NEED HELP!

Discuss our latest amp kit.

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Brad H
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Joined: Tue Jun 20, 2017 7:02 pm
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NEED HELP!

Post by Brad H » Fri Sep 01, 2017 1:41 pm

Just finished up drilling my cab for the chassis, and decided now was the time to test everything so I can install into the cab. Everything was good...until I throw the STANDBY switch. Immediately the mains fuse blows (4A fast blow). I took the chassis back into house and removed the voltage selector, thinking maybe the switch had a short. Everything was good, so I wired it back up as stated below.

Pulled the board to make sure there were no pinched wires, everything looked good, replaced the board. Going through everything now to make sure there are no stray wire strands jumping terminals, but really I'm not seeing anything that draws my attention. So I ran back into the garage and started over with testing. Preamp tubes light up, voltages are good coming in and heater voltages are all good. Negative bias voltage is good as well. That's all I get, because the next step is to throw the STANDBY. Another blown mains fuse. Can anyone offer some suggestions?

--voltage selector wiring--

PT primary common: rocker terminal 11 (bottom left)
Mains iec "N": rocker terminal 12 (top left copper)
Mains fuse: rocker terminal 25 (top right copper)
V selector center term: rocker terminal 24 (bottom right)

PT primary 120/220/240 voltage taps: corresponding terminals on V selector. I made sure I had the correct terminals by checking continuity between the different terminals and center terminal as I switched through the different settings, prior to hooking it up.

:what:

Brad H
New Member
Posts: 18
Joined: Tue Jun 20, 2017 7:02 pm
Just the numbers in order: 13492

Re: NEED HELP!

Post by Brad H » Fri Sep 01, 2017 6:39 pm

Think I got it! Had a ground in the wrong spot on the rectifier, which explains why the fuse blew the moment the standby switch was thrown...since it connects directly to the switch. Was getting weird continuity readings on the rectifier with the amp cold, so I suspected something wrong there, just didn't see until now! Crossed fingers!

danman
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Joined: Tue Sep 10, 2013 9:09 pm
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Re: NEED HELP!

Post by danman » Sat Sep 02, 2017 9:35 pm

What kind of amp are you building? Does the fuse still blow if you power up with all of the tubes removed?

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