# Super Reverb Help



## ampaholic (Sep 19, 2006)

I have a problem with my '68 drip edge SR (AB763) that I've been struggling with for some time. The issue, a noise, might not even be noticeable to some however it is annoying to me.
The noise is only present when a guitar is plugged in, volume turned up to 3 or 4, and plucking a string on the guitar. It's not easy to describe the noise however a "pop" might be most accurate although I've often considered it as more of a whooping noise. When it happens you can see a corresponding, very slight, blue flash in one power tube. No noise at idle.
Here's what I've tried thus far:
- I reversed the power tubes and the flash stayed with the socket, ruling out power tubes.
- since the flash is only on one power tube I've assumed that the issue is somewhere between the phase inverter and the speaker. Tried new PI tube of course.
- On a whim I tried new coupling caps to the PI.
- the amp has been recapped (all electrolytics), although it was probably 7 or 8 years ago. Sprague Atoms used at the time.
- I have cleaned and re-tensioned power tube sockets. They're clean as a whistle but just in case i also took a little file and scraped out the inside of the pins.
- all voltages and bias are bang on. I actually use the amp with an "Amp Preserver" so that line voltage is at a period correct 117 VAC.
- A couple of years ago I replaced the 470 ohm screen resistors with NOS military grade Allen Bradley 2 watt.

As I type this I'm trying to recall if I ever replaced the 1500 ohm resistors on the power tube sockets. Pretty sure that I have but can't recall exactly.
I'm also wondering about a bad tube socket. I can't see any evidence of arcing but perhaps it might not be obvious?

I've owned this amp several years and having been in a church for the first 40 years of its life it is super clean and sounds killer.

Any advice or suggestions would be appreciated!


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## nonreverb (Sep 19, 2006)

Lots of things possible here. Plate load resistors were still the 1/4 watt type at this time. Possibly one is going south. Not an uncommon problem in that era Fender.
What colour are the coupling caps...brown with yellow lettering? If they are, they were the worst batch Fender ever used. They didn't last long during the Super's production and for good reason. Since you say it's a blue flash suggests the tube is merely reacting to a loud signal coming from somewhere earlier in the circuit.....that's my guess.



ampaholic said:


> I have a problem with my '68 drip edge SR (AB763) that I've been struggling with for some time. The issue, a noise, might not even be noticeable to some however it is annoying to me.
> The noise is only present when a guitar is plugged in, volume turned up to 3 or 4, and plucking a string on the guitar. It's not easy to describe the noise however a "pop" might be most accurate although I've often considered it as more of a whooping noise. When it happens you can see a corresponding, very slight, blue flash in one power tube. No noise at idle.
> Here's what I've tried thus far:
> - I reversed the power tubes and the flash stayed with the socket, ruling out power tubes.
> ...


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## StevieMac (Mar 4, 2006)

Check all solder joints to & from the PI tube socket. I had something similar happen recently and wondered about the PI, though a tube swap didn't resolve it. Wiggling the PI tube with the amp on made the noise much worse however so I immediately suspected soldering. Anything even remotely questionable around the PI was resoldered and now no amount of wiggling causes any noise. I'd start by wiggling that tube then...


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## bcmatt (Aug 25, 2007)

Reflowing a bit of solder on all the joints couldn't hurt to make sure the connections are good on any that you might doubt. Also, make sure any wires aren't broken but still sort of touching.


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## ampaholic (Sep 19, 2006)

nonreverb said:


> Lots of things possible here. Plate load resistors were still the 1/4 watt type at this time. Possibly one is going south. Not an uncommon problem in that era Fender.
> What colour are the coupling caps...brown with yellow lettering? If they are, they were the worst batch Fender ever used. They didn't last long during the Super's production and for good reason. Since you say it's a blue flash suggests the tube is merely reacting to a loud signal coming from somewhere earlier in the circuit.....that's my guess.


Coupling caps are blue "molded" type. As for plate resistors do you mean the 100K resistors on preamp tubes? I had myself convinced that the problem was phase inverter or power tube circuit related.


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## ampaholic (Sep 19, 2006)

StevieMac said:


> Check all solder joints to & from the PI tube socket. I had something similar happen recently and wondered about the PI, though a tube swap didn't resolve it. Wiggling the PI tube with the amp on made the noise much worse however so I immediately suspected soldering. Anything even remotely questionable around the PI was resoldered and now no amount of wiggling causes any noise. I'd start by wiggling that tube then...


Hmmm.... I've checked every solder joint in this amp with a magnifying glass and a chopstick. But take a look at pin 1 of the phase inverter socket. I kind of passed over this thinking that it was solder flux runoff as other pins had somewhat similar looking spots but perhaps it is arcing?

Photo with flash:








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Without flash:










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## jb welder (Sep 14, 2010)

Just looks like flux to me.
Are you familiar with the blue glow that is fairly common around power tubes when passing signal? Is that what this is? If that is the case, don't waste time getting distracted by it as it's normal. If it's the typical blue glow, I'd be wondering if maybe the other power tube _isn't_ fully working or getting signal. Have you checked the screen resistors?
Is there any other symptom other than that pop?
Can you record it and post?


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## ampaholic (Sep 19, 2006)

jb welder said:


> Just looks like flux to me.
> Are you familiar with the blue glow that is fairly common around power tubes when passing signal? Is that what this is? If that is the case, don't waste time getting distracted by it as it's normal. If it's the typical blue glow, I'd be wondering if maybe the other power tube _isn't_ fully working or getting signal. Have you checked the screen resistors?
> Is there any other symptom other than that pop?
> Can you record it and post?


I am familiar with the blue glow and this certainly resembles that but seems to occur, or at least is exaggerated, in sync with the popping noise. I had tried new tubes and the problem persisted however I have not checked screen resistors. I replaced them a few years ago but of course that doesn't mean they are good. I will do that for sure.
I had considered trying to record the noise and may give that a try.
Thanks for all the great suggestions!


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## loudtubeamps (Feb 2, 2012)

A guess......high voltage spike,for sure.
I know u checked, but I would take a very close look at the tube socket face in question for faint signs of a carbon path between pins 3 & 4.
Has the amp to your knowledge ever blown a fuse? Cheers, d


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## ampaholic (Sep 19, 2006)

loudtubeamps said:


> A guess......high voltage spike,for sure.
> I know u checked, but I would take a very close look at the tube socket face in question for faint signs of a carbon path between pins 3 & 4.
> Has the amp to your knowledge ever blown a fuse? Cheers, d


Got the flashlight and magnifier out and looked as close as I could at this. Top, bottom, sides of the socket and looking down in at the pins as much as I could it sure looks clean.
In the 12 years I've owned the amp it's never blown a fuse.

As soon as my wife's migraine passes I'm going to try and do a recording. :-(


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## loudtubeamps (Feb 2, 2012)

ampaholic said:


> Got the flashlight and magnifier out and looked as close as I could at this. Top, bottom, sides of the socket and looking down in at the pins as much as I could it sure looks clean.
> In the 12 years I've owned the amp it's never blown a fuse.
> 
> As soon as my wife's migraine passes I'm going to try and do a recording. :-(



gotcha'...any signs of carbon on either or both tube bases?


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## ampaholic (Sep 19, 2006)

loudtubeamps said:


> gotcha'...any signs of carbon on either or both tube bases?


No, nothing. Pins look good too.


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## ampaholic (Sep 19, 2006)

An update on this issue: it appears as if the problem has been resolved. After many months of chasing my own tail on this issue I determined that the problem was not phase inverter or output section related as I had myself convinced. As it turns out the blue flash that followed the popping noise was simply a byproduct rather than an indication that the noise was centred on one side of the circuit. Once that was determined I started looking hard at the power supply and ended up finding a bad connection on the 1K, 1 watt resistor under the doghouse cover.
I've been giving the SR a good workout the last couple of weeks and it sounds exceptional.

I have to send out a big thank you to forum member JB Welder who provided some patient offline guidance. Without his assistance I'd still be chasing my tail!


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## PulienJier (Dec 5, 2014)

Happy for you! 
Folks here are pearls. They have an infinite amount of knowledge and they are willing to share without a second taught.


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