Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: g-man on April 26, 2014, 11:22:57 am
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It's less of a concern because by that stage in the amp, we not only have voltage/signal swings in the tens of volts which completely swamp the teeny little glitches we call "thermal noise" in the preamp stages....but we are "pretty much" done amplifying the input signal, as well, at least voltage wise.
Some people report more and some report less improvement from changing out the plate resistors. Obviously it depends upon how noisy the amp is to start with. I had a '65 Pro Reverb that was all stock as far as front end but had been modded to quad-6L6. I had used that amp for well over a decade in clubs and on the road five-six nights a week and I bought it used in the first place then had it in storage for probably another 7-8 years. The plate resistor change on that amp took it from full-time ocean hiss and constant appear/disappear rat noise to SILENT!! <<--I also did the standard cap job on the original date-stamped electrolytics under the doghouse, and knew I was going to do so---"whether they needed it or not", but at 45 years...they need it. However, having just found this forum at the time and heard about plate R's, I decided to just do the plate R's as a partial step and see what the difference was from only changing the plate R's. "Jaw-dropping" would be the term I would use. Dramatic.
A '69 SF Deluxe Reverb I have, as well, went from "Geez, I have to change out these tubes" or "Dang, I thought I changed out these tubes a couple of months ago" to "Did I flip the standby switch to on?" Really became very quiet, very stable, nice. That amp had also been modded to 4x (yes, 4) 6L6's and I took it down to 2 x 6L6. Now it's a great amp, solid, quiet. W/JBL D-120.
It really depends upon how used is used, how sensitive you are to such noise, and it quite possibly depends upon whether the amp was stored/used in more humid environments. Me, I play quieter, jazzier, cleaner and I'm fairly sensitive to amp noise. Maybe in a loud club setting for a rockier or more metallic player, it wouldn't matter so much.
There's simply nothing you can do to a good old Fender that is so cheap yet offers such a big prospect for improvement. To me, it's almost automatic to change those out. If the thing is open on my bench, it gets done.
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Change ALL plate resistors , PI too.
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Almost too good to be true for how easy it is, isn't it?
I gave a pal of mine a SF Vibro-Champ and suggested he change out only the two 100K plate R's those amps have. He said the difference was dramatic.