Squeal, phhhutt, mmmmmmmmmmmmmmm - are you OK, hun?

Snags

Last night, just as I was getting lined up for an online thingy, my Tweaker 112 (15w combo) emitted a spectacularly unpleasant screeching sound, subsequent to which there is still internal glow, and hum, but bugger all sound output.

I'm hoping it's just that a valve or two have crapped out, and all being well will check this tomorrow, but ... it's apparently loaded with 12AX7 in the pre-amp (fine, have loads of those and/or ECC83) and 6V6 in the power amp. Not so fine - my only spares owing to other amps are EL84.

Can I just stuff an EL84 in, instead of a 6V6?  If I can, do I need to swap both 6V6 or is it OK to run one of each in the power amp?

If a valve swap doesn't sort it the next question is going to involve "Who's a good amp tech in Herts?".

ICBM

Have you ever looked at a 6V6 and an EL84?

No, they are not even physically interchangeable let alone electrically. But it does sound like a power valve has probably gone, and taken the HT fuse with it - that will still let the filaments light up.

John_A

a 6V6 has 8 pins and el84 has 8, they are different sizes and totally different layout, so not interchangeable at all I'm afraid

DartmoorHedgehog

Regardless of whether the amp circuit would be happy with an EL84 (somebody else will probably answer that later), I'm pretty sure the socket is physically different so a direct swap wouldn't be possible.  It may be possible to get an adaptor, but you may as well just get some spare 6v6.

midlifecrisis

i used this guy a couple of years ago. old school, repairs in shed in back garden, very good, reasonable price. https://www.facebook.com/malcrawley139/ ;

Snags

Thanks all.

And no, @ICBM , clearly I have never looked at both valves together

Up until now everything I've had as used EL84 so that's the only thing I know, other than that some valves are "basically the same but with different model names" and some are "very much not the same thing at all, oh no".

A quick Google wasn't mad helpful (conflicting inferences) so I figured some ritual humiliation of ignorance on here would get a swift solution. And it did

I guess I'll be spotting for a couple of 6V6 then, before getting the screwdriver out.

Snags

Bloody hell, this is the bit where I hate valves, as I never know where to look for info.

So, the amp comes loaded with 6V6GTA.

Karitone have 6v6-S and GT

Hotrox have options for GT, s, GT-STR, STR-417, -R and -C

Neither have GTA.

According to Wikipedia (hrm) the GTA has a "controlled warm-up period" whereas the GT doesn't

I can't find anything to indicate whether this is significant, or whether the only thing that matters (physically and electrically) is that it's a 6V6 of some kind and the rest is just minor window-dressing around how it might sound, or ...

So as per usual, one ends up faced with a bunch of choices and no clue as to what basis to make them on.

<penelope_pitstop>

Heyalp!

</penelope_pitstop>

ICBM

Don't worry, any variety of 6V6GT is fine.

Snags

Many thanks.

I probably shouldn't bother so much, but then you hear tales of people doing dumb things by plugging in the wrong component and letting all the smoke get out, and think "Is this an occasion where it matters, or where it really doesn't?".

Snags

If I may beg the court's indulgence...

Swapped power valves,  fitted new fuse, worked for about 5 seconds then phut, no noise and a hot smell. Fuse blown.

Before I contact a tech, is there any mileage in swapping V3? I'm guessing not as I assume that's part of the pre-amp and pre FX loop, which still works. Just checking because on the diagram its position visually groups it with the power section, and I don't know enough to know where the inverter (?) sits in the circuit.

ICBM

No, a preamp valve fault won't blow a fuse like that.

Do one last test if you have another spare fuse, if you didn't before you fitted the new valves - remove the power valves, replace the fuse and power up. If the fuse blows again (I expect it to, unfortunately) then you need a tech. It's *just* possible that both one of the old valves and one of the new ones is faulty, but not very likely...

Snags

OK, will do that. I've got 9 more fuses to go ...

And thank you, I very much appreciate the help 

McToot

Snags said:

OK, will do that. I've got 9 more fuses to go ...

And thank you, I very much appreciate the help 

So what happened Pete? I'm waiting to see if you made sad, smokey headway into the fuse stash... I had a Tweaker head and it never gave me any trouble but I have heard some of the earlier ones were a bit flakey...

Snags

I've confirmed the local amp guy is working and will be ringing him on Monday.

No idea how old this one is. I got it pre-loved off here, and it's been trouble free up until now. 

Snags

As I know everyone (i.e. @McToot) is waiting for news on this even more intensely than a tabloid editor looking for a royal gaffe ... dropped it off with a lovely local tech yesterday, who has just dropped me a line to say "the power PCB has tracked out", which I assume is tech for "the power PCB is utterly shagged".

So now we wait to see how much and what lead time for a replacement.

ICBM

Snags said:

... dropped it off with a lovely local tech yesterday, who has just dropped me a line to say "the power PCB has tracked out", which I assume is tech for "the power PCB is utterly shagged".

So now we wait to see how much and what lead time for a replacement.

Not necessarily. The usual fix for this is to cut away the burned area(s) and jumper over any missing traces. It can be a big job if the damage is extensive, but can usually be done without replacing the board. If the board is available fairly cheaply that can be the better way though.

McToot

Snags said:

As I know everyone (i.e. @McToot) is waiting for news on this even more intensely than a tabloid editor looking for a royal gaffe ... dropped it off with a lovely local tech yesterday, who has just dropped me a line to say "the power PCB has tracked out", which I assume is tech for "the power PCB is utterly shagged".

So now we wait to see how much and what lead time for a replacement.

I think, like Meghan, this poor Tweaker felt so unloved that it considered suicide. Pete, I suggest you call Piers to interview the amp: forget about a tech. 

Snags

Revisiting this for no obvious reason, the saga continued but has now (probably) ground to a halt.

Long story short:

• tech couldn't get anywhere on the spare part front
• I picked the amp up, and "did my own research"
• contacted Anderton's who are still isted as a UK disti. After some to and fro they put me in touch with a bloke who was supposed to represent Egnator, only it turned out that bloke wanted to talk to the tech, not me, so ...
• dropped the amp back off with the tech, who took requested photos and corresponded with "Blad" the Egnater geezer
• Egnater geezer initially said "They never do that sir, send pics and when I've seen it I'll send a new bit"
• Pics sent
• Egnater geezer changed tune to "We don't have any of those, but if you send the board to us we'll repair it"
• Tech is of the opinion that the board is FUBAR and not repairable because both tracks and insulation are completely shot, so he doesn't want to dick about sending them the board because it's a waste of time

So, I'll be picking up my cabinet of spare parts at some point, and will have to decide whether to ask Blad to accept me sending the board in, or whether to get an opinion from A N Other tech which is probably a hiding to nothing (the guy who has it has been doing this stuff for years, has a great rep, and has sorted other kit out for me before just fine). Or whether to just put it up in the classifieds as "spares or repair" with full disclosure.

Bugger.

ICBM

You may be lucky and find someone with the same amp but with a fried transformer, and either buy his one for the board or sell him yours for the PT...

DartmoorHedgehog

Does Blad the Egnator live in Transistorvania?

Snags

Ha! California based on the postal address.