Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ajeffcote on March 24, 2013, 04:51:15 pm
-
The layout for the AB763 shows dropping resistors for the power rail of 1K and 4.7K, for use with 6L6s, right? So if I use 6V6s with those values, how will the amp sound compared to using dropping resistors values of 10K and 10K, which I believe I read is the correct R values for a Deluxe Reverb?
-
The layout for the AB763 shows dropping resistors for the power rail of 1K and 4.7K ... correct R values for a Deluxe Reverb?
You're building a Deluxe Reverb? Then use the 10k/10k values as found in the original amp.
I found out the hard way that the AB763 board doesn't match every blackface amp, though it does match most of the bigger models.
So if I use 6V6s with those values, how will the amp sound compared to using dropping resistors values of 10K and 10K ...
It's not really about sound but that supply voltages will be higher than expected through the phase inverter and preamp.
-
Voltages will be higher, that is understood. But what does that mean to me as a guitarist? What differences will there be in application? Higher voltages mean more headroom, no? Lower voltage, quicker breakup, softer attack?
The layout for the AB763 shows dropping resistors for the power rail of 1K and 4.7K ... correct R values for a Deluxe Reverb?
You're building a Deluxe Reverb? Then use the 10k/10k values as found in the original amp.
I found out the hard way that the AB763 board doesn't match every blackface amp, though it does match most of the bigger models.
So if I use 6V6s with those values, how will the amp sound compared to using dropping resistors values of 10K and 10K ...
It's not really about sound but that supply voltages will be higher than expected through the phase inverter and preamp.
-
Voltages will be higher, that is understood. But what does that mean to me as a guitarist? What differences will there be in application? Higher voltages mean more headroom, no? Lower voltage, quicker breakup, softer attack?
Sweeping generalizations about it will give you a wrong impression, because there's always exceptions or other factors that come into play.
All else being equal, if you have a triode with a 300v supply and another with a 90v supply, the higher voltage triode should have greater output voltage (which you might interpret as headroom).
Problem is, if you bugger the biasing you can make the 300v triode distort before the 90v triode and have less output.
But what does that mean to me as a guitarist? What differences will there be in application?
By the time Fender got around to building the blackface amps, the wide variation in characteristics of different models in the Fender lineup generally evaporated. Fender evolved to essentially one amp circuit (except the Champ, VibroChamp, Princeton and to an extent the Bassman), with models differentiated by type/number of output tubes and size/number of speakers. That gives a consistent sound across the model lineup with the difference being power and whether the amp had Reverb/Tremolo.
As a rule, Fender designed the amp's supply voltages to take an input signal and deliver a signal big enough to drive the output tubes installed in the amp to make the power the catalog claims. You're probably not going to improve on Fender's design by much. Therefore, I'd say just build the thing the way Fender designed it.
If you want to tinker, then afterwards drop in the 1kΩ and 4.7kΩ resistors. The amp will still work, and will largely sound the same. If you have a preference for the altered values, keep em.
-
If you want to tinker, then afterwards drop in the 1kΩ and 4.7kΩ resistors. The amp will still work, and will largely sound the same. If you have a preference for the altered values, keep em.
In fact, you could just build it 10k/10k, then parallel a 1k across one 10k resistor for the 1k (909R...close enough) and parallel another 10k across the remaining 10k for the 4.7k (5k actual....again, close enough) to see what the differences would be.
If you liked the tone better with the lower resistances/higher voltages, you could swap them out at that point.
$0.02
G
Edit: I re-reading HP's post, this MAY have been exactly what he was saying in the first place... :BangHead:
-
Edit: I re-reading HP's post, this MAY have been exactly what he was saying in the first place... :BangHead:
No, you offered a better idea. I had envisioned just unsoldering the old resistors and replacing with new. But what you describe lets him jumper resistors in with alligator clips to taste-test before heating up an iron.
I like it!
-
> parallel a 1k across one 10k resistor
> $0.02
Closer to $0.24.
-
I like that idea! Thanks. :icon_biggrin: