71 Fender Twin Reverb Hum attenuated by knob even W/o tubein

[creaturesleeper]

OK this is driving me nut's...I have a 71 fender twin pre master volume. It has a hum which seems to come from the reverb circuit. Even with no load and everything on zero and the reverb pan and tube pulled you can still attenuate the hum with the reverb knob. This amp also has the typical vibrato opto tick but I found the fix for that...just a simple capacitor placement. Any Ideas where my reverb problem is coming from? Is it the reverb transformer? It does this with the 12AT7 Tube pulled and the Pan unhooked
Thanks!

[Mudcloth]

This may be a shot in the dark, but it might be the reverb pot. Try either jumping the terminals with a clip [try different combinations i.e. 1-2, 1-3, 2-3] and see if the hum goes away or replace the pot with the correct ohm pot. I believe it's a 100K linear pot. Good luck.

[PretendMusic]

So, I asked my friend, John, who is a long-time Fender amp-repair Pro, about this problem...
(BTW, He also owns several vintage Fender Amps, himself.) And, here's his reply:

"Without seeing it, I'll have to guess.
So, I am in no way responsible for being wrong when guessing...

The Fourth tube from the RIGHT, looking at it from the back, is the Mixer section of the circuit. Tube V4B, specifically, on the schematic.
With all of the reverb parts removed, as you mentioned, what's left is a 7025 (12AX7) tube, with an open input. Of course, it will hum with
the reverb knob turned up, much like a guitar cord plugged in with the other end open and the volume turned up.

Now, with the circuitry intact (all the reverb parts re-installed) and the
same hum still present, the culprit could be:
the tube, V4B,
the cathode-bypass cap attached to it (25uF/25V),
an open circuit in the reverb tray or cables (transducer maybe?),
a bad resistor,
dirty tube sockets,
a power supply problem,
all of the above,
or something else that I haven't considered, because I can't see it or test it, myself.
Note that there were variations on everything that Fender made during this period.

But, in my opinion, these were such bad-sounding amps. They're CBS at it's worst. With a squashed power supply.
No bias adjust, except for hum balance. They have a solid-state rectifier. As a result, they're very brittle sounding.
No soul. Perfect for that Nashville twang. And not really, not even for that...

I wish I could be more helpful...
But, here's a link to the Twin Reverb's schematic:
http://www.ampwares.com/schematics/twin ... _aa270.pdf

Good Luck..."
-JM

I just tend to use my Johnson J-Station, these days, myself, with the S/PDIF out, direct into my DAW... so, I'm no help.
-Chris

[creaturesleeper]

So, I asked my friend, John, who is a long-time Fender amp-repair Pro, about this problem...
(BTW, He also owns several vintage Fender Amps, himself.) And, here's his reply:

"Without seeing it, I'll have to guess.
So, I am in no way responsible for being wrong when guessing...

The Fourth tube from the RIGHT, looking at it from the back, is the Mixer section of the circuit. Tube V4B, specifically, on the schematic.
With all of the reverb parts removed, as you mentioned, what's left is a 7025 (12AX7) tube, with an open input. Of course, it will hum with
the reverb knob turned up, much like a guitar cord plugged in with the other end open and the volume turned up.

Now, with the circuitry intact (all the reverb parts re-installed) and the
same hum still present, the culprit could be:
the tube, V4B,
the cathode-bypass cap attached to it (25uF/25V),
an open circuit in the reverb tray or cables (transducer maybe?),
a bad resistor,
dirty tube sockets,
a power supply problem,
all of the above,
or something else that I haven't considered, because I can't see it or test it, myself.
Note that there were variations on everything that Fender made during this period.

But, in my opinion, these were such bad-sounding amps. They're CBS at it's worst. With a squashed power supply.
No bias adjust, except for hum balance. They have a solid-state rectifier. As a result, they're very brittle sounding.
No soul. Perfect for that Nashville twang. And not really, not even for that...

I wish I could be more helpful...
But, here's a link to the Twin Reverb's schematic:
http://www.ampwares.com/schematics/twin ... _aa270.pdf

Good Luck..."
-JM

I just tend to use my Johnson J-Station, these days, myself, with the S/PDIF out, direct into my DAW... so, I'm no help.
-Chris

I appreciate the input...the amp actually sounds rad live but I'm trying to clean it up some for recording purposes...I'll look into those other thing's...

[creaturesleeper]

So, I asked my friend, John, who is a long-time Fender amp-repair Pro, about this problem...
(BTW, He also owns several vintage Fender Amps, himself.) And, here's his reply:

"Without seeing it, I'll have to guess.
So, I am in no way responsible for being wrong when guessing...

The Fourth tube from the RIGHT, looking at it from the back, is the Mixer section of the circuit. Tube V4B, specifically, on the schematic.
With all of the reverb parts removed, as you mentioned, what's left is a 7025 (12AX7) tube, with an open input. Of course, it will hum with
the reverb knob turned up, much like a guitar cord plugged in with the other end open and the volume turned up.

Now, with the circuitry intact (all the reverb parts re-installed) and the
same hum still present, the culprit could be:
the tube, V4B,
the cathode-bypass cap attached to it (25uF/25V),
an open circuit in the reverb tray or cables (transducer maybe?),
a bad resistor,
dirty tube sockets,
a power supply problem,
all of the above,
or something else that I haven't considered, because I can't see it or test it, myself.
Note that there were variations on everything that Fender made during this period.

But, in my opinion, these were such bad-sounding amps. They're CBS at it's worst. With a squashed power supply.
No bias adjust, except for hum balance. They have a solid-state rectifier. As a result, they're very brittle sounding.
No soul. Perfect for that Nashville twang. And not really, not even for that...

I wish I could be more helpful...
But, here's a link to the Twin Reverb's schematic:
http://www.ampwares.com/schematics/twin ... _aa270.pdf

Good Luck..."
-JM

I just tend to use my Johnson J-Station, these days, myself, with the S/PDIF out, direct into my DAW... so, I'm no help.
-Chris

I appreciate the input...the amp actually sounds rad live but I'm trying to clean it up some for recording purposes...I'll look into those other thing's...

Oh by the way tell your friend thanks for trashing the best thing in my life....thats exactly the advice I was looking for.....ummmm not

[creaturesleeper]

So, I asked my friend, John, who is a long-time Fender amp-repair Pro, about this problem...
(BTW, He also owns several vintage Fender Amps, himself.) And, here's his reply:

"Without seeing it, I'll have to guess.
So, I am in no way responsible for being wrong when guessing...

The Fourth tube from the RIGHT, looking at it from the back, is the Mixer section of the circuit. Tube V4B, specifically, on the schematic.
With all of the reverb parts removed, as you mentioned, what's left is a 7025 (12AX7) tube, with an open input. Of course, it will hum with
the reverb knob turned up, much like a guitar cord plugged in with the other end open and the volume turned up.

Now, with the circuitry intact (all the reverb parts re-installed) and the
same hum still present, the culprit could be:
the tube, V4B,
the cathode-bypass cap attached to it (25uF/25V),
an open circuit in the reverb tray or cables (transducer maybe?),
a bad resistor,
dirty tube sockets,
a power supply problem,
all of the above,
or something else that I haven't considered, because I can't see it or test it, myself.
Note that there were variations on everything that Fender made during this period.

But, in my opinion, these were such bad-sounding amps. They're CBS at it's worst. With a squashed power supply.
No bias adjust, except for hum balance. They have a solid-state rectifier. As a result, they're very brittle sounding.
No soul. Perfect for that Nashville twang. And not really, not even for that...

I wish I could be more helpful...
But, here's a link to the Twin Reverb's schematic:
http://www.ampwares.com/schematics/twin ... _aa270.pdf

Good Luck..."
-JM

I just tend to use my Johnson J-Station, these days, myself, with the S/PDIF out, direct into my DAW... so, I'm no help.
-Chris

I appreciate the input...the amp actually sounds rad live but I'm trying to clean it up some for recording purposes...I'll look into those other thing's...

Oh by the way tell your friend thanks for trashing the best thing in my life....thats exactly the advice I was looking for.....ummmm not

[Mudcloth]

I love my mid 70's Twin. I've had it 20 years and it's just such a solid amp. About 15 years ago it was modded back to being partially blackfaced. I wanted to try some new speakers and the shop I took it to mistakenly put in two 16 ohm Celestions, forming an 8 ohm load. This might be why I like it so much, though. I used it at a recording session a couple of months ago and the guys went crazy over it.

Anywho, I always find it mildly humorous when someone disses on a Twin. My favorites being "They're too loud", "They're too clean", and "You've got to turn it up real loud before it breaks up" as if it didn't come with a volume knob and you don't own any foot pedals. If you want an amp to break up at 15-22 watts, buy a Deluxe. If you want an amp to break up at 3-5 watts, buy a Champ. If you want an amp with tons of headroom that you can get a bunch of sounds with, buy a Twin.

If you can't get a silverface Fender Twin, even unmodded, to sound good then you're doing something wrong. Then again, I'm not one of those guitar players that seeks the "ultimate" tone, as if there were only one. I happen to think there are a million beautiful guitar sounds to be had, which is probably why I have so many amps.
Rock on with your Twin, son. I hope you get it back up soon.

[FNM]

How can you hear the hum with no load?

[creaturesleeper]

How can you hear the hum with no load?

On with no input....maybe the wrong term...the speakers are still connected.....

[FNM]

So the master volume doesn't affect the hum?

Also, stick a 'dummy plug' (one with the tip and ground connected) in the input and see if it stays the same.

[creaturesleeper]

So the master volume doesn't affect the hum?

Also, stick a 'dummy plug' (one with the tip and ground connected) in the input and see if it stays the same.

Actually the volume and reverb both affect it...The volume gets noisier right between 5 and 7 and than quiets down around 10...but the reverb pot just makes it louder all the way up...I think this may be an input tube issue...the power tubes are all new and it's been recapped as well...with the dummy plug there was no difference....I should really just have a tech look at it...theres some other random low squeal/ static happening as well...It may have some other caps going bad besides the main ones which were replaced

[creaturesleeper]

So the master volume doesn't affect the hum?

Also, stick a 'dummy plug' (one with the tip and ground connected) in the input and see if it stays the same.

Actually the volume and reverb both affect it...The volume gets noisier right between 5 and 7 and than quiets down around 10...but the reverb pot just makes it louder all the way up...I think this may be an input tube issue...the power tubes are all new and it's been recapped as well...with the dummy plug there was no difference....I should really just have a tech look at it...theres some other random low squeal/ static happening as well...It may have some other caps going bad besides the main ones which were replaced

And just to add to the confusion the serial number says it's a 67 blackface #A24462 which doesn't really make sense cause it has a silver faceplate with blue TWIN REVERB AMP...it is the AB763 circuit....Ohhh Fender....This doesn't really solve my issue though....just makes me scratch my head some more....Thanks for all the help everyone!

[Scodiddly]

The very first year of the silverface was still mostly blackface inside. If there's a sort of beading strip around the grillecloth then you've got one of those units.

[creaturesleeper]

The very first year of the silverface was still mostly blackface inside. If there's a sort of beading strip around the grillecloth then you've got one of those units.

It's a 70 I was looking at some misinformation.....I opened er up and it seems someone did some surgery inside already...maybe they were trying to blackface it I dunnow...I'd like to fix this myself but I think I'm gonna take it in to Leighton Audio here in Portland and have em take a look... they only work on old tube stuff. It's a pretty simple circuit all point to point wired etc. but I'm not having much luck troubleshooting so far...I need to invest in a voltmeter to really test anything further

[FNM]

So you are just pulling the reverb tube when you test this out? I would get a 12ax7 and a 12at7 and swap 'em around with every tube separately and see if that does anything.