HELP!!!!!!!!!!!!!!!!!!!!

shelby1420 · 3743

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Offline shelby1420

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on: February 24, 2012, 12:41:28 PM
Shite shite shite!!!!!!!! OK, so I bought (2) 47uf 100v caps and put them in the place of the (2) 100uf 450v caps and (4) 100uf 100v caps in place of the (4) 220UF 250V caps.  then I removed the (2) 1.2kohm resistors leaving those holes open and then also the (2) 360ohm resistors replacing those holes with 2 triad c7x chokes.............put the tubes in and turned it on, crackle crackle from the amp itself and then the fuse went???  Checked wires comin in and all looks ok, did a double check of the caps and three of the six are bulged at the end, they are all in the right way, facing the same way!!!!   what have I done??

Enjoying the music

Rick


Offline Jim R.

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Reply #1 on: February 24, 2012, 12:54:17 PM
Rick,

Those caps are nowhere near high enough voltage rated for the positions you put them in.  The only caps on the ps board that can be subbed with lower voltage caps are the cathode bypass caps for the 2a3s -- which should be about 100v or greater.

Hopefully the caps took the brunt of the damage, which you can test by replacing the old ones (and the fuse) and starting over.

Hope this helps,

Jim

Jim Rebman -- recovering audiophile

Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).

s.e.x. 2.1 under construction.  Want list: Stereomour II

All ICs homemade (speaker and power next)


Offline corndog71

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Reply #2 on: February 24, 2012, 12:59:00 PM
You swapped a 450v cap for a 100v cap?  That's just begging for fireworks.

The world was made for those not cursed with self-awareness.

Rob


Offline shelby1420

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Reply #3 on: February 24, 2012, 02:05:04 PM
Hey guys, this is where I got the idea and values, from a sticky and these are PJ's words here;

Grainger is correct; I'll just add some details.

The parafeed cap is 3.3uF, 630v or higher. Anything from 1.6 to 4uF is OK with the 2A3, and 3.3 to 8uF for the 45. The interstage cap is 0.1uF, 630v or higher. These caps are located on the frontmost terminal strips and there is a good bit of room for larger parts.

On the power supply board there are two 1200 ohm resistors and two 360 ohm resistors (the latter only for the 2A3) in parallel. For the 2A3, these can be removed and replaced with a choke that has about 270 ohms resistance. I would suggest at least 5 henries, and at least a 60mA current rating; a widely available spec is 10 henries 90mA such as the Triad C7-X. For the 45, you need 1200 ohms DC resistance and 40mA rating. I can't find any with enough resistance so you would need to add a resistor in series. The Hammond 154G (9 henries, 40mA, 700 ohms) in series with a 500 ohm 5 watt resistor should work.

The last power supply caps (100uF, 450v) and the cathode bypass caps (220uF 250v) are isolated from the signal current loop by the plate choke impedance, and hence less important than the signal-path caps above. Nevertheless, they are not insignificant and can be replaced with better parts. The 100uF can be smaller if you have installed the filter chokes, I'd guess 27uF minimum - otherwise use at least 100uF. The bypass caps can be smaller, say 47uF minimum, and the minimum voltage rating would be 100v - we use the larger values because we use them everywhere and buy tons of them. Both of these caps can also be bypassed with smaller high-quality caps, leaving the electrolytics in place.

All of the above power supply parts are located on the PC board and there is no room for larger parts on the board - so you'd have to get kind of creative. I would keep the chokes well away from the audio transformers so you don't accidentally pick up some added hum. Remember the power supply is pseudo-dual-mono so you need two of everything!

The cathode bypass caps are in parallel electrically with the cathode resistors, under the C4S board, and there is a little room there for replacements, or for a smaller, high quality bypass while leaving the original electrolytics in place. You might find room there for a high-voltage bypass cap as well - notice there are extra B+ holes on the PC board for just this purpose. Be careful about the heat from the cathode resistors - heat will damage caps quickly, so maintain as much space between caps and resistors as you can.

Hope that helps. Perhaps it should become a sticky.

Enjoying the music

Rick


Offline Jim R.

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Reply #4 on: February 24, 2012, 02:26:29 PM
Hi Rick,  Here are the relevant sections and my comments:

 The 100uF can be smaller if you have installed
the filter chokes, I'd guess 27uF minimum - otherwise use at least 100uF.

Ok, so you installed the choke, so the 47 uf is good here...

 The bypass caps can be smaller, say 47uF minimum, and the minimum voltage rating would be 100v

This means the cathode bypass caps (perhaps this needs to be clarified a bit), and exactly what I said above.  This does not mean these bypass caps...

The cathode bypass caps are in parallel electrically with the cathode resistors,
under the C4S board, and there is a little room there for replacements, or for a
smaller, high quality bypass while leaving the original electrolytics in place. You
might find room there for a high-voltage bypass cap as well - notice there are extra
B+ holes on the PC board for just this purpose.

Ok, this is probably where you got confused -- PJ is talking about 2 different things here -- a small high quality film bypass for the cathode bypass caps, located near the big cathode resistors on the 2a3s, and on the other hand, a set of holes in the psu board for some high quality film bypasses for the 100uF B+ electrolytics -- rated at least 450v.

Yes, I can see where it can be a confusing read, but the B+ in this amp is much higher than 100 v -- as demonstrated by the readings you should get as instructed by the manual (which I don't have on this computer, so can't look up right now, but I think it's in the neighborhood of 400v.

Again, hopefully it was only the caps that took the hit and the transformers are all ok.

-- Jim


Jim Rebman -- recovering audiophile

Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).

s.e.x. 2.1 under construction.  Want list: Stereomour II

All ICs homemade (speaker and power next)


Offline shelby1420

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Reply #5 on: February 24, 2012, 02:34:31 PM
D'oh what a dumbass!!!!!  Now I got it, thanks man!!!

Enjoying the music

Rick


Offline Jim R.

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Reply #6 on: February 24, 2012, 02:36:37 PM
Rick,

No, not a dumbass -- I can see where it can be a somewhat confusing read.

Anyway, glad to be able to help,

Jim

Jim Rebman -- recovering audiophile

Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).

s.e.x. 2.1 under construction.  Want list: Stereomour II

All ICs homemade (speaker and power next)


Offline Paul Joppa

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Reply #7 on: February 24, 2012, 05:27:13 PM
I'll add my apologies. I try to find a compromise between exhaustive detail and frustrating brevity, but I can't say I always succeed!

I should have talked about voltage ratings in general, in addition to the capacitance ratings. For electrolytic capacitors, the ideal is to have the actual voltage between 50% and 80% of the rated voltage. Higher voltages can compromise performance (lifespan and leakage current, primarily) while operating at lower voltages can result eventually in a loss of ability to withstand the (much higher) rated voltage. For example, the power supply caps are rated 250 when they are running about 200v, and 450 when they are running about 400v. (The 200v and 400v are because the power supply is a voltage doubler.) But the cathode bypass runs about 60v, so a 100v cap would work fine - but we have a ton of 250v caps in stock, and if they lose their capacity to withstand 250v, who cares? They will still withstand 100v forever, and 60v is not going to be a problem.

Unfortunately, I posted with the assumption that this was familiar territory to readers so I was not clear about it. But I am very enthused about the "each one teach one" aspect of this hobby (and in fact any DIY hobby), so I feel a little bad about having failed with a critical element of that post.

Perhaps we should make up some resource of general considerations about replacing components. So far, this forum is the best we've been able to come up with. Bottlehead cannot - of course - guarantee the results of changing components, but it's such an educational and rewarding activity that we can't bring ourselves to object to it.

Paul Joppa


Offline Grainger49

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Reply #8 on: February 25, 2012, 03:23:47 AM
PJ,

How about a sticky in each product's folder with design values and voltages?  For instance, IIRC, Seduction uses 400V caps that could be 200V caps; Eros uses a 1uF 630V that is designed at 0.47uF (you have encouraged me to try my KK Teflon 0.22 and I haven't had the inclination to upgrade yet).



Offline Jim R.

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Reply #9 on: February 25, 2012, 03:46:06 AM
I'll second Grainger's idea.  I just spent a good amount of time yesterday trying despeately to find the cathode bias values for the output stage of the original s.e.x. -- I found it, but it would be really nice if all these values were tabulated somewhere.

And PJ, I hope you understand that I was not trying to criticize -- having written a number of technical manuals for a wide spectrum of end users, I've run up against the same problem many times.  Any undertones of criticism were meant strictly in a constructive sense.

-- Jim

Jim Rebman -- recovering audiophile

Equitech balanced power; uRendu, USB processor -> Musette DAC -> 5670 tube buffer -> Finale Audio F138 FFX -> Cain and Cain Abbys near-field).

s.e.x. 2.1 under construction.  Want list: Stereomour II

All ICs homemade (speaker and power next)


Offline Doc B.

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Reply #10 on: February 25, 2012, 06:41:45 AM
Not to belabor the point, but the caps that were removed had the voltage rating printed right on them. And all of that information is already published in the manual, in the parts list. In my experience our customers should modify things any way they want, but the greatest benefit comes from doing this only after they build the design in its stock form.

The issue I have with posting the parts lists is twofold - one, that I don't care to share our designs in that much detail with those who have not purchased a kit. The other half of the issue is the potential hellstorm for us packing these kits, because if we start listing all the cap values people will call us and ask us to leave two of these out, one of those, a couple of these because they are going to change a bunch of caps and resistors and would we please recalculate the price. Packing these kits requires a very systematic approach to get it right and we are barely keeping up these days. When you have to get up to 300 little parts into a kit box without any errors, it's extremely difficult to adjust some percentage of them to a different part count. To put it more simply, we will just screw it up.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.


Offline Grainger49

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Reply #11 on: February 25, 2012, 09:41:29 AM
I have to agree with Dan on this one.  Scuttle my suggestion.



Offline shelby1420

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Reply #12 on: February 26, 2012, 06:02:34 AM
Hey guys, popped the old caps in, tested the unit and all is well!!!  She sounds lovely, even a little cleaner then before the mod, ( maybe imagining that but that's what my ears think :) )  Couple of things I think are important to clear up here......At the very least I should take FULL responsibility in that I did not let folks know on the board that I am NOT an expert but rather learning as I go along , also I am used to (  having successfully built 5 Bottlehead kits and counting ) THE best instructions for kit building, bar none!!!! Dan, I think your comment re the voltages marked right on the caps removed is a little oversimplified....... as with SOME modifications with BH gear and other gear I have worked on changing this or swapping that can and in fact has caused values to be different, sometimes by a great deal........  I read something by Paul ( much more skilled then I in this arena)  that I thought said if you add this by swapping this then values can change , even now as I read it I still see how one would think this..........  chance for all of us to learn here I guess, bottom line, BH rocks for product and product support!!!!

Enjoying the music

Rick


Offline Doc B.

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Reply #13 on: February 26, 2012, 08:10:27 AM
I see your point and I didn't really mean to oversimplify. I was just making that comment with respect to the notion of putting up the stock parts specs in a sticky. The thing about modifying is you gotta take a few risks to learn something new. Heck, we just pulled some totally fried resistors out of our 300B preamp prototype, because we ran what we had on hand even though I knew it was running them right at the limit. You did an experiment, and it all worked out in the end. Well done!

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.