Fender DRRI OT replacement

[retrorod]

I am replacing the output transformer in a DRRI. I neglected to write down which connection the center tap connected to when I pulled the old one to test it. My 'memory' thinks it went to CP3..? But not sure...and I cannot tell from the schem/diagram... Can anyone help me out? Thanks, Rod
http://www.schematicx.com/schematic/...ier-schematic/

[txstrat]

The schematic says CP15 for the B+. Look in the schem right after the stand by switch.

[überfuzz]

Do you have any spec for the new transformer? You might wanna check all connections before you fire up...

By the way, why go changing the transformer..?

[retrorod]

The schematic says CP15 for the B+. Look in the schem right after the stand by switch.

Thanks alot...Not sure why I missed that on the schematic diagram. That gets my DC voltage on the plates. I had determined by testing that the original OT was shot. Some fireworks in the rect. may have caused it. I have hooked up the replacement OT but am getting a squeeling/squall type sound after warm-up. This will go away when I turn the bias pot counter-clockwise...Any advice

[retrorod]

[QUOTE=überfuzz;184614]Do you have any spec for the new transformer? You might wanna check all connections before you fire up...

By the way, why go changing the transformer..?[/QUOTE

Thanks Uber, The transformer is correct for this amp. The amp was blowing fuses and through diagnostics, I determined that the OT was bad(open, shorted) Not sure what caused it. The Rect. tube was arcing before fuse blow. New Rect. tube and got loud blaaaa! even with the output tubes removed befor blowing fuse. Something bad going on...Rod

[MWJB]

First stop, if it started after replacing the OT, is to swap the brown & blue wires at the 6V6 pin 3s, sounds like you have the OT polarity wrong.

Fireworks in the rect can't blow an OT, fireworks in the rect could be caused by excess current draw from the tubes, bad filter cap. What is your power tube plate current now?

DR OTs are pretty bullet proof, you usually have to do something really wrong to blow one...check speaker, speaker connections, speaker wire & jack plug.

[retrorod]

Thanks for the advice. I will check what said. Probably tomorrow. will report back. Rod

[überfuzz]

I was just curious because I've never seen any of the transformers toasted in any amplifier I've been fixing. And yet it seems very common to just, 'replace the Output transformer'. Like MWJB said check for gnarlys before you run the new transformer. If you fried the original output transformer you're probably going to put the same pressure on the new one, if you don't fix what finally got the original.

[Alex R]

I saw one of these with shorted turns once, for no good reason I could determine. I've replaced quite a few HRDL OTs of course. One likely scenario - intermittent short in output tube causes sparks in rectifier and fries OT. Or an intermittent speaker connection could cause all of this too. +1 on swapping the plate leads around.

[retrorod]

Thanks to all for the help and suggestions so far. I should describe the beginning of this amp repair. The '65DRRI belongs to a working musician friend. Its a 2001 and gets played alot. He was at a gig and had the amp on standby while taking a break. When he returned, the amp was dead with a blown fuse. He replaced it and the fuse blew again instantly. I got it to the shop and ran another fuse(2a slo-blo) and fired it up(after checking the rect and 6V6's on a tester for shorts)(determined none)Upon applying the B+ there was some flash in the chinese 5AR4 and a loud honking buzz through the speaker. I shut it down immediately. Replaced with a new 5AR4. Rect. held OK but had the same loud buzz from speaker.I Shut it down immediately. I then removed the output tubes and powered up again. -same loud buzz from speaker(speaker ohms out OK). I removed the OT and did continuity checks on primary and secondary. Was showing open/short from CT to one of the plate leads. I then ordered a direct replacement OT from Antique Electronic Supply and thats where I,m at. I fired it up through a current limiter and am showing no shorts at this time. Just the squeeling noise after warmup. I will switch the leads later today after my day job. I will check into the speaker leads as well.
At least, this is how I remember the chain of events...Rod

[MWJB]

In my experience, amps don't like being put into standby for long periods. I only use the standby for initial warm up, then throw back into standby for a short while before powering down & unplugging. Really treat it as a mechanism just to get your heaters up to snuff before applying dc.

[retrorod]

Thanks all for the help and great advice! I switched the plate wires and it did the trick. The amp is doing well. Running fine. MWJB, I never heard anything bad about puttin the amp in standby mode for 30-40 minutes. Thats interesting. This incident seemed to have taken out the rect, output tubes and the OT. Jeesh!