5E3 OT question

[mac dillard]

I order a Magnetic Components 5E3 OT, model 40-18022 for an amp I am building. Didn't look at the spec sheet very close as I have use this OT before. Seems as though there has been a change made to it. They now ground one side of the secondary to the transformer frame. This is probably the way the original was made. My question is will I have a ground loop with the OT grounded this way? I am considering un soldering it and connecting it to the speaker - side.

(I did see the other thread)

[Bruce / Mission Amps]

I think it should be OK... no ground loop.
Many of the old 50's output trannys were like that and its the way the Mercury Magnetics 5E3 OTs are made too.
I don't use either of those as mine are custom made but, if I did use them, I would be sure to use a small star washer under and over the tangs of the channel mount to get a really good grip on the chassis for a good ground and bolt it down real tight.

[mac dillard]

Thanks for the reply Bruce. I would think star washers with loctite would work..I'm going to cut the ground wire, splice it and ground the speaker and OT like I always have. I'll leave a little wire on the frame such that I can go back if needed.

[Bruce / Mission Amps]

Its the super compressed (near zero) space between the points of the star washers with respect to the chassis and the channel mount of the OT you want... not any lockite or glue! The star washers really dig into the metal of the chassis and the channel mount.
Oh, one more thing, I've noticed that some of the OT's channel mounts have a lacquer on them to keep them fresh looking.... sand all that off to bare metal where your star washer meet the metals.

[mac dillard]

I was thinking loctite for the nut not the star washer.

[Bruce / Mission Amps]

OK.... use a KEP nut instead... it has a star washer built into it and when torqued down correctly, they are really hard to vibrate loose!!

[Big Mike]

Timely info...

I was given a self lead mercury OT for my kit build by a friend. (he'd had it as a replacement in a earlier original Octal pre deluxe...he had that OT repaired so this was a freebie woot!).

Thanks Bruce!

[mac dillard]

Finished the amp using the 40-18022 OT. It is a Fender 5B3 clone using 6SL7 preamp tubes. Was concerned about the grounding of the OT. Just to report that there were no problems with the OT. The amp is very quiet.

[tubeswell]

Finished the amp using the 40-18022 OT. It is a Fender 5B3 clone using 6SL7 preamp tubes. ... The amp is very quiet.

And the tone...?!

[mac dillard]

And the tone...?!

I really like it. I have a Tung-Sol (new production) in the V1 position and a Sovtek in the V2 position. Power tubes are EH's, speaker is a WGS 12" Reaper. I will tweak the B+ rail voltage some to see what happens. Right now I am running 340 VDC on the Power tubes. When I can justify it I want to change the Pre amp tubes to NOS tubes. Cheapest ones I have seen are $20 each. Guess I will watch e-bay and see what I can find.

I have built this amp before using 6SC7 tubes and it really sounds good. Friend is playing it and is out of town town right now. Need to get the two together and see how they sound. Just something about those octal pre amp tubes that I really like.