Howdy guys, need help with a Fender 65 SRRI.

[renshen1957]

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 bull months ago)70, 71 (They feed pins 2 and 7 off the PT)

- New Sovtek 5881's (I was going cheap in case I mucked it up again)

I've gone over the schematic with a fine tooth comb and all of the wiring is now as it should be.

I went to bias the beast, with the bias pot turned all the way down as it should be before beginning, and when I flip the power switch it's NOISE CITY even with every potentiometer on the front turned down to zero.

The reading at the bias resistors with the bias pot turned all the way to the left (down) is .044 and .043mV which is still WAY too high.

I don't get it.

Here's a video. Pardon my rambling.

http://youtu.be/G1eQPlac-sM

Hi,

Some random thoughts off the top of the knoggin:

What are the voltages without the tubes?

Is there noise without the tubes?

Is there noise without a Guitar plugged in?

Have you tried the new Sovtek 5881 in another amp first?

Have you cleaned the pots and checked if the input jack is grounded properly?

You shouldn't have much if any signal with pots turned to zero.

Others will add their input.

Best regards,

Steve

PS My last post prior to thread's hiatus was about starting from scratch. I worked on a Fender Super 60. I found besides the evidence of prior repairs, a resistor burnt up. Simple repair to fix the OD that didn't work. I checked over the PCB to determine why the component failed. Everything checked out. Then fired up the amp, another resistor went up in smoke! It took out the 6V3 heater winding on the PT!

So now I am out a MC PT, and the darned amp was still an issue. So I Gutted the amp, and built a Super Reverb black face circuit (what the owner originally wanted but couldn't afford), and offered the owner a choice, try the amp out, if you don't like it, let me purchase the amp for the price you paid or if you do like it pay me the original agreed upon repair charge.

Sound crazy? I actually made more money off the deal (he kept the amp) and was referred to build other amps. After that I changed my policy, no PCB amp repairs. It Wasn't Worth The aggravation. However my other electronic business took off, but that's another story.

[Ravie]

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 won't hurt anything?

>>Is there noise without a Guitar plugged in?

That noise in the video is without anything plugged in and everything turned down to zero.

>>Have you tried the new Sovtek 5881 in another amp first?

No. I suppose I could try them in my Pro but I'm gonna guess that's not the issue.

>>Have you cleaned the pots and checked if the input jack is grounded properly?

No. For that I have to pull the circuit board out so I was kinda leaving that to serendipity, though I could easily spend some time and do that.


So, am I okay to pull tubes (like say, pull the power tubes and turn it on? pull preamp tubes (all of them at once?) and turn it on?

I wonder what the odds are that the recitifier tube is on it's way out and is causing issues...

As far as voltages go...the only place I checked was pin 8 on the rectifier and it was 512V which is quite a bit higher than the specified 433 or 432 number on the schematic, however we have slightly hot electricity in this house anyway (the wall socket is giving 122V) so I wasn't sure. I know when I biased my Pro a while back it was a lot higher in that amp than what the schematic said too, but that amp continues to work beautifully and biased out just fine.

[Ravie]

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 in one by one...and found my culprit channel: V6, a 12AT7 that looks to drive the power tubes. Swapping it back and forth with the V1 AT7 makes no difference. As soon as there is power on that tube/position when the amp is on, I get noise.

Next?

[Firestorm]

Just to clarify: you get that noise when V6 is the only preamp tube installed?

[JazzGuitarGimp]

Just to clarify: you get that noise when V6 is the only preamp tube installed?

+1 This would be the next thing I'd try. If the amp is quiet with only V6 (and power tubes) installed, then put V5 back and retest. Keep working your way back to V1 to find out which tube is causing the noise.

[Ravie]

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 phase inverter)

[Ravie]

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.

[ampfab]

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

[Ravie]

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...

[JazzGuitarGimp]

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...

The noise in your video confirms that it's not reversed OT wires.

Is it possible that the PI socket pins have loosened up, and need to be tightened?

Is the PI socket soldered directly to a pc board, or are wires to each pins of the socket used? If it's a pc board mounted socket, you might try resoldering all of the pins on that socket.

EDIT: I see spell check got me on desoldering. I've changed it from desoldering to resoldering

[pdf64]

I seem to remember seeing reports of bad plate resistors on the phase splitter of RI etc Fenders.

[Ravie]

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 those specifically. Some of the others in that quad did at least give me the right readings. Not that that means anything necessarily...

I cleaned the socket and tightened it a bit. It made no difference.

The Sockets are bolted to the chassis and have individual wires to them that come from the PCB

[Ravie]

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 board back up and reflowed some of the solder joints.

This is really getting on my nerves...

[Ravie]

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 resistors...

[Ravie]

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 and spray all of the pots...they're all junky inside.

What a horrid excuse for a Re-issue.