# Deluxe Reverb Hummmmmmmmm



## Lincoln (Jun 2, 2008)

A BF deluxe reverb that was built recently.....after about 2 days of playing it developed a 60hz hum. It's in both channels, and is not affected by volume or tone controls. It stops when you pull the phase inverter tube (V6). None of the other tubes in the pre-amp have any affect on it. Moving wires around doesn't change it either so I don't "think" it's lead dress issue. It's got a virtual center tap on the heater circuit. Only thing strange is pin #7 on V4 is quite microphonic. It stops being microphonic when V4 is removed. 

Anybody got an idea or suggestion? :smile-new:


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## Steadfastly (Nov 14, 2008)

It seems that it's got to be that V6 tube or its connections.


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## StevieMac (Mar 4, 2006)

Steadfastly said:


> It seems that it's got to be that V6 tube or its connections.


Based on what exactly? Pulling the PI simply prevents signal from the preamp getting to the power section. On what basis then has it "got to be" an issue with V6 or it's connections? Just curious about how you arrived at your conclusion...


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## nonreverb (Sep 19, 2006)

Primary B+ filter cap would be my first guess....


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## jb welder (Sep 14, 2010)

Are you sure it's 60hz, or could it be 120hz?
So if you only have V6 and the power tubes in, the hum is there? But with V6 removed and the power tubes in, the hum is gone?
Then I would think Steadfastly is on the right track that the V6 stage seems involved.


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## epis (Feb 25, 2012)

Did you try to replace the output tubes ? If you did, check out soldering job in output area and power supply.


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## Steadfastly (Nov 14, 2008)

StevieMac said:


> Based on what exactly? Pulling the PI simply prevents signal from the preamp getting to the power section. On what basis then has it "got to be" an issue with V6 or it's connections? Just curious about how you arrived at your conclusion...


Just reasoning. I am not expert but if that is where you get the hum, it sounds reasonable to me that is where the problem lies. 

Of note, there was a similar question asked a couple of weeks ago. Several suggestions were made and one of the members here who seems to really know his amps suggested that it had to be the tube. It turned out there was a "rattle" in the tube. It was replaced and fixed the problem. Just saying you may have a similar problem. One way to find out is to replace it.


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## Lincoln (Jun 2, 2008)

jb welder said:


> Are you sure it's 60hz, or could it be 120hz?
> So if you only have V6 and the power tubes in, the hum is there? But with V6 removed and the power tubes in, the hum is gone?
> Then I would think Steadfastly is on the right track that the V6 stage seems involved.


I have a frequency generator and I dialed up 120 just to see. It is for sure a 60hz hum. 

Yes, V6 removed & power tubes installed there is no sound/no hum. 

The V6 was an 12AT7, I tried a 12AX7 as well as a 12AU7, and the volume of the hum never changed.
Tried a different pair of 6V6's, no change. Tried another GZ34, no change.

Do output transformers ever hum? It's a used DRRI transformer, not a new one.

- - - Updated - - -



nonreverb said:


> Primary B+ filter cap would be my first guess....


I don't have anything to test caps with. It "looks" alright as far as the joints go. I may just replace it. I have another one.


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## WCGill (Mar 27, 2009)

Just clip your replacement cap piggyback style on the other caps to see if the hum improves. If it does, then it's a bad cap. If not, keep looking. Careful here, that cap will stay charged for some time.


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## jb welder (Sep 14, 2010)

Have you checked the virtual centre-tap resistors?


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## Church-Audio (Sep 27, 2014)

Lincoln said:


> A BF deluxe reverb that was built recently.....after about 2 days of playing it developed a 60hz hum. It's in both channels, and is not affected by volume or tone controls. It stops when you pull the phase inverter tube (V6). None of the other tubes in the pre-amp have any affect on it. Moving wires around doesn't change it either so I don't "think" it's lead dress issue. It's got a virtual center tap on the heater circuit. Only thing strange is pin #7 on V4 is quite microphonic. It stops being microphonic when V4 is removed.
> 
> Anybody got an idea or suggestion? :smile-new:


Check your bias and other voltages check for red plating. Use chopstick to whack board can you make it worse? Could be a bad solder joint. Or worse a bad cross connection in between the boards. I have also seen cloth wire on these kits crush together in between the boards and start to conduct. I would be surprised if you had bad caps unless your using cheap caps. Atoms or f&t are pretty reliable.


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## nonreverb (Sep 19, 2006)

It's rare but I've had bad electrolytics right out of the box. It could be a faulty solder joint on a supply cap as well.



Church-Audio said:


> Check your bias and other voltages check for red plating. Use chopstick to whack board can you make it worse? Could be a bad solder joint. Or worse a bad cross connection in between the boards. I have also seen cloth wire on these kits crush together in between the boards and start to conduct. I would be surprised if you had bad caps unless your using cheap caps. Atoms or f&t are pretty reliable.


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## jb welder (Sep 14, 2010)

While I won't completely rule out caps or filtering, if they were a problem the hum should be 120hz and not 60hz.
60hz issues are more often grounding or heater or shielding issues.


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## nonreverb (Sep 19, 2006)

Indeed...perhaps a bad ground where the two channels are summed together. One quick way to eliminate the power supply is an ac meter reading on the B+.
Would you happen to have a picture of the chassis for us to look at?




jb welder said:


> While I won't completely rule out caps or filtering, if they were a problem the hum should be 120hz and not 60hz.
> 60hz issues are more often grounding or heater or shielding issues.


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## loudtubeamps (Feb 2, 2012)

If replacing the phase inverter with a confirmed healthy one does not solve the problem, I would be looking at the bias supply filter cap as well as any significant differences between current draw on the output tubes.


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## Church-Audio (Sep 27, 2014)

What's your plate voltage on the phase inverter??? I would check all the vales of resistors and the .1uf caps for leakage in the phase inverter. If you can't test them swap them out for good ones.


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## jb welder (Sep 14, 2010)

loudtubeamps said:


> I would be looking at the bias supply filter cap


 Good point, I forgot that bias is half-wave rectified, so bias filter issues will give 60hz hum rather than 120hz hum main filters will give :smile-new:.


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## Church-Audio (Sep 27, 2014)

I just want to say I think it's really nice how we all try to help each other around here. It's nice to see. Some of us are competitors but we are all keen on helping each other out with solutions and the years and years of experience that some of us have.


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## Lincoln (Jun 2, 2008)

Well, I had the amp back on the bench last night. 
I re-did the whole filter cap board. Changed out all the 16uF filter caps for 20uF caps.
While I was in there I re-soldered a whole bunch of my ground connections on & around the
pots and in the preamp section too.
My hum dropped to what I would call a normal level. Certainly livable. I'd call it success.

Thank you very much everybody who took the time to fire off ideas. You guys are great! :sFun_cheerleader2:


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## nonreverb (Sep 19, 2006)

Great suggestion! Bias supply definitely could cause the symptom as well.



loudtubeamps said:


> If replacing the phase inverter with a confirmed healthy one does not solve the problem, I would be looking at the bias supply filter cap as well as any significant differences between current draw on the output tubes.


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