Hello all. I will preface this by saying I have spent merely two days researching tube amp repair, and I have learnt a lot but I'm obviously still inexperienced. First I looked into how to make the amp safe to work on, so I am aware of what to do there (discharge the capacitors). As far as I can tell, this is the main concern for safety re: amps? (My source: YouTube)
I was given a Pignose G40V amp for free, along with a power transformer, with the information that the husband of the lady who gave it to me got the component in order to fix the unit but had no idea how to do it and it was left from then on. I found the order slip for the transformer and it looks like it was ordered in 2008, and I don't know when the amp was last working before that - so we're looking at 10 years inactive to begin with. There are also what look to be 3 unused Marshal ECC83 tubes, boxed, as an added bonus with what I was given.
In this case, is it even worth trying to replace the PT - or am I getting beyond my depth with an amp that has been inactive for so long, in that it will more than likely need other parts replaced or serviced? Visually, I can see nothing wrong with the capacitors or any components on the PCB or otherwise within the case.
I initially thought it would be a simple situation of replacing wire for wire, however the old PT was already removed and the "new" one has different wire colours. I have followed the schematic, so I know I'm looking for 324vac that goes to the first tube, and 7.2v going to the pcb. I watched several videos breaking down how to identify the lead voltages for amp PTs but this one is quite a bit simpler, I have 2 yellow and 2 red wires snipped in the case, and 2 yellow, 1 brown and 1 black on the replacement transformer. Deduction would submit the 2 yellow on the new transformer are high voltage ac and the brown / black wires are the 7.2v... But I'd like to test this, and of course I question why the different coloured black and brown. I tried to search for the part or even the place it was originally ordered from, but I came up short.
I guess I'm just looking for heedings, warnings and advice. Should I pass this project on, or carry on researching? Is it too much for a beginner / too dangerous, or is it doable?
Thanks for your time in advance.
I was given a Pignose G40V amp for free, along with a power transformer, with the information that the husband of the lady who gave it to me got the component in order to fix the unit but had no idea how to do it and it was left from then on. I found the order slip for the transformer and it looks like it was ordered in 2008, and I don't know when the amp was last working before that - so we're looking at 10 years inactive to begin with. There are also what look to be 3 unused Marshal ECC83 tubes, boxed, as an added bonus with what I was given.
In this case, is it even worth trying to replace the PT - or am I getting beyond my depth with an amp that has been inactive for so long, in that it will more than likely need other parts replaced or serviced? Visually, I can see nothing wrong with the capacitors or any components on the PCB or otherwise within the case.
I initially thought it would be a simple situation of replacing wire for wire, however the old PT was already removed and the "new" one has different wire colours. I have followed the schematic, so I know I'm looking for 324vac that goes to the first tube, and 7.2v going to the pcb. I watched several videos breaking down how to identify the lead voltages for amp PTs but this one is quite a bit simpler, I have 2 yellow and 2 red wires snipped in the case, and 2 yellow, 1 brown and 1 black on the replacement transformer. Deduction would submit the 2 yellow on the new transformer are high voltage ac and the brown / black wires are the 7.2v... But I'd like to test this, and of course I question why the different coloured black and brown. I tried to search for the part or even the place it was originally ordered from, but I came up short.
I guess I'm just looking for heedings, warnings and advice. Should I pass this project on, or carry on researching? Is it too much for a beginner / too dangerous, or is it doable?
Thanks for your time in advance.
Lots of details to consider here. How you answer will determine your course of action.
First, the time versus money equation. Do you have the time to properly troubleshoot and repair this machine? Since experience is short, the method here is slow and methodical. It could take a lot of time to get it done. Otoh, if you have a fat wallet, the entire process could be accelerated by paying a competent tech to repair it quickly.
The other question is about equipment. Do you have the tools and instruments to test and repair the amp? If not, the purchase price of things like a multimeter, soldering iron, solder, pliers, signal tracing tools, and other hand and electrical tools weigh against the price of pro repair.
Also, the parts you have on hand may or may not be useful. You may end up needing to purchase more parts. One never knows what the previous owner did or didn't do to the equipment. The entire project begins as a gamble slash mystery. Lucky for you, the amp was donated, so you have zero investment so far. Some tech work must be done to get a better glimpse of how bad off the thing is. No way to tell until then.
First, the time versus money equation. Do you have the time to properly troubleshoot and repair this machine? Since experience is short, the method here is slow and methodical. It could take a lot of time to get it done. Otoh, if you have a fat wallet, the entire process could be accelerated by paying a competent tech to repair it quickly.
The other question is about equipment. Do you have the tools and instruments to test and repair the amp? If not, the purchase price of things like a multimeter, soldering iron, solder, pliers, signal tracing tools, and other hand and electrical tools weigh against the price of pro repair.
Also, the parts you have on hand may or may not be useful. You may end up needing to purchase more parts. One never knows what the previous owner did or didn't do to the equipment. The entire project begins as a gamble slash mystery. Lucky for you, the amp was donated, so you have zero investment so far. Some tech work must be done to get a better glimpse of how bad off the thing is. No way to tell until then.
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I hope you have the AC input wires also. Piece of cake to fix.
The reason for transformer failures are often too much current draw. So when testing if either of the output tubes glows red or violet turn it off immediately.
Good chance the electrolytic capacitors have dried out. So I would make a light bulb box to first test it.
The reason for transformer failures are often too much current draw. So when testing if either of the output tubes glows red or violet turn it off immediately.
Good chance the electrolytic capacitors have dried out. So I would make a light bulb box to first test it.
See what I mean? "Please fabricate or find a current limiter" was a first response. Mine would be to pull all of the tubes and measure resistance at key locations before applying any power. This is after the power transformer is figured out. Multimeter and safety equipment required as well as a workspace.
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First, read everything Rob Robinette has to say. Particularly about safety, start up and trouble shooting
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First, read everything Rob Robinette has to say. Particularly about safety, start up and trouble shooting
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The problem here is not that it stood unused for 10/20 years but that you are inexperienced.
And it´s not an amp which one day stopped working and was left as-is , which can be troubleshooted the normal way, with more or less Forum members help, but one which never worked (as far as you are concerned) , is incomplete, has been messed with, and you can´t ask that guy about what he did.
Personally I would publish it on EBay as-is , telling the full story: "it belonged to a friend who passed away, he bought a new PT which he didn´t get to mount, it´s still unused in box, has 3 new unused 12AX7 tubes, nice project for a technically mided guy" and go for the best offer. I bet you will sell it *qiock* ... I would buy it from you if I were in the USA, go figure.
But it needs a Tech minded guy, who can read schematics, take a couple voltage measurements wnd who preferrably has already built something with his own hands.
Mind you, therte´s lots of such guys out there !!!
Just don´t go crazy on the asking price.
They will want to see pictures of thbe transformer, any markings or labels on it and maybe its box.
Both from $$$, time and safety this is the best advice I can give you.
Don´t mess with mains or very high voltage ... both of which are involved in replacing and setting up a power transformer.
And it´s not an amp which one day stopped working and was left as-is , which can be troubleshooted the normal way, with more or less Forum members help, but one which never worked (as far as you are concerned) , is incomplete, has been messed with, and you can´t ask that guy about what he did.
Personally I would publish it on EBay as-is , telling the full story: "it belonged to a friend who passed away, he bought a new PT which he didn´t get to mount, it´s still unused in box, has 3 new unused 12AX7 tubes, nice project for a technically mided guy" and go for the best offer. I bet you will sell it *qiock* ... I would buy it from you if I were in the USA, go figure.
But it needs a Tech minded guy, who can read schematics, take a couple voltage measurements wnd who preferrably has already built something with his own hands.
Mind you, therte´s lots of such guys out there !!!
Just don´t go crazy on the asking price.
They will want to see pictures of thbe transformer, any markings or labels on it and maybe its box.
Both from $$$, time and safety this is the best advice I can give you.
Don´t mess with mains or very high voltage ... both of which are involved in replacing and setting up a power transformer.
Thanks all for your responses! I have a multimeter and workspace as repair is a past time of mine, but generally automotive / mechanical / woodwork / instruments and simple electronics like phone /guitar hardware replacement is my realm of experience.
I have the AC input wires, those were easier to figure out. At least by deduction, looking at the schematic and they're the same colour as the old PT (white and black).
There are a few repair cafés and makerspaces in my city, so I might ask around there and see if I can bring it and be guided by someone with more experience to avoid disaster
I have the AC input wires, those were easier to figure out. At least by deduction, looking at the schematic and they're the same colour as the old PT (white and black).
There are a few repair cafés and makerspaces in my city, so I might ask around there and see if I can bring it and be guided by someone with more experience to avoid disaster
If you can get local guidance from an amp tech , this would be a good amp to learn from. It sounds like you do want to gain some knowledge and experience on tube amps and this amp design is fairly "standard", the circuit boards actually look pretty robust from what I saw on the web. The thing that needs to get sorted is the mystery replacement transformer, is it the right voltages and VA ratings for this amp, and if not, it may be expensive to procure the correct one. The most $$ in a tube amp repair is the power and output transformers, the rest of the parts are fairly inexpensive in comparison.
Ok so the question here is what to do first. You want to do all kinds if preliminary testing on parts and assemblies before you try to fire up the whole thing. Chassis, individual tubes, and both power and output transformer should be proven to be a go individually.
I would decode the pt and ot first. Just measure ohms across all of your windings for a ballpark of what winding is what. Voltage ratio is the square root of ohms ratio. Make sure none of the windings are open or shorted to each other or the core.
Once resistance checks point in a favorable direction, you can feed some low voltage ac into a low voltage winding and read the induced voltages on the higher voltage windings to verify proper values. A super simple rig to do this is a cellphone and your favorite signal generator app connected to the headphone output in series with a few ohm power resistor for current limiting. Adjust the volume of the phone for a volt or two of signal at the winding, then measure the voltage across the other windings. Super safe, not enough power to smoke or shock.
I would decode the pt and ot first. Just measure ohms across all of your windings for a ballpark of what winding is what. Voltage ratio is the square root of ohms ratio. Make sure none of the windings are open or shorted to each other or the core.
Once resistance checks point in a favorable direction, you can feed some low voltage ac into a low voltage winding and read the induced voltages on the higher voltage windings to verify proper values. A super simple rig to do this is a cellphone and your favorite signal generator app connected to the headphone output in series with a few ohm power resistor for current limiting. Adjust the volume of the phone for a volt or two of signal at the winding, then measure the voltage across the other windings. Super safe, not enough power to smoke or shock.
While you are checking the chassis guts and transformers, try to find someone with a tube tester that can verify that the ones you have are ok. The more homework that can be done to verify that the parts work properly before the whole thing is assembled, the higher the probability of a successful repair. The more unknowns that can be eliminated up front the better. If you end up chasing down a loose connection or a bad two dollar part, there will be very little tail chasing involved.
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