Faulty Valve..

Si_

I've had a bit of bad luck with my BE100 recently.. blew a Pre-amp valve 4 weeks ago, and looks like I popped a power amp valve last night.. Amp crackled and went off after about 2 mins blowing the main fuse.

Picked up some spare fuses today at Maplin to get it back up and running and check it out. Turned it on and saw this..  no prizes for spotting the faulty valve. I quickly turned it off after it became super nova bright and hot

The one next to is was starting to show the same signs, I'm not sure if this is a 2nd faulty valve (How unlucky would that be), or if it's a side effect of the first valve.

Dave Friedman has been great and promptly replied to all emails and is sending me a full matched set of replacement valves (shame he's in the USA so will take a while to get here).

It just shows that no matter how expensive the amp is, or wether it's hand wired, or Chinese sweat shop made, we'll all at the mersey of the valve manufacturers.

richardhomer

Si_;22977" said:

at the mersey of the valve manufacturers.

Bloody Scousers!

karltone

Si have you switched the valves to the other positions to see if the problem follows the valve or the socket. Could be valve problem or bias problem. Though more likely the valve.

ecc83

Unless those valves are known to be total ***t to get two fail in the same "mode" at once is stretching coincidence?

Since they are both on the same side they probably share a grid circuit and my money would be on a bias failure.

Hmm, now think about it, if they share grid circuits the really forked one is probably buggering things for its mate.

Dave.

ICBM

Almost certainly a valve fault, since a bias fault on that side would make both valves glow equally badly. They will share a bias supply, and only one will be faulty - or at least, was initially. In fact, the faulty one might be the second from the right (number 3 if you number them left to right), rather than the one on the far right (4) which may be the 'innocent victim' - a grid short on one valve will often make the *good* one on the same side run hotter than the bad one.

Swap 2 and 3, and see if 4 is still the one with the worst problem. If it is you know 4 is the faulty one - if 1 now shows the same problem it's 3. Unfortunately if it's 3, 4 may also be damaged now so make sure you only try the test for just long enough to see if the fault follows valve 3, or you'll risk damaging 1 as well.

p90fool

@ICBM, I bet you're awesome at that find-the-pea-under-the-three-cups thing.

ICBM

p90fool said:

@ICBM, I bet you're awesome at that find-the-pea-under-the-three-cups thing.

Not really. My daughter baffled me for about ten minutes with that turn-three-cups-over trick the other day ).

Si_

Strange..

I tried swapping 2 and 3 as suggested and all was OK (didn't actually play through it, but all valves looked ok), so I swapped them all back to their original positions, and again, all looks Ok..

I assume it's an intermittent valve fault and no something more major as @ECC83 suggested. 

ICBM

Si_ said:

Strange..

I tried swapping 2 and 3 as suggested and all was OK (didn't actually play through it, but all valves looked ok), so I swapped them all back to their original positions, and again, all looks Ok..

I assume it's an intermittent valve fault and no something more major as @ECC83 suggested. 

Yes, but you need to find it, because it *will* do it again, and the more it does the more the risk of it damaging the amp as well.

Try tapping the valves quite hard. That will sometimes trip a valve with an intermittent short into showing itself. If it doesn't, crank it up loud. One or the other will probably do it.

Si_

I'll give that a try tomorrow. Dave is sending me 4 new valves so I'll just swap all of them to make sure.

Si_

ICBM said:

Si_ said:

Strange..

I tried swapping 2 and 3 as suggested and all was OK (didn't actually play through it, but all valves looked ok), so I swapped them all back to their original positions, and again, all looks Ok..

I assume it's an intermittent valve fault and no something more major as @ECC83 suggested. 

Yes, but you need to find it, because it *will* do it again, and the more it does the more the risk of it damaging the amp as well.

Try tapping the valves quite hard. That will sometimes trip a valve with an intermittent short into showing itself. If it doesn't, crank it up loud. One or the other will probably do it.

No amount of tapping seems to being on the issue so I'm going to install the 4 new valves when they arrive and scrap 3 and 4. Will keep 1 and 2 as spares.

timmysoft

Valves are a thing of the past. Let's petition for a solid state Friedman.

ICBM

Si_ said:

No amount of tapping seems to being on the issue so I'm going to install the 4 new valves when they arrive and scrap 3 and 4. Will keep 1 and 2 as spares.

Sensible. Whichever one was the cause, the other one has been stressed heavily anyway. I'm just such a skinflint I don't like to throw away any valves which are working at all and I can use for testing, even if I wouldn't want to put them in a completed repair .

Adji

Hopefully it is nothing major mate. Valves are like light bulbs eh? Some will go years and years, others last five mins.