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Odd discovery inside a 43 year old Fender amp

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Posted on June 4, 2015 at 13:30:34
Alpha Al
Industry Professional

Posts: 2958
Location: N. Carolina
Joined: February 16, 2004
Contributor
  Since: December 3, 2015



1972 Fender Vibro Champ amp. It came to my shop not working. Screen resistor was burned in two, power tube had shorted out. Fixed it fairly quickly.

When testing it, I heard a loud crackle on bass notes. Look at pin 8 of that 12AX7 socket. It had never seen solder!

I asked the customer about it. His reply: Oh yeah, it's always done that. I fixed that, too.

 

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RE: Odd discovery inside a 43 year old Fender amp, posted on June 4, 2015 at 13:53:12
6bq5
Audiophile

Posts: 4387
Location: SF Bay
Joined: August 16, 2001
 You never quite know what you will find - until it is in front of you....
Happy Listening

 

RE: Odd discovery inside a 43 year old Fender amp, posted on June 4, 2015 at 15:33:07
unclestu
Dealer

Posts: 5851
Joined: April 13, 2010
 HAve seen that on modern amps that were hard wired also. In one case the wiring was done so well you barely tell that it wasn't soldered and the amp once warmed up, made no noise....

 

RE: Odd discovery inside a 43 year old Fender amp, posted on June 4, 2015 at 18:29:50
FenderLover
 I've never seen that in a tweed, blackface, or early silverface era Fender amp. In later silverface amps (~1980s) you see horrible blobby soldering. Never no soldering.

This VC seems to have good soldering --- where it was applied.

8^)


When you say screen resistor, you mean the 1k-ohm, 1-watt resistor on the filter cap can side of the circuit board? Most Champs and VC didn't have a separate screen resistor on the 6V6GT socket. Like Deluxe Reverbs.


Thanks!

 

RE: Odd discovery inside a 43 year old Fender amp, posted on June 5, 2015 at 05:40:36
dls123
Dealer

Posts: 1214
Location: Beautiful B.C.
Joined: April 15, 2003
 I do mostly stereo tube amps and preamps, but I also do 5-10 guitar or bass amps every year for local musicians. Last year a guy brought in a Fender that was a modern production tube amp made in Mexico, well modern in that it was made in the early - mid 1990's as I recall. He wanted me to re-cap the power supply and he said the reverb circuit had never worked correctly and could I look at it. So I replaced the power supply caps for him and biased it and then looked at the reverb circuit, and sure enough, one of the electrolytic caps on the board had been soldered in backwards at the factory. Put a new cap in there with the right polarity and the reverb worked fine. I understand that mistakes can be made, but you think they would quickly test all of the functions on an amp before then sent it out the factory door!

 

RE: Odd discovery inside a 43 year old Fender amp, posted on June 5, 2015 at 07:04:37
Alpha Al
Industry Professional

Posts: 2958
Location: N. Carolina
Joined: February 16, 2004
Contributor
  Since: December 3, 2015
 Yes, the 1K was burnt in two. Technically it's part of the Pi filter, but I called it a screen resistor because it is between the plate supply and the screen grid.

 

RE: Odd discovery inside a 43 year old Fender amp, posted on June 5, 2015 at 07:40:02
Crazy Dave
Audiophile

Posts: 14371
Location: East Coast
Joined: October 4, 2001
 I suspect that the people assembling this stuff have on idea how it works.

Dave

 

RE: Odd discovery inside a 43 year old Fender amp, posted on July 28, 2015 at 08:15:16
DEAF AS A BAT
Audiophile

Posts: 2
Location: California Central Coast
Joined: July 28, 2015
 Oh yes, one never knows... "Bad Sponge Count" strikes again !

Around 1992 I horsetraded something or other piece of gear for a blackface Fender MusicMaster head. The owner was an 18 year old "kid" starting out playing guitar in a band. It was his first amp. But after I repaired its non-functional reverb stage, it came back to my shop soon with the same problem.
And every time he transported it, a resistor would blow. On the last repair job I made prior to making the trade, as I was sliding the chassis back into its tolex-covered enclosure, I thought I saw something strange lying below the tagboard-to-controls wiring.

Sure enough, I fished out a small, high quality pair of chain-nosed pliers, which was stamped with "F-11". The tool had apparently been left in there since its final assembly in Fullerton. When the amp was jostled around it would short some point in the reverb section and repeat the cycle. Free tools provided with your new Fender Amp? Oops.



Please, mine your own bismuth, so you won't be mining mine !

 

RE: Odd discovery inside a 43 year old Fender amp, posted on July 29, 2015 at 01:01:04
DEAF AS A BAT
Audiophile

Posts: 2
Location: California Central Coast
Joined: July 28, 2015
 CORRECTION The amp was a Fender Bandmaster not the non-existant "Musicmaster". Brain Fog...
Please, mine your own bismuth, so you won't be mining mine !

 

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