Tracing noise problem, TwinRev.

[nosaj]

All we're doing is testing for noise. Your not to be playing it yet.
nosaj

[Sea Chief]

All we're doing is testing for noise. Your not to be playing it yet.
nosaj

So I could safely just have 1 6l6 in & sound would still come from the speakers-?

[nosaj]

Just do what dave said and lets move on. Hell take all the power tubes out pick 2 and put them in these slots
You want to pull one from each side of the OT, so that's either (V7+V9) or (V8+V10) or (V7+V10) or (V8+V9).

If you still get noise in those positions, do it again but with the other 2 tubes. Note the locations where you do and don't have noise.

I'm of the mind where you found the cracked ceramic that voltage is creeping through there. What position was that in?
nosaj

[Sea Chief]

Just do what dave said and lets move on. Hell take all the power tubes out pick 2 and put them in these slots
You want to pull one from each side of the OT, so that's either (V7+V9) or (V8+V10) or (V7+V10) or (V8+V9).

If you still get noise in those positions, do it again but with the other 2 tubes. Note the locations where you do and don't have noise.

I'm of the mind where you found the cracked ceramic that voltage is creeping through there. What position was that in?
nosaj

The cracked socket is V8. Im not quite understand ing the term ' each side of the OT' ( or might this imply on the schematic, that the OT is situated between these 4 tubes somewhere.. presumably midway, between v8 & v9 perhaps?).

Ok the reason for your sequence suggestion though is what.. because to turn the amp on, a balance of some proportion is needed ( why I have no idea, safety purposes?), therefore these 4 combinations provide a balance, so the amp won't blow up & my toupe fly off?

Thsnks SC

[nosaj]

just do the test suggested and you can work on your understanding later.
nosaj
https://www.premierguitar.com/diy/as...-lower-wattage

[Chuck H]

To put it simply,..

Looking at the tubes from any vantage the two on the left are connected to one lead from the OT and the two on the right are connected to the other side of the OT. Simply pull one from each side. That's it.

The "two inner or two outer" thing is just an easy way for bonehead guitarists to 'get it' so they don't blow up their gear.

The cracked socket is a concern. I could see leaving it alone (grudgingly) if the amp is working. But with your symptoms it could just as likely be the cause of an intermittent high voltage (and possibly arching) contact.

The good news is that we're onto something could definitely be causing your issue. The bad news is that, under the circumstances, you should replace that socket!

I don't know which side (left or right pair of power tubes) has the char mark and which side has the cracked socket. If they are on opposing sides you should pull those two tubes and fire the amp up. If the noise disappears I would probably just replace both sockets.

[Sea Chief]

To put it simply,..

Looking at the tubes from any vantage the two on the left are connected to one lead from the OT and the two on the right are connected to the other side of the OT. Simply pull one from each side. That's it.

The "two inner or two outer" thing is just an easy way for bonehead guitarists to 'get it' so they don't blow up their gear.

The cracked socket is a concern. I could see leaving it alone (grudgingly) if the amp is working. But with your symptoms it could just as likely be the cause of an intermittent high voltage (and possibly arching) contact.

The good news is that we're onto something could definitely be causing your issue. The bad news is that, under the circumstances, you should replace that socket!

I don't know which side (left or right pair of power tubes) has the char mark and which side has the cracked socket. If they are on opposing sides you should pull those two tubes and fire the amp up. If the noise disappears I would probably just replace both sockets.

Hi Chuck, understand that now, & can visualise the brown lead from under going to one 'side' of these four tubes .. & the blue lead going to (or from ) the same spot on the other 'side'. I think this correlates to the two sides.

Yes I'll defo replace that socket. Know what type is a like for like on these? Id want to put same type in, holes need matching too.

So is it feasable, that current or voltage, could nip across a physical gap such as found in this socket? IE there are no pin to pin physical connections going on here, afaik/ cannot see how possible just by a separation/ crack in the ceramic surround.. so only possibility is electricity jumping across A to B.

The word Arc, & my imagining the scene from star wars when luke gets zapped by the emperor: was that arcing from his fingers to luke's nutsack ( i think he was aiming for)-? Quite a gap there. But was that 'arcing'?

Thanks, SC

[Chuck H]

Yes, the Emperors arc is a good example, and... the reason it can happen is that an intermittent contact temporarily reduces current allowing voltage to rise. The higher the voltage the further it can jump. In a guitar amp those voltages can be quite high (much higher than the measured HV for reasons I won't go into now) and when the amp is conducting intermittently voltage peaks can built up and then are suddenly unmitigated. Think of those piezo electric starters for gas BBQ grills that build a charge and suddenly release it making that click sound as the arc flashes across the electrodes.

You don't actually need to pull only one tube from each side. You're not going to be playing through the amp forcing it to conduct signal power. You're checking for noise. You can plug in just one tube and twiddle the volume control to see if the noise is present. If no, plug in the next tube, etc. Looking for a socket and/or tube that's misbehaving. If you discover that there is only one tube that does it in any socket or one socket that does it with any tube then you'll have found your problem and isolated it.

And there's still a chance that you now have both bad tube/s AND socket/s because a failure in one caused a failure in the other. This kind of coincidence isn't unusual in repairs. We hope for a chance at a cut and dry diagnosis but good old Murphy pokes in often enough keep us on our toes.

[Sea Chief]

Yes, the Emperors arc is a good example, and... the reason it can happen is that an intermittent contact temporarily reduces current allowing voltage to rise. The higher the voltage the further it can jump. In a guitar amp those voltages can be quite high (much higher than the measured HV for reasons I won't go into now) and when the amp is conducting intermittently voltage peaks can built up and then are suddenly unmitigated. Think of those piezo electric starters for gas BBQ grills that build a charge and suddenly release it making that click sound as the arc flashes across the electrodes.

You don't actually need to pull only one tube from each side. You're not going to be playing through the amp forcing it to conduct signal power. You're checking for noise. You can plug in just one tube and twiddle the volume control to see if the noise is present. If no, plug in the next tube, etc. Looking for a socket and/or tube that's misbehaving. If you discover that there is only one tube that does it in any socket or one socket that does it with any tube then you'll have found your problem and isolated it.

And there's still a chance that you now have both bad tube/s AND socket/s because a failure in one caused a failure in the other. This kind of coincidence isn't unusual in repairs. We hope for a chance at a cut and dry diagnosis but good old Murphy pokes in often enough keep us on our toes.

Thanks Chuck, this is the sort of clear guide I need with my limited abilities/ understanding. Im diving in now to do these tests.. been too busy last few days.

Grateful, SC

[Sea Chief]

Ok so done a few more tests. No joy afterwards/ noise resolutely exactly the same.

Swapped around the power tubes, in pairs, to rule out the sockets definitively as the cause. I then replaced the standby switch too.

Not sure what to do next. At the moment I still have v1 and v6 in (the rest of preamp ones removed). Switching the tubes around, made no difference suggesting the issue isn't within these, or the sockets.

Do I have to always have v6 in when putting in even 1 power tube alone? Can you just have say v9 in... & all other tubes pulled?

Thanks for any ideas, SC

[nosaj]

Please state location of cracked tube socket and a pic please.
nosaj

[Sea Chief]

Please state location of cracked tube socket and a pic please.
nosaj

Hi nosaj. Its v8.. & a very thin crack going sideways across it, I doubt I could photo it tbh. I'll try in 15 mins.

Could anything untoward in it, be affecting thhings if v8 is pulled though? I sort of assumed with it's tube pulled, means it's then 100% not affecting the circuit.

Thanks, SC

[nosaj]

I'm curious what pins the Crack is between.
nosaj

[Sea Chief]

I'm curious what pins the Crack is between.
nosaj

Will do a pic in a few mins. But if Ive got v1, v6, v7, v10 in.... & noise exactly the same, doesn't that completely negate looking closer at v8 socket as the possible cause?

Off to try do best pic I can, with an ipad..

[Sea Chief]

I'm curious what pins the Crack is between.
nosaj

Best I can do. Green marker arrow..