amp is b0rked. any ideas?

stewart · Post by **stewart** » Mon Jan 13, 2014 11:55 pm

firstly: I know shit-all about amps. I know what most bits *are* but not what they do.

right, this evening my Selmer Treble n' Bass crapped it. I switched it on, and could hear speaker hiss. I noticed it sounded weird when I plugged in, but had my guitar/bass channel cables the wrong way around. when I switched them over the signal was weak, thin and distorted and making a fizzy noise. I switched the amp off, checked the speaker cable connection, switched it back on, no sound. Dead. the power light came on, however. popped the back off, the valves were warm (although not very). I reseated them (they looked a bit wonky). powered up again, nothing. the valves didn't light up or start getting warm. at this point I said "fuck it", because we had stuff to get on with in rehearsal, so just put it to one side and used another amp.

before I contemplate a repair guy, anything I could try/investigate/prod carefully? I'll be back at the studio on Thursday.

;_;

bluesngrunge · Post by **bluesngrunge** » Tue Jan 14, 2014 4:29 am

Pop those filter caps out and give em a good shake.

benecol · Post by **benecol** » Tue Jan 14, 2014 8:18 am

Poster above has HILARIOUSLY advised you do something which could well kill you. Which is, of course, how we roll in the knowledge forums. Sounds like you've done most of the relevant stuff that you can - think a cap's gone west. You could try substituting some of the valves if you've got another valve amp at home, but I don't think it'll be that. It's one for a shop. Don't fanny around inside the amp, since there are voltages in there that could kill you, even when it's not plugged in.

Post by **Mike** » Tue Jan 14, 2014 11:38 am

benecol wrote:Poster above has HILARIOUSLY advised you do something which could well kill you. Which is, of course, how we roll in the knowledge forums. Sounds like you've done most of the relevant stuff that you can - think a cap's gone west. You could try substituting some of the valves if you've got another valve amp at home, but I don't think it'll be that. It's one for a shop. Don't fanny around inside the amp, since there are voltages in there that could kill you, even when it's not plugged in.

+1

bluesngrunge - your posting is as crap as your name. And your name is REALLY crap.

Keep this sort of bollocks out of the knowledge forums when people are asking for genuine help. Warning number 1. There won't be a second.

Fakir Mustache · Post by **Fakir Mustache** » Tue Jan 14, 2014 1:03 pm

Probably won't fix the amp, because it sounds like another issue, but check the fuses.

Also, try to read the values on them (sometimes it's hard), and see if the correct types were inserted. The wrong type could have possibly fried something.

Progrockabuse · Post by **Progrockabuse** » Tue Jan 14, 2014 1:46 pm

bluesngrunge wrote:Pop those filter caps out and give em a good shake.

is this before or after sticking a fork in the toaster?

as others have said, don't touch it. take it to a tech and get it checked. better than fried stewart brains

dezb1 · Post by **dezb1** » Tue Jan 14, 2014 4:57 pm

What if he's already dead after taking BnG's advice...STEWART!!!!! NOOOOO!!!!

dezb1 · Post by **dezb1** » Tue Jan 14, 2014 5:04 pm

What if he's already dead after taking BnG's advice...STEWART!!!!! NOOOOO!!!!

Brandon W · Post by **Brandon W** » Tue Jan 14, 2014 5:19 pm

dude..not fucking cool at all. please don't do that again.

stewart · Post by **stewart** » Tue Jan 14, 2014 6:38 pm

yeah, i know about not prodding capacitors, thankfully :-/

i did consider the fuses actually, but the holder compartments obviously haven't been opened in 40-odd years and i didn't have a big enough screwdriver to tackle them at the time. the only glass fuses i have are 10A and 6.3A, i think one of these was a 1.5, but i can't remember offhand.

i have a couple of spare toobz knocking around but from previous experience they don't both go at once. it seemed as if whatever part of the amp powers them had shat it.

i'll take it to someone qualified, just wanted to see if i could eliminate a few things in case i was missing something obvious.

dezb1 · Post by **dezb1** » Tue Jan 14, 2014 6:45 pm

STEWART LIVES!!!! (said in a Brian Blessed voice)

Bacchus · Post by **Bacchus** » Tue Jan 14, 2014 7:43 pm

Have you tried turning it off and on? Is it plugged in at the back.

laterallateral · Post by **laterallateral** » Tue Jan 14, 2014 7:51 pm

It kind of sounds to me like your power tubes were on their way out and blew the fuse when they failed, when you powered the amp back on, that third time.

Could be as easy as replacing the fuse and the power tubes but getting an appraisal at a repair shop couldn't hurt.

stewart · Post by **stewart** » Wed Jan 15, 2014 12:01 am

BacchusPaul wrote:Have you tried turning it off and on? Is it plugged in at the back.

you still working on that IT helpdesk?

stewart · Post by **stewart** » Wed Jan 15, 2014 12:03 am

laterallateral wrote:It kind of sounds to me like your power tubes were on their way out and blew the fuse when they failed, when you powered the amp back on, that third time.

Could be as easy as replacing the fuse and the power tubes but getting an appraisal at a repair shop couldn't hurt.

I'll take a multimeter up with me on Thursday, will tell me if the fuses have blown.

NickS · Post by **NickS** » Wed Jan 15, 2014 10:59 am

I've worked on Mk.1, Mk. II and Mk.3 and still have my hand-drawn schematics for a couple of them. If the heaters are not lighting up orange, there's no volts to the heater chain - which is one cause of no output. Could be a bad connection at the transformer or first valve base (I've not come across this on the T'n'B 50 but I have on the Vox AC50)

Which model do you have?

stewart · Post by **stewart** » Wed Jan 15, 2014 12:22 pm

It's a mark 3, 50w.

It was working fine last time I used it (naturally), and was making sound for 10 minutes after power up this time, which makes me think something's popped or burned out.

As an aside, I guess I maybe shouldn't use a vintage head for gigging, or at least get a flight case for it, I suspect it rattling around in the back of a van won't do it much good.

NickS · Post by **NickS** » Wed Jan 15, 2014 2:15 pm

Schematic at vintagehofner.co.uk >here<
According to that, there is a .5A fuse in the HT secondary winding, but that wouldn't stop the heaters glowing. If the main input fuse blew it would stop the power light from coming on. You could check the mains input with a multimeter to see if it's open circuit; if it is open circuit between somewhere between the 230v winding and 0v the neon would still glow.

Sloan · Post by **Sloan** » Wed Jan 15, 2014 6:53 pm

pour blood on it

stewart · Post by **stewart** » Wed Jan 15, 2014 7:54 pm

NickS wrote:Schematic at vintagehofner.co.uk >here<
According to that, there is a .5A fuse in the HT secondary winding, but that wouldn't stop the heaters glowing. If the main input fuse blew it would stop the power light from coming on. You could check the mains input with a multimeter to see if it's open circuit; if it is open circuit between somewhere between the 230v winding and 0v the neon would still glow.

what d'you mean by heaters?

I'll take my meter up with me, but surely if the valves don't light up it's clear I won't be getting a circuit right through? I guess that's not necessarily how something like an amp would work...