Tracing noise problem, TwinRev.

[Chuck H]

I'll just check mains earth tho.

Well, yes. Please.

So I will do a super-clean of all other preamp tubes' socket pins now, & re-tension ( all 45 of them ).

Yikes.

[nosaj]

What are you cleaning them with?
nosaj

[Helmholtz]

A potential safety issue should always have top priority - especially with 245VAC and high humidity.

[Sea Chief]

My concern is still whether we have a valid schematic or not, as this is essentially a 'build'. If the ch.1 volume drop (only when V2 thru V5 are out) is a constant, we either have a gross wiring fault, or an invalid assumed schematic. If the latter is the case, all troubleshooting goes out the window.

Not so. Not if it worked perfectly before,once it was originally rebuilt with a few alterations, a la 'blackface'.

This is just another excuse to just bail out & not help me, encouraging others to as well it seems to me.

I am finally getting somewhere: please just stay on board & help-?

Thanks.

[Sea Chief]

Early on it was reported that Ch.1 was a certain volume with all tubes installed, then Ch.1 had significant drop in volume when V2 thru V5 were removed.
It would be useful to know if this is still the case.

Hi g1. Now this is a helpful post..

Yes, this is definitely the case. So all tubes are back in. Ive just super-cleaned & retentioned the preamp sockets beforehand too. Vibrato channel seems better, but a sudden pop was dissapointing to hear, playing through this channel after anout 15 mins. Some mild slight funny noises in bckground.

Now then this big disparity in volume between channels remains, suggesting something definitively wrong with Normal channel.

If Vibrato channel's vol knob is 1, to get the same approx volume, I need to have Normal's vol knob at 2.5.

And there's some distortion playing this channel too... highly unusual for a twin/ the other channel is clean as a whistle.

And.. oddly with a tele, just bridge pickup, the distortion is very apparant ( just neck pickup.. & this extra dose of distortion, is gone). Odd.

[g1]

That did not answer my question you quoted at all. Please re-read the quote in post #139.
It has nothing to do with the vib. channel or volume differences between the channels.
It is in regard to only ch.1.
Ch.1 uses only V1, V6, and the power tubes (in normal blackface or silverface wiring). So verify that the Ch.1 volume is the same whether V2 thru V5 are in, or out.

[Sea Chief]

That did not answer my question you quoted at all. Please re-read the quote in post #139.
It has nothing to do with the vib. channel or volume differences between the channels.
It is in regard to only ch.1.
Ch.1 uses only V1, V6, and the power tubes (in normal blackface or silverface wiring). So verify that the Ch.1 volume is the same whether V2 thru V5 are in, or out.

Ok I must have read your question as " verify that ch1 volume is the same ( as ch 2 volume ) ".. as usually the same, implies, the same as something else.

So if the question was clearer.. anyway:

Right. Regardless of whether v2,3,4,5 are in or not... ch 1 volume remains the same.

It is not as it should be.

---

There is definitely, undoubtedly, something amiss with ch1. This could be a bad component( I'd have thought most likely, & surely the easiest to test, with voltages (?) consistant with a blackface TR, or, a SFTR, as there is no difference to them in this ch1 area: in fact the same " start of circuit input area" layout occurs from one BF & or SF fender model to another).

Or it could be -admittedly- a wrong ch1 input area wiring situation ( I will go over my build in this area meticulously tomorrow: suffice to say, I am 98% certain this ch1 was tested, & worked correctly, when the amp was "reborn".. ie did not sound like this: this tells me my wiring is good... but... I will check again).

I would suggest the bad component is most likely, as this surely, would be most likely to cause the crunchy popping sound over a wiring mistake, becuase components fail, wiring tends to stay intact. A failing component... I mean isn't crunchy popping noise simply consistant with this component bad state-?

I cannot think of any other logical reasoning than these two possibilities; one likely, the other highly unlikely.

A cap, or a resistor, or a pot then. I mean surely it HAS to be one of these 3 suspects. No?

[gui_tarzan]

This may be nothing. Have you looked at this area for conductance between the 250pf treble cap solder points and the screw in the pre-amp? That looks way to close for my taste. I don't mean just visually, I mean check for an actual connection - even momentary - between the screw and the solder joint. Not from the board itself, but rather the potential solder joint bleedover.

[nosaj]

This may be nothing. Have you looked at this area for conductance between the 250pf treble cap solder points and the screw in the pre-amp? That looks way to close for my taste. I don't mean just visually, I mean check for an actual connection - even momentary - between the screw and the solder joint. Not from the board itself, but rather the potential solder joint bleedover.

Good eye. Use your meter on ohms to check from screw to solder.
nosaj

[Chuck H]

Sea Chief, I think you STILL haven't entirely answered the question...

Does channel 1 volume go up with V2 through V5 in place?

EDIT: And... Sorry to hear the POP! happened after cleaning sockets.

[Sea Chief]

This may be nothing. Have you looked at this area for conductance between the 250pf treble cap solder points and the screw in the pre-amp? That looks way to close for my taste. I don't mean just visually, I mean check for an actual connection - even momentary - between the screw and the solder joint. Not from the board itself, but rather the potential solder joint bleedover.

Hi Tarzan, thanks for this.. Ive just removed the board mount screw, & lifted board up a bit for a definite gap to the under-board. No change unfortunately.

Appreciate your consideration though, & pic. This 250 pf links underneath correctly to the 1st wire onto the board point ( on the pic, directly north, with a resistor heading SE direction). So I think this conductive aspect can be eliminated as cause. Certainly the cap legs don't test for continuity to the screw.

But the cap itself? Well I tapped it on numerous occasions with my wooden whatnot, it didn't produce any extra noise. No component did.

Is there any way of testing this cap, sitting where it is I wonder? Hmm..

[gui_tarzan]

Not really. I have a capacitor tester on my meter and one of those standalone units that checks ESR too but it has to be out of the circuit to be accurate.

[nosaj]

Good eye. Use your meter on ohms to check from screw to solder.
nosaj

Do this
nosaj

[Sea Chief]

Do this
nosaj

Yup I did this as I mentioned in #146. I made sure it was placed with room to this cap, made very sure on building it. And as I said I undid screw, took it out, & the noise was not affected/ stayed put. And tested for continuity again when I put screw back in.

We can rule out this screw. But not the cap though. I may as well just replace it as a 'test' as I have no proper cap tester.

Thanks SC

[Sea Chief]

Sea Chief, I think you STILL haven't entirely answered the question...

Does channel 1 volume go up with V2 through V5 in place?

EDIT: And... Sorry to hear the POP! happened after cleaning sockets.

Apologies if I haven't ( I have been trying to!). Trouble is, I can't make total sense of your question! Does ch 1 volume go up? Erm.. well yes it goes up if you rotate the vol knob. Im not understanding the question sorry.

Do you mean does ch 1 noise go up with v2 to v5 in place maybe?

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" I would like to answer that question in two ways. Firstly in my usual voice, then in a sort of silly high-pitched whine" ( monty python). Sorry, just reminded me.

SC