5F6A/8417 80W

[David Root]

You're right Merlin. I finally figured out what was wrong yesterday, after splitting plate resistors on V1, V3 and V5 to no avail. So I disconnected the reverb and the problem disappeared. I do need to put that grid leak on V3B before I reconnect it though. It's funny how you can look at a schematic hundreds of times and not see something so obvious is missing! Must be Oldtimerz creeping up on me. The dry signal feeds into V3B out of phase with the wet signal, I will probably just eliminate it.

Part of the problem is this was a rebuild of a previous design and I kind of took the reverb for granted because of that. I will review it and simplify it.

I have been rereading and referring to your book thru all these tribulations, so I now have 470k gridstoppers on the main preamp tubes including the anode mixer, and I slugged the power tubes with 150 pF from grid to cathode.

The amp sounds nice and clean and I have to put the gain back in V1 to get the 80W back. It should be around 50. I cut back V2 to about 23 gain and it now has 68k plate and cathode resistors, still has just over 205VDC on that CF cathode so I put in the 100 ohm resistor and the arc protection.

I cut V5 down to 2.2 gain by splitting the plate resistors in the ratio of 1:4. I think I will leave that because the 8417s don't really need any gain from the PI, I measured them at 22. They are quite stable and the bias doesn't wander about as I had been told it might.

Your book has been very helpful to me. Thanks for all the work you put into it. One suggestion for the 2nd edition--you need a better proofreader.