Reverb Deluxe but not quite

[guile]

Measure DC across the 1R bias sense resistors.

Both powertubes measure around 22 mA.

[guile]

So I should change the 64uf cap can?

Too much work to change it out completely. Wire it up so you only use the first half.

Excellent! This loosened up the amp considarebly. Great stuff, thanks!

[xtian]

Measure DC across the 1R bias sense resistors.

Both powertubes measure around 22 mA.

Perfect.

Sounds like lowering the reservoir cap value helped!

[guile]

What will the extra gain yield (removing 220k resistor)?

Like mentioned above, the 220K to ground cuts the gain in half at that point (gain factor 0.5). It's like you had a volume pot there and dialled out half the volume.
Removing the resistor means you'll hit the phase inverter with the full power coming out of V1B. You'll have considerably less headroom.

If you still want some attenuation, you could experiment with different values for the resistor to ground. Like, a 1M would give you a gain factor of about 0.8, etc.

More sparkle and less shrill highs is a tougher one. How does the bright switch work for you, if installed?
Just for experimentation, if you have components at home, I might try to install a very small cap in series with a resistor over that 220K resistor (not the one going to ground).
But the bright cap over the volume pot should pretty much do the same. If it's too much, put a resistor in series with that one.

What speaker do you use for this amp?

Would a potentiometer be a good idea to put in place of the 220k resistor? If so, what value?

I have a bright switched installed (with push/pull pot). I like it only with the treble at 9-ish. It brings up the upper highs as it is supposed to, but lacks meat.

What other 220k resistor do you mean?

I have Celestion G12 Vintage 30 installed; should be well played in.

Thanks!

[xtian]

Would a potentiometer be a good idea to put in place of the 220k resistor? If so, what value?

Those two 220K resistors form a voltage divider. Same function as a pot. You're dumping some percentage of the signal to ground. Do you need an extra volume control there? Probably not. Up to you.

[didit]

So I should change the 64uf cap can?

Too much work to change it out completely. Wire it up so you only use the first half.

Excellent! This loosened up the amp considarebly. Great stuff, thanks!

Good to hear it worked for you.

[guile]

I changed the cap can to 32 uF. I also modded the suggested 220k resistor to 440k. Some extra gain without losing too much clean.
I'm very pleased with the suggestions and learned a lot.

Thank you Xtian, Ian, TUBEDUDE, didit, Lynxtrap!

[Lynxtrap]

Great!
You could hook up a temporary pot of say 500K-1M in series with the resistor to ground. Tweak it while you play, and when you are happy with the sound, measure the total resistance over the pot and resistor. Then choose a resistor as close as possible to the ohm reading to put there permanently.

[guile]

Great!
You could hook up a temporary pot of say 500K-1M in series with the resistor to ground. Tweak it while you play, and when you are happy with the sound, measure the total resistance over the pot and resistor. Then choose a resistor as close as possible to the ohm reading to put there permanently.

Good idea!

[guile]

Too much work to change it out completely. Wire it up so you only use the first half.

Excellent! This loosened up the amp considarebly. Great stuff, thanks!

Good to hear it worked for you.

Just out of curiosity, would an even smaller can cap, say 16 uF, make the amp even more loose?

[didit]

Excellent! This loosened up the amp considarebly. Great stuff, thanks!

Good to hear it worked for you.

Just out of curiosity, would an even smaller can cap, say 16 uF, make the amp even more loose?

Though not something necessarily recommended, a smaller cap will. Loosen too much and it falls apart, but lots of older designs had just 16uF. Look back at 6G3/5E3/5D3/5C3.

.. Ian

[guile]

Great!
You could hook up a temporary pot of say 500K-1M in series with the resistor to ground. Tweak it while you play, and when you are happy with the sound, measure the total resistance over the pot and resistor. Then choose a resistor as close as possible to the ohm reading to put there permanently.

I found this: https://robrobinette.com/AB763_Modifica ... olume_Mod_

Isn't that what we were talking about?

[Lynxtrap]

Great!
You could hook up a temporary pot of say 500K-1M in series with the resistor to ground. Tweak it while you play, and when you are happy with the sound, measure the total resistance over the pot and resistor. Then choose a resistor as close as possible to the ohm reading to put there permanently.

I found this: https://robrobinette.com/AB763_Modifica ... olume_Mod_

Isn't that what we were talking about?

Your link isn't taking me straight to the mod in question so I'm not sure. But the master volumes on Robinette's page are post phase inverter master volumes as far as I can see. That's something entirely different.

I was talking about the 220K resistor to ground where you now have a 470K. If you are happy with 470K, the experiment is unnecessary.

But if you would want to really want to fine-tune the value of that resistor, you could hook up a temporary pot in place of the resistor (or in series with it) just to find out what resistor you want there permanently.
You hook up the pot and tweak it until you're happy with the sound. You then measure the total resistance over the pot (and resistor).
Say you get a reading of about 700K. Then you remove the pot and solder in a permanent 680K resistor.

[guile]

Great!
You could hook up a temporary pot of say 500K-1M in series with the resistor to ground. Tweak it while you play, and when you are happy with the sound, measure the total resistance over the pot and resistor. Then choose a resistor as close as possible to the ohm reading to put there permanently.

I found this: https://robrobinette.com/AB763_Modifica ... olume_Mod_

Isn't that what we were talking about?

https://robrobinette.com/images/Guitar/ ... Volume.pdf

[Lynxtrap]

https://robrobinette.com/images/Guitar/ ... Volume.pdf

That is a very simple version of a post phase inverter master volume (PPIMV).

As you may know, a phase inverter sends two separate signals to each output tube (or pair of tubes in a 4 tube amp) in a push-pull output stage. These two signals are out of phase with each other.
The MV pot blends those signals, thereby cancelling (since they are of opposite phase) a variable amount of volume before the power tubes.

It is usually seen in amps without negative feedback and is often thought to work best in such amps. I have one myself.
Rob thinks it also works fine in amps with NFB such as the Bassman.