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

[2002tii]

Tim wrote:

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

Amen.

>>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.
>
>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.

Correct.  The VFO drifts due to temperature change.  If you don't 
want it to drift as much, leave the radio in standby with the ovens 
on (back panel switch S-106).  But BE WARNED -- the heater 
thermostats sometimes fail shorted and cook the VFO to destruction.

>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.

To the (not insubstantial) extent that the microswitches arc and 
stick, the inrush limiter may help.  But they also tend to fail due 
to mechanical problems, which an inrush limiter won't address.  The 
real cure is to install a more robust microswitch.  I wouldn't think 
they would be hard to find, although I've heard folks complaining about it.

Best regards,

Don