nfb resistor question
Moderators: pompeiisneaks, Colossal
nfb resistor question
I have a jtm45 with radio spares ot running a 8 ohm load I have a 27 k resistor in there now would a 47 k make the amp a little more gainy?
Re: nfb resistor question
Yes. For more fun and gain, leave the 27k fixed and insert a 100-250kB pot in series. Adjust to taste.
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Re: nfb resistor question
Just note that you will be driving the output tubes harder so they will clip sooner, as such you may also want to bias them a tad cooler depending on what your ears tell ya!
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Re: nfb resistor question
As for the pot in series on the NFB, I prefer 100k lin or 250k log.
This way you have more control on the whole range.
This way you have more control on the whole range.
Re: nfb resistor question
So when a higher value NFB resistor is replaced making the amp a little more gainy, resulting in clipping sooner; will drive the output tubes harder ?Stevem wrote:Just note that you will be driving the output tubes harder so they will clip sooner, as such you may also want to bias them a tad cooler depending on what your ears tell ya!
I also see, if one had a high plate voltage, that biasing a little cooler will prolong tube life, but more importantly dial in a tone that one is satisfied with.
If one has a 47k upped to a 100k, then I would be conscious of biasing a tad under (to taste of course) and have the option of the 3 taps. (something like that ?)
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Re: nfb resistor question
Do you have pics of the outside and inside? I just finished updating a '64 JTM45 and you're right, it does need a little more gain than stock but boy are they sweet.
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Re: nfb resistor question
First thing I do on a 45 is swap a 470k divider pair in place of the 270ks before V2. Mostly about bringing the 'chest' out a little.
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Re: nfb resistor question
Doesn't that make the bright input even brighter?Reeltarded wrote:First thing I do on a 45 is swap a 470k divider pair in place of the 270ks before V2. Mostly about bringing the 'chest' out a little.
Re: nfb resistor question
yes, 22k + 250k pot into 16ohms secondaryColossal wrote:Yes. For more fun and gain, leave the 27k fixed and insert a 100-250kB pot in series. Adjust to taste.
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Re: nfb resistor question
This is a real 45, not a reissue or clone? +1 Please post good picts.