Hey all
Does anyone know the basic resistor mod so you can use 6L6 valves in an original EL34 model
There were issues with earlier EL34 models with the valves running too hot and causing issues. Mine is an original and I prefer 6L6 anyway
i have the schematics and I think it’s resistor R7 that needs changing but there’s no rating on the diagram and obviously need to know what I need to change it to
All of this info was on the Cornford forum but as it’s now shut its becoming extremely difficult to obtain tech advice. The Cornford users FB page members aren’t very technical minded either
Many thanks
Comments
The schematic shows 180R 7W for the 30W cathode-bias model with EL34s. On that basis, assuming they were running the 34s pretty hot at 25W at idle, with a B+ of around 420V (the PT secondary is listed as 300VAC), that gives roughly 60mA per valve, 120mA total, so a cathode voltage of around 22V. I would be looking for around double that voltage with 6L6s to get the same sort of dissipation, so I would ideally go for 360R 10W, possibly as high as 390R, and probably not lower than 330R. You may have to experiment slightly though since if the current draw is different it may affect the B+ voltage.
If you can't get a 360 easily then you can just use an extra 180R in series with the existing one, if there's room to fit two.
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