Amp gets transformer rewind, still has same problem!! (Rant)

Flyboy

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If amp make sound, any albeit bad sound, the power supply can't be very bad. And now with an new PT it make same bad sound ??? Yes amp can have two different issues but PTs usually work or not work? Bad filter capacitors can function erratic and tubes too.

See, I'm no amp tech but wouldn't the filter caps be one of the first things to check along with the PT?
 

Flyboy

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Furthermore, there is a dearth of amp techs up this way. I have known this guy for years and want him to do the right thing by me. Failing that, I open a PayPal case against him, which will undoubtedly ruin the relationship I have with him.
 

Kev-wilson

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I'd have to question as to whether the 220v/240v would have damaged the PT, I don't think it would, and iIrc UK mains has a 6% tolerance (EU 10%).
 

VintageSG

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Furthermore, there is a dearth of amp techs up this way. I have known this guy for years and want him to do the right thing by me. Failing that, I open a PayPal case against him, which will undoubtedly ruin the relationship I have with him.

As others have stated, an overvolt on the primaries of 10% will not futz a transformer. A transformer will not make the noises, nor be responsible for the noises you describe.

Filter caps can, will, do, enjoy allowing all manner of crud and noise through when they dry out. Coupling/decoupling caps can be problematic if they allow AC where DC should live, and vice-versa.

He's dropped the ball. Dropped it onto a spike. A spike in a cess pit. He needs to wade through the crud, retrieve the ball, repair it and reinflate, then wash the ball and return it.

I've dropped three links to techs around the Nottingham area who are well known and respected. No particular reason aside from they always seem to crop up in recommendations.
 

Burning Fingers

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I see no mention of you stating it was the power transformer that was "repaired"... if it was the output transformer then I agree that the output transformer leads need reversing.

The extra voltage the amp saw when it got hit with 240v while it was set for 220volts would not damage the power transformer but could have caused the power supply capacitors to get hit with more voltage than they could cope with and left you with a largely unfiltered power supply.

No one has asked this yet so I will...have you verified that the 2 pin din to 1/4 inch jack is working ok...does your meter read 8 ohms ( the speaker impedance ) across the 2 din pins ?.
I ask that because I would like to believe that your tech did actually test the amp before returning it you and, if he did, that really only leaves the speaker cable and speaker as the possible culprit....but I doubt it.

Good luck and we will be interested in the outcome.

I have attached the schematic in case anyone is interested.

echolette_m40_sch.jpg
 

Flyboy

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I see no mention of you stating it was the power transformer that was "repaired"... if it was the output transformer then I agree that the output transformer leads need reversing.

The extra voltage the amp saw when it got hit with 240v while it was set for 220volts would not damage the power transformer but could have caused the power supply capacitors to get hit with more voltage than they could cope with and left you with a largely unfiltered power supply.

No one has asked this yet so I will...have you verified that the 2 pin din to 1/4 inch jack is working ok...does your meter read 8 ohms ( the speaker impedance ) across the 2 din pins ?.
I ask that because I would like to believe that your tech did actually test the amp before returning it you and, if he did, that really only leaves the speaker cable and speaker as the possible culprit....but I doubt it.

Good luck and we will be interested in the outcome.

I have attached the schematic in case anyone is interested.

View attachment 1054042
When the amp was sent to him I did not send the speaker cable (the initial one I made, the 2-Pin Din -> 2 phono split that fed the Bassman cab). I assumed he'd have his own, as he mentioned the 2-Pin DIN, so I presumed he had his own cables for testing. In the interim, when he had the amp, I bought a Juke Tone Royal Blood and a 1 x 12" 8 Ohm cab and made a 2-Pin DIN -> 1/4" for that; it tests clear for continuity.

So, given that I initially tried it through two of Bassman speakers and then through the Juke Tone - each with different, known-good leads - I get the same sound: a loud buzzing, which fades away to a hiss as the M40 is powered off.
 

Flyboy

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I see no mention of you stating it was the power transformer that was "repaired"... if it was the output transformer then I agree that the output transformer leads need reversing.































































































































The extra voltage the amp saw when it got hit with 240v while it was set for 220volts would not damage the power transformer but could have caused the power supply capacitors to get hit with more voltage than they could cope with and left you with a largely unfiltered power supply.































































































































No one has asked this yet so I will...have you verif possible culprit....but I doubt it.































































































































Good luck and we will be interested in the outcome.



































































































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I have attached the schematic in case anyyone is interested.







































































































































































To clarify:























































I
 

Flyboy

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This from my tech:-

'The windings on one side of the primary were shorted together causing excess current in the output valves.'
 
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Burning Fingers

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'The windings on one side of the primary were shorted together causing excess current in the output valves.'

Your tech saying "one side of the primary" is a little confusing as there is no primary transformer...just a power and an output transformer both of which have primary and secondary windings. Maybe it is just a difference in terminology.

If the power transformer primary windings were shorted then surely the fuse would have blown or if it didn't blow and far too much voltage was passed onto the rest of the circuit then lots of components could have been destroyed.

So I'm thinking your tech means the primary windings of the output transformer were shorted and this caused excess current through the power tubes.

If that was the case then your power tubes may well be cooked and causing the horrible hum that I have heard many times in amps with crook power tubes... I'd also expect some small component damage associated with the power tubes.

If you have any spare power tubes try swapping them out.

I really doubt that the amp was tested before being returned to you.

Take it to another amp tech rather than to the guy who gave it back saying it was fixed.

Anyone can build amps if they follow the directions...that doesn't mean they know anything about tube amp fault finding and repair.
 

Burning Fingers

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Wow...that's some noise going on there ! . :oops:

Sounds a bit too "alive" to be mains hum related ...more like a power tube(s) that went south or an output transformer problem.

Pity you are 9500 miles away or I would offer to sort it out for the cost of any part(s).

First thing I would do is try known good power tubes and then preamp tubes and take it from there.
 

Flyboy

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Wow...that's some noise going on there ! . :oops:

Sounds a bit too "alive" to be mains hum related ...more like a power tube(s) that went south or an output transformer problem.

Pity you are 9500 miles away or I would offer to sort it out for the cost of any part(s).

First thing I would do is try known good power tubes and then preamp tubes and take it from there.
That's very kind of you! ;-)

I'm too busy with work these next few days. I'm off on Monday and that's when it's going back to the amp lad.
 

Peegoo

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@Flyboy

WOW. So this amp has never worked properly since you got your hands on it.

It's an older one, so you should be able to look at the wiring and solder joints on the preamp and power tube sockets to see if anyone's been poking at them with a hot soldering stick.

I'm wondering if something is miswired.

Is there any guitar signal at all getting from the input jack to the speaker?
 

Flyboy

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@Flyboy

WOW. So this amp has never worked properly since you got your hands on it.

It's an older one, so you should be able to look at the wiring and solder joints on the preamp and power tube sockets to see if anyone's been poking at them with a hot soldering stick.

I'm wondering if something is miswired.

Is there any guitar signal at all getting from the input jack to the speaker?
No. I bought it from Poland in December 2019. Then Covid hit and it sat untested until this year (I know) when I powered it on after making the speaker split. The Polish seller that it 'powers on and works'; obv BS.

TBH, I haven't put a guitar through it as the noise is worrisome. Will do tonight.
 




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