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FDP Forum / Amp Mods, Repairs, and Projects / Fuse blowing after about 5 minutes

Previous 20 Messages  
JJuran
Contributing Member
******

Boston Area

Oct 7th, 2017 08:50 AM   Edit   Profile   Print Topic   Search Topic

Yes - reflow. Something's not connected. Also, if you can, lift the bias circuit board from the chassis to see if something's shorting down there.

(This message was last edited by JJuran at 10:56 AM, Oct 7th, 2017)

vanceen25
Contributing Member
***

United States

Vance Erickson
Oct 7th, 2017 11:00 AM   Edit   Profile   Print Topic   Search Topic

OK, fixed it.

I was getting ready to reflow the joint between the bias resistor and the bias diode when I saw that the leg of the resistor was lifted away from the solder! Once I got the solder off I saw that the leg of the diode was just lying on the metal grommet in the bias board, not in it.

So clearly I did a very bad job when I soldered those components in a couple of years ago. I don't mind telling on myself if it helps someone else.

In case it interests anyone, the fuse first blew when I was trying out the trick of bridging the reverb input and output with a cable with a 330k resistor soldered in. Sounded great for about five minutes (lots of extra gain controlled by the Reverb knob), then the fuse blew. I thought my "mod" had caused the problem, but it was really just moving the amp around to make the connections in the back. The wonky speaker /attenuator connection was another red herring. Never assume.

The power tubes are fine, btw.

(This message was last edited by vanceen25 at 01:02 PM, Oct 7th, 2017)

pdf64

UK

Oct 7th, 2017 01:05 PM   Edit   Profile   Print Topic   Search Topic

Good find; it's amazing how lucky you can be with this sort of stuff sometimes, but eventually luck tends to run out!

avspecialist

USA/Connecticut

Bobby Roadrunner
Dec 24th, 2017 06:57 AM   Edit   Profile   Print Topic   Search Topic

I had the same issue in my 67 Super Reverb, mine turned out to be the original Mullard GZ34 was slightly bad. I replaced it with a new one, the problem went away.

Previous 20 Messages  

FDP Forum / Amp Mods, Repairs, and Projects / Fuse blowing after about 5 minutes




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