I am sick of failing amplifiers

[Kingrex]

The picture looking directly down on top of the pot with the volume knob towards the front or bottom of the image. That black wire (copper shield/grnd with hot signal in clear tube) coming in from the left side comes directly from the RCA on the back of the amp. The same type wire going to the right goes to the circuit inside of the amp.
For the short term, I will try and get a pipe cleaner with very little Deoxit on it into the slit on top and clean the contacts.
A more long term fix may be removal of the pot all together and replacing it with some other device like a resistor or transformer or something. I am happy to use an external preamp with the amp. For now, I want it to function for a few more months. Hopefully cleaning will do the trick.

The internal volume was put to me as a manufacturer design as I was trying to get this built up to a stock Black Shadow MKII.

 

[Kingrex]

Fortunately I have been watching a doctor series on TV. I was able to apply my newfound medical expertise and perform surgery on the amp. I was able to get a pipe cleaner with Deoxit G100 into the swiper. I brushed it well and ran the swiper back and forth many times. While at it I cleaned all the tube pins, RCA, speaker jacks, speaker cable ends and power inlets. I also changed the speaker cable to my Inskustik 2404 AIR. An amazing amount of oxidation came off it all. The potentiometer is adjusting without popping. The microphonic tube is also quiet. The amp is performing at a much higher level.. The notes hand longer and play more real. Piano has more body and resonance. Weight is full and fleshed without being congested or wooly. Faster. More punch and hit. Details are clear and intelligible. I am very happy with this amp now. Took a hell of a long time and a pile of money. But I finally have a SET I can say I am proud of and happy with. One of my fails is finally a success.

 

[Atmasphere]

Fortunately I have been watching a doctor series on TV. I was able to apply my newfound medical expertise and perform surgery on the amp. I was able to get a pipe cleaner with Deoxit G100 into the swiper. I brushed it well and ran the swiper back and forth many times. While at it I cleaned all the tube pins, RCA, speaker jacks, speaker cable ends and power inlets. I also changed the speaker cable to my Inskustik 2404 AIR. An amazing amount of oxidation came off it all. The potentiometer is adjusting without popping. The microphonic tube is also quiet. The amp is performing at a much higher level.. The notes hand longer and play more real. Piano has more body and resonance. Weight is full and fleshed without being congested or wooly. Faster. More punch and hit. Details are clear and intelligible. I am very happy with this amp now. Took a hell of a long time and a pile of money. But I finally have a SET I can say I am proud of and happy with. One of my fails is finally a success.

A lot can be said for cleaning contacts! This is one reason silver is a bad idea for tube sockets- tin plated contacts don't corrode nearly as fast. Like gold, tin resists corrosion. That's why you can buy 70 year old tube sockets off of eBay and they still work fine.

IIRC that amp uses a 6DJ8? If yes, that tube is prone to microphonic issues. Finding one that isn't microphonic pays off nicely.

 

[Kingrex]

Ok, for the tech heads. 1 amp has some hum. I have moved all the tubes around. What stays consistent is that the noisy amp is very microphonic. If you tap the input or driver tube its loud out the speaker. The other amp not at all. I can move the input and driver. The noise stays with the one amp.
Thoughts. What should I check.

 

[MarkusBarkus]

...both plugged into same outlet/run?

 

[adrianywu]

Ok, for the tech heads. 1 amp has some hum. I have moved all the tubes around. What stays consistent is that the noisy amp is very microphonic. If you tap the input or driver tube its loud out the speaker. The other amp not at all. I can move the input and driver. The noise stays with the one amp.
Thoughts. What should I check.

What is the tube complement ? Does it use directly or indirectly heated tubes ? Are the filaments supplied with AC or DC ? Is the hum 120Hz or 60 Hz ?

 

[treitz3]

Also, is this the same hum that you solved earlier on tonight (as mentioned in another thread, after pressing on it)?

Tom

 

[Kingrex]

Also, is this the same hum that you solved earlier on tonight (as mentioned in another thread, after pressing on it)?

Tom

That's only part. Further invesigation showed this furter anomoly.

 

[Kingrex]

What is the tube complement ? Does it use directly or indirectly heated tubes ? Are the filaments supplied with AC or DC ? Is the hum 120Hz or 60 Hz ?

E88CC input and a 7116 driver.
I don't know how it operates.
Pretty sure 60 cycle hum. Need to doule check.

 

[Kingrex]

...both plugged into same outlet/run?

Yes

 

[Kingrex]

Ok, for the tech heads. 1 amp has some hum. I have moved all the tubes around. What stays consistent is that the noisy amp is very microphonic. If you tap the input or driver tube its loud out the speaker. The other amp not at all. I can move the input and driver. The noise stays with the one amp.
Thoughts. What should I check.

I'm going to add something. Putting a weight on top and controlling case vibrations helps. But even damped, its super microphonic on the input tubes. The power tube not as muck. I can tap that and it does not reaonate like the input and driver will when tapped.

Christ. I thought I was done futzing with these. I do not want to hand these back to a tech after giving him $6k last time. I am so done spending money.

 

[treitz3]

Do you have some spare input tubes?

Tom

 

[DonH50]

Ok, for the tech heads. 1 amp has some hum. I have moved all the tubes around. What stays consistent is that the noisy amp is very microphonic. If you tap the input or driver tube its loud out the speaker. The other amp not at all. I can move the input and driver. The noise stays with the one amp.
Thoughts. What should I check.

Microphonics usually indicate a bad tube, though can also be caused by something else being loose. I would start by swapping tubes one at a time from the good amp to the bad and vice-versa to see if it is a tube (hopefully as that is the easiest thing to replace). If not, then use a plastic probe or rod to tap and push around and see if you can identify the connection or component causing the problem. Hopefully not the output transformer... I would also visually inspect the resistors, especially cathode resistors, for signs of damage (burn marks) and if possible measure their value (after the amp has been off long enough for all power caps to discharge, and with the amp unplugged). Hum could also be a bad cap; check decoupling (power rail) caps for bulging and measure if possible (but that usually has to be done out of circuit).

With any luck solving the microphonic issue will fix the hum issue. If it's not just a bad tube troubleshooting gets harder.

HTH - Don

 

[DasguteOhr]

normally a russian 6n23p is used in the input. if the tube is wired srpp then e88cc is not a good choice as a replacement. firstly e88cc is wired differently from the heater, and secondly 6n23p has a higher Uf/k value and is better suited to SRPP circuit. 6n23p has a shield between the triode systems pin 9 must be grounded, with e88cc pin 9 is the grounding point of the heater when heated with 6.3 V.
Sorry ignore that I misread on the homepage is a 6922 not 6n23p


I already wrote to you about microphonics there isn't much that can be done except replacing it. There is nothing that can be done about mechanically loose grids in the tube.

 

[adrianywu]

I would start with the basics and measure all the voltages. Coupling caps could become leaky before they fail, and this is a warning before a catastrophic failure that takes out your tubes and possibly the output transformer. Noise and microphonics would be the least of your worries in that case. Or it could be as simple as a signal wire touching or getting too close to a component. I have had this issue before when the input wire was touching the plate load resistor of the input stage, due to poor workmanship (mine !).

 

[Atmasphere]

I have moved all the tubes around.

What is meant by this? Did you swap them for their mates in the other channel? If yes my first response is you might have thought you did so but somehow that microphonic tube stayed put. Since I doubt that, perhaps you can describe what you mean by 'microphonic'. If you're talking about a sputtering sound, that's not microphonics.

I've seen coupling capacitors get microphonic although that is quite rare. Oddly, some military hermetically sealed Teflon caps I encountered about 35 years ago turned out to be really bad in this regard. Someone had installed them in an ARC SP10 and it was not until I had replaced them all that the microphonic problem went away.

If weight on the amp reduces hum, the chassis is resonating to the power transformer's vibration. It might simply be that the bolts that hold the transformer itself together are loose. If you decide to try tightening them, since you're already going to be in there consider finding non-magnetic stainless bolts to replace them. The stock bolts should also be equipped with insulating washers at either end and possibly also a cardboard tube along its length to help insulate the bolt from the laminations of the transformer. The bolt can act as a magnetic short to the transformer and cause it to heat up; hence the washers and the like; but they are not a 100% cure. A thermal camera can reveal this problem- if the bolts are running hotter (after an hour or two) than the rest of the transformer then this is a problem and the non-magnetic bolts (or better insulators) are a good idea.

 

[andromedaaudio]

I can attest to that .
The CAT jl2 sign power amp although fine sounding had transformer hum .
I didnt go to.through all that atmasphere suggested i simply put some weights on the transformer casing and it reduced it somewhat .

I suppose Ken Stevens decided to fix the the issue with the CAT Jl5 amourphous core which is basically as noise free as my former
Boulder transistor amplifier.

In 14 years of owning CAT tubegear i changed the tubes of the preamp once .
And i had 1 KT 120 tubefailure.
Never had an issue , always topsound .
I do travel a lot so i dont listen that much but still.

 

[Kingrex]

It was my intent to get into them today and visually confirm the amps are identical and to look for loss connections.
How do I blead off caps? Can I wire a 10K heavy green resistor from my crossover spares and use that from the cap to ground? Or will they blow up from the high voltage and current.

 

[Atmasphere]

It was my intent to get into them today and visually confirm the amps are identical and to look for loss connections.
How do I blead off caps? Can I wire a 10K heavy green resistor from my crossover spares and use that from the cap to ground? Or will they blow up from the high voltage and current.

Do you have a DVM? I'd simply check the power supply Voltages and see if they are a concern. If the supply has significant Voltage (over 200V) then the 10K resistor needs to be able to handle some power- 5 Watts recommended.

If a connection is lost the amp is likely to simply not work. SETs are pretty simple and are likely to not run at all if a single connection is lost.

 

[Kingrex]

Do you have some spare input tubes?

Tom

I do. But I moved all the tubes from one amp to the other and the issue did not follow. I first moved the E88cc and the 7119. No change. Then I moved the 845. No change. I don't think its the tubes.

What is meant by this? Did you swap them for their mates in the other channel? If yes my first response is you might have thought you did so but somehow that microphonic tube stayed put. Since I doubt that, perhaps you can describe what you mean by 'microphonic'. If you're talking about a sputtering sound, that's not microphonics.

I've seen coupling capacitors get microphonic although that is quite rare. Oddly, some military hermetically sealed Teflon caps I encountered about 35 years ago turned out to be really bad in this regard. Someone had installed them in an ARC SP10 and it was not until I had replaced them all that the microphonic problem went away.

If weight on the amp reduces hum, the chassis is resonating to the power transformer's vibration. It might simply be that the bolts that hold the transformer itself together are loose. If you decide to try tightening them, since you're already going to be in there consider finding non-magnetic stainless bolts to replace them. The stock bolts should also be equipped with insulating washers at either end and possibly also a cardboard tube along its length to help insulate the bolt from the laminations of the transformer. The bolt can act as a magnetic short to the transformer and cause it to heat up; hence the washers and the like; but they are not a 100% cure. A thermal camera can reveal this problem- if the bolts are running hotter (after an hour or two) than the rest of the transformer then this is a problem and the non-magnetic bolts (or better insulators) are a good idea.

New input transformers, from Audion. New Output transformers, from Electroprint. Not sure what you mean about cardboard tubes. The output is U core. But it has a bell and feet. I can only hope Audion shipped the Toroid input with a SS bolt in the middle. What a joke if they did not.
There is still Mu metal around one side of the input toroid. I could see if moving it stops a spray of EMI into to circuit. Its currently oriented between it and the output transformers.
I sort of don't think that is the issue. I think its a wire pressed up against something. I have seen a wire from the balance pot across the 845 hard pressed against a choke on the one amp. I wonder if something is going on there. Or if other wires are run to close to something somewhere else. I will try and mimic the wire layout in the more quiet amp. I hope the tech left some wiggle room.

I need to bleed off the caps before I do this. Per other post, is there a best way to do this?