Posts Tagged ‘e-Bay’

49’er & Fake Transistors

A recent posting to Yahoo's 'GQRP' reflector spurred discussion of the growing number of fake transistors being seen on e-bay. A builder enquired about the low efficiency noted in his recently built Chinese '49er' kit.

I recently bought one of the Chinese Forty-9er transceiver kits off ebay and on receive it works well. It certainly transmits, but the power is down to 800mW and the driver transistor is getting very hot. I'm not expecting a lot of power from it, but power claims are 1.8W to 3W. I'm more concerned about the hot driver transistor. The following link shows the circuit diagram.

http://www.ebay.com/itm/DIY-kits-Frog-Sounds-HAM-Radio-QRP1-8W-CW-Transceiver-Receiver-7-023MHz-/121507448525

I've checked for spurious oscillation (a problem I've had before), but can find nothing. Does anyone have any ideas for why the transistor is getting hot?

It was suggested that the transistor in the PA may not be up to specs and even be a 'fake' as these types are commonly noted on e-bay, selling for prices that are too good to be true.
 
Without taking a close look at your built kit, my suspicion would be the PA transistor. The schematic provided in the listing to which you provided a link shows a D882 as the PA transistor. This is a 2SD882 transistor is a garden variety audio amplifier transistor at best. Some data sheets show a fT of 100 MHz. These 2SD882 transistors are listed and sold by the handful on eBay for a couple of dollars for a dozen (plus and minus). Perhaps substituting a good quality better suited to RF duty transistor would be the ticket. Perhaps something like a 2SC1971. But before you start looking for listings for a 2SC1971 be aware of the fake ones that also quite prominent on eBay and sell for only a few dollars. On eBay search for "eleflow" this is brand name of a manufacturer who is making good quality substitute devices for a number of the popular CB and HAM radio PA transistors - user name on eBay is weazle66. His listing for this particular device is 27187465609 BUT you will pay as much for this replacement PA transistor as you did for the kit ... To find out more about some of these fake replacement transistors, search for "FAKE 2SC1969 RF transistor" or "FAKE NEC & MITSUBISHI RF TRANSISTORS" on youtube. The poster has a number of such video postings. Searching Google for "fake transistors" or such will turn up much interesting.

The problem was eventually sorted out by exchanging transistors:

Firstly, thanks for all your help. Initially, I replaced the Chinese PA transistor with a BD139 and that increased power output to 1.2W and reduced the heating of the driver. Key down and it took perhaps 20s to get "finger hot", rather than 10s. Tonight I changed the driver transistor to a 2N3904 as used in the original Forty-9er and the driver heating seems to have gone away. A small heatsink on the PA transistor allows it to run at 1.4W output for 30s of keydown without any drop in power or the heatsink getting any more than warm.
Thanks for all your help and I hope this helps someone else.

A search of Youtube videos shows several builders that have split some of the RF devices open in order to compare die sizes of suspected fakes with the real thing:


Earl Andrews, VE3GTC, has gone to considerable effort to test and compare many of his transistor purchases and indicates that there are a lot of devices coming out of China that are outright fakes and have no hope of meeting the specs that you might expect. His interesting website has a lot of details about testing as well as a very comprehensive 'for sale' list of reliable devices. Earl also suggests using caution when buying e-bay Chinese electrolytics as his measurements of ESR values indicate that many do not pass specs.

If you have purchased fakes or have found a Chinese source of the real thing, please let us know ... I'm sure there are plenty of dealers selling the real thing out there.

More e-Bay

This week, three items for the workbench arrived...one of them the wrong item, but instead of complaining, I'll keep it.

First off were some 40-pin male pc board breadboard header strips, standard spacing. These will come in handy for making connections to both pc boards or to perfboard. At a cost of ~8 cents per strip and free delivery, hard to beat.



Next were some 2-pin screw terminal block connectors ... nice for a finished-look on a pc board or perfboard power connection. These came in at ~12 cents per connector.



The third item I had ordered was a small pre-built LM317 regulator board as I hate building these and they do come in handy.


However, this was not what I received (a first!). Instead I received a similar-looking AF amplifier board. It is easy to see why they might get easily mixed up by someone quickly throwing orders together for shipping. The AF board was about twice the cost of the $1.43 LM317 board and I can probably use at least one of them in my next lightwave receiver project.


A final item was ordered, from the U.K., some 250 solder lugs for just under 6-cents each, including shipping.


These are becoming very pricey domestically and are even difficult to find at a good price on e-Bay. With the Canadian dollar taking a big hit lately, bargains are even harder to find ... but I think I did OK.

E-bay Resistors From China

During the past few projects I'd noticed a serious diminishing of my 1/4 watt resistor stock and decided to see what was available from e-Bay.

Many of the dealers in China were offering various packages at reasonable prices and it is hard to resist 'free shipping'.

After narrowing things down I decided on one particular dealer, electronics-salon, who had only five minor complaints in over 17,000 transactions during the past 12 month period. As well, he seemed to be selling only high-quality components, unlike many of the sellers from China.

The offering was for:

0 to 10M ohm 1/4 Watts Axial Lead Carbon Film Resistors Assorted Kit.
E-12 Series 86 Values, Total 860 Pieces (Each 10).
Resistance Tolerance : +-5%.
Rated Power : 1/4 Watt.
100% New, Never Used.
RoHS Compliant
.


With free-shipping, the cost was just over one-cent per resistor and would nicely re-stock my 1/4W trays as well as provide me with many more values to choose from than at present...hard to resist!

So...what happened?

Courtesy: http://www.ebay.ca/
The resistors arrived, packaged as shown, at the normal 'free-shipping' (slow) rate, which I don't mind. I selected three values to test and three samples of each value...120K, 68K and 8.2 ohms.
All resistors were within their 5% tolerance rating except for one of the 8.2's which measured 7.6 ohms... 2% out of tolerance.


I next smoke-tested a 680 ohm resistor for five minutes at slightly more than 1/4 watt dissipation. Measuring the resistor immediately after revealed that there had been no change in resistance.

Overall I am pleased with this purchase and would buy from this particular e-Bay seller in the future.

Building …. ’29 – Style


As mentioned in an earlier blog, the annual winter Bruce Kelley (BK) QSO Party, usually spurs some new construction of transmitters styled after those that were popular in the late 20's and early 30's. The main stipulation for entry into the two-weekend affair is that transmitters must be self-excited (no crystals) and use tubes that were available in 1929 or earlier.

Initially this might seem a difficult task, and that was my first reaction when first learning of the vintage operating event. Once I had learned more about these types of transmitters and actually listened to the BK action, I knew that it was something that I really wanted to do. After seeing several inspiring videos from Neil (WØVLZ) and Joe (N2OUV), demonstrating their homebuilt '29 TNT transmitters, I knew it was something that I really had to do! Perhaps the videos will grab you as well:


See more of this transmitter in action here.




One of the first things that might seem impossible to obtain would be a suitable tube that was available in 1929. Most of the tubes used in transmitters back then were designed for receivers, usually audio tubes that were pressed into RF oscillator or amplifier service. In the dirty-thirties, larger RF tubes were expensive and beyond the reach of most amateurs unless they had deep-pockets.

Tubes commonly found in BK transmitters are the type 10, 210, 45, 245, 27 and the 227. All of these types are still available today with some being more costly than others.

The most common tube is the type 10 or 210 which is also available in a military format, still NIB, as the VT-25. This is the same tube used in the WØVLZ transmitter.

This tube can easily handle the 10W power requirements imposed by the BK and then some.
Typical prices range from $50 and up.

The next most popular is the 45 or 245, which is pretty well maxed-out at around 5-7 watts. The cost of a 45 is about half that of a VT-25.


The widely available and inexpensive 27 / 227 will produce 2-3 watts of output...more than enough to work across the continent under normal conditions. The low cost (around $5) makes these particularly attractive for the first-time builder as a transmitter using a pair of these (or more) in parallel is an easy way to get started.



Here is a list of popular tubes that could be used for BK-eligible '29-style transmitters. There are probably more but these are the ones seen most often:


Suitable tubes are always available on e-Bay and from dedicated online tube-sellers. A quick Google-search will turn up several sellers, with prices and condition. Of course, one of the first places to look should be any of your ham friends with deep junk-boxes, especially those that have been building or amassing parts for many years. Check out the next ham fleamarket...especially those dusty old boxes under the seller's table. And...there are probably several hundreds of basements still filled with suitable old parts, just waiting to be liberated....seeking them out is all part of the '29 building fun.

Once a decision has been made to go forward with a '29 project, the first thing is to decide on the type of transmitter to build. There were three popular designs back in the late 20's, each with their own pro's and con's. I'll tell you more about these next and give you a few suggestions for getting started.

In the meantime, see what your 'oldest' ham acquaintance might have in his basement and keep an eye-out for any ARRL Handbooks from the early 30's as they are full of valuable building ideas....and you may wish to check-out K7JPD's ideas for finding old parts.

E-Bay, China, and Free Shipping!

I read about many homebrewers purchasing electronics from China on e-Bay. Many of these are major purchases such as test equipment, FM handhelds, antennas etc. The vast majority seem to be happy with their experience while some are clearly not.

I recently had the choice of buying from Chinese suppliers when shopping around for a new Rigol oscilloscope but must admit that I whimped-out when it came time to buy and chose to buy from a U.S. dealer who would also honour the warranty. I did end up paying slightly more, considering shipping and exchange rates but I do not regret my choice.

I have however made some smaller purchases from China, in an attempt to 'test the water'. I have seen some very attractive pricing on many homebrew-related goodies that would cost much more if purchased in North America and I reasoned that buying a few lower priced items would be a good way to test the quality. Politics aside and with a tiny bit of guilt, over the past few months I have purchased:

    2 packages of HSS 1mm drill bits for PC work @ 25 cents each from



3 solderless breadboard jumper-wire kits @ $5.50 each from




 
10 small HC49 28MHz crystals @ 18 cents each from

 


50 sheets of PCB thermal transfer paper @ 20 cents each from
 




5m of RG174 coax @ 30 cents / ft. from
 

I happily admit that in all cases, I have been very pleased with not only the quality of the items received but also in the service. With the high cost of shipping anything to Canada, I find the 'free shipping' for all of these items to be particularly attractive.

Although all of these items are available from many e-Bay sellers in China, I think it pays to carefully search feedback records before purchasing. In many cases, a high rating does not always tell the story. I look for high volume dealers that have very few complaints within the past year. Check what complaints are being made...if it is the quality of what is being sold, then go elsewhere, as some dealers do a high volume of selling junk while others have only single-digit or even zero negative feedback.

It will still be some time, if ever, before I feel comfortable buying any high priced items from China but if you were brought up in the 50's, you will probably recall when buying from Japan was an invitation for disaster and look how that turned out!


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