twin reverb trouble HELP!!

oledon · 8th December 2011

Hi folks I'm new around here,

I have a 76-77 fender twin silverface. 20 years ago I blew stock fender speakers and left it sit till just last spring, bought new speakers, power tubes and ground switch. Did work but excessive hum. Hum was getting worse and I noticed one power tube red plating, thought just a bad tube so I put the old fender in there. Later switched them back and ok. last night hum got high pitched and amp smoked. Checked it out a resistor on power tube burned out. While I was looking around I noticed tube sockets where deteriorated, would this cause the problem or more likely weak caps and if so how do you check micro farads without un-soldering wires.

sorry so long, thanks for any feedback don

nedorama · 9th December 2011

You may have a problem with screen resistors, caps, tubes not being biased, or all f the above. Your amp is more than due to have filter caps replaced as well as any out of spec components.

It's time to take it to a competent amp tech and have them fix.

For better Fender amp advice, I'd go here:
Fender® Forums • View forum - Vintage Guitar Amplifiers (anything before 1985)

but they'll probably tell you the same. Very knowledgable folks.

oledon · 9th December 2011

thanks for the comeback, no doubt you are correct about filter caps. i can most probably handle the job i just need a point to specs and diagrams. will try the link you sent, thanks

nedorama · 10th December 2011

Quote:

Originally Posted by oledon

thanks for the comeback, no doubt you are correct about filter caps. i can most probably handle the job i just need a point to specs and diagrams. will try the link you sent, thanks

The Fender Field guide Brands: Fender; Line: Twin | Ampwares
will have the schematics for all the different flavors of Twin Reverbs.

drbob1 · 14th December 2011

Yup, the Fender Amp Field guide is an invaluable resource. When you get in there, you'll find more you need to replace than just the power supply caps. I'd read up on it in Aspen Pittman's book or one of Gerald Weber's. If the power supply caps, grid resistors and electrolytic caps in the overall circuit are updated, then clean the sockets (Caig Gold). Then tube it and check the bias.

8th December 2011	#1
oledon Gear interested Joined: Dec 2011 Posts: 2 Thread Starter	twin reverb trouble HELP!! Hi folks I'm new around here, I have a 76-77 fender twin silverface. 20 years ago I blew stock fender speakers and left it sit till just last spring, bought new speakers, power tubes and ground switch. Did work but excessive hum. Hum was getting worse and I noticed one power tube red plating, thought just a bad tube so I put the old fender in there. Later switched them back and ok. last night hum got high pitched and amp smoked. Checked it out a resistor on power tube burned out. While I was looking around I noticed tube sockets where deteriorated, would this cause the problem or more likely weak caps and if so how do you check micro farads without un-soldering wires. sorry so long, thanks for any feedback don

9th December 2011	#2
nedorama Lives for gear Joined: Jan 2008 Posts: 1,242	You may have a problem with screen resistors, caps, tubes not being biased, or all f the above. Your amp is more than due to have filter caps replaced as well as any out of spec components. It's time to take it to a competent amp tech and have them fix. For better Fender amp advice, I'd go here: Fender® Forums • View forum - Vintage Guitar Amplifiers (anything before 1985) but they'll probably tell you the same. Very knowledgable folks. __________________ nedorama Monkey Boy Studios Summit 2BA-221, TLA-50 mBox Pro 3, Pro Tools 10.1.3 Radial JDI x 2, ProD2, ProRMP '65 Bandmaster 2x12 combo with Dr. Z Brake Lite, '65 Showman, '74 Princeton, '77 Princeton Reverb, Dr. Z. Mini Z Head, Dr. Z 1x12 Cab, pedals, George L's cabling

9th December 2011	#3
oledon Gear interested Joined: Dec 2011 Posts: 2 Thread Starter	fender twin thanks for the comeback, no doubt you are correct about filter caps. i can most probably handle the job i just need a point to specs and diagrams. will try the link you sent, thanks

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14th December 2011	#5
drbob1 Lives for gear Joined: Nov 2009 Posts: 1,420 3 Reviews written	Yup, the Fender Amp Field guide is an invaluable resource. When you get in there, you'll find more you need to replace than just the power supply caps. I'd read up on it in Aspen Pittman's book or one of Gerald Weber's. If the power supply caps, grid resistors and electrolytic caps in the overall circuit are updated, then clean the sockets (Caig Gold). Then tube it and check the bias.