Distorted Reverb- SF Super Reverb

[kinggabbo]

I have a '72 Super Reverb that I am fixing up. One of the last problems I am having is that the reverb gets very distorted when you turn the reverb up above 3 or 4. It is emphasized even more if the volume is turned up. There is plenty of reverb but alot of distortion as well.

I replaced V3 and V4 tube with a new one and there was no change. V3 is an 12AT7 and V4 is a 12AX7.

Measured voltage on the reverb tube (V3). It is measuring 471V . Checked 22K resistor connected to pin 8. Measured a little low, it was about 15K. Don't know if that would affect it. Check 1M resistor connected to pin 7. Measured about 1M. Checked resistance on Reverb pot, measure about 95-96K.

Any help would be greatly appreciated.

[Jazz P Bass]

Fender Reverb

Did you check the pan & the cables?
Loose wires, saggy springs, transducers flopping around?

[kinggabbo]

Did you check the pan & the cables?
Loose wires, saggy springs, transducers flopping around?

Nope haven't checked the pan. I will take it out and look at those things. Just didn't know what to look for in it that might be bad until now.

What do I check as far as the cables? They don't SEEM to be shorting or working intermittently.

[Bruce / Mission Amps]

Measured voltage on the reverb tube (V3). It is measuring 471V . Checked 22K resistor connected to pin 8. Measured a little low, it was about 15K. Don't know if that would affect it. Any help would be greatly appreciated.

Well, there is no 22K resistor on the 12AT7 cathodes.... 2.2K maybe.
If you measured 15K then that resistor is bad anyhow... but, use a 2.2K to 2.7K.

[kinggabbo]

Well, there is no 22K resistor on the 12AT7 cathodes.... 2.2K maybe.
If you measured 15K then that resistor is bad anyhow... but, use a 2.2K to 2.7K.

LOL sorry about that I meant 2.2K. It probably measured 1.5K too. I'll check it again today though just to be sure.

[kinggabbo]

Checked reverb pan and cables. Resistance is at 1-3 Ohms on the input side and 170Ohms on the output side. Measured it at the RCA jack and the transducers(??). Measured the same. Everything looks intact in the pan. Very nice.

Only think I noticed is that some of the shielding is becoming frayed on the reverb cable near where it plugs into the input side of the pan. Just frayed a little.

Could it perhaps be a bad capacitor in the reverb circuit, maybe connected to V3 or V4?

[kinggabbo]

Ok measured that 2.2K resistor again today and got infinite resistance. I must've measured the one next to it last night instead (I was tired...it is measuring around 2.2K, I think it should be 820Ohms anyway). So I guess that means the 2.2K resistor is no good?

Would that cause the distortion I'm talking about?

[Bruce / Mission Amps]

Ok measured that 2.2K resistor again today and got infinite resistance. I must've measured the one next to it last night instead (I was tired...it is measuring around 2.2K, I think it should be 820Ohms anyway). So I guess that means the 2.2K resistor is no good?

Would that cause the distortion I'm talking about?

Yes, I bet if the 12AT7 reverb driver tube's cathode resistor is open, the tube is running with no DC bias.
The bypass cap, if installed on the socket or the eyelet board) is bypassing AC to ground so it kind of works but sounds awful.
Use a 2K2 to 2k7 @ 1/2 watt... not an 820. The reverb sounds better to most players with the larger value cathode resistor and a 22uF bypass cap.

[kinggabbo]

OK, I replaced the cathode bypass resistors and caps on both V3 and V4. No change.

One question I have. I measured the resistance of the resistor before installed, 2.2K. I measured it after I have it installed and I get infinite resistance. Is this correct? I measure the correct voltage going to the resistor. But when I measure both sides of the resistor for resistance, it is infinite. Maybe it's supposed to be like that. I don't know.

Any other suggestions?

[kinggabbo]

Saggy Springs

Actually, I read something in a previous post by Jazz P Bass about possible saggy springs. How tight should they be?

I looked again in my pan and to me, they do look saggy but I don't know the correct tension for them.