Tube Amp Archive

All said and done: Replaced several of the 100k plate resistors, replaced several caps and resistors associated with the power tubes, fixed the power tube wiring which was wrong from the factory, put in new power tubes (I chose Sovteks out of cheapness, but they actually sound pretty nice biased to ...

Since I had some 100k resistors laying around after replacing the resistors on the PI tube plate, I deicded to replace a few more, mostly on the normal channel. All of the noise associated with the PI tube are gone and the Normal channel is perfectly quiet, but now I've got quite a bit of TV/hiss/wh...

Changed the R54 and R55 resistors...Yep, that was it. Problem is, the amp is still...I don't know. I would call it playable but it is obvious to me that there is still noise there. The vibrato channel is noisy unless I have something plugged into the footswitch jack. I need to pull the control board...

R54 and R55 are the plate resistors for the PI tube (V6) They are rated for 82k and 100k, respectively. They measure .409Mohm and dead short, respectively (as in, the needle does not move whatsoever on the 100k resistor) This is with one end desoldered on each. Sooooo, I guess it's the plate resisto...

When I was working on this amp before I replaced one of the ouput jacks on the back. I've got the Green Wire to positive and black to the ring. There is a gray "FB" wire which I've also got on the tip (presumably positive juding from the schematic) Does that seem correct to everyone? I took the boar...

I think I read that, too. Is that the quad of resistors just before the tube? R49,50,51,52? I am not able to get a read on on 55/54 with them still on the board so I'm not sure if those would be part of the equation but I'd have to pull up the board to muck with them. Well, any of them I suppose but...

ampfab wrote:Reverse the output transformer to plate wires? reversed neg feedback.

Nope. The OT wires are all color coded and the connections on the board say what color they accept. I've checked them twice...

This is interesting. the very last post on this page. His was a reissue as well. maybe I should check those connectors.

http://forums.fender.com/viewtopic.php?t=69117

EDIT: Nope, not the connectors.

Volume on either channel does not change the sound whatsoever.

Correct. V6 position is the culprit, but it is not the tube itself, it's the PI section. It makes the noise if there ARE tubes in V1-5 and it makes noise if there are NOT tubes in V1-5. It makes no difference. The noise is there either way as long as there is a tube installed in V6 position (the pha...

Okay some updates: I decided to be sure the bias pot wasn't wired backwards from the factory. It is. Dammit. So I've got the tubes set to .034mV right now (a bit over 16 watts dissipation at 471 Volts on Pin 3) Good. That's over. Now... I pulled out all of the preamp tubes and started putting them i...

Thanks guys: To Answer Steve: >>What are the voltages without the tubes? Without which tubes, specifically? All of them? Just the power tubes? >>Is there noise without the tubes? Again, I haven't really pulled any, but I can go through. Is it safe to pull tubes tube by tube to see what happens? That...

Bringing this thread back from the dead as I've just now finally had some time to mess with this amp. I replaced: - Bias resistor with a 33k in place of it's 27k. - V8 Power Tube Socket with brand new - Capacitors at positions 27, 28 (104's) - Resistors (which I blew messing around like a frustrated...

So you're saying I would need to increase that to maybe a 33k or 39k, rather than going down to a 15k?

So, I was thinking.. If I can't lower the bias voltage to the best number(at rock bottom I had .44...that number only got bigger...), Can I change the resistor to a lower resistance value to get more positive? (bias voltage speaks in negatives, right? So I would be letting more positive voltage in t...

Yeah. I was retesting (I have two meters and they like to give me different answers so I was retesting a few things) and suddenly my voltage on Pin 3 just up and went away. I couldn't figure out why. Suddenly my test probe arced, a big flash happened, it burned up the heater resistors and instantane...