Twin Reverb.. last issue.

[Greg_L]

Hi Greg,

can you be more specific? Apart from " using solder" Im not sure how to answer this question.

Thanks, SC

Well I'm not sure which version you're dealing with, but on many layouts there is a loop of wire on V3 that connects the plates. This little loop is high voltage, loops around the tube socket, and can induce crappy noises in the reverb circuit. I've certainly had it happen to me. Sometimes looping it to the other side of the tube socket, or if you can, making it just a straight jumper across the base of the socket helps.

[Sea Chief]

Well I'm not sure which version you're dealing with, but on many layouts there is a loop of wire on V3 that connects the plates. This little loop is high voltage, loops around the tube socket, and can induce crappy noises in the reverb circuit. I've certainly had it happen to me. Sometimes looping it to the other side of the tube socket, or if you can, making it just a straight jumper across the base of the socket helps.

Hi Greg. Thanks for this.

Im still unclear as to this " loop of wire on v3". Ive just looked at my v3, but can't see any wire 'loops'. Ive just no idea what you mean.

I have two across-pin connections though (within the pins) on the top.IE pins 3 & 8 are connected via this " across- pin" link, & another pair.

Are these what you are referring to-?

[Greg_L]

Hi Greg. Thanks for this.

Im still unclear as to this " loop of wire on v3". Ive just looked at my v3, but can't see any wire 'loops'. Ive just no idea what you mean.

I have two across-pin connections though (within the pins) on the top.IE pins 3 & 8 are connected via this " across- pin" link, & another pair.

Are these what you are referring to-?

What circuit do you have?

3 and 8 are cathodes. Are 1 and 6 connected to each other at all?

[Sea Chief]

Would anyone in uk let me borrow a 12at7? There is a tiniest chance all 3 of my 12at7 I swap around ( without, it seems, any difference occcuring ) are no good & have caused this new noise by failing within the timeframe of the last 6 weeks the amp's been on the bench. Tho I doubt it hugely.

Im this desperate now, last-gasp, clutchin at straws efforts etc.

If in a jiffy bag & squashed a bit.. it'll go through the RM perpex slot thing, so 96p 2nd class to post. I'll return it of course & paypal back a quid.

Thanks, SC

[Sea Chief]

What circuit do you have?

3 and 8 are cathodes. Are 1 and 6 connected to each other at all?

Aha I see your loop now. Ok yes 1&6 like so. Then 2&7, 3&8 are tied together within the pins/ on top of the tube.

It used to work fine. This means then, by logic, that unless Ive messed about with the lead dressing since, or just moved the wires about, or have unsoldered some wires/ changed some aspect.... which I can absolutely vouch for 100%..... then the actual surity of the build, IE me wrongly attatching a to b.... is ruled out.

The amp worked great. Quiet. Lush reverb. No background noises at all. For a year. There MUST be some validity to this situation/ this fact/ that shows therefore that my work building it prooves that no " mistakes "per se were made in this process. So we must avoid all reference to the possibility of a wiring mistake as it is not useful & another red- herring, surely.


Thanks, SC

[Greg_L]

Aha I see your loop now. Ok yes 1&6 like so. Then 2&7, 3&8 are tied together within the pins/ on top of the tube.

It used to work fine. This facet mean, by logic, that unless Ive messed about with the lead dressing, or just moved the wires about, or have unsoldered some wires/ changed some aspect.... the actual surity of the build, IE me wrongly attatching a to b.... is distinctly if not 100% ruled out.

The amp worked great. Quiet. Lush reverb. No background noises at all. For a year. There MUST be some validity to this situation/ this fact.

If this amp worked well, then my work building it prooves that no " mistakes "per se were made in this process. So we must avoid all reference to the possibility of a wiring mistake as it is yet another red- herring.

Thanks, SC

Wiggle that loop around with a chopstick and see if the noise changes. Don't assume your work is flawless and perfect. You might have bumped something somewhere and it only takes a little wiggle of wires to create noise...or fix noise. It's an easy test. Wiggle the loop of wire and listen...or look on a scope if you have one.

[Sea Chief]

Wiggle that loop around with a chopstick and see if the noise changes. Don't assume your work is flawless and perfect. You might have bumped something somewhere and it only takes a little wiggle of wires to create noise...or fix noise. It's an easy test. Wiggle the loop of wire and listen...or look on a scope if you have one.

Hi Greg, ok will do. But it hasn't moved one mm, since 1978.. its a firm wire that if I nudge it, it does not budge.

Something has happened, since it's been on the bench, within the last 6 weeks. Something MUST have happened. I can only apply logic:

1. Slim possibility all 3 of my 12at7 tubes have all simultaneously failed at once. Tiniest possibility, almost negligeable.
2. I nudged a wire. Tiny possibility as they are all solid core, Ive not poked or touched any of them, & all remain steadfastly where they were.
3. The tank suddenly acts up. Tiny possibility: no moving parts, all checked, contacts cleaned super well.
4. The connecting wires suddenly fail. Tiny possibility, they have barely even moved, connectors super cleaned.
5. Amp rca connectors suddenly fail: tiny possibility, all totally fine, not changed 0.0005% in 6 weeks.

I think Im beaten by this now. But even with all the help, Im flabbergasted this couldn't be sorted. Thanks though, SC

[Sea Chief]

Hi chaps. Just an update.

I changed the single 82k for a 1w. So now all 100k's & this 82k changed for 1w ( all in a sort of triangle-pair joining together, I think coming from the anodes).

Strangely, once tank & pedal leads connected back up, the amp sounds much better. The bad reverb ERRBUZZ sound above 4 is now a more usual hum. The POP noises have gone it seems for good, no background noise with it too. Whine awol. Just normal healthy amp hum. Great... if I've affected this change:

Expecting to find the removed 82k blown or reading wrong... it checks out fine with a DMM. So I have no idea, why the amp now sounds better. But hey-ho.

---

So I have one last summit to mount. The tremolo. When speed is 10, it sounds like a motorboat. Very prominent dud-dud-dud-dud ( annoying slight drop in volume too switching it on, but is this facet always true of these trem circuits?).

Could I squeeze a bit more patience from you to help me tackle this?

Thanks if so, SC

[nosaj]

A reflowed solder joint perhaps since you replaced the 82k you also laid down new solder.
nosaj

[pdf64]

Noisy components may measure ok on metrics other than noise, just as components that measure out of spec on other metrics may not be noisy.
Noise is one thing, value is another, parasitics yet another.

Regarding the trem, is it a new issue or since the rebuild, has it always been like that? If the latter, maybe its HT feed isn’t adequately decoupled?
In a TR AB763 it’s fed from the screen grid node. But the TR 135W uses a different arrangement, with a potential divider on the HT.
A schematic of what you’ve got is needed, verbal descriptions aren’t very helpful, as assumptions, possibly incorrect, are kinda inevitable when trying to reverse engineer by that means.

Also the precise detail of the 0V common arrangements you’ve made with the rebuild may come into play and cause this type of thing if, as seems likely, they don’t conform to the original design.
And the original design relied on all 0V common to chassis connections being good; 40 odd years of surface tarnishing / corrosion / loosened fasteners may degrade such connections.

[Sea Chief]

Noisy components may measure ok on metrics other than noise, just as components that measure out of spec on other metrics may not be noisy.
Noise is one thing, value is another, parasitics yet another.

Regarding the trem, is it a new issue or since the rebuild, has it always been like that? If the latter, maybe its HT feed isn’t adequately decoupled?
In a TR AB763 it’s fed from the screen grid node. But the TR 135W uses a different arrangement, with a potential divider on the HT.
A schematic of what you’ve got is needed, verbal descriptions aren’t very helpful, as assumptions, possibly incorrect, are kinda inevitable when trying to reverse engineer by that means.

Also the precise detail of the 0V common arrangements you’ve made with the rebuild may come into play and cause this type of thing if, as seems likely, they don’t conform to the original design.
And the original design relied on all 0V common to chassis connections being good; 40 odd years of surface tarnishing / corrosion / loosened fasteners may degrade such connections.

Hi pdf. Its a new issue.

There isn't a schematic for -any- amp that has one component changed from the original. That doesn't mean though that such amps cannot be fixed.

All these 4 issues have occured after I successfully rebuilt it ( tested & checked out & worked fine for a year+) so; the idea of conformity isn't relevant -just- to attempt to fix this IF it was working fine. If it worked fine, then logic says it can work fine again.

The continual idea of my rebuild being 'wrong' has been put to bed a number of times anyway already (& the conductive board hypothesis). It may not be identical, but it is not wrong.

Whether it seems logical to " just call it an AB763" for arguments sake or not I don't know, but surely it seems sensible to just do so, or I cannot progress. Surely some voltages will determine if it falls in the AB763 camp?

unfortunately though I can't understand the technical details nodes etc.

Thanks, SC

[Sea Chief]

A reflowed solder joint perhaps since you replaced the 82k you also laid down new solder.
nosaj

Indeed nosaj. But extremely unlikely if in 20 years, Ive never reflowed a single joint resulting in any difference, I'd think myself.

If those two solder joints -are not as likely- to fail as the component in between them.. which is surely correct.. then the arrow points more towards the resistor. It was 1/2w.. I would venture to say it was underpowered as being the cause (replaced with a 1w).

I realise y'all are dying to say " there you are! Told you! You're build is bad!"... but there's no proof, not one eg as of yet, in two threads.

Thanks, SC

[nosaj]

Well you do make it extremely hard to troubleshoot with your limited capabilities and means of understanding so all we can do is throw hail marys. An hope that you fix it.

by the way what is your vocation?
nosaj

[Sea Chief]

Well you do make it extremely hard to troubleshoot with your limited capabilities and means of understanding so all we can do is throw hail marys. An hope that you fix it.

by the way what is your vocation?
nosaj

Great help that thanks.

All Im after is someone to help me fix an AB 763 trem motorboat noise. Not to keep challenging me on my build quality, which has stood up to & passed each & every bit of continual scrutiny.

For all intents & purposes it is a typical AB763 type trem. Yes it has a bigger transformer, but this difference -can- be put aside to just try & offer some help, surely. I'd go further & say for all intents & purposes the bigger xfmr might well be completely irrelevant anyway, just to tackle this noise that is.

As far as I know this is a common problem. But so common as there to be such a plethora of possibles, replies, threads on all manner of sites.... meaning I am completely boggled & do not know where to even start. Hence asking on here.

SC

[nosaj]

For all intents and purposes motorboating usually has to do with capacitors not doing their job requiring replacement.
nosaj