Question for Fender Amp gurus...

Mark Herrick · Post by **Mark Herrick** » 25 Dec 2003 2:19 pm

I'm looking at this Twin Reverb that my brother has and would like to clean it up a bit. I pulled the chassis and it looks a little grundgey. (I found a couple of dead bugs in there...) Is there a cleaner (like De-Oxit or something) that I can use to safely spray it out? The tube sockets seem to be a little gummy. Looks like grease or something.

Also, the tube chart is missing from this amp so there is no date code. We dated it to around '73 since the transformer codes were all either '72 or '73. I can't tell what kind of speakers it has though. They are black stamped steel and on the back is a Fender logo and "Fender Musical Instruments", "Special Design Speaker" and the number 005379. There is another number partially obscured by the Fender label: ???737. The dust caps on the speakers are paper and about 1 3/4" in diameter.

And more: There are two screwdriver pots on the amp that I would like to know about. One is on the back chassis panel near the first preamp tubes (V1, V2, V3) and the other is on the chassis bottom near a small transformer that sits between two large transformers.

I know it's a lot to ask on Christmas day, but thanks for any help! And Merry Christmas!

Jay Ganz · Post by **Jay Ganz** » 25 Dec 2003 2:38 pm

Any type of contact cleaner will work, just
don't over do it. After spraying the socket,
work the tube in & out a little. The sockets
might also have to be re-tensioned. The
speaker is probably an Oxford (with the
Fender blue label). The back adjustment
is a "hum balance" & the one underneath
is probably for bias.

David Doggett · Post by **David Doggett** » 25 Dec 2003 9:15 pm

How do you adjust the hum balance? Do you just turn it and see what happens to the amp hum? Does this work on the hum with the volume up or the hum with the volume down? Does this thing really work? I was under the impression that if an amp huums badly, it needs work. This "hum adjust" seems too easy.

Jay Ganz · Post by **Jay Ganz** » 26 Dec 2003 7:57 am

Well, that depends. If there's really something
wrong with an amp causing it to hum, like
dried out filter capacitors, bad ground, or
something...the adjustment won't fix that. You will notice an increase or decrease
in the hum when you adjust the amp with the
volume up though.

Bill Hatcher · Post by **Bill Hatcher** » 26 Dec 2003 7:59 am

The hum balance I believe balances the filament voltage on the tubes. Turn it until you find the spot that has the least amount of hum. That's all.

Brian Wetzstein · Post by **Brian Wetzstein** » 26 Dec 2003 2:31 pm

How to you re-tension a tube socket? I have a deluxe reverb that has a loose power tube. Sometimes it just needs a wiggle to get some juice flowing again, but I would love to fix it.

Back to topic....
I think spraying compressed air into the chasis will be fine. I usually use the vacum cleaner on mine first.
Brian

Murnel Babineaux · Post by **Murnel Babineaux** » 26 Dec 2003 7:33 pm

The Hum Balance control changes the resistance to ground, increasing one side of the AC filament line while decreasing the other. This is how it "balances". The other control is for balancing your output tube bias. This control won't change initial plate current, but moreso creates a balance. Chances are, if the output tubes electrical specifications match, this control won't need adjustment, as long as the control is set equal. When this control is "out of balance" with "balanced" tubes, the amp will hum, as well.

Happy New Year !

MB

Bill Hatcher · Post by **Bill Hatcher** » 26 Dec 2003 8:18 pm

Brian.

To retension a socket, first drain all the voltage off the amp-just turn the amp off and flip up the standby switch and let it set for a while or do the same, take a large low value resistor and touch one end to the center tap of the output transformer and the other to ground or just take a pair of insulated handle needle nose pliers and do the same as the resistor. MAKE SURE THE AMP IS UNPLUGGED.

Having done this, take the largest needle or smallest jewelers screwdriver or machinist scribe and just insert it into the socket between the phenolic and the metal and close up the round section that grabs the tube pin. You do not have to close it up much to improve the "grab". Also you might want to spray a little contact cleaner in there and either use a tiny brush or just insert a tube in and out once or twice to clean any oxidation out.

DO THIS AT YOUR OWN RISK. TUBE AMPS CARRY LETHAL VOLTAGES AND CAN SPOIL YOUR DAY IF YOU DO SOMETHING STUPID.

Brian Wetzstein · Post by **Brian Wetzstein** » 26 Dec 2003 10:48 pm

thanks Bill. Maybe I will try it with a sturdy toothpick or something non metal.
wish me luck.
brian

Mark Herrick · Post by **Mark Herrick** » 28 Dec 2003 1:17 pm

Thanks!

I also heard from someone yesterday that a good way to discharge the capacitors is to turn the amp on, let it warm up, then while the power switch and standby switch are still in the "on" position, unplug the amp and let it sit for a few minutes. (Hope this is right, I'm going to try it in a few minutes...)

This same person also mentioned that for the tube sockets, use a fully volatile cleaner that does not leave a residue; for the pots he said to use a cleaner/lubricant (one that does leave a lubricating residue.)

Roger Kelly · Post by **Roger Kelly** » 28 Dec 2003 3:00 pm

or......you can, if re-tensioning doesn't do it, apply a VERY SMALL amount of Solder on each pin of the tube that goes in that socket, and the pins should make contact with the expanded socket. I have done this before, and it will stretch out the life of your tube socket. If that don't do it, get ready to replace the tube socket. Good luck!

Larry Behm · Post by **Larry Behm** » 30 Dec 2003 5:04 am

Send the whole amp to Ken Fox and let him do his magic, you will not regret it.

Larry Behm