Marshall 2204 CSA HT Fuse

[Helmholtz]

Your voltage measurements are not clear to me. No tubes is including preamp tubes?
It would be better if you post a generic 2204 schematic and refer to specific circuit points.

In any case something like 250V at the reservoir cap would indicate a severe problem. Any signs of ecap heating?

I have to ask: Did you observe correct ecap polarity? Wrong polarity may cause the cap to explode.

You should monitor mains current while testing.

[bobloblaws]

No tubes is including preamp tubes?

That's right, no tubes at all.

It would be better if you post a generic 2204 schematic and refer to specific circuit points.

preamp nodes -> e.g. V1 plates.

I have to ask: Did you observe correct ecap polarity?

Yes, the terminals on these cans are clearly marked and as I said I double checked the wiring. Note that when I stuck a set of tubes back in after the fact it ran normally and I measured nominal voltages. At this point my only concern is whether the caps are OK or whether I should replace them.

You should monitor mains current while testing.

I have a current meter in line with the mains power.

[Greg_L]

On top of that, they were not allowed to have 16ohm outs, as that can deliver enough voltage to be a safety hazard. (for those of us who might be tempted to hang on to the speaker cable while hitting a power chord with amp set on 'eleven' )

Lol wait, is this true? No, can't be, can it? I've always wondered why the Canadian Marshalls don't have 16ohm taps.

[Helmholtz]

I have a current meter in line with the mains power.

Can you reproduce the ~250VDC at the first HT filter/reservoir cap? If yes, what't the mains current?
Does the amp have a third HT fuse before the reservoir cap? If yes, you can connect your meter instead of the fuse and measure DC current.

And please do find and post a 2204 circuit of that era to make sure we speak about the same things.

[bobloblaws]

Can you reproduce the ~250VDC at the first HT filter/reservoir cap? If yes, what't the mains current?
Does the amp have a third HT fuse before the reservoir cap? If yes, you can connect your meter instead of the fuse and measure DC current.

I'm not trying to troubleshoot anything at this point, just looking for advice on whether to replace the caps.

[Helmholtz]

I'm not trying to troubleshoot anything at this point, just looking for advice on whether to replace the caps.

Voltages and currents will show if the caps are good or leaky. Cap value is no useful indicator.

[bobloblaws]

Voltages and currents will show if the caps are good or leaky. Cap value is no useful indicator.

OK, gotcha, I'll look into it further, thanks.

[g1]

Sorry for the derail again, bobloblaws, but while we wait on your data...

Lol wait, is this true? No, can't be, can it? I've always wondered why the Canadian Marshalls don't have 16ohm taps.

As far as I know, yes this is the reason. And Helmholtz, the number I saw was 40V, so that would explain the 50W version also being affected I think.

Madness. That's our Canadian nanny state.

Somewhat, but I don't think it's all on them. They gave the requirements, and Marshall decided how they wanted to comply. I'd think the other companies had to respond to the same safety regs.
Fender had a CSA Twin with a thermal cutout in series with the mains fuse. But none of these other implementations.

[Helmholtz]

And Helmholtz, the number I saw was 40V, so that would explain the 50W version also being affected I think.

I just wondered because in European safety standards the safety limit is 50Vrms.

https://en.wikipedia.org/wiki/Extra-low_voltage

[g1]

I just wondered because in European safety standards the safety limit is 50Vrms.

https://en.wikipedia.org/wiki/Extra-low_voltage

I don't know what it would have been at the time of the JCM800, but they now have a CSA exemption for under 30VRMS for certain things.

[bobloblaws]

Can you reproduce the ~250VDC at the first HT filter/reservoir cap?

No, as I said earlier, after popping the tubes back in the voltages appear to be in the right ballpark.

And please do find and post a 2204 circuit of that era to make sure we speak about the same things.

I'm attaching the schematic(s) with the specific voltages recorded on the various nodes. The ripple at the reservoir cap is 1.2VAC.

I'm just worried about handing back the amp to a paying customer if those caps have been compromised. I've never seen new caps that far out of spec (or at least appear to be so).

[Helmholtz]

Thanks.
Voltages look ok (I would actually have expected more like 315V instead of 325V at the V1 node). No signs of bad caps.

I've never seen new caps that far out of spec (or at least appear to be so).

If the caps are rated at 50µ +30%/-10%, 66µ would be "out of spec" by 1µ, provided your meter is accurate enough.

Higher than rated capacitance per se is no quality issue. I kind of like it, because it actually gives improves ripple filtering and promises a longer service life.
But you almost never see cap values above rated (I surely measured around a hundred) with small sized asian caps.

I never saw a cap that showed increased real capacitance (i.e. measured with a quality C-meter) after any (mis)use.

[g1]

One other thing, those are all 500V F&T cans, right?
You said without tubes the B+ went to 480V. So under no circumstance did you do anything to compromise the caps.
If you really think there is something wrong with the caps, it is a factory defect and you should return them.
I'm not sure what kind of cap meter you have, but you want to be very sure about it.

[bobloblaws]

One other thing, those are all 500V F&T cans, right?

Yes

One other thing, those are all 500V F&T cans, right?
You said without tubes the B+ went to 480V. So under no circumstance did you do anything to compromise the caps.

Yes, initially I measured 480V on the reservoir cap. But then I measured very high voltage (400+) on the V1 node. Not much later I measured a more reasonable 200+ at the same point, but when I went back and measured voltage at the reservoir cap again it was also down in the 200+ range, which is when I shut it down. As stated, since then I've run it with tubes installed and the voltages have been more or less normal. So when I saw the unusually high capacitance readings I couldn't help thinking there was a relationship between that and the less than ideal and apparently fluctuating voltages I measured without tubes installed. Could that have simply been the new caps "settling in", for lack of a better term? Maybe I'm making to much of the fact that I powered it up initially without tubes. I've never had an issue with Fender amps doing that and I've never seen anyone advise against it.

I'm not sure what kind of cap meter you have, but you want to be very sure about it.

I'm using a Fluke 175 and I double checked with a Hioki 3802. What do you mean "you want to be very sure about it"?

[Helmholtz]

But then I measured very high voltage (400+) on the V1 node

That's normal before preamp tubes filaments have reached operating temperature.

measured voltage at the reservoir cap again it was also down in the 200+ range

That value doesn't seem to make sense. Either the amp must have drawn enormous HT current, which would have shown in the mains current and would have blown at least the mains fuse.
Or the amp has some intermittent connection (rectifier diodes, fuse holder, HT wires).

At any rate increased capacitance won't lower voltages.