EQP-1A noise

We have a Pultec clone which started to make strange noises recently. Actually I know this sound from my Deluxe Reverb, where cleaning the sockets or changing tubes helped. But I just can't seem to find the source of this one here.
I already checked the voltages, changed the tubes, cleaned the tube sockets, changed the anode resistors, resoldered the solder points, ... nothing helped!

Any idea what else might be causing these clicks and pops?

Here is a sample I recorded with my RME Babyface Pro - all the gains at 0, amplified by 24dB so it's easier to hear.
https://www.dropbox.com/s/ty13qttz69s4ldd/pultec_noise%2B24dB.wav?dl=0

Any recent changes to the setup prior to these noises? And you've verified it's not something else in the chain??

I do know interconnects and power strips can get goofy sometimes...

Which clone is it?

scott2000 said:

Any recent changes to the setup prior to these noises? And you've verified it's not something else in the chain??

I do know interconnects and power strips can get goofy sometimes...

Which clone is it?

Click to expand...

Thanks for your reply!

I changed the tubes a few months ago, but everything was fine until now, nothing else changed in the setup.
It's definitely the Pultec, I've had it hooked up in three different places with different cables and inputs.
I'm not sure if I should post the manufacturer, as it's commercially available....  but I attached a pic of the inside.

andow said:

I already checked the voltages, changed the tubes, cleaned the tube sockets, changed the anode resistors, resoldered the solder points, ... nothing helped!
Any idea what else might be causing these clicks and pops?

Click to expand...

cathode resistors.

If it's a commercial product have you contacted the manufacturer?

Do you have an oscilloscope? Maybe check voltages and such with a DMM?

Jumper the grids of V2 together with a little alligator clip jumper on the grid side of the 1M resistors or whatever way is convenient (obligatory high voltage warning here). If the noise goes away, that means it's coming from upstream in which case you can jumper the grids of V1 together. This will at least eliminate upstream parts of the circuit which can help you focus your efforts.

It could be leakage in the output transformer, a common transformer problem. And hard to diagnose. Ideally disconnect the primary centre tap and use a megger to establish the leakage to ground.

gridcurrent said:

cathode resistors.

Click to expand...

This

squarewave said:

If it's a commercial product have you contacted the manufacturer?

Do you have an oscilloscope? Maybe check voltages and such with a DMM?

Jumper the grids of V2 together with a little alligator clip jumper on the grid side of the 1M resistors or whatever way is convenient (obligatory high voltage warning here). If the noise goes away, that means it's coming from upstream in which case you can jumper the grids of V1 together. This will at least eliminate upstream parts of the circuit which can help you focus your efforts.

Click to expand...

Of course I did contact the manufacturer and he sent me a picture with the test points for the voltages which are fine. After a few mails back and forth his conclusion was that the noise level would be normal for analog equipment...  ???

I jumpered the grids of the ECC82 and the noise was still there. So I changed the cathode resistor and capacitor but still no luck...

radardoug said:

It could be leakage in the output transformer, a common transformer problem. And hard to diagnose. Ideally disconnect the primary centre tap and use a megger to establish the leakage to ground.

Click to expand...

I never used a Megger,  but wouldn't the high measurement voltage destroy the output transformer?

andow said:

Of course I did contact the manufacturer and he sent me a picture with the test points for the voltages which are fine. After a few mails back and forth his conclusion was that the noise level would be normal for analog equipment...  ???

Click to expand...

Well you might want to consider the signal level that you're putting in and gettting out. You need to put a lot of signal into it to really exercise the full dynamic range of it. You need to put enough signal through so that it clips and then back off a little. Then adjust the input level of the downstream gear. If you just set the downstream gear to max and then adjust what's going into the EQP-1 to suit, the level going through the EQP-1 could be very low in which case you're just listening to the noise floor and maybe some noises inherent to tubes. Meaning it could mean that you just need to pump up the volume.

andow said:

I jumpered the grids of the ECC82 and the noise was still there. So I changed the cathode resistor and capacitor but still no luck...

Click to expand...

Which tube? V1 or V2? There are actually two cathode resistors on V2. If it's V2 that is actually a good result in a way because it almost certainly means that the noise is in the final output tube stage which consists of just the two tube / cathode resistor / capacitor elements and OT. So, if we are talking about V2, and it was successfully jumpered (does signal get through with V2 jumpered?), then you have narrowed things down quite a bit.

andow said:

I never used a Megger,  but wouldn't the high measurement voltage destroy the output transformer?

Click to expand...

Umm, no, and thats the whole point! If your transformer is leaky, it will make noises! Transformers are made to withstand the voltage that the Megger applies, and you can usually vary the applied voltage. A transformer like this should easily withstand 500 volts.

squarewave said:

Which tube? V1 or V2? There are actually two cathode resistors on V2. If it's V2 that is actually a good result in a way because it almost certainly means that the noise is in the final output tube stage which consists of just the two tube / cathode resistor / capacitor elements and OT. So, if we are talking about V2, and it was successfully jumpered (does signal get through with V2 jumpered?), then you have narrowed things down quite a bit.

Click to expand...

The ECC82 is V2, so the final output stage. If I connect the grids of the tube (so that no input signal is passing through) the noise is still there. Of course I changed both cathode resistors and caps, so this leaves me with the impression that the output transformer is the problem, right?

Unfortunately in the meantime the noise got even worse! 
Here is another recording from an RME UFX line input (+4dBu):
https://www.dropbox.com/s/896hfr2f7b5cpez/01-180620_1048.wav?dl=0

Update! The Pultec is silent again!  ;D

So here's what I did:
When the noise occured the first thing I did was obviously change the tubes, which did not make any difference so I put the tubes back in. Then I changed anode resistors, cathode resistors, cathode capacitors, cleaned and retightened the tube sockets and resoldered the solder points. I the course of doing so the noise was getting more and more and after narrowing the problem down to the output transformer I tried another tube again and voilá: the noise is gone!  8)