Fireworks in my valves!

[John T]

Originally Posted by Infinitely Baffled

.........I have the impression from your post, John, that using 5U4GBs avoids the problem simply by substituting a more robust component. Or are you saying that there maybe isn't a problem anyway with the PSU capacitors?

Certainly not! However, from your earlier posts you infer the problem appears to be influenced by the choice of valve. Bearing in mind, as I said before, this is not an unheard of problem, a change of valve maybe the answer. In my experience, particularly in the case of Svetlana 5U4's, they can resort to flashover when they are becoming somewhat "mature" and it's a lot easier to in pop a new valve(s) than soldering new components - particularly if your experience of this sort of thing is somewhat limited!

Trouble shooting of this type can often be a case of trial and error and personally I always prefer to go for the easy "trials" first, before embarking on major surgery!

[Haselsh1]

Mr Yarland here again...!!!

Why does the rather vociferous response to this thread really not surprise me...??? Why are there so many 'experts' on this forum whose sole purpose it seems, is to make assumptions...??? One really should not assume.. it merely makes an 'ass' out of 'u' and 'me'. I rest my case m'lud.

[andrew ivimey]

You never made a case, you just got snotty!

When I'm wrong, I'm wrong and happy to admit it - Not sure I am wrong here about the electric side of things, just the willingness to repeat that Chinese amps are ****... and you proved that for me.

No, its a jolly good larfffff and peeps on this BB know that. I am always happy to help someone and can get down to brass tacks. If for example INFBaff were 'round the corner' I'd be happy to weigh in and electrocute myself for him but I get the feeling he is down on the coast and I am the other end of the railway line.

One of the last things you snapped off at me was that somehow what makes us different is a) I am muddle headed and a fool (maybe - lawks eh!) and b)I have megabucks expensive system so can deride the financially challenged for having **** chinese amplifiers. Have you looked at the gallery, ever!? Those are the amps I build. Almost all of them share one thing in common, CHEEPNISS. - and that's the way it can stay.

I was only trying to warn peeps off the false economy of buying from Hongkers and environs.

Nevertheless, bestest to thee and thine. I've got the dinner to get on.

[Richard]

Another rect is easy to try but IB's tried 3 others already. The amp has a sensible 22uF first cap and has worked well for 5 years which suggests something is on the way out. Really it should take any 5u4 without trouble.

John, paralleled rects (such as in Kit6550) should have balancing resistors fitted. You may well experience differences between types/samples when used without as the flash is caused by one section doing more work than the other and different valve types/samples may be more equal in sections. (This does not apply in this 300B amp which uses the sections as separate diodes.) I feel sure this was an oversight with those WAD amps and have written it up in the faq http://wduk.worldomain.net/forum/showthread.php?t=3859

Rich

[John T]

Point taken Rich. However, I haven't fitted balancing resistors because, as previously stated, the GB's did it for me

Oh Gawd! that's done it! Now I've said that, the next time I switch on, the amp will blow up!

[Greg.]

I notice IB comments on an £80 cap. That suggests some upgrading has already been done. Can you let us know what exactly are the caps you've got fitted and for how long? Are the cooking items or something more refined?

[Infinitely Baffled]

Hi, all. there are one or two upgraded caps and other bits and bobs, in the amplifier. They have all been there since first build which was in 2002. I know, upgrading before even having built the standard version screams "more money than sense", and that's probably the case (though in truth not much of either) - but anyway, that's how I did it. Most of the improved components were in other bits of the amplifier (better cathode by-pass caps for the 300Bs, for the 5687s and for the 6SN7, better signal coupling capacitors etc) but as far as the power supply is concerned the upgrade comprised the substitution of a giant Elna Cerafine cap value 330uF 500v in place of the originally specified item of 220uF 450v. This corresponds to the cap at position C8 in Richard's circuit diagram earlier in the thread. The thing is stupidly large and is slung under the chassis hoizontally like a torpedo and connected into its PCB by means of jumper-wires. (Looking back at the bills from Audionote, I see I have mislead you all. It was in fact a £40 item, not the £80 I originally quoted - it must just have felt like 80 at the time!). I think that was the only upgrade in this bit of the set.

In any event, I have read carefully all the excellent advice you guys have been kind enough to offer, and I think what I ought to do is replace the first pair of caps which lie downstream of the 5U4 - maybe just as a precautionary measure, and then see how things look. If I am still getting indications of arcing, then C8 (the biggie) is next for the amp graveyard and then further on through the series of caps on the power supply board until I am sure my lovely amplifier is back in fine fettle. It is funny, really - the amp has spent most of its life being asked to drive a pair of ESL57s, and performed perfectly. That's a bit of a tall order for Kit One (7 w.p.c.). But it is only recently that it has been given light duties of driving a pair of Tannoy 10" Monitor Golds that the trouble has started. Maybe it enjoyed the abuse!

Thanks to all who have contributed to this highly erudite (and highly entertaining) thread, in particular for the suggestions and the kind words of encouragement. It's much appreciated. Cheers. Infinitely (though less than before) Baffled.

[richardcooper2k]

only just read this thread

i have had a kit 1 for a number of years and the thing that often goes on them is the 100v 220uF cathode bypass caps on the 300b. i have had 100v standard black gates go on me. to stop it happening again the solution is to use 160v rated or higher caps. many people use black gate N or WK as you can get higher voltage in these(but they are more expensive). try some cheap higher voltage ones first to see if the problem goes away

when the cathode bypass goes it often takes out the 300b and the rectifier valve. usually you can see the 300b plate glowing red on the side of the rotten cap which is often bulging

this has come up on the audio note kits forum before too

there again it could be something else thats already been mentioned.....