[The problem is under loading in order to give the modulator a break is not helping.
The mod xfmr ratio is too high and a higher load impedance (less I same V) of the 6146 trio is headed in the wrong direction to provide headroom for the mudulator.
Dave,
I have had this same discussion with many others, many times. all that I can tell you is that with My Valiant, it works for the better. As many times as we have worked, you have heard my Valiant many times. No one has ever complained about how it sounds. When I load it to 360mA it sounds like a typical valiant, at 275mA it sounds quite good.
Under loading changes the impedance that the modulator plates see, but the turns ratio of the iron is still the same. So, lighter loading does increase the impedange that the modder plates are lookin into, but in some cases this works for the better and looks in your favor.
In extreems, too light of a load can kill a transformer, but in this case the loading on the transformer is still sufficient to suppress the transient spikes from the voice peaks.
All I know is that it works for me, and I have been running my Valiant that way for many years without any problemz.
Frank,
Another scheme which may have some merit is to put some additional voltage on the modulators. I believe currently Johnson only puts maybe 650V on the modulator tubes. Just adjust the static resting current accordingly for the proper class of operation. You can put quite a bit of voltage on 6146's without any issues. Many ways to do that, but a very simple way is to add a pair of HV SS diodes to the secondary of the Valiant's HV CT xmfr. Then run those diodes into a large value filter capacitor network. That should produce greater modulator voltage to easily permit 100% modulation. The final supply would still utilize the choke input supply so nothing would change there. They use just a plain hi C filter network all the time in linear amps and the modulator demands would be similar to that. The key is to have enough C to support not only the peak modulator current but to reduce any ripple component to an acceptable level. My goal would be to keep everything inside and not any drilling and blasting. An inrush circuit should be utilized in the primary to limit peak rectifier current at turn on due to the added Hi C cap bank. As long as primary voltage PTT was not used the inrush circuit could be cheap and dirty with a properly rated thermistors although I prefer a relay shorting out a primary inrush resistor after the filter capacitors are charged.
Joe, W3GMS
