AAARGH!
The amp still makes hummmmmmmmm after the transformer potting! Only happens if speaker is connected! I tried it without the speaker and it was silent!
The amp still makes hummmmmmmmm after the transformer potting! Only happens if speaker is connected! I tried it without the speaker and it was silent!
Tomorrow im doing JMFaheys varnish method! I spoke too! It sounds like its still the transformer buzzing and then coming out of the speaker.
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I had the transformer in the varnish overnight and its now hanging outside to dry! If this works ill be really happy!
Something I noticed yesterday was that if I have the chassis out of the cabinet and power it on I cant hear the transformer noise (no speaker connected), if I put it back into the cabinet and power it on (no speaker connected) I can hear the buzz, I think the cabinet amplifies the noise. anyway it sucks coz the moment I connect the speaker buzzzzzzz out of the speaker again.
If the transformer potting does not fix this would anyone know of anyway to stop this noise from going onto the speaker?
I can live with the buzz if its not going into my amps speaker.
Something I noticed yesterday was that if I have the chassis out of the cabinet and power it on I cant hear the transformer noise (no speaker connected), if I put it back into the cabinet and power it on (no speaker connected) I can hear the buzz, I think the cabinet amplifies the noise. anyway it sucks coz the moment I connect the speaker buzzzzzzz out of the speaker again.
If the transformer potting does not fix this would anyone know of anyway to stop this noise from going onto the speaker?
I can live with the buzz if its not going into my amps speaker.
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maybe the amp was designed for 220VAC, while we have up to 240V nowadays.
check if the buzz disappears at a lower voltage. could be the onset of saturation ..
check if the buzz disappears at a lower voltage. could be the onset of saturation ..
It could be, ill will only be able to have a look in a day or two when the transformer is dry.
We have 220/230 50Hz here in south africa
The amp has a fuse rating of 230v so I think it should be fine.
Hope all goes right.
What I fear (hope it does not happen) is that the first potting compound layer blocks the inside and does not let the new varnish get deep inside.
That said , *maybe* it's not the actual transformer buzzing but the strong magnetic field around it is making the iron chassis vibrate, pushing/pulling it 50 or 60 times a second.
You might try to mount the transformer not straight touching the chassis but separated from it by a cardboard shim (think 1 or 2mm: a single corrugated cardboard rectangle / 2 or 3 cereal box cardboard thicknesses / single sheet spongy EVA rubber) or 4 cardboard/fiber/rubber grommets .
To test whether it might help, loosen/pull the mounting bolts and separate the transformer body from chassis with some cardboard to check if it helps or not.
What I fear (hope it does not happen) is that the first potting compound layer blocks the inside and does not let the new varnish get deep inside.
That said , *maybe* it's not the actual transformer buzzing but the strong magnetic field around it is making the iron chassis vibrate, pushing/pulling it 50 or 60 times a second.
You might try to mount the transformer not straight touching the chassis but separated from it by a cardboard shim (think 1 or 2mm: a single corrugated cardboard rectangle / 2 or 3 cereal box cardboard thicknesses / single sheet spongy EVA rubber) or 4 cardboard/fiber/rubber grommets .
To test whether it might help, loosen/pull the mounting bolts and separate the transformer body from chassis with some cardboard to check if it helps or not.
Im afraid of that as well! but there was some gaps in the transformer that the potting compound did not touch were I could see the copper wire from the transformer so I hope enough varnish could have gotten inside.
I will try doing the shim if I still have buzz.
The amp sounds great now but that buzz oh man!
I cant find any info on what transformer to replace this one with.
I think ill have to get a new transformer, as this one is gone.ha.
Here is the schematic for the amp.
http://www.amparchives.com/album/Ma... & 8100 80W 1x12 Combo & 100W Head/index.html
I think ill have to get a new transformer, as this one is gone.ha.
Here is the schematic for the amp.
http://www.amparchives.com/album/Ma... & 8100 80W 1x12 Combo & 100W Head/index.html
Not so sure it's gone yet.
1) you might have miswired secondaries;, to check disconnect secondaries, pull them from the board and tape ends just in case.
2) FWIW you might have miswired *primaries* recheck connection, always using the lamp bulb limiter
3) *absolute* worst case, that's a quite generic power transformer
, 30+30VAC secondaries, 120/150VA transformer size.
28+28VAC is still fine, if you get one.
Or a used power transformer from a similar rated amp, 70/80W driving a single 12", say a Peavey Bandit / Fender Performer /Crate-Laney-Ampeg-Fender M80-etc.
You might find a "dead amp" for $5 at a garage sale, Salvation Army, etc. and pull the transformer from there.
Or a local tech might have a suitable donor amp in his junk pile.
Hope it's not really dead.
1) you might have miswired secondaries;, to check disconnect secondaries, pull them from the board and tape ends just in case.
2) FWIW you might have miswired *primaries* recheck connection, always using the lamp bulb limiter
3) *absolute* worst case, that's a quite generic power transformer
, 30+30VAC secondaries, 120/150VA transformer size.
28+28VAC is still fine, if you get one.
Or a used power transformer from a similar rated amp, 70/80W driving a single 12", say a Peavey Bandit / Fender Performer /Crate-Laney-Ampeg-Fender M80-etc.
You might find a "dead amp" for $5 at a garage sale, Salvation Army, etc. and pull the transformer from there.
Or a local tech might have a suitable donor amp in his junk pile.
Hope it's not really dead.
I was hoping that I miswired something but it seems that al the wiring is in order and its still shorting out.
Ive opted to have it rewired, it is the cheapest option.
Im just cleaning the transformer hehe its full of potting compound and varnish.
Many thanks for the info on what PT to get!
Would it be good if I get a toroidal PT? In case I get one for a decent price.
IF only we had these thing like garage sales and amp techs here in South Africa 😀
Many thanks for all the help!
if you don't disconnect it from to circuit how are you sure it's the transformer and not an output transistor that failed?
You're welcome 🙂
Argentina is similar to SA in quite a few ways, one being not much of garage sales, and used stuff being ridiculously expensive , that meaning over 60% to 70% perice of new stuff, crazy.
Both based on being very far away from main markets (USA/Europe/Japan) , paying very expensive freight plus Customs Tariff .
That said, you have at least 1 VERY good Tech I personally know, he goes by the name of diydidi on the Music Electronics Forum, I suggest you contact him at least to say "hi" and add him to your Mail list just in case you or a friend needs a good, serious Tech .
A toroid will be fine, but you will probably have to mount it outside the chassis, hanging from it, and drill a couple holes for the wires.
The original one, if rewound (which I suggest), will fit perfectly in the original chassis cutout.
Just make sure he impregnates it well in varnish 😉
Of course, he will use the proper one.
The home use, air dry "oil paint type" varnish I had suggested is light, its solvent is similar to turpentine, not too different from kerosene(paraffin in UK), and chemically weak, does not attack plastics nor other varnishes; I fear the polyurethane one you used first had a strong solvent (think acetone/ethyl ether/MEK) so it evaporates *quick* before it chemically hardens, problem is that such strong solvents eat through many of modern wire Enamels, including those used in 90's Marshalls.
Argentina is similar to SA in quite a few ways, one being not much of garage sales, and used stuff being ridiculously expensive , that meaning over 60% to 70% perice of new stuff, crazy.
Both based on being very far away from main markets (USA/Europe/Japan) , paying very expensive freight plus Customs Tariff .
That said, you have at least 1 VERY good Tech I personally know, he goes by the name of diydidi on the Music Electronics Forum, I suggest you contact him at least to say "hi" and add him to your Mail list just in case you or a friend needs a good, serious Tech .
A toroid will be fine, but you will probably have to mount it outside the chassis, hanging from it, and drill a couple holes for the wires.
The original one, if rewound (which I suggest), will fit perfectly in the original chassis cutout.
Just make sure he impregnates it well in varnish 😉
Of course, he will use the proper one.
The home use, air dry "oil paint type" varnish I had suggested is light, its solvent is similar to turpentine, not too different from kerosene(paraffin in UK), and chemically weak, does not attack plastics nor other varnishes; I fear the polyurethane one you used first had a strong solvent (think acetone/ethyl ether/MEK) so it evaporates *quick* before it chemically hardens, problem is that such strong solvents eat through many of modern wire Enamels, including those used in 90's Marshalls.
Very similar indeed!
Thanks will do and get diydidis contact details! Ive got another amp here thats been to a "tech" but still no luck haha, amybe he diydidi can sort me out.
I got in contact with a place here were I stay that will do a rewind for me or make me a new one. The bobbin is pretty much full of varnish and polyurethane XD ive cleaned most of it but still its not good. It seems like the varnish never really dried, I suspect that the polyurethane coating is preventing it from drying properly. I had it in the boiling sun for 3 days.
Luckily the rewind is very cheap!
I dont think the polyurethane came in contact with the coils as It was too thick and dried very quickly< the amp was still working after that, I suspect I messed up with the varnish XD should have opted for a thinner varnish imo.
Its funny just recently the manufacturers started to put the word kerosene on the paraffin bottles.
One last thing I think could have ruined the transformer and this is 100% my doing, I tried to make a small gap for the varnish to go into, I scraped away some of the polyurethane and it seemed like I made 2 tiny marks on the coil. Will that cause the transformer to short out?
Very probably.
Good they can rewind a new one for you.
If possible, ask them to use the stronger enamel wire used to rewind motors, not the lighter "self soldering" enamel type which Marshall used (the kind that needs no stripping, just evaporates with molten solder temperature).
Just tell them this and they'll know what I'm talking about.
Of course, they might have just one kind available and no choice possible.
Many think using "motor" type wire (Class "F" or "H" , guaranteed to 170C or 180C), , which is rated for high RPM, heat, vibration, is overkill ... and it's usually so, but guitar amps are often abused, overloaded, fit with oversized fuses, etc. so it's not a bad choice.
Personally I use nothing else in my amps, way over 10000 delivered (not a typo, guess I'm around 12000 or 13000, lost count) since 1969 and in all that time haven't siin more than 3 or 4 burnt transformers .
Although quite a few were seen with toasted brown paper tape wrappings, half fused twisted plastic bobbins ... but wire intact.
Good they can rewind a new one for you.
If possible, ask them to use the stronger enamel wire used to rewind motors, not the lighter "self soldering" enamel type which Marshall used (the kind that needs no stripping, just evaporates with molten solder temperature).
Just tell them this and they'll know what I'm talking about.
Of course, they might have just one kind available and no choice possible.
Many think using "motor" type wire (Class "F" or "H" , guaranteed to 170C or 180C), , which is rated for high RPM, heat, vibration, is overkill ... and it's usually so, but guitar amps are often abused, overloaded, fit with oversized fuses, etc. so it's not a bad choice.
Personally I use nothing else in my amps, way over 10000 delivered (not a typo, guess I'm around 12000 or 13000, lost count) since 1969 and in all that time haven't siin more than 3 or 4 burnt transformers .
Although quite a few were seen with toasted brown paper tape wrappings, half fused twisted plastic bobbins ... but wire intact.
thanks will do!
They are should be able to use that wire as they are a big company.
I asked them to make me a new one, just finding out what that will cost me, the old one is pretty toasty, at least the bobbin isnt in good shape anymore, the laminations are still good! I hope they can reuse those and use a new bobbin.
thats alot of amps 😵 😀
Im eager to get the transformer fixed, the amp was never broken, just abused, broken scratchy stuck pots, tons of dust inside, rust on the speaker frame, cob webs, crap replacement caps and cheap resistors. I just sorted all that out. got all good parts in there now.
Just the buzzing that was/is working on my nerves.
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