[AMRadio] Screwiest Elmac problem ever

[JimTonne]

John and Jim et al:

With a 500 volt supply, 100% modulation would need 500 volts peak
( 1000 volts peak-to-peak ) out of the modulation transformer secondary.
You are about one-third of that, about 10 dB below the correct value.
I'd place money that the transformer has shorted turns if the drive to
the modulator tubes is correct.

- Jim Tonne   W4ENE



On 5/16/2021 12:00 AM, sparky52 at cox.net wrote:
> Hello
>
> Looking at the schematic here ,I'm not sure 300 v pk to pk is enough if you have 500 volts on the plates from the power supply and 220 vdc on the screens. 300 volts pk to pk is only around 110 volts rms The modulator should be able to put out 40 watts ,not going to get there with the pk to pk that low across a 5 k .
>
> Don't know what kind of test equipment you have ,but if you can check the input output of v6 and v7 and then check the screen voltage on the v8 and v9 ,they were notorious for causing problems in the 5881 , once we get those readings then we can go from there. Anxious to see if you have 500 volts on the plates of 5881 .
> If you have some spare tubes you can do what Jim suggested ,if not lets see what we can do to narrow the problem down. 300 volts pk to pk is not alot ,if you have 300 rms or avg then we have different ball game here,but I'm going on the 300v pk to pk in your previous email. Keep the faith the old girl will eventually get fixed ,just takes some time.
>
> John ac7xh