Group Buy Interest?

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antichef said:
First fire, then explosion -- kickass! Maybe a car chase next?

Are these caps of the variety that you should drain before futzing with?
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If we were talking about 10,000 uF 500V or something, I'd say yes. 1,000 uF at 25-35V is probably enough to bite you a little or shoot some tiny sparks if you charge it up and suddenly discharge it (as I did with some 2,200/35 caps when I forgot to solder to the input of the voltage regulator in my power supply rework last week---oops!), but it's not a huge safety risk, IMHO.

Besides, they're tied to the power supply rail of the audio boards. Merely shutting the power switch off will cause the audio circuitry itself to discharge them fairly rapidly over the course of a couple of seconds or five.

BTW, just to clarify, explosion of capacitors is usually in the form of them slowly splitting open and leaking black, sticky goo. It's not an explosion in the "fire" sense of the word so much as the "may explode or leak if disposed of in fire" sense of the word. That said, if you replace these caps, be sure to get the polarity right. Putting one in backwards will result in a fairly loud explosion---again, not fire, but it sounds like a firecracker when it happens. :D

Fortunately, these are not the main power supply caps, so it is unlikely that a failure of these will cause any permanent damage to the gear unless they go off like a firecracker, in which case you might get corrosive, potentially toxic electrolyte everywhere. :)
 
I have to disagree; caps are spec'ed at rated voltage and rated temperature for rated life; conditions within those parameters should not cause the caps to fail explosively. Really, the manufacturers have to be conservative, so they wouldn't rated the caps at 25V if they really couldn't take it. Unless it gets near 85C inside the case, they should live a normal life--and the rule of thumb for cap life is 2x the rating for each 10C decrease in ambient temp from the maximum.

Or if one of these caps sees unregulated voltage off the transformer secondary, that could be a problem in the event of a mains AC overvoltage condition . . . even so, I would bet these caps aren't that easy to destroy.

I continue to be very concerned about the emitter resistor on the output transistor, that does exceed its rating by several times when the gain switch passes the pop position, and there has already been one destructive failure. That is a serious problem.
 
dgatwood said:
I can't say this strongly enough: for anyone who owns a 73, you should IMMEDIATELY replace ALL THREE...
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I need to say thanks publicly to dgatwood and the others who are testing and documenting the ACMPs. You guys rock.

I'm hoping someone eventually comes up with a mod/upgrade kit for each of the ACMPs, possibly including an external power-supply (unless other hum repairs are effective).

Even better than a kit would be a service. I'd gladly ship my ACMP-84s to anyone who can offer a comprehensive repair and/or upgrade.
 
recordinghacks said:
I need to say thanks publicly to dgatwood and the others who are testing and documenting the ACMPs. You guys rock.

I'm hoping someone eventually comes up with a mod/upgrade kit for each of the ACMPs, possibly including an external power-supply (unless other hum repairs are effective).

Even better than a kit would be a service. I'd gladly ship my ACMP-84s to anyone who can offer a comprehensive repair and/or upgrade.
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Well, send it here. I will take a look.

Best, M
 
MsH, we'll have to agree to disagree on this one. That's only a 4% safety margin. The last piece of gear I had with caps that had margins anywhere near that low leaked electrolyte in short order, and they ended up recalling tens of thousands of units.... :)

With very, very few exceptions, every electrolytic cap I've seen in a commercial device has at least a 25% margin, and most of the decoupling caps I've seen are specified with several hundred percent margin (40V caps on a 5V line). That's overkill, admittedly, but a mere 4% margin on a decoupling capacitor goes way too far the other direction.

BTW, if the website for the manufacturer is accurate, it appears that these capacitors are rated at the actual breakdown voltage. That means that all it takes is a 4% voltage transient and those caps are damaged. They apparently don't build in any extra margin. That means there's a small enough margin that I'd be really uncomfortable trusting it. Call me paranoid, but I think if it were safe to go with a 4% margin, the bean counters at computer companies wouldn't allow the engineers to specify a 25-33% typical margin. :D
 
Out of idle curiousity, has anyone compared their actual shipping cost to the the USPS online calculator?

I've lost count of how many parcels I've had posted from the US, but I've nearly always checked the shipping costs with the USPS online thingy and rarely noticed sufficient difference to cause me concern........................until now!!! No matter which way I enter estimated dimensions or weight (which is a known factor), the USPS facility indicates the possibility of some serious over-charging, at least for o/seas destinations.

For o/seas guys buying pres, this possibilty, dumped on top of the fact that the justifiable frustrations o/seas guys are already feeling are unlikely to be reduced by the GB organisers......eg: there's sweet fuck all possibility that any warranty (if it really exists), will be of any use to GB'ers outside the US.........would just be the icing on the cake:rolleyes:.

:cool:
 
chance said:
..... it seems that PSW seems to be a central meeting ground between here, GS, and prodigy. When I have time, I'll pop in to PSW and hope any news will get spread around.
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Could someone post some links to the specific threads on GS and PSW where this discussion takes place? I'm a member of both of those boards, but I only look in occasionally. And I've never seen any obvious discussion there that seems to tie in with this thread. Obviously, I'm just not looking in the right place.
 
dgatwood said:
Call me paranoid, but I think if it were safe to go with a 4% margin, the bean counters at computer companies wouldn't allow the engineers to specify a 25-33% typical margin. :D
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:D funny -- but they're usually not concerned with "extra-contractual" (my word, not theirs) cost if it doesn't hit the books, so you'd think they'd be going for 4% (or 2% if there weren't any returns)
 
dgatwood said:
MsH, we'll have to agree to disagree on this one. That's only a 4% safety margin.
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No, it would be a 4% margin at the rated temperature. If the case isn't 85C (which I certainly hope it is not), there is more cushion than that. Try to destroy a cap on a bench sometime for fun . . . :eek:

I agree, it would be nice to have more margin, but I don't think it's that big of a safety issue.

And watch the bean-counter comments :p Really, the only issue there is whether or not the engineers hit their budget. If the engineers didn't foresee unit failures and budget the warranty costs, that's their own stupid fault :p
 
P. Glaser said:
I must have missed that one. Link or details please? Thanks.

:D
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https://homerecording.com/bbs/showpost.php?p=3077887&postcount=7124

Oh, and dgatwood, I see that reading old posts crazydoc had measured the transformer secondary at 27V, presumably AC, that would clearly exceed 24V at peak (38V). So if any of these caps are before the regulator, I agree that's a problem. After the regulator; they may have a shortened life, but I would expect it would be like 5 to 10 years rather than 15 to 20 . . .

I also remembered I am supposed to be sending replacement resistor to that poor fellow, but I can't find the resistors at the moment . . . :o Have to clean up the old parts box today . . .
 
mshilarious said:
I also remembered I am supposed to be sending replacement resistor to that poor fellow, but I can't find the resistors at the moment . . . :o Have to clean up the old parts box today . . .
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Jason - PM me a mailing address and I'll send a single resistor that matches the spec - I've got a couple.
 
structuredloud said:
I've assumed that the custom transformers and electronics have been put on hold until shipping / fixing things are sorted out. Is this in fact the case? If not is there different contact / info pages other than what were posted on page 249?
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I'd like to know about this too. My ACM-1200 isn't functional and I'd like to upgrade it as soon as I can. There are alot of mods online to make the 460 more like a c-12 but I'm not sure that that's the flavor I wanna go for.
 
mshilarious said:
https://homerecording.com/bbs/showpost.php?p=3077887&postcount=7124

Oh, and dgatwood, I see that reading old posts crazydoc had measured the transformer secondary at 27V, presumably AC, that would clearly exceed 24V at peak (38V). So if any of these caps are before the regulator, I agree that's a problem. After the regulator; they may have a shortened life, but I would expect it would be like 5 to 10 years rather than 15 to 20 . . .
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I was assuming that he was measuring 27Vpp. If that's 27Vrms, then the 35V parts in the PSU are running above their ratings....
 
mshilarious said:
You don't want to match the spec, you need a 2W resistor there.
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Has anybody studied the switch to find out what this whole "popping" position on the switch is? Is it a spot where the switch is momentarily not making any electrical connection? Is this the gain switch? I lose track. :)

Oh, one more thing.... If you swap that part for a part with higher current handling, what are the odds that this will simply shift the failure to another part?
 
dgatwood said:
Has anybody studied the switch to find out what this whole "popping" position on the switch is? Is it a spot where the switch is momentarily not making any electrical connection? Is this the gain switch? I lose track. :)

Oh, one more thing.... If you swap that part for a part with higher current handling, what are the odds that this will simply shift the failure to another part?
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I gather the switch is make before break, but that's just a guess, and somehow that screws with the output transistor bias.

I don't think any other parts are likely to fail there; the output transistor should be plenty robust, and the series resistor supplying the output stage is smaller value (12R?) and 1W.
 
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