[MRCA] VRC-12

[B. Smith]

Filament voltage?
Z

On 12/9/2016 2:03 PM, Ray Fantini wrote:
>
> Have an issue with the VRC-12 dropping output power from 35 watts to 
> maybe 5 watts then down to almost nothing after it has been 
> transmitting for more than three or four minutes. All the HV supplies 
> are good and the voltages don’t drop. The grid drive to V6101 is good 
> at around 100 mW and stays constant regardless of output or lack 
> thereof and when the power drops off see a decrease in the load on the 
> 28 volt supply feeding the radio as suspected because the amplifier is 
> not working as hard as it was. Checked the one tube on my TV-10 and it 
> was ok but the PA tube don’t look tube checker friendly, also intend 
> to disassemble the whole mess this weekend and clean the contacts on 
> the band switch along with also checking power prior to the output 
> filter but also wanted to ask here in case anyone had expense with 
> this radio and what PA tube failure looks like or other issues in the 
> PA. If allowed to cool down can go back and get full power for three 
> or four minutes but after it starts to fail won’t get full power until 
> after the radio has been off for a while.
>
> Attached is a JPEG of the amplifier, all comments welcome!
>
> Ray F/KA3EKH
>
>
>
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