Speaking of Turkeys I had one, or so I thought. The Turkey of which I speak is a Drake TR-3. This radio was a Christmas gift from my son and his XYL several years ago. It was a tech special, and I did get it working but it just didn't seem right!
I thought given my time constraints today, this might be something I could attack a small piece at a time. Two problems remained. The first was to get the 9 MHz BFO crystal on just the right frequency so that the LSB and USB crystal filters would work properly. It all boiled down to a deft touch on the zeroing trimmer. This was a long-drawn-out process, but I finally got there.
The second problem had me stumped! While the receiver worked it seemed deaf. I could hear signals, but you had to crank the volume wide open. A check of all the tubes and a tube swap of the four 12BA6's (all in the receiver) did not change a thing. An item on the schematic (almost hidden) finally came to my attention.
This item is a #12 light bulb. I am guessing its purpose is to act like a fuse. I suppose because the TR-3 was intended as a Mobile Rig, should you get too close to a RF Signal it would light up or blow and your rig would be protected. This would also work for a lightning strike with the antenna connected which is more likely the reason.
Should also mention this light bulb is inside the RF cage right near the antenna terminal. Most TR-3's did not have a cage cover so dangerous HV is present. Mine had a cover likely from a TR-4. This bulb plugs into a two-pin socket.
I pulled the cover off and removed the bulb to see if it was open. For some unknown reason I powered on the radio and found that the signal levels were as before with the bulb installed. Boom it must have been a burnt-out bulb. No! A check with the Ohm Meter and the bulb was good!
The antenna circuit passes through the bulb on receive and then to Transformer T9 which is shared with V7 (12BA6 RF Amp) and the 12BY7 Driver tube. My thoughts were a bad T9. So, I plugged the #12 back into its socket and put the cage cover back on. Turning on the radio suddenly was a pleasant surprise! The receiver was blasting out signals at low volume levels and I could even hear signals on 10M.
So, what happened? My theory is that the two pins had oxidized over 60 years and were a high resistance. Inserting and reinserting the bulb cleaned things up. It is a Turkey no more.
Thus, another not so obvious light bulb problem as I had with a Ten Tec Trition II.
Now I see why the Drake TR-3 was such an innovation and threw down the gauntlet to the Collins KWM-2. A PTO with 1 kHz linear dial readout at half the cost sure made for great marketing fodder.
BTW Bill, (N2CQR), the PTO is not solid state like in the TR-4 but uses a 6AU6 and has been found to be pretty stable.
73's
Pete N6QW