# Help with noisy reverb on a BF super



## Brunman (Apr 12, 2019)

Hello everyone I am having some trouble with a 66 BF super Reverb amp ( ab763) and was hoping for some direction to fix the 120 cyl hum ( not positive its 120) from the reverb. I have had some help with this amp from a previous post and different issues were taken care of but I have not been able to get the reverb to stop the noise. I have studied the circuit and changed some older caps but it has not changed anything,
Some clarification on the issue , ,the noise starts right away when you turn up the reverb POT, volume could be completely down and gets louder as it is turned up, the reverb tank does work just with a lot of hum,I have tried changing the tubes, have removed and checked some of the caps off the board while replacing with newer ones.
The only thing that had stopped the sound was when I was testing voltage on one of the .1Mf 200v blue caps , the hum went away.
My Question is would the reverb OT cause this ? or is it still some Caps /Resistor I'm missing in the schematic, would appreciate any advice on this one, thanks


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## Hammerhands (Dec 19, 2016)

Does it have the original braided metal reverb cables?


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## StevieMac (Mar 4, 2006)

Are you certain the issue's _not_ with the tank or connections to it? Have you tested the amp with a different tank and/or cables? 
Not meaning to sound overly simplistic but I surprise myself all the time by missing the obvious.


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## Brunman (Apr 12, 2019)

Hammerhands said:


> Does it have the original braided metal reverb cables?


I was using the original foot petal that came with it, thinking that may be the problem, I bought a new one and it did not change anything.


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## Brunman (Apr 12, 2019)

StevieMac said:


> Are you certain the issue's _not_ with the tank or connections to it? Have you tested the amp with a different tank and/or cables?
> Not meaning to sound overly simplistic but I surprise myself all the time by missing the obvious.


I do not have another tank but have cleaned the connections as best I can. Hmmm wondering if there is a test with a meter that may tell me if it is bad. eg resistance or a short in the tank.


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## Paul Running (Apr 12, 2020)

Brunman said:


> I do not have another tank but have cleaned the connections as best I can. Hmmm wondering if there is a test with a meter that may tell me if it is bad. eg resistance or a short in the tank.


Time to bring the scope out and track it down.


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## Jerome (Dec 4, 2015)

Tank should have a 2 ohm input , and a 200 ohm output reading with your meter. Disconnect the rca inputs at the amp , and measure across the rca jacks on the cables.


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## Brunman (Apr 12, 2019)

Paul Running said:


> Time to bring the scope out and track it down.


I wish i had a scope


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## Brunman (Apr 12, 2019)

Jerome said:


> Tank should have a 2 ohm input , and a 200 ohm output reading with your meter. Disconnect the rca inputs at the amp , and measure across the rca jacks on the cables.


Stevi sent me in that direction so I checked the cables and came out with 2 ohms on the input and 712ohm on the out put. no shorts while i was checking that and looking at the schematic I noticed some small voltages on the electrolytic 25-25 's and rechecked them with 1 measuring 25v instead of 8v. Im going to replace that one and see if changes things.


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## jb welder (Sep 14, 2010)

First thing is what is the history of the amp? Did it ever work right while in your posession?
If not, you should check that the tank has the right numbers on it (4AB3C1B).

Also, try it with the no footswitch connected.


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## Paul Running (Apr 12, 2020)

First thing is to isolate the source of hum. Without a scope: try grounding the control grid for the reverb recovery stage and listen for hum.


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## Brunman (Apr 12, 2019)

while i was checking that and looking at the schematic I noticed some small voltages on the electrolytic 25-25 's and rechecked them with 1 measuring 25v instead of 8v. Im going to replace that one and see if changes things


jb welder said:


> First thing is what is the history of the amp? Did it ever work right while in your posession?
> If not, you should check that the tank has the right numbers on it (4AB3C1B).
> 
> Also, try it with the no footswitch connected.


yes this was one of the things wrong when i got it. JB you had helped me awhile back with getting the bias/voltages correct and after I replaced some of the ceramics I got the channels to quiet right down.But the reverb was always super noisy and now Im just wasting time changing out components hoping I will get lucky. number on the tank inkstamped 4 C2D1B on the side are 57 77 340 everything els is pressed in the Accutronics -PAT no-Made in USA etc.


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## Paul Running (Apr 12, 2020)

"The only thing that had stopped the sound was when I was testing voltage on one of the .1Mf 200v blue caps , the hum went away."
You are grounding that point through the impedance of your meter. Faulty termination (electrical) of components will cause hum pickup...not good to have floating (electrical) components...you will discover that improper terminations (electrical) act like antennae...a tuned circuit, that will pass it down the signal chain.


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## jb welder (Sep 14, 2010)

Brunman said:


> number on the tank inkstamped 4 C2D1B on the side are 57 77 340 everything els is pressed in the Accutronics -PAT no-Made in USA etc.


Whatever is in the blank spot between 4 and C, it is the wrong tank regardless. The 'C' is why it is measuring 700 vs 200 ohms I think.

@Paul Running above mentioned grounding the grid to check that the amp side is ok. You can do that by shorting out the jack marked 'reverb output' on the amp itself. Either with a shorting plug, or a pair of needle nose or something. You want to connect the tip to shell of that jack.
If everything is then quiet, even with reverb turned up, the issue is the tank (or cables to tank).

The 25 vs 8 volts on that cap could be caused by that tube, but also check that the resistor it is across measures it's correct value.


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## Brunman (Apr 12, 2019)

Paul Running said:


> "The only thing that had stopped the sound was when I was testing voltage on one of the .1Mf 200v blue caps , the hum went away."
> You are grounding that point through the impedance of your meter. Faulty termination (electrical) of components will cause hum pickup...not good to have floating (electrical) components...you will discover that improper terminations (electrical) act like antennae...a tuned circuit, that will pass it down the signal chain.


Thanks Paul I am a novice at this electrical theory so i am just looking at the info on the schematic and trying to match what I think is the signal path, checking listed voltages, not really clearly seeing between the wired diagram.vs the schematic one. I am improving as i go and appreciate every ones help. I did JB suggested previously and did not notice much of a change with the foot switch in or out .


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## Jerome (Dec 4, 2015)

Here's a great read about reverb tanks .





Spring Reverb Tanks Explained and Compared | Amplified Parts







www.amplifiedparts.com




Yours should be a 4AB3C1B 
I would get the right tank before doing any more troubleshooting. If the input to the reverb recovery stage is not terminated properly , I think it will hum excessively . Jerry


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## Brunman (Apr 12, 2019)

jb welder said:


> Whatever is in the blank spot between 4 and C, it is the wrong tank regardless. The 'C' is why it is measuring 700 vs 200 ohms I think.
> 
> @Paul Running above mentioned grounding the grid to check that the amp side is ok. You can do that by shorting out the jack marked 'reverb output' on the amp itself. Either with a shorting plug, or a pair of needle nose or something. You want to connect the tip to shell of that jack.
> If everything is then quiet, even with reverb turned up, the issue is the tank (or cables to tank).
> ...


Checked the resister and it good 2.27k I will go ground the the grid.


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## Brunman (Apr 12, 2019)

Ok I just did as you suggested and the amp is quiet when i ground the grid, the cables measured resistance is like 0.2 ohms,no shorts. looks like I need to get the correct tank . Any one know a god website to grab a replacement


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## Hammerhands (Dec 19, 2016)

nextgenguitars.com has some, tubesandmore.com has many.

There's one guy who always suggests a MOD brand of tank...there are four or five other brands.

What do the wires to the tank look like?


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## Brunman (Apr 12, 2019)

Hammerhands said:


> nextgenguitars.com has some, tubesandmore.com has many.
> 
> There's one guy who always suggests a MOD brand of tank...there are four or five other brands.
> 
> What do the wires to the tank look like?


Wires seem good checked it with a different set of cables and it didn't change anything.


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## Hammerhands (Dec 19, 2016)

The original wires are braided and look like this.





Reverb Cable Kit - Vintage style RCA, 3 ft and 5 ft | Antique Electronic Supply


Fully Assembled version: Package includes two vintage style RCA cables: One 3 foot and one 5 foot. DIY Kit: Assembly required. Kit comes with one 3 ft. and one 5 ft. length of insulated braided wire and 4 RCA plugs. Solder RCA plugs onto the ends of the wires by stripping 3/8" of the white...




www.tubesandmore.com





Fender sells some like this.








Fender Amp Reverb Cables 48” Right Angle 0056931049 | Reverb


Brand New Genuine Fender 48″ reverb cables with right angle plugs. Long enough for use in any Fender amplifier.Fender part # 0056931000 , 0056931049 Authorized Fender parts distributor since 2001 Visit us on the web for thousands of cool & hard to find guitar & amp parts!




reverb.com





I think they are a little different than stereo interconnect cables. I know they have extra long pins, I think they can handle more current.

Is there still a bag?


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## Paul Running (Apr 12, 2020)

Brunman said:


> Thanks Paul I am a novice at this electrical theory so i am just looking at the info on the schematic and trying to match what I think is the signal path, checking listed voltages, not really clearly seeing between the wired diagram.vs the schematic one. I am improving as i go and appreciate every ones help. I did JB suggested previously and did not notice much of a change with the foot switch in or out .


Okay, make sure the contacts are clean in the foot switch jack, check their continuity with your Ohm meter (they are typically normally closed, like the input signal jacks of the amp), this is where it grounds the control grid for the recovery stage. If that grid is grounded and you are still hearing hum, it means you should proceed further down the signal chain until a grounded point removes the hum. This will move you closer to the faulty stage. Try to obtain a block diagram of your amp...it will help you see the overall structure of the amp and show a quick view of the signal path, then move to the full schematic for detailed troubleshooting.


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## Brunman (Apr 12, 2019)

Looks


Paul Running said:


> Okay, make sure the contacts are clean in the foot switch jack, check their continuity with your Ohm meter (they are typically normally closed, like the input signal jacks of the amp), this is where it grounds the control grid for the recovery stage. If that grid is grounded and you are still hearing hum, it means you should proceed further down the signal chain until a grounded point removes the hum. This will move you closer to the faulty stage. Try to obtain a block diagram of your amp...it will help you see the overall structure of the amp and show a quick view of the signal path, then move to the full schematic for detailed troubleshooting.


I think I get what your saying and the hum disappears when I short out the reverb output jack on the amp. I did notice the hum change a little bit when touching the foot switch but that is just what you mentioned earlier with the antenna effect .As others have suggested the tank is the wrong number and does not match the resistance so I think I will get the correct one and see if thats it.


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## Brunman (Apr 12, 2019)

Hammerhands said:


> The original wires are braided and look like this.
> 
> 
> 
> ...


Thanks Hamer they look like are the original ones and seem to check out ok, I did switch them out with some RCA ones and they did not change noise.I think I might try the MOD tank it sounds like they come with the cables connected to them ready to plug in.


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## Chitmo (Sep 2, 2013)

If you just wanna get rid of it due to frustration I’d gladly dispose of it for you


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## Brunman (Apr 12, 2019)

Chitmo said:


> If you just wanna get rid of it due to frustration I’d gladly dispose of it for you


Lol not at that stage yet and what would I do with all the spare time I would have if not working on this amp...


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## Brunman (Apr 12, 2019)

jb welder said:


> Whatever is in the blank spot between 4 and C, it is the wrong tank regardless. The 'C' is why it is measuring 700 vs 200 ohms I think.


Thanks again for your help JB
What model do you think this tank was for its not showing up as a replacement for anything, that i can find so far.


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## Paul Running (Apr 12, 2020)

Brunman said:


> Looks
> 
> I think I get what your saying and the hum disappears when I short out the reverb output jack on the amp. I did notice the hum change a little bit when touching the foot switch but that is just what you mentioned earlier with the antenna effect .As others have suggested the tank is the wrong number and does not match the resistance so I think I will get the correct one and see if thats it.


Yeah, the impedance will have an impact on the driver stage performance. Most driver stages use a transformer with an 8 ohm secondary impedance and it would be preferable to match impedances, especially with tube operated circuitry.


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## Brunman (Apr 12, 2019)

Paul Running said:


> Yeah, the impedance will have an impact on the driver stage performance. Most driver stages use a transformer with an 8 ohm secondary impedance and it would be preferable to match impedances, especially with tube operated circuitry.


Thanks for your help Paul


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## StevieMac (Mar 4, 2006)

The MOD tanks are MUCH better sounding than the Accutronic equivalents IMO.


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## dtsaudio (Apr 15, 2009)

Brunman said:


> Checked the resister and it good 2.27k I will go ground the the grid.


Did you find the cause of that voltage being so far out? If not that needs to be investigated before anything else.


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## Brunman (Apr 12, 2019)

dtsaudio said:


> Did you find the cause of that voltage being so far out? If not that needs to be investigated before anything else.


Thanks for Checking in Dan. No I am not sure why would it would be so far out when all the other 25uf-25v electrolytic are close to spec.I did take it out and replaced it with a new one and no change. 
JB mentioned that it may be the tube so I checked it and turns out I had the wrong one in there. Switched it out and its now reading 9v


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## Brunman (Apr 12, 2019)

Found some info on the tank Accutronics Products and Specifications
4- long tank standard size
space - (this is the missing no. )--Input impedance
C- (3rd no.)--output impedance--10k ohms
2- decay time medium
D- input (insulated) output (insulated)
1-no lock
B- Horizontal -open side down
I am assuming the 2nd no is missing because of the space,it may be the other way around but I read 2ohms at the input and 715ohms at the output. looking at the table in the link the missing no might be an A (1 ohm = 8 ohm) input and the output almost matches up with the C (800 ohm= 10k ohm).
Someone did write in ink above the input an (8) and a (5k) on the output, not sure what it means though. I cant find any amps that were associated with it so who knows how it got put in the old 66...


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## dtsaudio (Apr 15, 2009)

Not only is the output impedance way to high, which means you will lose signal, but it also has an insulated output, not a grounded output. If the recovery circuit doesn't ground the spring properly it will hum.


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## loudtubeamps (Feb 2, 2012)

a bit late to the party and didn't have a chance to read through but...just in case. Have you tried turning the tank around ?


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## Paul Running (Apr 12, 2020)

Correct terminations...they are easily overlooked, the tree and the forest syndrome.


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## Brunman (Apr 12, 2019)

dtsaudio said:


> Not only is the output impedance way to high, which means you will lose signal, but it also has an insulated output, not a grounded output. If the recovery circuit doesn't ground the spring properly it will hum.


I think it is grounded at least to the tank, the out side shield wire of the output has been soldered to the tank in one spot.


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## Brunman (Apr 12, 2019)

loudtubeamps said:


> a bit late to the party and didn't have a chance to read through but...just in case. Have you tried turning the tank around ?


if you mean switching the wires ,yes (by accident) but the tank is clearly labeled input (tank)-----input (amp) and output (tank)--- output (amp) That is how its hooked up.


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## Paul Running (Apr 12, 2020)

Confirm continuity with your Ohmmeter.


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## Paul Running (Apr 12, 2020)

Unless wires are out of place and connections are poor, it should be very quiet. These amps are typically very quiet, if the cables and wire locations are as the spec. pictorial layout...like a photo of the chassis indicating how and where the cables are routed. If you are familiar with guitar wire routing in the guitar cavity, you know that it can be sensitive to EMI which 60Hz being a dominant source, (unless the cavity is shielded)...same idea with your amp.


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## loudtubeamps (Feb 2, 2012)

Brunman said:


> if you mean switching the wires ,yes (by accident) but the tank is clearly labeled input (tank)-----input (amp) and output (tank)--- output (amp) That is how its hooked up.


No, not switching the leads, the tank....physically rotating it 180° (end to end) to change the orientation of the tank (transducers) in relation to the transformers in your amplifier. If the tank is mounted the wrong way, hum (EMF) can be introduced into the rev. circuit via the tank.


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## Latole (Aug 11, 2020)

Hammerhands said:


> nextgenguitars.com has some, tubesandmore.com has many.
> 
> There's one guy who always suggests a MOD brand of tank...there are four or five other brands.
> 
> What do the wires to the tank look like?


I read a guy who by a Mod reverb tank and reverb is not as good as original Accutronics reverb


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## Latole (Aug 11, 2020)

Any standard audio cables work fine, no need " special" Reverb cable


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## Brunman (Apr 12, 2019)

loudtubeamps said:


> No, not switching the leads, the tank....physically rotating it 180° (end to end) to change the orientation of the tank (transducers) in relation to the transformers in your amplifier. If the tank is mounted the wrong way, hum (EMF) can be introduced into the rev. circuit via the tank.


ok I see what your saying, as far as orientation go's the tank really can only fit one way or the leads are too short.


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## nonreverb (Sep 19, 2006)

Brunman said:


> ok I see what your saying, as far as orientation go's the tank really can only fit one way or the leads are too short.


By far one of the most common problems with reverb hum. Tank changed and intalled backwards. The radiation from the power transformer induces hum in the output coil of the tank. Not as common on a Super as the distance from the transformer to the bottom of the chassis is farther but stranger things can happen. Is it possible the tank is a replacemet?


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## Brunman (Apr 12, 2019)

nonreverb said:


> By far one of the most common problems with reverb hum. Tank changed and intalled backwards. The radiation from the power transformer induces hum in the output coil of the tank. Not as common on a Super as the distance from the tank to the bottom of the chassis is farther but stranger things can happen. Is it possible the tank is a replacemet?


I think it is a replacement. The mismatched identification number doesn't match the output impedance. I am going to buy the correct one and see if it makes a difference.


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## loudtubeamps (Feb 2, 2012)

Brunman said:


> I think it is a replacement. The mismatched identification number doesn't match the output impedance. I am going to buy the correct one and see if it makes a difference.


Or...take a few minutes...grab some longer RCA cables that will allow you to turn the tank around and see if the hum is reduced...might save the cost of a new tank...worth a try..yes?


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## Brunman (Apr 12, 2019)

loudtubeamps said:


> Or...take a few minutes...grab some longer RCA cables that will allow you to turn the tank around and see if the hum is reduced...might save the cost of a new tank...worth a try..yes?


Yup, its worth a try. I'll keep you posted


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## Brunman (Apr 12, 2019)

Update ,the MOD tank I ordered from NextGen showed up and fixed the noise completely. No buzz when I turn on the reverb switch like it use too, reverb sounds good and strong. Amp is almost silent with a small hum as you increase the volume.The only other thing making some noise is the foot switch when on the floor(basement concrete), if I move it around or touch it the noise disappears. Going to check the grounds and clean them up. I want to thank all of you guys for the help again ,this forum is the best.


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## Latole (Aug 11, 2020)

" Amp is almost silent with a small hum as you increase the volume."
-Brunman

With guitars plug or not ? 
To test amp noise/ hum, don't plug anything to the amp.

To silent a old amp ; clean in put jack shorting contacts to gound. The are often "dirty".
All 100K tubes's plate resistors may need to be replaced by new one.
3 prog AC wire with a good ground is a must.
Good 12XX7 tubes. Close matched 6L6, not more than 8 ma between them


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## Brunman (Apr 12, 2019)

Latole said:


> With guitars plug or not ?
> To test amp noise/ hum, don't plug anything to the amp.
> 
> To silent a old amp ; clean in put jack shorting contacts to gound. The are often "dirty".
> ...


Thanks Latole, I was checking without anything plugged in and after I installed a new set of Mullard pre-tubes. I will check the 100k resistors as you suggest and clean the grounds again. Is there any other resistors that would need some checking while Im in there? The amp is way better now, with the old tank I could not use the reverb at all.


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## Latole (Aug 11, 2020)

You can't check ( reading ohms) the 100K resistors.
It is the humidity in these resistors who may do some noise, their value

If everything is ok, then you may suspect these resistor and replace them by new one.

Did you understand I don't talk about grounds ( " .. and clean the grounds again"...) ?
I talk about input jacks N.C contacts to ground.


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## Brunman (Apr 12, 2019)

Latole said:


> You can't check ( reading ohms) the 100K resistors.
> It is the humidity in these resistors who may do some noise, their value
> 
> If everything is ok, then you may suspect these resistor and replace them by new one.
> ...


Yup I knew what you were referring to. If the old resistors are causing the noise now I may just change all of them .


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## nonreverb (Sep 19, 2006)

A word of caution: The noise generated by bad carbon comp resistors is more of a frying egg sound. Some will inevitably start arcing inside (hence the frying egg sound). Going in and replacing them all is debatable. An example of this was an interesting situation that happened once when I did just that on a customer's BF Deluxe Reverb. Changed tham all out and all the cathode caps as well. As much as it cleaned up things, he was a wee bit miffed that it changed the sound he was used to. I now proceed to inform customers that a sweeping replacement of parts can...and sometimes will, change the way the amp sounds. I let them decide whether the essentials get replaced or all of them. That said, bulging electrolytics are always replaced no matter what.


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## loudtubeamps (Feb 2, 2012)

Low freq. hum at idle....bad grounding, possibly lead dress, failing filters and the number one culprit I have found over the years is a weak/ bad pre-amp tube.


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## jb welder (Sep 14, 2010)

And always check the bias caps. Lots of people overlook them when doing filter caps, but they are even more critical.
Hum from bad bias caps will be 60Hz rather than 120Hz due to half wave rectification in bias circuit.


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## nonreverb (Sep 19, 2006)

jb welder said:


> And always check the bias caps. Lots of people overlook them when doing filter caps, but they are even more critical.
> Hum from bad bias caps will be 60Hz rather than 120Hz due to half wave rectification in bias circuit.


Yes indeed! It should be the first to go.


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## Brunman (Apr 12, 2019)

Thanks for the info guys ,I was going to change all the resistors but decided only to change the ones that were out of spec. Turns out the only ones that were bad were most of the 100k 's in the pre-amp section, all were out about 20% higher. I did use carbon comp just in case it made a difference in sound, but I can't hear anything different. The amp is dead quiet with nothing plugged in unless turned full.
JB, we we did some trouble shooting last year and dialed in the bias pretty good, you mention the bias caps are you referring to the neg. bias cap that is close to the transformer or something else. She is sounding pretty sweet with the MOD tank, but waiting for the Accutronic tank to show up so I can compare the two.


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## jb welder (Sep 14, 2010)

Brunman said:


> you mention the bias caps are you referring to the neg. bias cap that is close to the transformer or something else.


Yes. Behind the pilot light is a little board with a diode, resistor, and cap. That cap is the one that is sometimes overlooked but can cause big problems if it goes bad. That resistor should always be checked also.


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## Brunman (Apr 12, 2019)

OK yes that was changed to a 100uf/100v before I bought the amp, so not sure of the age. I replaced the resistor and left the diode. Should I install a 25uf/50 or a 50uf/50 or keep the same value that was in the amp, I am running a 5u4, so if I am correct it may need the extra voltage, what do you think.


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## jb welder (Sep 14, 2010)

Brunman said:


> OK yes that was changed to a 100uf/100v before I bought the amp, so not sure of the age. I replaced the resistor and left the diode. Should I install a 25uf/50 or a 50uf/50 or keep the same value that was in the amp, I am running a 5u4, so if I am correct it may need the extra voltage, what do you think.


I would stick with the 100uF/100V there. The extra voltage is a reliability upgrade in that spot. The increase in capacitance is not going to impact the tone in any significant way, but I wouldn't go much higher than 100uF there.


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## Brunman (Apr 12, 2019)

Great, I will change that one out before I button it up and just enjoy it for awhile. Next project on the bench will have to have a reverb tank in it seeings I will have an extra one. Thanks to all for the help,take care out there.


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## nonreverb (Sep 19, 2006)

Brunman said:


> OK yes that was changed to a 100uf/100v before I bought the amp, so not sure of the age. I replaced the resistor and left the diode. Should I install a 25uf/50 or a 50uf/50 or keep the same value that was in the amp, I am running a 5u4, so if I am correct it may need the extra voltage, what do you think.


A 5U4 will work but does drop more voltage. A potential issue tough, is stress to the old power transformer due to the extra current draw to power the 5U4's heaters.


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## Brunman (Apr 12, 2019)

My mistake I don't know why I wrote down 5U4 on my paperwork, I just checked the amp and it has a 5AR4 not the 5U4. This should be a better setup??


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