'66 Super Reverb needs some help

[bondieffects]

I recently acquired a '66 Super Reverb, it sounded great in the shop, however upon getting it home and checking it out I noticed that the Normal Channel passes signal only when the volume is turned to upwards of 4, the taper which would normally be spread across that entire range seems to between 4-5 and then upwards of 5 is business as usual.

The Vibrato channel on the other hand passes signal even when the volume is at minimum, but the tone controls do not work and it sounds muddy right up until just before 3. After 3 it behaves normally.

Are these things symptomatic of anything obvious?

Upon inspection it seems the previous owner decided replace several of the Ajax Blue caps with something yellow, and all in the Vibrato channel. I'm not sure why. A few of the ceramics and several resistors have also been replaced. I haven't had a chance to look in the doghouse yet, but I'm fairly certain he had replaced some or all of the electrolytics as well.

I've ordered most of the parts to get it back to it's original state, including replacement Ajax's and Carbon Comps.

[Firestorm]

Clean all the pots. Use the expensive stuff from Caig. Deoxit Fader something or other is what CaiLube is called now. Don't use contact cleaner or WD40 or any other damned thing. Then see where you are.

Pots could be shot, but if they're CTS they can be fixed rather than replaced if need be.

[bondieffects]

Thanks, I have some Deoxit Fader Lube on the way.

I was poking around a bit more and it seems that the previous owner may have tried to do this to it. Who knows.

There is a mod suggested by Torres and Mike Thompson. It involves:

1. Change the plate resistors from 100k to 220k. Bypass the one on the second gain stage with a 500pF or 750pF cap.

2. Change the slope resistor from 100k to 56k, the bass and mid cap from 0.1uF and 0.047 uF to 0.022uF each and the treble cap from 250pF to 500pf.

3. Give the V1a cathode a separate 2k7/0.68uF network to ground.

4. Change the output coupling cap after V1b from a 0.047uF to a 0.022uF.

5. Change the cathode of V1b from 1k5/22uF to 2k2/1uF.

6. If my memory serves me right install a grid load resistor after the 0.022uF output coupling cap of 2M2.

[Structo]

Clean all the pots. Use the expensive stuff from Caig. Deoxit Fader something or other is what CaiLube is called now. Don't use contact cleaner or WD40 or any other damned thing. Then see where you are.

Pots could be shot, but if they're CTS they can be fixed rather than replaced if need be.

I have to say I bought some DeOxit D series contact cleaner a while back.

I found a perfect use for it the other day.

My wife bought an old exorcise machine that had a computer on it to keep track of cycles and stuff.
It didn't work of course.
I took it apart and noticed it used button batteries that were all corroded.
That green looking crap.

I sprayed it with DeOxit and it almost immediately dissolved it.

Clean as a whistle after I wiped it off.

Of course it still didn't work but I was happy with how the DeOxit worked.

BTW, don't use the contact cleaner on pots.
It can ruin them.

[bondieffects]

So I was thinking about it, and it seemed to be that the signal was shorting to output, and bypassing the tone controls, as until the volume knob reached about 2 1/2 the tone controls did not effect it and the signal sounded very muddy.

The normal channel as I had mentioned previously was behaving normally aside from the volume knob not working until about 4, so I decided to swap the preamp tubes from the normal and vibrato channels and that seemed to do the trick.

Easy enough, i ordered a replacement normal channel knob, though honestly I'm not sure how often I will use it, but I figured I might as well try and take care of everything at once.

[sunnydaze]

So I was thinking about it, and it seemed to be that the signal was shorting to output, and bypassing the tone controls, as until the volume knob reached about 2 1/2 the tone controls did not effect it and the signal sounded very muddy.

The normal channel as I had mentioned previously was behaving normally aside from the volume knob not working until about 4, so I decided to swap the preamp tubes from the normal and vibrato channels and that seemed to do the trick.

Easy enough, i ordered a replacement normal channel knob, though honestly I'm not sure how often I will use it, but I figured I might as well try and take care of everything at once.

I'm not sure I understand what you mean by "took care of it". What did switching the preamp tubes from the normal and vibrato channel fix?

Did the tube originally in the normal channel make the vibrato channel work correctly, or the other way around?

If switching pre-amp tubes only corrected one of the channels, makes me think the problem was one of the tubes. If it fixed both channels, maybe reseating the tubes in the socket corrected the problem. Why do you think the problem is the normal channel volume pot? I

just wondering.

Thanks
Mike

[bondieffects]

I think the problem was in the preamp tube from the vibrato channel and so replacing it with the tube from the normal channel fixed the issue. i think the normal channel most likely just has a bad volume pot and so the bad tube, that was originally in the vibrato channel exhibits the same problems as it did before, but I never use the normal channel so it doesn't really bother me. I ended up just throwing out the bad tube since I won't be using it.

[sunnydaze]

That makes sense.

Thanks for clarifying.

Good luck with the repairs.

Thanks
Mike

[sunnydaze]

delete double post

[roadkingbluzs]

I've ordered most of the parts to get it back to it's original state, including replacement Ajax's and Carbon Comps.[/quote]

Any updates on your Super Reverb? I also have an early Super Reverb that needs attention. All caps seem to be original with a master volume mod , pot inserted in the normal channel front jack. I will be removing. Sounds killer as it is but I can see signs of fatigue on the power filter caps. these are great sounding amps. Good luck!