Short reverb spring recommendation, anyone?

[Diverted]

Good info on heater wirings. Thank you. And also: I am not a fan of PVC or teflon wire coating and so for regular wiring I will never use any other wire other than Hoffman's awesome cloth solid core. It's a million times better than any other cloth-clad wire I've found. Pick some up if you haven't tried it yet!

ANYWAY, so, the plot thickens and I could use some advice. I think this will either be a very complicated or extremely quick question/answer:

When I first asked my stepdaughter what she wanted out of the amp and if she wanted one channel or two, she said just one would be fine. Okie dokie, that's what I did.
She came over last night to play it and while she LOVES the amp, she now says "I wish it had two channels, one for guitar and one for my vocals, each with their own volume control." D'oh! Why didn't you say that before? That's a 23-year-old for you :)

Anyway, adding a second reverb channel should be easy as I have an extra triode that is currently not being used. So I can do that by running that second channel to where the first goes (input grid of second gain stage) and use switching input jacks on each channel to ground out the unused one when both aren't in use.

HOWEVER she also asked if I could make the reverb on each channel switchable; that is, having the ability to turn off reverb on either channel while still having it go to the other one. That way she can have dry vocals and wet guitar, or wet vocals and dry guitar, etc.

I don't see how I can do this the way the amp is built, but I'm wondering if more experienced people could see a way. To me it looks like reverb is either on or off, no in between. Am I right?

Would moving the second gain stage post-reverb allow any possibilities?

I assume she will ask me to change some other fundamental part of the amp next time I see her but for now I want to sort this one out.

Thanks!

[sluckey]

Adding another channel is easy enough. And having reverb on both channels is easy. But being able to switch reverb on and off independently on each channel becomes quite involved.

Sometimes it's OK to just say no.

[Diverted]

Those were my thoughts. It looked like it was going to be a rabbit hole.
Two reverb channels it is!

[Diverted]

The never-ending questions continue
I am trying to close in on a better circuit and could use some advice. The amp is playing well but is very gainy and quite loud. I'm worried I'm overloading the gain stages as I'm getting very, very little clean headroom. Amp starts breaking up almost immediately and I would like to clean it up and allow me to turn the volume up past 2 or 3 without it getting too loud.
I've made some changes in red to the schematic, including a 470K grid stopper resistor, smaller bypass cap on a gain stage, smaller coupling caps etc. Most of the changes were recommended by Rob Robinette and others, and from just fiddling around. They help but I need cleaner!
Earlier on in the thread someoen mentioned a voltage dropping circuit to dump some of the signal off the input to ground. I don't know how to go about accomplishing this.
Looking at the schematic, what would you do to reduce gain in this amplifier and make it run cleaner? Would you try anything else apart from that voltage dropping idea? Just looking for options.

And another very simplistic question as I've never fiddled extensively with gain, etc.: Will having such "hot" gain in this amp lead to problems with reliability, tube life, etc. ?
My main hope is to get the amp running clean and smooth. Thanks!

[SILVERGUN]

Here's one way.
I edited your schematic and inserted a voltage divider. As it is now it will reduce the signal level by 50% at that point.
It doesn't 'have to' go there, but it could.

Besides that, you could put the additional gain stage where sluckey had suggested and use a 12AU7 to reduce gain.

Also try getting rid of the bypass cap on the added stage altogether.

[PRR]

The 3.3Meg:560K reverb mixer.... isn't the lower leg on a Fender not 560K but a value like 100K or 50K?

That would do the same as Silvergun's added divider, but simpler. And you can start by tacking 330k 220K 150K etc across the existing 560K until the thing is less un-tamed.

[Diverted]

Thanks for the suggestions, Sluckey and Silvergun. It looks like that lower leg resistor is 470K. I'm going to leave it as is.
I got some help on the issues from Rob Robinette, who suggested a voltage divider different than Sluckey's, but still as effective. Was going to try both but I'm just going to leave it as is for the moment. The divider is a 680K resistor into the wiper of the volume control. The resistor works to send a good portion of the signal to ground.
I tried a few different values and settled on the 680K that Rob suggested. What a difference. The amp sounds outright fantastic. Breakup around 7 on the dial and clear, sweet tone below that. Prior to this I couldn't turn volume up past 2 or so without hardcore overdrive. It's a different amp.

Anyway with all this shuffling and swapping of parts the amp is a tangle underneath. I may build another one for my stepdaughter keeping the same schematic but an updated and cleaned up layout for her. Then I'll hang on to this one :)
Again, many thanks for all the help. Here's an updated schematic of where the amp's at right now.

Thank you!

[Diverted]

Hopefully this will be the last bug to sort out!

I rewired the amp for a second channel with independent tone control. Had one triode left and stepdaughter asked for it :)
Anyway the amp has an issue I'd like to try to sort out:
It has the Rob Robinette feedback switch, which has 1. negative feedback with 1500 ohm PI bypass resistor in circuit; 2: No negative feedback but 1500 PI bybass resistor in circuit; 3. Normal 5E3 mode with no negative feedback and bypass cap/resistor in place.

When in negative feedback mode the reverb pot performs smoothly, with effect gradually increasing as you go up. At full volume the amp is loud and reverb is full and thick.

In 1500 PI bypass resistor mode (no negative feedback) the reverb becomes faint/shrill and the volume reduces at about 6 or 7 on the reverb dial.

In bypass resistor/cap mode, the reverb cuts out pretty much and volume drops significantly around 4 on the dial. The reverb comes and goes after that point, cutting in and out for lack of a better word up to the full range of the dial.

Switch is wired correctly. Any ideas? All solder joint checked etc.

[sluckey]

Maybe the NFB phase is wrong. Swap the OT primary plate leads and report back.

[Diverted]

I switched it some time ago; was getting a squeal in one position (forget which) so reversed the phase. That cleared it up. Just for the heck of it I’ll switch back after work tonight and see what happens 👍 thabks.

[Diverted]

Output primaries are in phase. Reversed and got the squeal, so switched back.
Problem persists. Very strange, I'll have to post a video. Who knows, with the rat's nest it could be a lead dress issue. I've changed the wiring so many times it's getting a bit sloppy in there. What do you think?
Any other ideas? Thanks!

[SILVERGUN]

Hopefully this will be the last bug to sort out!

I rewired the amp for a second channel with independent tone control. Had one triode left and stepdaughter asked for it :)
Anyway the amp has an issue I'd like to try to sort out:
It has the Rob Robinette feedback switch, which has 1. negative feedback with 1500 ohm PI bypass resistor in circuit; 2: No negative feedback but 1500 PI bybass resistor in circuit; 3. Normal 5E3 mode with no negative feedback and bypass cap/resistor in place.

When in negative feedback mode the reverb pot performs smoothly, with effect gradually increasing as you go up. At full volume the amp is loud and reverb is full and thick.

In 1500 PI bypass resistor mode (no negative feedback) the reverb becomes faint/shrill and the volume reduces at about 6 or 7 on the reverb dial.

In bypass resistor/cap mode, the reverb cuts out pretty much and volume drops significantly around 4 on the dial. The reverb comes and goes after that point, cutting in and out for lack of a better word up to the full range of the dial.

Switch is wired correctly. Any ideas? All solder joint checked etc.

This all sounds much more like a circuit mistake or mis-wiring issue than a lead dress issue.

[Diverted]

I agree. Going over it, but nothing yet. Will update if something changes. Hoping!

[Diverted]

Well I've isolated the problem to the reverb circuit but am not having much luck finding errors. I am sure they're there though
With reverb on (foot switch not grounded) it seems like the dry signal is getting drowned out. Volume can't be control by either channel volume knobs. However the reverb knob increases the amp's volume as you turn it up. So the wet signal is getting through but not the dry.

With the reverb input grounded, I obviously get no reverb but both channels behave as they should. With reverb grounded out also the feedback switch works as it should.

I'm going to have to keep retracing this issue. It's pretty baffling but at least I know where to look.

[Diverted]

Found the issue, wired the 470K ohm resistor off the reverb wiper out of position. Put that back in place and the problem was mostly fixed; played with the lead dress a bit and that didn't hurt. The only thing I'd say now is that in the feedback switch's stock fender position, with volume/tone/reverb dimed, I'm getting some feedback that only subsides when I turn down the reverb. It's pretty minor but there.