[Amps] 2x8877 question

[Joe Isabella]

Are you swamping the Valiant??  That rig does about 150W AM Carrier.  That puts your PEP around the 600W level... Isn't that a lot of steam for even a pair of 8877s??
 
Joe,
N3JI


"R.Measures" <r at somis.org> wrote:


>Hello gang.
> I have a amp running two (2) 3CX1500A7 tubes. It was built to use on 75m
>AM. Here is the problem. With it keyed....no modulation....the grid
>current is about 40-50 mills. When speaking though the grid current peaks
>to 200+ on voice peaks.

• 200mA of grid-current multiplied by the 8877's typical
grid-cathode driving potential of 57Vrms = 11.4w of grid dissipation.
The rated grid-dissipation of a pair of 8877s is 50w. What problem, Stan?

>Using the "load" to bring it down really brings
>down the output. I have ran other amps (Alpha 89,Command 2500E,etc) and
>have had no problem keeping the grid peaks down by advancing the load. But
>only loosing 100-200 watts output. The transmitter is a Johnson Valiant.
> I am wondering if I increase the bias voltage from the current 8.2 to say
>12 or 16 volts if this will help out. I know I will have to drive it a bit
>harder to get a given output with the higher bias voltage,but that is no
>big deal.
> Any help from the knowledgeable would be greatly appreciated.
>
>PS....plate voltage is 3900v under load.
>
>Take care,Stan
>
>
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