#1
Hello everyone!
I have a 92 fender twin that has been giving me problems for about 6 months. first, a very nasty crackle at recording levels. it was independent of the knobs and guitar, and I had it repaired twice by 2 different techs, with no success (worked fine for ten minutes and then the crackle came back). I did some research and I think I managed to isolate the problem. I think there must be something wrong with the V2 valve socket (the second one counting from the last Output tube?), as the crackle would happen only when a valve was inserted there, and even with brand new 12ax7's.

Now, I came back from my summer holidays to keep trying to isolate the problem further, but to my surprise, there is no longer any sound coming from the amp, not even a crackle. however if i turn the volume up all the way, i hear a very distorted, low volume guitar signal coming through.

ANy ideas if these two problems could be related, and revolving around the v2 tube socket?also, is the logic behind diagnosing the tube socket as the culprit correct? I'm asking because I have spent over £200 in trying to get this f**ker fixed with no result and I would like to tell the next tech where to look first to avoid massive charges.
Any help would be greatly appreciated.

Thanks in advance!
#2
V2 meaning a preamp tube socket right?

If that is the case then I don't think they are related. I say that because you should be able to run your amp without preamp tubes but I'm not an expert on Fenders. If you've taken it twice for repair already - I would demand that whoever is doing the work get fixed properly. Was this under warranty? Ooops. 92, I'm guessing no.

It could be bad socket and the power tubes have now died as coincidence?

You need someone like CECAmps, Cathbard, Roc8995, ECistheBest, or someone like that to jump in here.
#3
I had a Fender Twin, it was doing the exact same thing, crackling, going silent, and then getting that very distorted but very quiet signal coming through. I bought it used, but from a guitar shop, so I took it back, they had a look at it, and then they 'fixed it'. Took it home, worked fine for two weeks, then the same problems came back. So I just took it back to the shop and got my money back because I didn't want to have to deal with it anymore.. A few months later I went back into the shop, the guy said that they completly retubed it and sold it to someone else who is 'very happy' with it.

So have you tried completly retubing it?
"In modern music, a lot of people are really stuck on the example, asif it were the idea. It takes millions of examples to articulate an idea, so don't get stuck on the f*cking example." - Joshua Homme, 2008.
#4
No, haven't tried retubing it. I did get a new 12at7 and 12ax7 and replaced them one by one to see what the problem was... that's how I realised that no matter how many combinations I tried, the V2 socket always seemed to be the problem: if i took the valve out, there would be no crackling as well as no guitar sound, while if i took out other valves, the crackling would be there and no guitar sound. A complete retubing would cost around £160 at £20 per valve, and if that's not the problem i'll end up with a handful of valves in one hand and a crap amp in the other... and as you said, obviously no more warranty (plus, i bought it used).
it's so annoying , cos I really like this amp, and I am just waiting to have it repaired for good so I can order a zendrive from Hermida audio and use it with my strat... but until i can get the cash together i guess it's just amp modelling through my computer...
by the way, do you guys think that if it's not the valves, it would cost an arm and a leg to repair? what kind of malfunction causes the sound to die like that?
cheers.
#5
Quote by sinner.man
do you guys think that if it's not the valves, it would cost an arm and a leg to repair? what kind of malfunction causes the sound to die like that?
cheers.

First find out what V2 is responsible for in your Twin. Get a schematic. It is probably a gain stage but it could be for something else. You say if you pull V2 you get no sound and with V2 in - you get crackle. But now you have very low volume/no volume whatsoever?

Like Kanthras said - it could be a loose/cold/bad solder joint. If you don't touch anything you could pop her open and look. If it is a simple solder repair (or the like) it might be (close to nothing or it could be) $40 per hour times no more than 2 hours. You might have better luck finding someone locally that help you. Friend/EE student from a school/craigslist.

If it end up being a deep dive with lots of traces being done and caps replaced or a socket replaced it could get expensive. Again I'm not an amp tech so I'll shut up now
Last edited by 311ZOSOVHJH at Aug 13, 2010,
#6
If it's not the valves, it could be a matter of resoldering one joint, which would cost you nothing, but it could be that the whole thing is ruined.
"In modern music, a lot of people are really stuck on the example, asif it were the idea. It takes millions of examples to articulate an idea, so don't get stuck on the f*cking example." - Joshua Homme, 2008.
#7
^yeah, your right. The actual solder work itself takes 5 minutes.

sinner.man - if you do open her up I suggest only poking with a pencil or chopstick or toothpick (wood). Inspect the bottom of the V2 socket for scarring as well as the printed circuit board. Take pictures. Then move on to the various connections starting with where the insert jack is and moving along.

Amps can give you a nasty shock if you touch something with one or both hands. Trust me, it is real tempting to want to reach in and tug on something but don't do it. God forbid don't do it while the amp is on but that is the next step an amp tech might take. I would let the amp sit a day or two as well before doing this (precautionary statement - don't know Fenders).

Find someone to help you like I was saying. They don't even need to know too much about amps but they can help visually and with soldering etc. I also have a blog on biasing a marshall type amp the may be semi helpful. Get a schematic like I said, there is probably one on schematicheaven

oh, and if these power tubes are old it certainly could not hurt getting a new matched set online. I think these amps can be biased too so a fresh bias won't hurt. eurotubes.com has a bias vid on a Deluxe I think. I wouldn't buy tubes there because all he has is JJs but maybe try dougstubes.com or tubedepot.com


ok. maybe too much info
Last edited by 311ZOSOVHJH at Aug 13, 2010,
#8
thanks for all the advice... i think i would have been up for opening up the amp when there was only the crackling problem, but now there is no sound at all i think i am going to go for a pro repair. i mean, as i said earlier, i did that already, but no luck... i guess third time's a charm. i just want to stop forking over the cash for useless repairs!
oh by the way, if the order of the valves is correct in this layout, then i was referring to v7, not v2:
http://www.tdpri.com/forum/amp-central-station/88308-fender-twin-amp-tube-layout.html

i guess i was counting from the wrong end
#9
^wow. OK. V7.

Find out what V7 is responsible for if no one here doesn't already know. Contact fender.com too they can help a bit via email. You could still have separate issue of V7 and power tubes. If V7 was a phase inverter slot, for example - don't know, it could very well cause the power tubes to go.

Personally, I'd get new power tubes and take a look visually with underneath side of V7 socket.

Actually, you need to contact the owner of the shop and demand a working amp. Ask them to at least give you a free estimate of what is wrong.
Last edited by 311ZOSOVHJH at Aug 13, 2010,
#10
ok... I know the fender twin can work at half power if I pull the middle two power tubes and half the impedance, so I'll try that and see if i can at least get the sound back, albeit with crackle. Since the power tubes are all glowing a healthy orange colour, i don't assume they've died, but I'll check it and report back. at least that should show if the problem is in the output stage, right?
#12
I'd pick up a complete set of tubes... If nothing else you could rule that out, and have a spare set in the meantime.
Quote by Cathbard
Quote by Raijouta
Unless its electronic drums.

BURN THE WITCH!!!!!
#13
^as much as I agree that a retube would be order - the down side - is his crackle will still be there. Fix the root problem, and if you have to buy new power tubes to get her to purr then that is what is what you do. Again I have no idea what V7 controls. I believe you said you've tried new tubes in this slot and the problem is still there. I'm still not sure how old your power tubes are and they could have died along the way here. You did say they look healthy orange but that is not the sole criteria for them being healthy. At least with what I know.

please take some pics and report back
Last edited by 311ZOSOVHJH at Aug 13, 2010,