Bijou All Tube Futterman Headphone Amplifier
Dec 12, 2010 at 4:27 AM Post #3,736 of 4,278

You got it.
The amp has been running for about 4 hours, I left and came back 1 1/2 hours later to the smell of burnt electronics.
The big cap (C1) blew.  The fuse blew, probably saving a lot of parts.
Tested the transformer, its fine.  Tested the PS board after removing C1, its also fine -- giving me a B+ of 255 V.
Next would be to see if the amp boards are damaged.
I got the kit from Glass Jar, so its probably just a bad electrolytic.  Now, I'm also suspecting the other 2 big caps.  I wonder why it blew????

Sure you got the polarity on the caps  right?   Its odd that your B+ is 255V and these blew up,  could it be heat?
Dec 12, 2010 at 2:27 PM Post #3,737 of 4,278
Yeah, I double triple checked my polarities before first power on.  I'm thinking now that the caps probably needed reforming.  After fixing C1, I noted that C4 was almost hot to the touch, and C5 and C6 were warm after about 2 hours.  So I decided just to replace all the caps just to have peace of mind.
Dec 12, 2010 at 2:40 PM Post #3,738 of 4,278
something must be wrong... there is no chance that they all needed reforming...
Check your mains wiring, check you voltage ratings, check the input voltage. Something must be wrong.
Dec 12, 2010 at 3:50 PM Post #3,739 of 4,278
When I get the new caps, I'll check again.  There is definitely something weird going on.  Of the original caps, I only have C6 and C5 in there.  Both are warm after a few hours.  Then the weirdness sets in.I initially get 313VDC at R8, then when the caps are warm, it dips to 303VDC.  I check the AC from the transformer, its 260VAC, did not change at all.  Then it climbs back to 313VDC.  I move the volume to max, with a low impedance phone, it climbs to 320VDC, check transformer again its still pegged at 260VAC! 

If this behavior persists with the new caps, I might get a new EZ81.  It might have been damaged when the cap blew and tripped the fuse, which is a 3A fast blow.
Dec 12, 2010 at 4:05 PM Post #3,740 of 4,278
hmmm.. i suggest checking out the voltages cafefully against Cavallis's troubleshooting diagram. Somthing is going on that is probably not cap related. Could you still adjust the voltage (a good indication the fet is still intact)?
Dec 13, 2010 at 8:20 PM Post #3,742 of 4,278
If there is a large AC ripple current on the filter caps this could also damage them as it will cause them to heat up. If you have a scope just look at the voltage at the first cap to see what the AC component is.
The only other thing that I can think of is that the caps (as already mentioned) are in backwards.

Dec 14, 2010 at 2:11 AM Post #3,743 of 4,278
well the caps arrived (all panasonics) and I installed them around lunchtime.  More stable voltages and about 3-4 volts higher too at 317 volts at the first cap.  The amp has been burning in since then.  Even at full volume I dont see the 320volt peak anymore. 
I also found out why its the voltage sometimes dips -- its the microwave plugged into the same circuit in the kitchen.  I was heating up water and I just happened to measure, and I just caught it at 308vdc at the first cap and 253VAC at the tranny.  This sort of thing could drive anybody crazy.

Now if could only get my case I could finish this project by new years -- its out of stock and the seller is ignoring my request for refund.  Oh well, at least I could start listening in earnest.
  Thanks runeight for this my first tubey project!
Dec 14, 2010 at 5:14 PM Post #3,745 of 4,278
Is it worth getting the 370dax over the 270 for ~$18 more?

Might actually consider it as I am living in N. America now but may be moving back to UK in the next year or so.
Dec 16, 2010 at 8:01 AM Post #3,748 of 4,278
I went with the 370DAX. Finally got around to buying everything (except knobs.... looking for black ones in similar style to the ones the bottom of this page, but closer to 40 mm so they are a bit more prominent on the chassis). Going to get started populating the boards over the next day or two. I expect to get the rest of my accessories within three days and the enclosure in under two weeks!
Dec 20, 2010 at 1:11 PM Post #3,749 of 4,278
Hi, pretty new to the DIY stuff here.  Anyways, I am almost finished with my bijou build.  Just waiting on a few jacks and the transformer and it should be good to go.  I've been thinking about an enclosure for it and I have a few q.
Ideally, I'd like the tubes (at least on the amp part) to protrude through the top of the enclosure.would soldering the larger caps to the other side of the PCB to accomplish this be a bad idea, or are there easier solutions?  I saw one photo of somebody putting the tube sockets on the other side, but that looked like it required some extra custom wiring, which I'd rather not do, and also I don't think I want the entire tube sticking out.
As far as cooling is concerned, which parts heat up the most that I should account for in the enclosure design?
Also, does anybody know a good site that sells small quantities of interesting metal meshes?
Dec 20, 2010 at 1:19 PM Post #3,750 of 4,278
Small parts on amazon actually has quite a variety of metal meshes in 12x12 or 24x12 sheets (maybe bigger?) but they're pretty well priced like 10 to 30$ maybe depending on material / specifications and can get super saver shipping...
I dunno if brass / stainless steel / aluminum and the like are not interesting enough though ;O.

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