[Amps] The GU84B and GU78B tubes / some brief history

[Vic K2VCO]

I'm thinking about this issue now for my project 4CX1000A amplifier. The problem I see is 
the first element getting chopped by the screen relay pull-in time, which would have to be 
under 8 ms. to work.  I am going to use a fast bias switching arrangement along with the 
QSK RF relays as usual, but it would be nice to also switch the screen voltage.
Presently, I'm planning to have an "amp enable" switch which will turn on the screen 
voltage and connect the transceiver key out to the QSK relays. So the amp won't 
necessarily be 'armed' whenever it is warmed up and ready.
I have an extra vacuum relay that I could use for this, but Ian's board seems to be 
designed for a 12v relay in this spot!

On 10/30/2012 1:20 AM, Ian White GM3SEK wrote:
> The problem is how to switch these relatively high screen voltages RELIABLY at full QSK 
> rates. MOSFET switches have been tried, but are destroyed by the first HV arc that comes 
> along... so that means mechanical relays, which have their own different set of problems 
> including a limited mechanical lifetime. The best scheme I've been able to come up with 
> is to use electronic grid-block keying for QSK while *also* switching the screen relay 
> with a short hang-time to avoid it switching on individual dots and dashes. This gives 
> the advantages of both switching methods but requires some careful sequencing.

-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/