Bad amp grounding??

[Jon Snell]

Valve (tube) testers don't normally check for noise, just emission and short circuits unless you purchase an AVO or similar machine.

[Sea Chief]

Valve (tube) testers don't normally check for noise, just emission and short circuits unless you purchase an AVO or similar machine.

Which I guess means extra expense.. so not a viable option then, or we'd all have them.

As my confidence is so low, I'm still not able to say for definite what caused this issue, or whether I have solved it/ if it will reoccur.

I mean I think it was V1. But I'm sure some of you will say it can't be/ & it's got to be V5. Anyway, if noise has gone then great.

The only way I can establish if V1 was the problem, is to test just this tube. Is there anyone in UK on here with a tester, I could send it to I wonder? thx SC

[Chuck H]

The only way I can establish if V1 was the problem, is to test just this tube.

Nope.

It could be that V5 has an intermittent problem like oxide and/or grime on the pins, in the socket or questionable solder joints and you've solved for that simply by removing and replacing the tube one more time. Try putting the original V1 back in and report.

[Sea Chief]

Are the tube positions labeled on the amp V1 v2, etc?
Check with a local ham radio operator testers aren't that expensive locally and used.

nosaj

Hi nosaj,

your implication I'm sure being, that I am not distinguishing between the 1st preamp tube, & the last PI tube. No they are labelled both on the pcb, & outside on the chassis by someone, clearly V1 to V5.

I did swap these two round at some stage in proceedings, without any difference to the sound though. So it's lost as to what the heck went on/ will it reoccur/ have I even found the cause. If I could get a definitive 'it tests bad' on my PI v1 tube.. it would likely solve it.

Anyway, assuming it's fixed, I can say thanks to all for helping/ hugely grateful as always, & call it thread done. Now to sell the damn thing asap! Too many tubes in, is my opinion so it's a constant liability. I'm thinking musicman after this. No preamp tubes.

Thanks SC

[Jon Snell]

Which I guess means extra expense.. so not a viable option then, or we'd all have them.

As my confidence is so low, I'm still not able to say for definite what caused this issue, or whether I have solved it/ if it will reoccur.

I mean I think it was V1. But I'm sure some of you will say it can't be/ & it's got to be V5. Anyway, if noise has gone then great.

The only way I can establish if V1 was the problem, is to test just this tube. Is there anyone in UK on here with a tester, I could send it to I wonder? thx SC

Plug the valve into a friends amplifier to see if you can reproduce the noise. I have an AVO 160 which will test for gassy leaks and noisy electrodes but it has to be easier to plug the valve into another amp for the definitive test.
Most likely the cause was dirty valve socket/pins but who knows and does it matter as the issue is resolved.
I think it was my first post on the old thread I suggested replacing the valve, just to see if that helped.

[g1]

Trying to look back to figure out what was causing the issue, you can't omit C12. You were measuring a short (1.1 ohms) across it then you replaced it.
Now if you measure across it (and R24 in parallel), you will see that the short is gone and R24 reads it's proper value.

So you had a shorted cap, and a defective tube, both partly responsible for the problem. Either that or there never was a short across R24/C12 and it was some measurement error.

[Sea Chief]

Plug the valve into a friends amplifier to see if you can reproduce the noise. I have an AVO 160 which will test for gassy leaks and noisy electrodes but it has to be easier to plug the valve into another amp for the definitive test.
Most likely the cause was dirty valve socket/pins but who knows and does it matter as the issue is resolved.
I think it was my first post on the old thread I suggested replacing the valve, just to see if that helped.

Jon I dont know anyone in the country I live in who plays guitar, let alone has a guitar amp, with valves! But I could put it in my twin reverb in the 1st preamp position. But that amp terrified me with a sudden huge POP noise almost giving me a heart attack.. so no, Im not touching that amp right now in fact.

I did replace V5 very 1st port of call, with a new tube, but noise remained. So tube &/ or socket @ V5 was ruled out early on. Only pulling it resulted in ridding the noise. Therefore I guess the thinking was it must be something in the input area & all focus was on this alone. I thoughrally cleaned the sockets recently too. I would love to determine 100% what the cause was. I'm 60% sure it was v1 even with tests saying so, because, i have no confidence in myself in all this, & to have 'solved it' over any of you guys.. seems completely absurd. So prob found via a fluke, perhaps? Or am I an amp whisperer!?

I am getting very sick of valve amps is all I know. Next is the damn twin reverb to try & rid its noise, yet again, weeks spent on that without success until it frightened the daylights outta me so much Im now scared to turn it on. At least its working ok behind the noise. Hateful things valve amps.

SC

[Helmholtz]

Either that or there never was a short across R24/C12 and it was some measurement error.

As he measured 1.2V across R24 in the previous thread that doesn't seem unlikely. Oh well...

[Sea Chief]

Trying to look back to figure out what was causing the issue, you can't omit C12. You were measuring a short (1.1 ohms) across it then you replaced it.
Now if you measure across it (and R24 in parallel), you will see that the short is gone and R24 reads it's proper value.

So you had a shorted cap, and a defective tube, both partly responsible for the problem. Either that or there never was a short across R24/C12 and it was some measurement error.

I just don't know anything g1. I dont know even here, if you're suggesting now to measure across r24: to see if the short is gone to determine if its gone because of the replaced cap, or, becuase of the fact that the amp now works again.

Trying to figure out replies, is often half the battle for me. This is why I needed to start anew, boil my questions down to the tiniest incriments, so, I might have 50% chance of understanding any reply.

If the problem is simply a bad v1.. then chances are there was no short across R24/ C12. Is that right? I havent a clue. If I replaced C12, as I did, & this did not rid the noise... then.. does this definitively mean there was a bad c12, or does it definitively mean there wasn't one? I really am so utterly lost, my heads literally aching trying to understand what went on, plus trying to understand the replies I have to pick apart then try to process.

But all replies are much appreciated. i just wish there was a MES section 'for children' so I had a fighting chance of understanding things.

thanks SC

[Sea Chief]

As he measured 1.2V across R24 in the previous thread that doesn't seem unlikely. Oh well...

Please HH.. i did ask: please just dont refer back to anything on this old thread. Mixing info from both is impossible for me to deal with, plus due to the error I made on it mean the measurements cannot be relied upon to be correct. Hence starting a new thread. Scrap the old one.

I have not a clue what you mean by what you have just said in this reply too: Is 1.2 v good, very good, excellent, terrible, bizarre? And what does ' that doesn't seem likely' even refer to? What doesnt seem likely? In what context are we here?

This is a good eg of how hard it is, so often, to comprehend replies.

Thanks, SC.

[Helmholtz]

I have not a clue what you mean by what you have just said in this reply too: Is 1.2 v good, very good, excellent, terrible, bizarre? And what does ' that doesn't seem likely' even refer to?

My comment was directed at g1.

1.2V across R24 is a good value and means that C12 either was disconnected or good (i.e. not shorted).

[Sea Chief]

My comment was directed at g1.

1.2V across R24 is a good value and means that C12 either was disconnected or good (i.e. not shorted).

Ok understood the 1st sentence.

I understand part of the 2nd sentence, up to the suggestion that C12 might have been good.. but I do not understand the implications of this sentence.

Maybe I'm not meant to though, if the reply is directed to g1.

---

I would like to ask the opinion of whether my finding v1 was the problem (the phase inverter tube) has any validity in your opinion- but I just wouldn't be able to understand the replies! And I can't ask of you to speak to me as if I'm an 8-year-old, because it's extra effort for you to do so. 8 might be optimistic too.

So I think it'll just have to stick at "I might have solved it.. but.. I might not have solved it too" (!). Very unsatisfactory from an intellectual pov!

But if the damn thing works- hey who cares? (well.. ideally I'd like to know why it works now, & didn't before, for certain.. but I don't think it'll be possible).

Thanks, SC

[DrGonz78]

Hi Chuck, yes indeed I did have an input jack issue. No-one suggested a ground fault with the input jack yet. So it makes sense to start afresh here, then move on. Could I ask, could you help me out by telling me how I can completely test this input socket?

I'm going to call this resistance reading @ R24 test 1.

My measurement is 8.5 Ohms (I test the other side of R24, 8.5ohms). I have redone the test 3x to make certain done correctly. I plug a cord in, the amp is off, I measure from the input jack sleeve terminal (closest to the front of chassis) to either side of R24.

(Why this is different to before.. I have no idea. If relevant: I measure directly across R24 & get a reading of 6.6ohms).

Chuck, to get me going.. could you voice an opinion on whether my 8.5 ohms reading is ballpark correct, or not?

Thanks, SC

Sea Chief this statement is most confusing. You say your confused but your the one there with the amp doing the measurements and observations. Personally I just want to know why we measure only 6.6 ohms across R24 when we should read 1.5k without the C12 connected. With C12 connected we should read such a high resistance that the meter goes in O.L., open line. Oh well glad it works but still not satisfied with the solution to the problem since these measurements don't make sense.

[Helmholtz]

With C12 connected we should read such a high resistance that the meter goes in O.L., open line.

How this?

With a good C12 connected across R24, the reading should be 1.5k just as without C12.
Maybe you mean measuring only C12?

[Sea Chief]

Sea Chief this statement if most confusing. You say your confused but your the one there with the amp doing the measurements and observations. Personally I just want to know why we measure only 6.6 ohms across R24 when we should read 1.5k without the C12 connected. With C12 connected we should read such a high resistance that the meter goes in O.L., open line. Oh well glad it works but still not satisfied with the solution to the problem since these measurements don't make sense.

I agree it's most confusing. If I do a test (& I am meticulous with a good probe connection to every point, my MM is fine, it's plugs firmly in) & I get a figure, then I repeat the next day & get an entirely different figure.. you bet it's confusing! (but how do I know this isn't meant to be too-?).

Whether one test was done with amp off, the other with amp on I don't know: why the discrepency between what I measured before & here getting 6.6ohms is not known, not understood. I just expect to be generally as totally confused, as you are here re. this.

Gonz.. all I know for 100% certainty is the following:

When I put tube Z in @ v5, the amp does not work/ noise. When I replace this tube with another new 12ax7 (call it tube X) @ v5, the amp works.
But with the following additional note: up until today tube X has been in v5. And tube Z has been in v1 (amp not work/ noise).. it's always lived here in v1.

So, what (precisely) can be concluded from this.. I don't know other than to tentatively say (as seems logical) that "tube Z is bad" (so I'm not saying tube v5 is bad, not the socket either) . And of course also concluded is placing a bad tube in v5 means the amp does not work.

I'm only suggesting this: placing tube Z in v1.. & the amp does not work/ noise: so then the noise let's say "seems to follow tube Z whether it's placed in v1 or v5" (that's my 8-year-old-simple-simon crystal clear way to put my findings).

Surely then, there just -must- be some degree of truth, to say that the amp is bad/ noisy whether tube Z is in v5, or v1. This even seems like a concrete fact.
But, my confidence in saying even this is knocked with every reply, especially one saying 'its equally both a shorted cap & a bad tube', when i don't think a shorted cap has been established (has it? I haven't a clue: why don't I know this? because a resistance measurement within a test to see if a cap is shorted, is an arbitrary figure to me, eg if I get a reading of 580k or 2r.. the figures don't tell me anything, why not? because I am not versed in knowing the implication of the figures: until someone can interpret them, they remain meaningless resistance numbers to me).


Does that make any sense? probably not. thx SC