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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 08, 2012 6:05 pm
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aclempoppi wrote:
Part of the circuit or component mod deal, is that a change is made one at a time and given some time to let the rest of the amp adapt.


That's the scientific paradigm, Art. Reasoned, measured, and logical.

Rawk on!

8)

Arjay

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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 08, 2012 11:11 pm
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You know Arjay, I kind of fly by the seat of my pants. As long as I don't end up with a soggy bottom, yeah, it's Rawk On!!! Art

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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Sun Oct 14, 2012 12:49 pm
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Hey Guys

I finally cracked open the amp. The funny thing is how good she sounds when I'm not playing on the lower strings, classic clean Fender Strat sound....

Anyways, I wanted to upload some photo's to see if that would shed some light on the situation. It would appear that all the filter caps have been updated.

For Capicitor Draining (safety first)

In terms or properly draining the caps, I first used the "Switch amp on, switch standby down (as if the amp was in 'play mode', switch on switch off, so the caps drain into the power tubes) I carefully checked a few caps with a multimeter and I was only getting a small reading on the "200m" DC side of my meter. (About 1.7-1.8) I think the caps are safely drained. I just want to make sure Im 100% safe, and if there is anything special to watch out for in a silver face twin.

Next I'd like to look at the caps, and make sure they are the right one's. The guy who installed them, Im not sure if he really would have bothered to look at a schematic, though it's fairly safe to assume he would have matched was in there previously.

Please let me know if these photo's are helpful, and thanks to everyone for their advice and help.

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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 1:36 am
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The main power supply filter caps looked like they were replaced. Though, I can't see the two on the right right (under the foam). The values seem in range for an UL TR.

One thing that jumps out is the twisted filament wires. I've never seen a Fender amp with white wires. Usually, the color ranges from olive green (seen in "push-back" style wires) to milky-green in plastic-rubber insulated wires. This indicates a problem may have once existed in the heater line. Or UL amps run white heater wires. Worth investigating.

The blue coupling caps look original. These prolly should be checked out for leaking DC. Their seems to be one replaced cap (with an Orange Drop).

I'd check each sections plate and cathode-to-ground voltage. It'd be nice to have a tech really go over this amp thoroughly. You'd get a nice tone and a stable amp.

Good luck with it!


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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 8:09 am
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BMW2002Ti wrote:
One thing that jumps out is the twisted filament wires. I've never seen a Fender amp with white wires. Usually, the color ranges from olive green (seen in "push-back" style wires) to milky-green in plastic-rubber insulated wires. This indicates a problem may have once existed in the heater line. Or UL amps run white heater wires. Worth investigating.


Not just the heater wire, but there seems to be a lot of that white wire running around in the amp. There also seems to be a lot of other random colored wires in there. I've always been under the impression that Fender was pretty consistant in their color choice to differentiate between power, signal, heater, ground, etc. Maybe just wishful thinking, but it does make me question the originality of the amp wiring.

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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 8:27 am
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Bluesky, look at that PS rail. Looks like wrong wattage resistor in one position, no?

Kinda wondering about that tech.


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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 9:22 am
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BMW2002Ti wrote:
Bluesky, look at that PS rail. Looks like wrong wattage resistor in one position, no?

Kinda wondering about that tech.


+1

AFAIK those carbon-comps should all be 1-watters.

And I'd never trust those IC caps -- especially in an ultra-linear silverface.

JMOOC

Arjay

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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 10:41 am
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Hey guys

So, let me know if I'm completely out of my depth here. If I am, I understand and would greatly appreciate being pointed in the right direction. What books do I need to read to understand this stuff, where's the best place for a beginner to learn?

The blue coupling caps look original. These prolly should be checked out for leaking DC. Their seems to be one replaced cap (with an Orange Drop).

-What is the correct way to do this?

I'd check each sections plate and cathode-to-ground voltage. It'd be nice to have a tech really go over this amp thoroughly. You'd get a nice tone and a stable amp.

-I thought I had, twice. It seems as though my techs are looking at it and saying "well if it ain't broke…" Yes it turns on, yes it makes a decent sound, but the very specific issue I'm having with it remains unsolved. I might have to go to tech #3

Look at that PS rail. Looks like wrong wattage resistor in one position, no?

-Where is this? What do I Change?

AFAIK those carbon-comps should all be 1-watters.

And I'd never trust those IC caps -- especially in an ultra-linear silverface.


-I dislike the IC's as well, I have changed a few of them out on different fender amps…


The thing with tech's is A) they typically try to solve Obvious problems, not subtle ones. B) They absolutely can't stand to be told they are wrong, didn't do it right, or missed something…It's exactly the same with sound guys, they absolutely refuse to listen to the musician, right or wrong.

Thanks again for all your help


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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 10:56 am
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Retroverbial wrote:
BMW2002Ti wrote:
Bluesky, look at that PS rail. Looks like wrong wattage resistor in one position, no?

Kinda wondering about that tech.


+1

AFAIK those carbon-comps should all be 1-watters.

And I'd never trust those IC caps -- especially in an ultra-linear silverface.

JMOOC

Arjay


I'm not the best at reading resistor color codes (I prefer to measure everything), but if I read them correctly, I can't even find those values in the schematic Arjay provided.

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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 11:01 am
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Nor I, Bill.

And incorrect values will alter the supply voltages to one degree or another, compromising the amp's performance characteristics.

Arjay

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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 11:15 am
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ParksideDrive wrote:
Hey guys

So, let me know if I'm completely out of my depth here. If I am, I understand and would greatly appreciate being pointed in the right direction. What books do I need to read to understand this stuff, where's the best place for a beginner to learn?


That is probably the hardest question to answer that you have asked to date. :lol:

I have a BSEE from when tubes were still part of the curriculum. Arjay is a long time electronics tech. BMW2002ti is onto vacuum tube amp design and does a lot with vacuum hi-fi amps. Point being that the people here have many years of schooling and practical experience.

You might want to see if there are any electronics courses being taught in the schools in your area. Of course, they won't teach about tubes, but a basic electronics course would be helpful. As far as books go, Amazon has a number of good books on tube amp design as well as general amp books. The ones I have been studying are:

http://www.amazon.com/Vacuum-Tube-Circu ... y_b_text_y

http://www.amazon.com/Vacuum-Tube-Circu ... pd_sim_b_1

http://www.amazon.com/Circuit-Analysis- ... pd_sim_b_4

http://www.amazon.com/How-Hot-Rod-Your- ... pd_sim_b_6

http://www.amazon.com/Guitar-Amplifier- ... pd_sim_b_6

http://www.amazon.com/The-Guitar-Amplif ... pd_sim_b_8

http://www.amazon.com/Radio-Designers-H ... th+edition

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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 11:41 am
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+1

An outstanding bibliography!

Arjay

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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 12:36 pm
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After reading Bluesky and Arjay’s post on those power supply rail resistors, I looked at those again. There’s something amiss. It almost looks like the PS rail is a mixture of the UL TR, the Twin Reverb II, and the Evil Twin (red knob).

http://www.webphix.com/schematic%20heav ... _schem.pdf

http://www.webphix.com/schematic%20heav ... rev_II.pdf

http://www.webphix.com/schematic%20heav ... e_twin.pdf

Furthermore, I don’t believe the 47mfd/500VDC caps are of OEM nominal value. I’m afraid that you may need to have the components under the doghouse really looked at, again. I don’t believe you’d be able to get correct PS rail voltages. And anode plate voltages to the 12AX7 and 12AT7, with the current arrangement. At least, with the schematics available to me.

Sorry about that. Good luck!


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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 2:40 pm
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So does that make the OP's amp a Evil UL Twin II? :lol: :lol: :lol:

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Post subject: Re: Fender Twin Reverb Silverface Trouble
Posted: Mon Oct 15, 2012 3:51 pm
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bluesky636 wrote:
So does that make the OP's amp a Evil UL Twin II? :lol: :lol: :lol:


It makes it "NFG" until he can straighten out that mess that somebody left beneath the doghouse.

:mrgreen:

Arjay

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