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In Reply to: Re: el34s in a mac mc60 posted by MIchael Samra on July 28, 2006 at 08:47:36:
Hi Mike.
how can you run an additonal neg 2v on the grid of the el34s ?
let me know so I can do it.
Follow Ups:
Love
When I changed the original diode I put in a uf4007 and I had to put a 5.1k resistor in series with it to get the proper neg bias..The mac service lit calls for 435vdc on the plate and -47 on the grid at idle of course..When you change from the selenium to the silicon you have less drop and a high voltage out so the 5.1k limits that..I put in a 3.9k to raise it so now I have minus 49v on the grid.
Mike.
I did the same to mine and do you know trying difference resistor ranging from 3.3K to 5.1k made a difference in sound ? I think i like the 4.7k best and that is what got , so you might want to try this out . it will varies the negative voltages to the grids of the output tube by doing that and I think the diffrence is notable .
LOve
your are correct..Our line voltage may be a little higher than yours and thats why I run the 5.1k and you are correct in that if the tube doesnt conduct quite enough,it will be harsh.
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