[Milsurplus] [MMRCG] Fixed Screen Voltage in Plate Mod. Transmitter PA?

[Ray Fantini]

The DX-100 and Viking 2 have a big difference in what they are doing with the operation of the screen clamp, the Viking is a much simpler system just using the 6AQ5 as a screen clamp to protect the PA tubes by sensing drive. If you wanted to experiment with effects of modulation on the screen maybe you can start by looking with a scope at the plate of the clamp, the junction of R35 and R26 and seeing how much audio is present? C45 is the second half of a RF bypass to decouple the screens of the PA from the clamp but you can try experimenting with a larger value there to remove the audio that may be present on the screen bus but be careful because too much capacity will result in keeping the screen high when conditions of no drive exist. 
The real question is what's the effect of modulation on the screen of a 6146 in relationship to the output? Perhaps having modulation that in phase with the plate increases the efficiency of the tube?

Ray F/KA3EKH


-----Original Message-----
From: MMRCG at groups.io <MMRCG at groups.io> On Behalf Of David Stinson via groups.io
Sent: Wednesday, October 7, 2020 10:21 PM
To: Boatanchors at mailman <boatanchors at mailman.qth.net>; milsurplus at mailman <milsurplus at mailman.qth.net>
Subject: Re: [MMRCG] [Milsurplus] Fixed Screen Voltage in Plate Mod. Transmitter PA?


Thank you all for your insights into this issue.  I should have mentioned that the transmitters is a Johnson Viking II; similar to the DX-100 in some ways.
The parts quality in the Johnson is worlds better and they don't put 800 V on the 807s.

Once Ed and Arden mentioned the reactance of an audio choke in the screen supply, "the light bulb went on."  But of course, none of these ham transmitters have such a choke, so the idea of tagging the PA screens to unmodulated B+ is a no-go.

Thanks again,
GL OM ES 73 DE Dave AB5S

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus