Ever wondered what red plating valves look like .....

ESchap

If you ever wondered what red plating valves look like, check this out!   

Great photograph, borrowed from another forum.  This chap is having an issue with his 100 watt Blackstar S1.  No bias?   

If I saw valves like that in one of my amps, I wouldn't be taking a photo ... I'd be turning the amp off pronto!

ICBM

They're buggered anyway by now... no more harm to do as long as it doesn't cook something in the amp, and it *should* blow the HT fuse first.

That said, I once did some damage to an amp by not turning it off as pronto as I should - I was playing through a studio's Fender Twin, and the sound was getting progressively more farty and muffled. I looked over at it and there was a strange purple glow on the wall behind - a quick look in the back (there was no back panel on it) and one of the power valves had turned itself into a neon bulb. But it was so pretty that rather than doing what I should have and turning it off, I turned the whole amp round for the rest of the band to see . As I did, the heat melted the glass, the side of the valve was was sucked in by the vacuum making a little funnel, and a little purple flame shot out . Beautiful...

Unfortunately straight afterwards there was a nasty crackling noise and smoke, and the amp's main fuse (they don't have a HT fuse) blew. It had fried the valve socket. I did at least give the studio a reduced price repair though.

Yes, that Blackstar looks like it's got an overall bias failure. It could be as simple as one of the interboard connectors having made a bad contact, which is what caused this, in a Marshall DSL...

http://i.imgur.com/Ufd4Zjh.jpg

(Notice the funnels where the glass has melted, and then cracked as the cold air rushed in.)

It probably took several minutes - the owner said it was sounding unusually good for quite a while before the fuse blew! No other damage either, surprisingly.

(Edit - fixed image link.)

digitalscream

Yup, one of the valves in my JCA22H did that intermittently. Turned out to be a problem with the bias pot.

ecc83

Yes,

Most likely the cable from the middle board to the OP valve PCB but if so it will be the first time I know of it happening on an S1. I have had it work loose on an HT-100 and routinely cable tie the lead to prevent it happening again.

If the problem is in the bias circuitry I strongly advise getting it back to Northampton because the bias is tied up with the DPR circuitry and that is not a job for the amp beginner. But again, there is no history of trouble with the amps in that regard as far as I am aware.

ICBM would also be on the case I am sure!

 

Dave.

ESchap

I've only had it once, when I had a Bassman reissue.  That was with a brand new set of "matched" Winged C 6L6's from a certain supplier in North London.  Interestingly they matched fine on a tester at around 250V on the plates, identical ma/v outputs, but in a real environment (440v approx.) one red plated, even with the bias adjusted as low as it would go, fortunately only a dull red glow and not runaway.   To be fair the valves were replaced without quibble.

DefaultM

ICBM said:

They're buggered anyway by now... no more harm to do as long as it doesn't cook something in the amp, and it *should* blow the HT fuse first.

That said, I once did some damage to an amp by not turning it off as pronto as I should - I was playing through a studio's Fender Twin, and the sound was getting progressively more farty and muffled. I looked over at it and there was a strange purple glow on the wall behind - a quick look in the back (there was no back panel on it) and one of the power valves had turned itself into a neon bulb. But it was so pretty that rather than doing what I should have and turning it off, I turned the whole amp round for the rest of the band to see . As I did, the heat melted the glass, the side of the valve was was sucked in by the vacuum making a little funnel, and a little purple flame shot out . Beautiful...

Unfortunately straight afterwards there was a nasty crackling noise and smoke, and the amp's main fuse (they don't have a HT fuse) blew. It had fried the valve socket. I did at least give the studio a reduced price repair though.

Yes, that Blackstar looks like it's got an overall bias failure. It could be as simple as one of the interboard connectors having made a bad contact, which is what caused this, in a Marshall DSL...

http://theangelconversations.com/pics/MeltedEL34s.jpg

(Notice the funnels where the glass has melted, and then cracked as the cold air rushed in.)

It probably took several minutes - the owner said it was sounding unusually good for quite a while before the fuse blew! No other damage either, surprisingly.

How much would a repair on that cost? It sounds exactly like what happened when I was playing my Dad's Fender Twin.

ICBM

DefaultM said:

How much would a repair on that cost? It sounds exactly like what happened when I was playing my Dad's Fender Twin.

Hard to say without knowing what happened to the amp. With the Marshall it was just a case of removing the crappy jumper connector and soldering the wires directly to the PCB, replacing the valves and testing it. I forget exactly how much but it was probably around £30 plus the valves.

jamesrt2004

S1 does have infact 2 bias pots one for general bias voltage and a second to get the pairs even There was a problem with the ht series where one of the connectors in the amp would come loose and mess the amp up though so maybe something similar as it didn't seem too secure in my s1 50!

Panama_Jack666

Was in Off Topic and saw lots of banter about red plating valves, googled what red plating meant, it took me to another website that linked me straight back here! Back to where I started!

normula1

re: the owner said it was sounding unusually good for quite a while before the fuse blew

the best tone i've ever had was literally just as the smoke came out of the top of my amp and the flames started

Drew_TNBD

Egads!

Cirrus

normula1 said:

re: the owner said it was sounding unusually good for quite a while before the fuse ble

I've had that before - the only time I used proper NOS EL84s about 4 years ago in my AC30 it was the tone of gods, so much power, clarity, girth and authority in the sound for 30 seconds before they started SCREAMING through the speakers like a deranged synth and two of them were glowing bright red.

english_bob

Cirrus said:

I've had that before - the only time I used proper NOS EL84s about 4 years ago in my AC30 it was the tone of gods, so much power, clarity, girth and authority in the sound for 30 seconds before they started SCREAMING through the speakers like a deranged synth and two of them were glowing bright red.

That's why you should use NOS valves in the studio. Record 30 seconds, re-valve, punch in, repeat. AWSUM TOANS.

gubble

My Marshall MA50 redplated during it's first gig. The head started to glow a mystical orange colour whilst the volume dropped.

It's certainly the most spectacular thing that amplifer did in it's short spell with me. Certainly none of the noises that came out of it were decent

Cabicular

Wasn't it Josh Klinghoffers tech that said ' Yes John things often sound amazing just before they catch fire"

Cacofonix

Two of  my Nomad's valves redplated.

So I bought a new set of 4 Mesa valves.

Two of them redplated on install, so I put the two non-redplating old ones back in (if it's an amp issue, there's no harm in that), and it's been fine ever since.  Brand new valves redplating.  Grr.

ICBM

That does sound a bit odd... the chances of four valves independently having the same fault is vanishingly small. Even two is unusual.

Was it the same two valve positions in the amp? And was it two at the same end?

If so there probably is an intermittent bias feed problem to those two valves. If it wasn't the same two valves, it was probably only one each of the red-plating pairs. The two valves in each pair are linked so a fault in one can often make the other one red-plate as well, sometimes worse than the actual culprit.

Cacofonix

It was the same two positions, yes.  I didn't do a shuffle of them all so didn't check if it was an individual one, but when I took the old "good" pair and put them in the redplating sockets it was all good, and has been fine since.

You did mention bias resistors re: the Nomads, so it could have been an intermittent fault with one of those, perhaps.  I might get them replaced as a service item at some point if that's a likelihood.

Edit: they were at one end, too.  the pair nearest the middle of the amp (farthest from the power switch) iirc.