Tracing noise problem, TwinRev.

[Sea Chief]

Hi chaps,

I'm desperate to fix an issue once & all, going on 2 years I've been trying to get to the bottom of. My twin reverb ( ul 135 w, '78) has terrible backgound noise, unsettlingly loud, occasional POP actually is frightening. Im scared of the damn thing, & unplayable as it is.


I've done all I can with my knowledge: cleaned all tube & socket pins, pots. Ive swapped in known good tubes, swapped around tube to tube, to try for any obvious indicators. Nothing. My hunch now is a bad board resistor, or bad capacitor. So would it now be time to try to trace it? If so.. how?

History: I built it, or rather rebuilt it: a new main board was needed for an old blown TR, so walked through by Rift amps I rebuilt it using many original board caps & resistors, & many new board components too: at least logic dictates ruling these out, & it would far more likely be an original resistor or cap to blame: I know that the filter caps & power tubes are unlikely too, because these too were new.

All was well checked by us both, & it worked great for 1 yr.. then this dreaded noise started. And seems to have got progressively worse in the 2 yrs since.

A photo of the beastie here! Its a sort of hybrid between the original silverface & a blackface. New recifier design choke added etc.

Many thanks for reaading, SC.

[Sea Chief]

She has a repro faceplate..

[Sea Chief]

And some new 'udders' here on a new board ( also a bias circuit pot added).

Thanks for reading, SC

[Chuck H]

Are there any consistencies in the occurrence? ie:

only does it with a guitar plugged in

pop volume same regardless of volume knob

pop volume/tone affected by control settings

never does it when actually playing

only does it when actually playing

etc.

Or is it truly totally random and unpredictable and at the same loud volume regardless of any settings?

Are there any other accompanying sounds? Like a hiss preceding or following the pop? Any lower volume crackling noises, etc.

Any related info may help.

[Sea Chief]

Are there any consistencies in the occurrence? ie:

only does it with a guitar plugged in

pop volume same regardless of volume knob

pop volume/tone affected by control settings

never does it when actually playing

only does it when actually playing

etc.

Or is it truly totally random and unpredictable and at the same loud volume regardless of any settings?

Are there any other accompanying sounds? Like a hiss preceding or following the pop? Any lower volume crackling noises, etc.

Any related info may help.

Hi Chuck,



pop volume same regardless of volume knob... can't say for sure as only ever use it at 1 at very loudest. Seems to be same if vol at 0 tho.

pop volume/tone affected by control settings... no.

never does it when actually playing... noise always there regardless of playing over it or not, gtr plugged in or not.

Or is it truly totally random and unpredictable and at the same loud volume regardless of any settings? Yes.

Are there any other accompanying sounds? Like a hiss preceding or following the pop? etc. No just a general mix-mush of bad noise.

--

It did seem worse today than ever, tho 1st time Ive plucked up courage to turn her on in 6 months, & the trem was on innitially with bad very prominent motorboat dud dud dud noise, previously only a feint dud dud. Im not sure if of any relevence.. but worth mentioning.

Thanks SC.

[Chuck H]

Get a decent book or magazine to read and take a blow drier to the board for about thirty minutes. Any change?

[pdf64]

I strongly suggest not to use black fibreboard for new builds. It’s good for comedy value only, and most people don’t appreciate the humour.
The master volume of 70s models is pretty useful in making these amps usable if not playing on loud stages. Any benefit accruing from their removal seems somewhat questionable to me.
How about if all 9 pin valves except for those in V1&6 are removed. Only the normal channel will work, but does the noise stop?

[Sea Chief]

Get a decent book or magazine to read and take a blow drier to the board for about thirty minutes. Any change?

Well that's a new one on me! I think I get the thinking.. conductive board?

Now this prognosis was diagnosed once the dead duck was bought 4 years ago, by Rift amps ( who ran thru every other test beforehand ) coming to this rightful conclusion. So then I stripped it down, bought a new board, repopulated it as said new & original components as you can maybe see. New filter caps on new board & new power tubes, addition of a new choke, lastly some general circuit tweaks... & a whole new amp was born. We tested it. Worked great.

Shall I still try your hairdryer idea?

[Helmholtz]

As we have seen conductive grey fiberboards as well, I wouldn't restrict the warning to black fiberboards.

The hairdryer is meant to drive out the absorbed humidity, which is the main problem.

[Sea Chief]

I strongly suggest not to use black fibreboard for new builds. It’s good for comedy value only, and most people don’t appreciate the humour.
The master volume of 70s models is pretty useful in making these amps usable if not playing on loud stages. Any benefit accruing from their removal seems somewhat questionable to me.
How about if all 9 pin valves except for those in V1&6 are removed. Only the normal channel will work, but does the noise stop?

Hi pdf, well I had no reservations by Rift who got the board for me, & Ive never seen any other type included with mojo & TAD kits for eg.. surely they wouldn't be in such expensive & decent build kits if any issues with them.

The original board.. yes, this was (after 40 years & the amp in a very poor state in general ) proven to be conductive. But this new board's not even 4 yrs old.

If I have so many original resisitors & caps in ( muggins insisted keeping in for "original tone reasons", but Rift advised to swap all out ).. wouldn't the likelihood be that simply one, perhaps a resistor, is shot-? I admit this is coming from a naiive angle, but a logical one perhaps-?

I will certainly try your v2 to v5 removal idea tmrw. I put my back out lifting her onto my bench last weekend. Urgh. Still in pain!

Thanks SC

[pdf64]

Whatever its vintage, such fibreboard is simply not a suitable substrate material for high voltage, high impedance circuit boards.
For whatever reason, Fender chose to use it when better materials were available, so for accuracy I suppose, that’s what hobby builders also want to use. Such that may not be much demand for boards made out of a more appropriate material.
And mostly, the fibreboard doesn’t cause significant malfunction.
Hoffman may sell a turret board for the circuit, ie using a good material.
Of course at this stage, we can’t be sure that the issue is the board.

[stokes]

I would turn the amp on, no guitar plugged in.If you get the noise issues, start pulling tubes starting with V1, pull it, does the noise stop? If no, put it back pull V2 and so on till you pull one and the noise stops.That narrows it down to that section causing the problem.If you get all the way to the PI and the noise doesnt stop the problem is in the power section.

[Chuck H]

well I had no reservations by Rift who got the board for me, & Ive never seen any other type included with mojo & TAD kits for eg.. surely they wouldn't be in such expensive & decent build kits if any issues with them.

Don't blow smoke up yer own tutu. It's still a black paper fiber board AND:

It worked for awhile, then didn't.

You live in a relatively humid and cool climate where things tend to stay wet.

As Pete pointed out, that material isn't usually a problem, but sometimes, in some environments it ABSOLUTELY is, BUT,.. The "Mojo" of the material outweighs the number of problems they'll encounter by choosing an alternate material FROM A SALES PERSPECTIVE. Choosing THAT material to sell for boards cannot possibly have anything to do with the relative goodness of their product.

Nuff said

[Sea Chief]

I strongly suggest not to use black fibreboard for new builds. It’s good for comedy value only, and most people don’t appreciate the humour.
The master volume of 70s models is pretty useful in making these amps usable if not playing on loud stages. Any benefit accruing from their removal seems somewhat questionable to me.
How about if all 9 pin valves except for those in V1&6 are removed. Only the normal channel will work, but does the noise stop?

Hi pdf, ok Im obviously going to start with your pulling v2 to v5 because it's the simplest test.

Done this. Now with the vol pot at zero.. no noise.

Turning this vol pot... noise is directly affected, almost telling me the pot is dodgy (?).

When its turned up, i get significantly less volume than expected ( i need to turn to 3 to get say an equivalent acoustic gtr vol: usually vol 3 would be painfully loud).

The background noise is still there, but less prominently than with all tubes in.

--

The only other thing I noticed, was yesterday with all tubes in, & into Vibrato channel, it seemed unusually loud.. like I couldn't turn it to 1: but this might be due to not using this dreadfully loud 90w beast for ages, & using my MusicMan instead ( tho a beast itself at 65w).

Any more clues from this I wonder? Thanks SC

[Sea Chief]

Don't blow smoke up yer own tutu. It's still a black paper fiber board AND:

It worked for awhile, then didn't.

You live in a relatively humid and cool climate where things tend to stay wet.

As Pete pointed out, that material isn't usually a problem, but sometimes, in some environments it ABSOLUTELY is, BUT,.. The "Mojo" of the material outweighs the number of problems they'll encounter by choosing an alternate material FROM A SALES PERSPECTIVE. Choosing THAT material to sell for boards cannot possibly have anything to do with the relative goodness of their product.

Nuff said

I understand the implications of what you've said Chuck. Im just saying I find it hard to understand, if such board is so potentially problematic, that I would be sent such a potentially-conductive- issue-board by a very experienced Rift amps, just after concluding the very issue with it when I bought it as a cheapish dead duck to try fixing... was an old knackered 41 year old conductive board.

I must reitterate that there is no correlation between where it lived before ( manchester ) & the area here, which is as you remembered is indeed a wet climate.

Therefore (my point being) just because it had a conductive board prior to me dismantling the amp & binning it, there is no likelihood that this problem should " follow" the amp onto me using new boards repopulating them with both new, & even with/ using some original components. Approx 50 / 50 old to new.

I just wonder if just because I mentioned it had a conductive board originally, then the obvious suggestion might be being made that ' well if this issue happened with this amp before, then the chances of it happening again are much increaced' ( perhaps due to the amp's history I haven't made clear enough).

The chances should not increace if that old board was binned, the amp stripped down etc. That is just normal logic, IE it doesn't need me to have too much knowledge to be able to state that I don't think.

Thanks, SC