[R-390] QSK; standby reduced fil. voltage; separate B+ on/off

[Shoppa, Tim]

OZ1UF wites:
> 1. Does anyone have experience with an alternative idea for full QSK R-390A operation; ie. to avoid the clacking relay noise.

My conclusion is that break-in or QSK meant something different to the military than it does to hams. Or maybe that relay is just a relic of some spec written early on but which could never have done a CW op any good.

The clacking of the relays on every dit is just insane.

The full break in solution for the 390A should be just the same as for any good ham QSK setup in the 50's or 60's: a tube or fast relay T/R switch outside the receiver with muting of the receiver by injecting AGC voltage on the back panel.

I would never ever trust that clanky old relay in the 390A's antenna fitting to stop 100W or 1kW from getting into the 390A's front end.

> 2. Was thinking of running  always-on reduced standby filament voltage, especially on VFO - ( full voltage when operating)  for frequency stabilty
>    and prolonged tube life. I understand that commercial broadcast stations run never-off full filament voltage on their PA tubes to prolong life time.
>3. Adding a separate HV/B+ switch, maybe resistance stepped, so first reduced then full HV/B+ after filalment warm up (at full rated voltage).
>   (would have to consider effect on tube contra CR rectifiers C when switching HV/B+ current load).
>4. Just using an ac-line variac without a HV disconnect can be detrimental when plate/sceen current flows before filaments hav reached proper temperature.

I honestly don't think you have to do anything to protect any of the tubes. These are not fragile tubes, they are mostly ARINC-rated tubes with robust filaments and support structures designed for aircraft or mobile operation. Perhaps the most fragile would be the 12AU7A, but you will note that the ARINC 5814A was used by the military instead.

It is possible to measure VFO drift on warmup but I don't think that reduced standby filament voltage is any kind of solution to that.

As Roy pointed out, cathode poisoning could be possible if you had HV applied but no or low filament voltage.

I think inrush limiting has some value for the one component in the radio far more fragile than any of the tubes: the front panel power microswitch :-). If you want to do anything, just leave it in "on" all the time and switch power on/off externally via any means you have handy.

Tim N3QE