[Amps] input matching question on the YC156?

[craxd]

Hal,
The plate and a screen voltage if needed was killed the same time as the 
antenna relay opened. It was then applied as the antenna relay closed. 
Now this was using a smaller tube type (4CX250B) than a 3CPX5000. But if 
you have the switching relays in parallel, etc and their switching time 
is the same, it will work, or has in what I've done. You could also have 
the antenna relay switch in and out another relay to apply the B+ and 
any screen if needed. There's been some home brew amps wired up this way 
in the past, but not as many as leaving the B+ on the anode all the 
time. It's better to kill off the B- lead than to switch the positive 
lead in and out for the plate voltage due to arcing. Another way would 
be kill the cathodes connection to ground on idle. Keep in mind that 
even though I done this successfully with 4CX250B's doesn't mean it 
would work with your tube as well. The only real reason for doing this 
is to assure that if the control bias fails, there's not a run-away 
condition.

Will Matney

Harold B. Mandel wrote:

>Gentlemen,
>
>In reading the posts below do I detect a tendency to use a HV relay
>to switch the HV on and off every time the amplifier is keyed?
>
>Using the 3CPX5000 scenario posted before, would then the
>sequence (abridged) be:
>
>1. Apply HV-  (B- as Will espouses, below).
>2. Apply Bias.
>3. Trigger antenna relays.
>4. Apply drive voltage.
>
>5. Remove Dive voltage.
>6. Remove Bias.
>7. Remove HV-
>8. Unpick antenna relays.
>
>This sounds like a switching sequence nightmare! 
>If I'm running 4KV at 2 amperes on the plates, I need to 
>run serious vacuum relays (and I do, I do!), but they
>are huge and slow. I could see all this in a setup that 
>had long turn-around Tx/Rx, like RTTY bulletin stations,
>but what happens to PSK31, AMTOR and contesting
>operators when they want to "get up and go?"
>
>Hal Mandel
>W4HBM
>
>
>  
>
>>>Is this true even when the tube is biased into cutoff?  I've owned
>>>four commercially-made amps and all of them apply HV as soon as the
>>>power switch is turned on, but all four have the tube biased into
>>>cutoff.  Are you saying that is a design error?
>>>      
>>>
>>- Bill 
>>    
>>
>
>  
>
>>In any amps I've made, I did kill the B- lead for the HV until the 
>>antenna relay pulled in even though it was biased to cutoff on idle. 
>>The reason being is that if the bias ever failed while the amp was at 
>>idle,  you'd have a run-away situation that would happen fast. 
>>-Will
>>    
>>
>
>
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