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, VE3AB, 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.