Fender Reverb Values

[EVMode]

I’ve got a custom built AB763 style amp which is a single channel w/reverb. No tremolo. The reverb does not sound as good as a stock deluxe reverb and I’ve never been happy with it. The amp is a beast and sounds incredible, I just keep the reverb very low or off. I would like some help to identify any differences between my custom amp and a stock deluxe reverb reissue. Specifically the reverb section. The issue is the reverb sounds way too hot. Not that the mix is too high but the tone sounds like it’s about to take off for space in a non-musical way. As if the reverb send was set well above the normal range. I’ve tried using lower output tubes for the reverb and also got a replacement spring tank. Neither of these solved the issue.

Is it possible the reverb transformer is bad? Are there any component value difference which could be returned to stock values?


Transformers
Power: P-TF22723 (like a vibroverb)
Output: P-TF41318 (like a deluxe reverb)
Reverb: P-TF22921
Choke: P-CF22699

I’m currently running a pair of 6L6 power tubes at 440v biased to around 70% of max. 8 ohm output w/ single 12” speaker.

Tubes
V1: preamp (12ax7)
V2: reverb (12at7)
V3: reverb (12ax7)
V4: PI (12at7)
Power: 2x6L6 (or 6V6)
Rectifier: GZ34

Controls:
Volume
Bass/Mid/Treble
Reverb

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[Reeltarded]

Based on your description the driver stage is distorting the input of the tank? A simple way to trim it is with a divider network made from a 470k resistor (signal) and 470k to ground. A 50% cut will give you a clue if it is the right idea.

If you do a bounce test by turning the reverb up and banging your fist off the amp does the insanity bottom out as if the signal is overloaded at the input or does it reproduce the whole expected mayhem but crapped out sounding for the duration?

Is the tail of the reverb (audible) clearer or cleaner than the attack? Is there ever a time when the response clears up during the reverb sustain after smacking it?

It could even be as simple as a bad reverb control pot.

With an insulated probe, tick the signal path through the reverb portion of the circuit and find the junction where the signal does bad things. If you are working from the input to the output, the first unexpected response is the problem.

[pdf64]

It seems unlikely that the reverb transformer is bad.
More chassis photos from several angles, with sufficient resolution to read all component values, are required.
I think up to 60% of their limit is more appropriate idling design max rated valve types such as 6L6GC in fixed bias.
And given the 6k6 OT, idle current could be lowered without losing linearity.

[bepone]

what is the reverb tank code?

[EVMode]

It seems unlikely that the reverb transformer is bad.
More chassis photos from several angles, with sufficient resolution to read all component values, are required.
I think up to 60% of their limit is more appropriate idling design max rated valve types such as 6L6GC in fixed bias.
And given the 6k6 OT, idle current could be lowered without losing linearity.

Interesting note on 60%. Could you suggest any online resources which cover this topic with more detail, for my understanding?

Here is one I have available immediately. This should have most of the component values visible but maybe still missing if few of the vertically oriented components. Please let me know if this helps. I will also reply to another comment below, please read this one as it may be a relevant piece of information.

You may need to click and expand the image to full size/resolution to see the values.

781C5536-95C6-4EE1-A889-298AD36D93AE.jpeg

[EVMode]

what is the reverb tank code?

You bring up an interesting point. I believe this custom amp is usually paired with a short tank reverb. What I am using is the stock DRRI reverb tank (4AB3C1B ) and I’ve also tried an aftermarket “MOD” replacement. Both sound nearly identical.

I’m wondering if the reverb circuit in my custom amp needs to be tweaked for use with long tank design like DRRI? Which components would be different? Maybe the tank is actually too hot for the circuit…

This custom amp is usually built in a smaller head or cab. I asked for mine to be fitted into a DRRI chassis so I could use the existing combo I had. I’d prefer to keep the long tank if possible because I love that sound. I don’t mine swapping out components in the amp.

[EVMode]

Based on your description the driver stage is distorting the input of the tank? A simple way to trim it is with a divider network made from a 470k resistor (signal) and 470k to ground. A 50% cut will give you a clue if it is the right idea.

If you do a bounce test by turning the reverb up and banging your fist off the amp does the insanity bottom out as if the signal is overloaded at the input or does it reproduce the whole expected mayhem but crapped out sounding for the duration?

Is the tail of the reverb (audible) clearer or cleaner than the attack? Is there ever a time when the response clears up during the reverb sustain after smacking it?

It could even be as simple as a bad reverb control pot.

With an insulated probe, tick the signal path through the reverb portion of the circuit and find the junction where the signal does bad things. If you are working from the input to the output, the first unexpected response is the problem.

I’ve done the probe thing and tube swapping with no targeting of vibrational/harmonic issues. The best way I can describe is it sounds like way to much reverb send. Decay is long and intense, in an unmusical way. Especially compared to a stock DRRI.

[didit]

Hello --

If quick trace through what's visible from your posted photo is correct, the reverb driver tube is missing a necessary 2.2k cathode resistor. Should be one in parallel with 25uF/25V electrolytic, that does seem connected to pin 8 & 3 of that socket.

Best .. Ian

[sluckey]

the reverb driver tube is missing a necessary 2.2k cathode resistor. Should be one in parallel with 25uF/25V electrolytic, that does seem connected to pin 8 & 3 of that socket.

There would be NO reverb without that resistor. It's there, under the bypass cap. Because of the camera angle, the bypass cap totally hides it. Even the leads are well hidden.

[didit]

the reverb driver tube is missing a necessary 2.2k cathode resistor. Should be one in parallel with 25uF/25V electrolytic, that does seem connected to pin 8 & 3 of that socket.

There would be NO reverb without that resistor. It's there, under the bypass cap. Because of the camera angle, the bypass cap totally hides it. Even the leads are well hidden.

Agreed as I'd roughly the same thoughts, and was wanting to check its value. If you can see actual evidence your eyes are better than mine. If everything was correct the reverb would be working, and so yes if truly ungrounded the driver wouldn't conduct.

..

[sluckey]

The slightly fat cap lead is the only visual clue. Looking at how all the other cathode resistor/caps are installed makes me know it's just a camera angle trick. That and knowing that if the 2.2K were missing he would not be complaining about too much reverb.

[EVMode]

A quick update

I did some tube swapping this morning and lowered the gain of the reverb recover (V3) and this seemed to really tame the reverb. I think before I was just swapping (V2) as I was thinking the send was too hot. The reverb is still very thick and chewy compared to a DRRI which is more light/springy/drippy. But that could be more a character of the custom amp and not necessarily an issue.

So now I’ve got this for the reverb tubes.
V2 - 12AU7
V3 - 12AT7

Overall this amp has significantly more gain/breakup than a DRRI and I’m realizing that by using lower gain preamp tubes it really cleans it back up to more what I’m used to. The overdrive does sound very good but seems to overload in the reverb section and also I like the V1 to stay fairly clean for my style of playing, just edge of breakup. It’s a cool amp because I can really change the breakup/gain with tube swaps.

[jjman]

I would replace the 1meg grid leak on the driver tube with a 1meg pot, creating a send control. Then switch to 2 resistors after you determine the setting that sounds good. Also make sure the 500pf capacitor there is 500pf.