Tucker Transmitter is on the air.

[Opcom]

I have been real sick since then, not sure when I caught it but I think it's just a real bad cold and I might be getting better, maybe, so there's no way I'm going out in the cold building. Got the heat cranked to 78, and a pot of water boiling to keep the humidity up to 50% or so. Been in bed a lot.

suppressors in 3-500Z plates sounds good. There may be things I don't see on the scope. I can do that.

I want to change the bias supply to a low voltage variable unregulated bias and keep the front panel variac functional and original appearance.

Need to make a new supply something like 0-25V, a 2A bleed. The bias and screen supplies are all made on 19" panels that lie flat across 2 rails inside the TX. This should be simple and I can also keep the original around.

This way the layout can be preserved and a couple of high current low-L chokes can be used and make an LCLC filter similar to the existing higher-voltage one. Have not looked yet to see what is on shelves. A 2A bleed may be worthwhile considering the peak grid current allowable. The modulator bias meter is a 500V scale, but changing it is not mandatory, only changing the full scale needle deflection.

The original included driver transformer, a 40 watt CG-512, was made for tubes that use 2x the grid swing and 0.5x the grid current. It should be OK to keep using that because it's not near the power limit at all.

I realize it is shady to step up a 30W tube hi-fi amp's 4 Ohm output to 500 ohms using a power transformer then send it to a transmitter's 500 Ohm to modulator-grid-driver transformer, but there's already a plan for that and a backup.
I have a Norton amplifier with pp-par 838's driven by 6B4's and it has a 500 Ohm output, and there is also an Altec 1570b converted to a 1570x thanks to Bear sending me a 500 Ohm OPT for it. There is also a 500 Ohm output transformer or two around here if I want to build a speech amp from parts. The audio setup right now is temporary and was just for tests. There is an EQ and a couple of compressors, a Kahn phase rotator, and Altec mike mixer. There are a few audio bandpass filters, the typical +/-200 to +/-3500Hz types, as well saved from various equipments over the years. -so that all should help. I guess the audio is the second part of the overall thing.

I've read about "biasing on" a 3-500Z for class A SE audio purposes at lower range plate voltage in order to get the current up, example 1KV @ 400mA for SE class A. I'm not going to bias positive, I think. Keep it simpler.

Ok about the BC-939 rollers not being happy on QRO. They are big but not that big. The contact area is not the best on them either.

Thanks and happy new year! with I could be on the air, need to go get back in bed and get better.

[W2VW]

Just to be clear Patrick the 939 coils worked just fine until I used them on a really short doublet. This is uncommon.

Feel better.......

[Opcom]

The MFJ 989 tuner burnout finally got investigated. There is no real evidence that the balun got hot but it has not been completely removed and inspected and there is a slight stench. It is a 2:1 voltage ratio step-up balun. So, it makes 50 Ohms coming from the tuner into 200 Ohms for the dipole ladder line.

I bought two baluns from DX engineering. Toroid-type current baluns, not the ferrite bead ones.

measuring the antenna with a1:1 toroid core type 2-wire current balun shows me about 70-90 Ohms in most places of interest

The tuner sees 17-22 Ohms with its own balun. That is a burden of high current for it. 9.3A at the crest of the modulation cycle at legal limit. 4.1A at 500W.

measuring the antenna with a 1:2 toroid core type 2-wire current balun shows me about 15-25 Ohms in most places of interest.

This is similar to the tuner's balun result, but the measurement difference might be the voltage type vs current type + the individual antenna.

The larger stench is from the tuner's wattmeter/swr meter board. A 5-25pF trimmer capacitor caught on fire, and burning, fell loose from the soldering to the board. This might be repairable using a better cap. They used an inexpensive one. Also noticed was the tiny size of the coupler core and its very small center wire. That didn't burn though. I think it was peak RF voltage that blew up the meter circuit's trimmer cap. The tuner may not be able to tolerate high VSWR of 2:1 at its input at normal AM levels.

There was no real evidence of arcing or burning on the function switch, caps, or roller. It may be worth it to repair the tuner for use with lower power AM transmitters or sell it off to a SSB user.

Having looked at the MFJ coil and caps, it is easy to see the 939 military roller coils will be fine on a 1KW AM size tuner.