Twin (Reverb- popping/ rustling: noises).

[Sea Chief]

Hi y'all. Glad MEF back up running.

My Twin Reverb's had a few threads over past 2 years -all on this similar issue- & is still noisy.
But noise is definitely narrowed-down to the reverb.

Prior threads: had decided the loud POPS & general cruddy noise, was likely a conductive board. So I recently swapped in a new board, thick resin type, all new components. And a new rectifier board too. While checking wires for solidity, I found a loose heater wire @V2 pin 9 (impossible to see). SO the likely cause of the scary-loud POPS all along is my conclusion (& not a conductive board, or a mystery component failure which was my hunch).

After the new boards in though, the cruddy noise infuriatingly was still present behind the reverb. Pdf64 suggested pull the reverb ftsw to see if noise remains. It does. Also to swap V1 & V4. No change (V4 was recently renewed anyway).

So. Amp's well-behaved without the reverb, & the tremolo acceptable too (if not perfect). Only noisy with Reverb.

As you turn up Reverb knob noise gets progressively worse: under 3 = mild, above 3 = invasive-bad, very bad above 5.
Noise description: some mild pops, but generally an irritating, rustling-reverby-scratchy noise. Occasionally it's gone, other times comes & goes in patches.

If anyone had any ideas, much appreciated. SC

[Jon Snell]

Check the anode load resistors. If Carbon Composition (or as I call them 'Carbon Drifters', because they do), replace them with Metal Film or Metal Oxide for reliability.

[Sea Chief]

Check the anode load resistors. If Carbon Composition (or as I call them 'Carbon Drifters', because they do), replace them with Metal Film or Metal Oxide for reliability.

Ho Jon, thanks for reply. This new board you see, was built by a Pro amp builder here in UK; & going a full step further than simply replacing the old (possibly conductive) board for a thick new resin standoff type, all the board cap & resistors on it are brand new, & top notch quality too.

So I can rule some things out, straight off the bat. Resistors & board components/ Valves checked by my Pro (he even put some new ones in)/ sockets thoughrally cleaned multiple times.

The amp went to my Pro who did the best he could to try, but unable to locate the source of the nasty POPS (the source I found only by chance once back: a loose heater wire: I think this is a certainty, the main mystery finally solved after 2 years effort). He did numerous service-type things whilst it was with him, even replacing 2 power tubes. He then kindly sent me the new (populated) board, after we sort of went with the idea of a conductive board theory as I still found it noisy. We went with the consensus on here that that idea seemed logical, having tried & exhausted every other possible idea.

I had my doubts of the bad board, if folks recall. As the old board was only a few years old. But hey who am I to throw my hunch in the fray?

So I know it's Reverb related. Unoquivocally now. That hugely narrows-down the possibilities of the source of this particular resolute & perstering noise. But I don't know what next to check.

Thanks, SC

[Sea Chief]

A photo of the new board(s) installed, with all new non-CC resistors, & Vishay caps.

A huge ammount of work by me to transplant the new board in. So to find noise still persisting, esp after my Eureka! moment loose heater wire find, & after 2 years work on it, is almost unbearable.

But at least it's noisy in only in one section now . So it's kinda 85% fixed. Tantalisingly close.




Capt

[mikeydee77]

How old is the amp? Sometimes valve bases can be the source of noise. Bit like the board theory. You may be able to see discolouration to the insulation material, maybe not. Replacement is the only way to prove it either way.

Couple of other thoughts..

By the way I was thinking that the loose heater connection would not cause a pop as the heater warm up and cool time is going to mask it.. just a thought.

Assume reverb drive and recovery valves have been replaced?

[Chuck H]

It's a pretty build to be sure. But I wonder why they used CC resistors for plate loads and CF resistors elsewhere.?. The plate loads are where CC's are most likely to cause noise. At the same time the plate loads are where CC's are contributing some amount of compression. Which has been an attributed characteristic of this resistor type relative to the tone of these amps. My point is that there may be some reasoning to the resistor selection. That said... These are all new resistors and probably shouldn't be suffering moisture absorption or drift at this point. Somehow all the problems this amp had have carried over with a new board build!?! Did it ever work properly at least for a moment? I think it must have from the shop or they shouldn't have released it. Surely your prior toubles (which seem to still exist) were specified as target areas to fix?!?

Carbon composition resistors can absorb moisture that causes crackling and popping but that's typical of older resistors. That said I can't account for the coatings on newer CC resistors.

Are you showering with this amp? How wet is it where you live?

Otherwise you might try replacing the reverb transformer. You've gone so far with this amp already that this would seem like a marginal expense.

[g1]

What happens with the V3 12AT7 reverb drive tube removed? When you turn up the reverb you will get hum, but are the pops and noise still there?
If you can isolate whether the noise is in the drive side or recovery side of the reverb tank, that should help. I like Chuck's idea about the reverb drive transformer, removing V3 might tell you whether that is a possibility.

[Sea Chief]

How old is the amp? Sometimes valve bases can be the source of noise. Bit like the board theory. You may be able to see discolouration to the insulation material, maybe not. Replacement is the only way to prove it either way.

Couple of other thoughts..

By the way I was thinking that the loose heater connection would not cause a pop as the heater warm up and cool time is going to mask it.. just a thought.

Assume reverb drive and recovery valves have been replaced?

Hi MikeyD,

Well originally '78. But only the PT & OT & pots (& pots wiring) are original. And the 6x preamp valve sockets/ bases are original too. Hmm.

It's possible my loose heater wire find/ redo, isn't the root cause of the scary original POPS.. but IMO too much of a coincidence that once I did this, the major nasties were cured. The severed wire bare end was maybe touching a pin either side of 9, so I thought possibly conducting numnums to it.

Anyway. The power tube ceramics are new. But the preamp bases.. are old. I have contact-cleaned them a good few times, but this idea is really one of my last resorts. And I hadn't thought of this. My Pro did a BIG checkover you see, replaced a few tubes. So I'm confident if he says they check out, they're ok.

Is the reverb drive & recovery ones V3, & V4? I can always swap around an AT7 & 12ax7 from V1 etc.. as I know he put one new AT7 in, & 2x 12ax7's in.

Thanks for reply, SC

[Sea Chief]

Chuck H Hi Chuck, you've given me a compliment! Are you drunk or something?!

My very kind Pro made the new board, using his choice components. So resistors & caps.. I'm easily ruling them out. He'd not put used ones in: he put alot of work into the amp, to try find the cause of the noise, the sole problem it was sent to him to remedy. Tbh he was somewhat defeated. And by my saying the conductive board idea was a consensus opinion, by you guys, swayed him then to go whole hog & send me a populated new board. A last resort idea of his, as he felt he'd let me down. Then.. I found that loose heater wire, & most of the noise ceased. The nasty loud stuff I mean. This MUST be some correlation.

Yes as I've said many times, the amp when I rebuilt it 6 years ago (after I bought it as a dead dog TR bought off ebay) with some Blackface additions suggested by Rift like a choke, & you can see the slightly unusual recifier config he 'designed' for it too... worked great for 2 years. Reverb lush & quiet.

So it bears no resemblance to the original UL135w TR, apart from the cab, PT & OT behemoths that I swear at due to their weight. Even the speakers are modern Jensens. The faceplate is even a Blackface german repro (deutsche-perfect, naturally).

If it hadn't worked after I rebuilt it 6 years ago, perfectly & noiselessly........ I'd never spend any of you guys' time asking xyzab&c, over the last 2 years.

Reverb xfmr idea: thanks I'll note that, but hopefully try simpler trains of ideas before resorting to that swap out.

Cheers, SC

[g1]

Is the reverb drive & recovery ones V3, & V4? I can always swap around an AT7 & 12ax7 from V1 etc.. as I know he put one new AT7 in, & 2x 12ax7's in.

I want to know what happens with V3 socket empty.

[mikeydee77]

Yes pull V3 out and see if noise persists. If the noise is just the same then that rules out the drive side including transformer, valve, valve socket etc.

Could it be that the noise is there without reverb but just not all that intrusive? Reverb does sort of amplify / emphasise pops due to the decay. One obscure source of this can be loose UK mains plug wiring securing brass screws. A 78 amp will surely have an ancient mains cable.

[Jon Snell]

Ho Jon, thanks for reply. This new board you see, was built by a Pro amp builder here in UK; & going a full step further than simply replacing the old (possibly conductive) board for a thick new resin standoff type, all the board cap & resistors on it are brand new, & top notch quality too.

So I can rule some things out, straight off the bat. Resistors & board components/ Valves checked by my Pro (he even put some new ones in)/ sockets thoughrally cleaned multiple times.

The amp went to my Pro who did the best he could to try, but unable to locate the source of the nasty POPS (the source I found only by chance once back: a loose heater wire: I think this is a certainty, the main mystery finally solved after 2 years effort). He did numerous service-type things whilst it was with him, even replacing 2 power tubes. He then kindly sent me the new (populated) board, after we sort of went with the idea of a conductive board theory as I still found it noisy. We went with the consensus on here that that idea seemed logical, having tried & exhausted every other possible idea.

I had my doubts of the bad board, if folks recall. As the old board was only a few years old. But hey who am I to throw my hunch in the fray?

So I know it's Reverb related. Unoquivocally now. That hugely narrows-down the possibilities of the source of this particular resolute & perstering noise. But I don't know what next to check.

Thanks, SC

If you start at the reverb volume pot and work backwards, with your oscilloscope with a X10 probe, you will be able to find the source.
(If you have old style resistor, just because they are shiny and new doesn't mean they are any good). Can be a challenge to find!

[pdf64]

Does switching the reverb off at the footswitch stop the noise?

[Sea Chief]

What happens with the V3 12AT7 reverb drive tube removed? When you turn up the reverb you will get hum, but are the pops and noise still there?
If you can isolate whether the noise is in the drive side or recovery side of the reverb tank, that should help. I like Chuck's idea about the reverb drive transformer, removing V3 might tell you whether that is a possibility.

Hi G1, great to have you on board again. Appreciated.


Right then, pulling V3 (with the reverb ftsw plug removed so I know it's in ON mode)... mild amp hum only.

Turn the Reverb knob from 1 to 8 like so, & no change at all. Nothing nasty. Quiet amp. Just the mild hum.


Thanks, Capt

[Sea Chief]

Does switching the reverb off at the footswitch stop the noise?

Hi pdf.

Yes.

I'm only getting noise, when the Reverb is audible.

Reverb off.. & it's a nice, clean quiet amp again, just as it should be (even the Tremolo's acceptable too).

Capt