
It did require a change in how I operate. The Vibroplex Bug fingerpieces stick out further and I have the habit of placing my index finger out over the top of the Bug. The Intrepid doesn't allow for that. I have to curl my index finger down to avoid hitting the bracing for the pendulum.
Because there is less mass in the pendulum it operates with a much lighter touch than Vibroplex Bug. The pendulm movement is initated with less force and due to the isolation of the pendulum from the paddles you don't feel the pendulum moving as you do with a Vibroplex. I kinda like the feedback I get from Vibroplex pendulum. The Intrepid feels more like a single paddle key with an electronic keyer than a bug.
Because of the how the lever is split in the middle, the actual DAH contact is almost dead center in the key rather than toward the front. It is far closer to the DIT contact than a bug. I have no way to describe it other than to say it feels as if the DAH and DIT operations are more similar than they are different.
I tend to pivot at my wrist when I operate a Vibroplex bug, to control the timing of DIT to DAH transitions. That doesn't seem to be as necessary with the Intrepid. Again, it feels more like a paddle than a Bug.
The DIT contact is a sprung plunger that is always centered. This is one of the biggest problem areas on a Vibroplex Bug and Begali has masterfully designed the proper contact. Most Bug operators spend more time adjusting the U-spring to try and get proper contact than any other part of the key. I assume this level of precision is just not something that Vibroplex wanted to spend the time on in manufacturing.
The sprung teflon damper makes for clatter free operation. No more ker-thunk as you transition from DITS to DAHS. They key is markedly quieter in operation than any other Bug I've tried. The only other key that comes close is the right-angle Vizkey.
Conclusions?
This is a very fine piece of engineering. It will take me months to decide if stick with it over a Vibroplex Bug, but for now I'm thinking it was a fine birthday gift.
That's all for now
So lower your power and raise your expectations.
Rich, AA4OO https://hamradioqrp.com
The Endurance of CW in Amateur Radio
CW Spans a Century
I've enjoyed using my "new" GRC-9 radio for making CW and AM contacts over the past month. During that time I've also discovered https://worldradiohistory.com/Archive-Radio-News/ which has magazine articles about radio dating back to 1919. Reading about amateur operators building and using equipment at the time where CW (continuous wave) was beginning to replace spark-gap operation in wireless communication made me consider just how enduring the ability to communicate using CW and AM have been.
Prior to the introduction of continuous wave transmitters and receivers, the detector used for spark gap communication would have made it difficult to hear a CW transmission (lacking a BFO). So, even though wireless transmission and reception of International Morse Code dates back earlier than 1919; employing CW (continuous wave) to send Morse Code seems to have began its popularity around that time. AM (amplitude modulation) phone mode was also in use at the time, and grew in popularity during the 40's and 50's until more efficient voice modes overtook it in popularity for voice communication.
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| Radio Telegrapher School for Enlisted Specialists 1921 |
What other modes have remained as popular standards using standard ham equipment and continuously in use by amateur radio operators as CW?
My GRC-9 was designed near the end of WW2 (circa 1945), and was in continuous production for various armed forces around the world until around 1974 (3 decades is a long production run). My particular unit has a receiver manufactured by Telefunken in 1955 and a Lewyt manufactured transmitter from 1966. I have made CW and AM QSOs with other amateur radio operators whose equipment ranged from home-brew xmtr/rcvrs, Drake and Collins radios as well as shiny new Icom 7300 and Flex radio systems.
A modern amateur radio (typically a HF model) can be used to communicate with radios built 100 years in the past. The same might be said for AM fone (phone), but that mode has become a niche for a much smaller set of enthusiasts.
There are lots of new and exciting modes of communication in amateur radio. Many are pushing the boundaries of weak signal reception, or alternatively allow for high transfer rates of data. But it is somehow comforting to me to consider that amateur radio hobbyists have kept one mode in particular, CW, popular and in continuous use for over 100 years using equipment that remains compatible to communicate with one another. I wonder if that will be the case in another century?
That's all for now, so lower your power and raise your expectations
Richard, AA4OO
AN/GRC-9 aka “Angry Nine”
AN/GRC-9 - Long lived military comms
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| My lovely (and radioactive) RT/77-GRC/9 |
I don't recall where I first read about the Angry Nine, but it captured my imagination. I read everything I could find about them and decided it would be great fun to operate such an antique on the ham bands. There is no logical reason to desire such a QRP radio. The low power output on CW is indeed, 5 watts and high power is a pileup busting 15 watts. The AM transmission are 1 watt and 7 watts respectively. That's almost QRPp for AM mode.
I'd had some experience restoring old tube equipment; my Heathkit HW-101, Knightkits VFO and Hallicrafters keyer, and I figured I'd take the next plunge and learn to use a receiver-transmitter combination and see how mobile high-voltage power worked from Vibrators and Dynamotors.
These radios seemed to have been more plentiful in the surplus market 10 - 20 years ago. Now you'll occasionally see one come up on eBay or other sites, but often times they are in very rough shape or the they are foreign language versions. I bid on a few auctions over the past couple of years and the bidding always exceeded my threshold for what I thought it was worth. The one above was part of an auction from an individual who had actually trained on these units prior to deploying to Vietnam. Later in life he became interested in finding one and spent time in military surplus warehouses going through pallets of equipment to find one in good shape. This particular unit is made up of a Lewt manufactured transmitter and a Telefunken receiver. The original owner preferred the receiver characteristics of the Telefunken over the Lewt manufactured model, so he paired the two.
Many of these old units are radioactive, due to the radium paint used on the front panels to make the lettering glow in the dark. This particular unit is off the lower scale on the Geiger counter and must be handled with care. Basically, I have to be careful to not touch my face with my hands after operating the unit and wash my hands thoroughly. Radium emits Alpha particles, which are not especially strong but the resultant radioactive dust from the front panel shouldn't be breathed or ingested.
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| Hot receiver, in more ways than one |
The AN/GRC-9 is a set of components primarily comprised of the RT-77/GRC-9 receiver-transmitter, capable of operating between 2-12 MHz in CW, MCW and AM modes. MCW is a modulated form of CW that can be received by radios that do not have a BFO (i.e. a normal AM receiver).
It is a mid to late 1940's design and was first documented field use in the Korean War, and was in active use through the Vietnam War and continued to be maintained in US military warehouses until 1974. It was in use by other nations long after, most notably the Dutch military.
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| Out of the case, tracing a low B+ power problem |
Power on the move
Designed to be used in the field, both vehicle mounted and carried by mobile infantry; there were a number of ways to supply power to the unit. There were a few different Vibrator/Dynamotor units, that could operate from common DC voltages of the time (6v, 12v, 24v) as well as a hand cranked, field portable generator.
Keep in mind that the state of the art at the time of its design used vacuum tube technology and in the case of the RT/77-GRC/9 it required the following voltages:
- Transmitter Plates -- 475 - 580 v @ 100ma
- Transmitter Filaments -- 6.5 - 6.6 v@ 2 amps
- Receiver Plates -- 105 - 120 v @ 45ma
- Receiver Filaments -- 1.35 - 1.5 v @ 500ma
- Keying Relay -- 6.0 - 6.9 v @ 575ma
That's a tall order for mobile and portable power supplies but designers in the 1940's were quite clever in packing power supply units. I managed to obtain both the hand cranked GN-58 generator with the base chassis and seat for portable operations, and a DY-88 for fixed / mobile operations.
DY-88 mobile power supply
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| DY-88 set to 12v powered by Amateur 12v supply |
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| Vibrator power supply for low B+ |
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| Power filtering |
I supply the DY-88 from either an RV battery or an amateur 12v power supply. When in Standby the DY-88 draws less than 1 amp, but placing the radio in Send mode switches on the Dynamotor which draws 12 amps @12v, without key-down and up to 14 amps on high-output key-down. It will drain an RV battery pretty quickly at that rate if the radio is left in Send mode, and works an amateur power supply pretty hard as well. So don't expect to operate remote off a battery alone for too long if your having lengthy QSOs. An added benefit of the DY-88 is that when the enclosed Dynamotor is running you'll have a nice extra 85 dB of generator noise to accompany your listening pleasure.
GN-58 portable field hand-cranked power supply
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| Generator head in carry bag |
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| NOS Shiny |
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| Deployed |
The GN-58 is a tough workout since it has to be cranked by hand at 60 rpm continuously. Obviously, you need a partner unless you can figure out how to crank it with your feet while sending CW. You will also want that partner to help you carry the GN-58, and the accompanying accessory bag for the chassis and seat. IT'S HEAVY. I haven't weighed everything, but according to the manual that came with the set, the radio / generator / accessories including antennas comes out around 120 lbs.
If you have a BC-48 battery hooked up then your human power supply can pause cranking while your receiving. I have a BC-48 battery enclosure that has been gutted of the original, long-dead material and replaced with 10x 9v batteries in series for the low B+ and two D-Cell batteries in parallel for the receiver filament supply.
Accessories
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| Bag of goodies |
The radio itself has a carry bag, as well as a bag for the GN-58 legs and seat, the vertical antenna, and miscellaneous.
There's another bag (shown above) for carrying power supply cables, keys, hand mic, long wire and doublet antennas, external speaker, torture device headphones, torture device in-ear phones, as well as a box of spare tubes for the radio.
If you're traveling in a squad sized group, then many hands make light work, otherwise you're going to be making a lot of trips hauling your QRP rig up the hill.
Headphones
These Western Electric headphones clamp tightly over your ears sealing out QRM and squeezing your head like a vice. After 10 minutes I was confessing to sins I'd never committed.
In order to use the headphones the RT/77 receiver must be removed from the case and an impedance switch on the back, changed from 4000 to 250 using a screwdriver. The ham I bought my set from had constructed a CW audio filter along with an impedance switch on an outboard box, that allowed the use of the headphones without switching the impedance on the receiver unit.
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| Homebuilt CW filter with impedance switch |
Speaker
The external speaker is a rugged, high impedance device (4k Ohms), that after all these years can still output audio at high volumes without distortion. It has a built in thumbscrew clamp that allows it to be attached to vertical or horizontal objects.
Alternately, the thumbscrew can be used in combination with the vice-like headphones to extract information from a prisoner.
Antennas
The AN/GRC-9 comes with 3 antenna systems; a multiple section, whip vertical for quick field setup and mobile use, a long wire that can be quickly deployed in a fixed station as a sloper, and a doublet for best reception, transmission in a fixed location.
For testing purposes I have my radio hooked up to my 80m Windom, which it tunes very nicely on 80m, 60m, 40m and 10m bands.
When the weather warms a bit I will be taking the radio out for some portable use and I'll try it out with the antennas that are part of the AN/GRC-9 set.
Spares
As a military radio, it was expected that repairs should be performed in the field when possible. The radio shipped with spare tubes for the receiver-transmitter, as well as spare tubes and vibrators for the DY-88 power supply.
More to come
In the few days I've had the AN/GRC-9 the only problems I've encountered have been related to the old DY-88 power supply. Old vibrators cans are generally seized up, as was the case with mine. Eventually mine became un-stuck after repeated applications of power but there are some methods to restore truly frozen ones using AC current and light bulbs (see Notes section below).
I've made about half a dozen contacts on the ham bands, including a 40m contact to a station in TX which is kinda DX for my locale. I've received nice signal reports. I've specifically asked stations about my "chirp" during QSOs and they've reported it as "not bad" and "charming". When operating from the VFO (master oscillator) rather than a crystal, the GRC-9 will "chirp". It was considered an acceptable design trade-off at the time. I've listened to the transmitter from a remote WebSDR station to hear the chirp for myself, and I agree that it isn't extreme and lends some character to the station. The unit does drift about 200 Hz during a QSO which I also think is quite acceptable for it's age. It's possible that if I spent more time in Send mode prior to a QSO to allow the transmitter tubes to warm up the drift might be lessened, but keeping the radio in Send mode puts quite a load on the power supply (both the 12v supplying the DY-88 and the human cranking the GN-58).
The RT-77 Telefunken receiver doesn't offer much in terms of selectivity and on a crowded band there's a lot of stations to contend with in the passband. The outboard CW filter deals with this nicely, but it is so narrow that when shifting from Send to Standby, the resulting frequency shift often throws the station I'm receiving out of the filter's passband, so that's a bit tricky.
The receiver's tuning knob also is very coarse, in that fine adjustments are made by breathing on the knob. However it has zero backlash, which is amazing in a piece of equipment this old. The markings on the receiver are in 50 kHz intervals so the only way to really figure out where you are is to look at RBN for your spot.
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| 50 kHz spacing when reading the frequency on the receiver Note the 7.2 is 7.200 MHz in the 40m band |
Images
Enjoy the pictures of the AN/GRC-9
Notes
Instructions for restoring a vibrator to operation
VB-1 and VB-7 are interchangable. I think I recall reading somewhere that VB-7 is a "lightweight" version of VB-1 but I won't swear to that.
The base is 4-pin, and the pin numbers are counted as on a vacuum tube with the same base. I wish I could post an image here without uploading it somewhere but if it's possible I've not figured out how to do it. The pins count clockwise from 1 to 4 looking at the bottom of the vibrator or the wiring side of the socket. The two large pins are 4 and 1 and the two small ones are 2 and 3.
There are two basic types of vibrators, called Series and Shunt. The Series type has a contact in series with the coil. VB-1, 7 and 16 are all Series types. I'll skip the Shunt type for now.
Pin 1 is common. Pin 4 is coil. Pin 2 is the NO (Normally Open) switching contact and Pin 3 is NC (Normally Closed). To test a VB-1/7, use an ohmmeter to check continuity from 1 to 4. If the reading is infinity, the coil could be open but this seldom happens. The problem is probably the vibrator contact. If the reading is a few ohms, connect +6 VDC to Pin 4 and -6 VDC to Pin 1. The vibrator should run. If it doesn't, most likely the contact is welded. About the only solution is to open up the vibrator, unstick the contact and try to burnish the burn marks out of the contact.
If the vibrator does run, go to the end of this screed and do the final test.
If the reading is infinity, here's how to use the two or three lamps to (usually) fix the vibrator. SAFETY NOTE: bear in mind you are dealing with either 120 or 220 VAC. If you jury rig the hookup, do all of your connections and disconnections with the "rig" not connected to the AC line. In other words, don't touch anything except the plug on the line cord or (if you go to that much trouble) the ON-OFF switch when the line cord is plugged in.
Connect the hot side of the AC line cord to one side of both lamps. Connect the ground side of the AC line cord to Pin 1 of the vibrator (or socket if you use one). Connect the other side of one of the lamps to Pin 4 and the other lamp to Pins 3 and 2. If you splurge and use three lamps, connect the "cold" side of the second and third lamps to Pins 2 and 3 respectively.
Check all the wiring and when satisfied all is OK, plug in the line cord. Probably nothing will happen immediately. Within a few minutes to a few hours lamp 1 should begin flickering and you should hear the vibrator hum. Run the test until the second lamp begins to flicker or until both the 2nd and 3rd lamps flicker.
If you are only using two lamps, when the 2nd lamp begins to flicker, wait 1 or 2 minutes then remove power (unplug the line cord). Connect the 2nd lamp only to Pin 2 and plug in the line cord. If the 2nd lamp flickers, remove power, move the 2nd lamp connection to Pin 3 and apply power. In either case (with the 2nd lamp now connected to pin 2 or 3 only), let the test run until the 2nd lamp again flickers.
For a final test, connect one lamp to Pin 2 and one to Pin 3. Connect 6 VDC to Pins 4 and 1. With the vibrator vibrating apply power to the two lamps. They should flicker alternately. Note that for this test, either use a 6 volt battery or a 6 VDC supply with both outputs not grounded. I wouldn't try to use the battery in the Jeep just in case you mis-identify which side of the line cord is grounded and which is hot.
Although a vibrator that is going to be fixed by this procedure will usually begin to work after say no more than half an hour, I have seen it take several hours. So if I have one that didn't start working fairly quickly, I'll let the test run up to about 8 hours max (or overnight) before giving up.
Robert
Gunner
USN Retired
MVPA 9480
Regulated voltage for Regenerative receiver project
Mr. Regula-tor
Building a regenerative tube receiver seems to have been a rite of passage for all hams of yesteryear. Although I built one from a kit (4-States QRP) as my first electronics project a couple years ago I thought I'd go for the real deal and build a vacuum tube regen receiver.
I'm building a design based around the 6SN7 tube. While I'm collecting parts and still locating a suitable chassis I decided to build a regulated power supply from the parts I have. Anyone familiar with electronics could probably whip this together in no time, but being the electronics newbie that I am, it is a slow process.
I'm using a transformer from a 1950's Heathkit VTVM V-7 that I parted out. It supplies the 6.3V filament voltage from one set of windings (yellow wires) those tested good. But the HV was an unknown as it was only half wave rectified when the transformer was used in the meter. That meter's rectifier and power cap had gone bad so I didn't know what condition the HV side of the transformer.
Breadboarded using a full wave rectifier created with 4 diodes, buffered by a 22uF electrolytic and a 10k resistor, I saw 189 volts, with no-load out of the high voltage side of the transformer. The amount of current the transformer could provide was still an unknown. I tested temporarily with a 2.5kOhm high wattage resistor and saw 56ma of current provided with a voltage sag down to 130V but the core of the transistor started heating up. Within half an hour it was over 120F so I discontinued that load test.
Fortunately, the regen circuit uses a ridiculously small amount of current for B+; about 4 to 5mA. Although I will likely change the audio side of the tube to deliver enough current for a speaker rather than the high impedance headphones in the current design, which may potentially double that to 10ma. For the first incarnation I'll stick with high-impedance headphones.
Fortunately, the regen circuit uses a ridiculously small amount of current for B+; about 4 to 5mA. Although I will likely change the audio side of the tube to deliver enough current for a speaker rather than the high impedance headphones in the current design, which may potentially double that to 10ma. For the first incarnation I'll stick with high-impedance headphones.
The regen power supply requirements called for [email protected] and 90V@4mA B+. The B+ voltage was based on using 10x 9V batteries and it stated that voltage wasn't critical but shouldn't fall much below 90V, going 12% above 90V should be OK.
Generally batteries are used with regenerative receivers because they are so sensitive to power supply noise, but I wanted to give the power supply a shot first and if it proves too noisy I can fall back to battery power for the B+ and just use the filament voltage provided by this transformer.
Since I have a OB2 voltage regulation tube I want to use. The OB2 regulates at 108V so that's what I'm going with. An OB3 would regulate at 90V, but I don't have one of those.
Generally batteries are used with regenerative receivers because they are so sensitive to power supply noise, but I wanted to give the power supply a shot first and if it proves too noisy I can fall back to battery power for the B+ and just use the filament voltage provided by this transformer.
Since I have a OB2 voltage regulation tube I want to use. The OB2 regulates at 108V so that's what I'm going with. An OB3 would regulate at 90V, but I don't have one of those.
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| OB2 in action... Glow baby, Glow! |
Calculating the resistor drop
A voltage regulating tube like a OB2 ionizes gas to maintain the voltage at the tube's specification. In the case of an OB2 it tries to maintain voltage at 108V. It requires a starting voltage higher than what it will regulate to, but ultimately can only dissipate so much current as it drops voltage. So, a resistor must be put in series ahead of the VR tube to limit the current it will have to dissipate. The resistor must be able to handle the current flowing through it, so that must be calculated as well.
The calculation for the dropping resistor resistance is:
Rdrop = (Vs - Vreg) / (Ireg + Isupply)So, in my case:
Voltage supply (Vs) = 189V
voltage regulation (Vreg) = 108V
regulator current (Ireg) the OB2 requires 5mA to do its job = 5mA
supply current (Isupply) the actual current required by the 6SN7 up to ~ 5mA
So, (189V - 108V) / (0.005A + 0.005A) comes out to a resistor value of 10,100 ohms. 10k is the closest standard size resistor and at 108V it should be able to dissipate 1.166 watts. So I'll need a 10k 2-watt resistor.
Parts is parts
Running the regulated power supply with a 10k Rdrop resistor for a few hours showed the transformer stabilize at 92F degrees at 70F amb. I was using a separate 27k 2-watt resistor to simulate the ~4mA load that the receiver will draw at 108V.
As you can see on the newly restored, trusty Heathkit VTVM; the voltage was holding steady around 108V. With that little current, the OB2 is not visibly glowing but with the lights out the violet colored ionization is visible.
Summary
I'm going to order a larger filter capacitor. The only one I had to test with was 22uF 360V and I'd like to use higher capacitance value of 47uF with a more appropriate voltage rating of 250V. I will also be adding 0.01uF caps at the input and output of the filter capacitor and I may add a 0.01uF across the OB2 pins 1/7 to further attenuate any RF noise.
With the current values I'm seeing 50mA ripple on my regulated voltage.
With the current values I'm seeing 50mA ripple on my regulated voltage.
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| A bit over 50mA ripple |
After I get the new capacitor and get the 0.01uF caps in play to filter out noise, I'll hook it up to the oscilloscope to check for ripple. I'll update the post at that time.
That's all for now....
So lower your power the old fashioned way, using a voltage regulator tube.
72/73
Richard, AA4OO
That's all for now....
So lower your power the old fashioned way, using a voltage regulator tube.
72/73
Richard, AA4OO
Metering High Voltage on the cheap
🗲 Heathkit VTM model IM-11 🗲
I recently got a taste for restoring and using vintage vacuum tube radio equipment. Using equipment that requires 800+ volts for making QRP transmissions is counter-intuitive to the spirit of QRP ham radio, but it's part of my journey as a ham, so I'm writing about it. Bear with me. Once I receive a near fatal shock I'm sure I'll move back to 12v powered equipment again.
Until then...
One of the first issues I ran into while testing the power supplies I restored for my vintage gear was how to measure voltages beyond the range of my digital multi-meter. Most consumer grade digital multi-meters (DMMs) can only measure up to 500 volts then display an error, or stop working altogether. Previously, I was able to measure voltages over 500V by making a voltage divider out of two 100k 1w resistors and taking my measurement from the middle of the two resistors, but it was precarious in use and added even more danger when working with this old equipment.
I'd looked at getting a DMM capable of measuring high voltage, but the recommended ones, like a Tenma 72-1055 Benchtop Digital Multimeter, start around $100. Used Fluke meters are even pricier. I'm sure buying a more professional DMM would be a wise investment. As I've evidenced many times; wisdom is omitted from my DNA.
So what did hams of yesteryear use?
Behold... Vacuum Tube Volt Meter
Vacuum Tube Volt Meter
This Heathkit VTVM model IM-11 was available at my local Hamfest (Rarsfest) for 5 dollars.Debugging
Five dollars is not a princely sum, but as with most things purchased from a hamfest, it required some attention.
The 55 year old 16uFd@150V paper, electrolytic power filter capacitor was likely a ticking time bomb so I replaced it with a modern capacitor for safety concerns. The closest one I had was a 33uFd@160V radial electrolytic. I don't think double the capacitance will be a problem for a filter capacitor, it will just make the transformer work a little harder when it's first turned on. I calculated the initial charge time and it's 393ms vs 190ms for the original cap. I think the 10k resistor and transformer can handle the extra 200ms heavy load on power up.
A few wires inside the meter had come loose from some very sparse solder points and a one intermittent connection in the range switch was especially troublesome to track down.
The biggest mystery to solve was oversensitive resistance readings in the Ohms mode. I replaced the C-cell battery in the battery cup and while I had it out I glanced at the + connection for the battery in the cup. I appeared to have oxidized at some point in the past and was discolored. I scraped it off until I saw shiny bits and thought all was good. I spent more time tracing the circuit and thought I had a problem with the switch itself or the 9x resistors in the range circuit, as suggested in the troubleshooting section of the manual. The problem turned out to be that oxidized bolt head that formed the positive battery connection in the battery cup. Scraping it had not provided electrical contact. In fact, when I removed the bolt (after having to disassemble the circuit board from the meter for the 2nd time), I filed down the head of the bolt and could find no conductive metal left. I'm guessing that a former leaky battery had converted the entire head of the bolt to a very hard, yet non-conductive material. I've never seen anything like it before and it proved to be a useful lesson.
I had to find a replacement bolt and that lead to working on my lawn mower and then mowing the yard... not sure how that progression occurred... Eventually I got the new bolt in the cup, the circuit board re-installed. Ohms tested accurately, put it all back together and noticed the #50 pilot lamp had stopped working (sigh). I removed the innards from the case one more time and got the pilot bulb settled (I think it's required to balance the filament circuit). While I had it apart for the umpteenth time, I decided to reconnect the 1/4" plug that a former owner had disconnected while keeping their original modification allowing 1 mega-ohm to be switched in for the outermost probe when DC functions are selected but switched out when AC or Ohm functions are chosen. I wanted to allow use of an original VTVM probe used in the 1/4" plug with its built-in 1 mega-ohm resistor.
Whew!
All-in-all, I probably spent 8 hours getting all the functions on my $5.00 meter to work, replacing old parts, undoing mods and aligning it for proper DC and AC readings. It's a good thing I don't count my time in the cost of these projects, otherwise I could have purchased a couple Fluke meters for the cost of my time.
What's the fun in buying something that works right the first time when you get it home, huh? Are we hams, capable of solving problems, or appliance users? Actually, it would have been nice if it worked without new parts and repairs, but I digress.
The 55 year old 16uFd@150V paper, electrolytic power filter capacitor was likely a ticking time bomb so I replaced it with a modern capacitor for safety concerns. The closest one I had was a 33uFd@160V radial electrolytic. I don't think double the capacitance will be a problem for a filter capacitor, it will just make the transformer work a little harder when it's first turned on. I calculated the initial charge time and it's 393ms vs 190ms for the original cap. I think the 10k resistor and transformer can handle the extra 200ms heavy load on power up.
A few wires inside the meter had come loose from some very sparse solder points and a one intermittent connection in the range switch was especially troublesome to track down.
The biggest mystery to solve was oversensitive resistance readings in the Ohms mode. I replaced the C-cell battery in the battery cup and while I had it out I glanced at the + connection for the battery in the cup. I appeared to have oxidized at some point in the past and was discolored. I scraped it off until I saw shiny bits and thought all was good. I spent more time tracing the circuit and thought I had a problem with the switch itself or the 9x resistors in the range circuit, as suggested in the troubleshooting section of the manual. The problem turned out to be that oxidized bolt head that formed the positive battery connection in the battery cup. Scraping it had not provided electrical contact. In fact, when I removed the bolt (after having to disassemble the circuit board from the meter for the 2nd time), I filed down the head of the bolt and could find no conductive metal left. I'm guessing that a former leaky battery had converted the entire head of the bolt to a very hard, yet non-conductive material. I've never seen anything like it before and it proved to be a useful lesson.
I had to find a replacement bolt and that lead to working on my lawn mower and then mowing the yard... not sure how that progression occurred... Eventually I got the new bolt in the cup, the circuit board re-installed. Ohms tested accurately, put it all back together and noticed the #50 pilot lamp had stopped working (sigh). I removed the innards from the case one more time and got the pilot bulb settled (I think it's required to balance the filament circuit). While I had it apart for the umpteenth time, I decided to reconnect the 1/4" plug that a former owner had disconnected while keeping their original modification allowing 1 mega-ohm to be switched in for the outermost probe when DC functions are selected but switched out when AC or Ohm functions are chosen. I wanted to allow use of an original VTVM probe used in the 1/4" plug with its built-in 1 mega-ohm resistor.
Whew!
All-in-all, I probably spent 8 hours getting all the functions on my $5.00 meter to work, replacing old parts, undoing mods and aligning it for proper DC and AC readings. It's a good thing I don't count my time in the cost of these projects, otherwise I could have purchased a couple Fluke meters for the cost of my time.
What's the fun in buying something that works right the first time when you get it home, huh? Are we hams, capable of solving problems, or appliance users? Actually, it would have been nice if it worked without new parts and repairs, but I digress.
Back to the story
This meter can measure up to 1500 Volts 🗲
The main reason I purchased this is to measure the high voltage in my tube equipment power supplies and 1500 VDC should just about cover it.
Although this meter uses a C-cell battery for measuring resistance, it runs off service mains to power the tubes which control the meter circuitry, so it must be plugged in to be used.
Although this meter uses a C-cell battery for measuring resistance, it runs off service mains to power the tubes which control the meter circuitry, so it must be plugged in to be used.
I love the look of its old "Gran Tran" power transformer inside the VTVM. They just don't make'em like they used to.
Wiring, lots of wiring
This model was made by Heathkit, from 1961 through 1968, and used typical point to point wiring of the time, making circuit tracing loads of fun.
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| Point to point wiring makes for interesting circuit tracing |
Shiver me timbers, it's got decks
It also refers to "front half" and "rear half". The "half" is referring to a side of the deck, so in the case of "front half" it refers to the side of a particular deck facing the front of the instrument, while the "rear half" is the side of a deck facing back (or toward you).
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| Clever voltage divider circuitry, what could possibly go wrong in this triple stack of wafer switches? |
The left knob controls on/off and meter functions while the right knob controls the rather elegant voltage divider.
A knob for every function and a function for every knob. NOTE: do not plug your headphones into the 1/4" jack on the front unless you want to experiment with personal electro-shock therapy. Better, yet, don't plug your headphones in there.
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| Not clearly shown in this photo, voltage divisions up to 1500 volts supported |
"...Weighed in the scales and found wanting"
Ok, how many of you understand that completely unrelated biblical reference?
I haven't used a meter like this since I used to plan my VFR flights using an E6B. My modern, digital multi-meter is fairly idiot proof in terms of reading the results. My DMM auto-ranges and displays the correct unit of measure along with the reading on its display. It works well for a dummy like me.
A VTVM on the other hand, has a number of scales that must be interpreted based on whether you are reading DC, AC or Ohms. Additionally, you have to pay attention to the range chosen.
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| Choose a reading... any reading, just use the correct scale Note: the needle isn't at zero in this photo because I had just plugged it in before taking the picture and the tubes hadn't warmed up. Ah, the joys of vacuum tube powered equipment |
The voltage markings for the range switch refer to the full scale reading. Resistance is the top scale, but let's ignore that because we're talking about measuring voltage... The second scale from the top is Voltage. Even though it appears to refer to DC for the numbers on the top and AC for the numbers on the bottom of that second scale that's not what's going on. The second scale is for both DC and AC. The numbers on the top are when you are using a range that is a multiple of 15, such as 0-1.5V 0-15V 0-150V 0-1500V. The numbers on the bottom of that scale are for the ranges using a multiple of 5, such as 0-5V 0-50V 0-500V. Clever eh?
You have to do a bit of math. For example, if you if you're using the 1.5V range take your reading and move the decimal place one to the left. So, a reading of 8 would represent 0.8V in the 1.5V range, while it would actually represent 8V in the 0-15V range and 80V in the 0-150V range, etc. See, hams were smarter in the 1960s.
Always start with a range larger than what you expect the voltage to be and reduce the range for a more accurate reading if it occurs in the lower 3rd of the range. The voltage divider set by the range knob is protecting the circuits so if you have it in too low a range and apply high voltage, bad things will likely occur.
Old school needle gauge. There's a lot going on behind that needle. It operates very smoothly.
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| Sporting some temporary probe hookups |
Making probes
This meter did not come with probes. I bought another older VTVM pretty cheap, for parts from a famous auction site because it was advertised as having a full compliment of probes, but alas, they were not usable. Even the 1/4" plug from those probes was a bust. However they did come with rebuildable probe "ends"
I used a RG-58 cable as the high voltage DC wire using only the center conductor and grounding the shield even though it is not used as the ground return. I also placed a 1/4 watt 1 mega-ohm resistor at the tip of the probe to limit any current through the probe cable. That cable terminates in the 1/4" plug and is wired such that it is out of the circuit in the Ohms position. I secured the cable into the probe body with some glue and used two layers of shrink wrap as a strain relief. I also put some shrink wrap near the probe tip as a bit of extra insurance.
I used a spare DMM cable for the outer positive banana plug feed used by the AC and OHMS circuit and made a heavily insulated cable with an alligator clip for the ground probe that goes to the other banana plug.
The outer probes are used for measuring resistance, AC and low volage DC. The center probe is used only for high voltage DC positive. Both positive probes would not be connected at the same time (as they are in the image below), and would present a shock risk if they were both connected when measuring voltage.
Summary
If you need a way to measure high voltage or are looking for a really eccentric meter to make common measurements harder than they should be get one of these VTVMs. They seem to be commonly available at hamfests and on famous auction sites for under $10.
Dazzle your friends next time they ask you to measure something for them, by whipping this not-so-little-puppy out of your back pocket and powering it up. As you're making your measurements quietly repeat "Mmmm, yes. Mmmm yes, I see now". They'll have no idea what you're referring to and be quite impressed.
That's all for now...
So lower your power and measure it with the low-range on your snazzy Vacuum Tube Volt Meter
72/73
Richard AA4OO
Remote VFO – Knight V-44
Everyone needs a remote VFO from 1955
Late night eBay surfing, and poor judgement led me to bid on a Knight V-44... and unfortunately won it...
The 1955 remote VFO was unique because it had a built-in power supply. It's also interesting that its base oscillation frequency is in the 160m band. Using harmonics from the base frequency means it doubles for each subsequent band (x2 for 80m, x4 for 40m, etc.) That doubling means it also multiplies the drift. Specified drift is 300Hz an hour. That doesn't sound too bad, but multiply that by x6 up in the 10m band and holy-smokes, it's drifting 1800Hz an hour.Note to self: Never browse eBay just before you go to sleep
That's gonna make operating CW like a game of chase, or hide and seek after every exchange.
This is gonna be fun.
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| Surprisingly the big dial is actually operating the variable cap through a reduction gear and it's very smooth |
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| Uses 4 tubes. Power supply up top, VFO circuits in the bottom to minimize impact of heat from the PS. |
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| Power supply |
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| old electrolytic power filter cap must be replaced |
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| 10k 7watt resistor had failed |
Replacement bits
The 450v electrolytic cap must be replaced for safety reasons. All the other components measured within 10% of specifications except for the 10k 7w resistor connected to the OA2 tube. It had gone up into mega ohms of resistance, which is likely when the VFO was taken out of use.Handwritten notes inside the chassis indicated the VFO tubes had been replaced in 1977. Until I get the replacement parts for the power supply I won't know the condition of the tubes.
Plans
Surprisingly, it outputs 10 volts of signal, so I may also build an output filter and use it as a QRPp transmitter on its own.
The possibilities are endless.
Update 3/21
Repaired
The replacement parts arrived from Mouser... A 500v 47uF electrolytic capacitor and a 10k Ohm 7-watt resistor. The new high wattage resistor is tiny compared to the giant, defunct resistor that was in there before, and of course the capacitor was about 1/3rd the size of the original. I used some spaghetti on the capacitor leads since the lead lengths were so much longer with the replacement cap. So the power supply section was now repaired.I also replaced the 2-blade, non-polarized, ungrounded, un-fused 1950's power cord with a 3-pin grounded plug and added a 1-amp/250v inline, replaceable fuse. So hopefully there's a reduced risk of death or fire now. Electrical safety didn't seem to be foremost on the minds of kit builders 60 years ago. The size of the 3 wire power cable and it's much thicker insulation didn't fit the opening in the back of the VFO as both the power cable and the VFO output come through the same hole, so I had to remove the insulation and use heat shrink to get things to fit. Additionally the large in-line fuse holder didn't fit well inside the VFO housing so the wiring is quite a bit more cramped in there than it was before.
After the components were replaced and the wiring was complete I plugged it in... no-smoke. Then I flipped the repaired switch (the phenolic disc for the on-off switch was broken in half when I received it), and wallah! The indicator light lit up through its pretty little blue jewel eye. So I knew the transformer was supplying 6.3v for filament. I heard a low hum from the little transformer and then the tubes began to glow. The OA2 was glowing it's pretty violet color, and no bad smells were emanating. I was ready to button it up and begin calibration.
The sparse instructions directed me to back out the tuning slug for the 80m band nearly to the end and screw in the slug for the other bands all the way, so I did so. I set the trimmer caps C1 and C2 to their fully engaged positions.
I carefully re-installed the front face holding the VFO and PS sections it in its heavy-duty case, taking care to get all the new power cord/fuse wiring inside the VFO section from binding up on the sharp edges of the case as it went in. In screwed in the plentiful 10 screws that holds it together and Bob's your uncle. Well, maybe Bob isn't your uncle but I just wanted to say that.
I had already attached an RG-58 coax to the output inside the VFO and run it out the hole with the new power cord, so I then installed a BNC connector on the end of the RG-58 to make hookup easy. I like BNC connectors because they are secure and I have lots of adapters for different connectors. I then connected the VFO output to my Elecraft CP1 RF coupler and terminated the other end with my ugly dummy load. I connected the RF coupled cable to the Oscilloscope and turned everything back on.
Calibration
I let it warm up 20 minutes or so. The cabinet does not get very warm, just about 15 degrees above room temperature. That's actually a good thing, from what I've read. If the VFO is at room temperature then it's more susceptible to the variations of that room temperature. Having the case stabilize above room temp can make the VFO more stable.I had my frequency counter attached to an output from the oscilloscope. In the 80m band setting with the VFO dial set to 3.5 Mhz the freq-counter was reading around 1.75'ish. The VFO primary oscillation roams around the 160m band and generates the first harmonic in the 80m band. The freq counter had trouble tracking due to all the harmonics, and the output on the oscilloscope was not very pretty because it was showing the primary frequency with the first harmonic interfering.
I was unable to properly calibrate the VFO using a frequency counter, due to the interference from the harmonics, so I turned on my SDRPlay, software defined radio. It can display up to 10 mHz bandwidth but for this test I was displaying 2 mHz bandwidth so that I could easily see the harmonic for the band I was calibrating.
That made quick work of calibration. I adjusted the variable capacitor C1 (near the bottom left hand side of the VFO) for the 80m band and adjusted the one above it for the remainder of the bands. I was able to verify that adjusting the VFO dial in the CW portions of the bands was extremely accurate with regard to frequency.
It appears to work like a charm. I hooked up a key and even sent some test messages and listened to them on the SDR. I'd been advised to not key the VFO directly because it tended to chirp but frequency stability was much better than I expected. Over the course of an hour that I was calibrating I saw very little drift after the initial warm-up.
Here's a little video demonstrating the completed calibration...
That's all for now .
So, warm up your Tubes and spray some RF into the air.
73
Richard ,AA4OO
Need a Vacuum Tube?
Superstore for Vacuum Tubes
When I started restoring my Heathkit HW-101 I thought it might be difficult to find replacement tubes. I initially only looked on eBay for tubes but then I was directed in a boat anchor forum to the vacuum tube superstore... findatube.com
Bob Dubush offers tubes at prices well below what you'll find on eBay. When you order from findatube you'll receive NOS (new open stock) tubes in their original boxes and may receive them in a nifty original store display box... Ah I can smell the 1950's
So if you've been looking for a good source for all your classic vacuum tube needs visit...
That's all for now...
So fire up that high voltage power supply and warm your shack the old fashioned way
73
Richard AA4OO
