Layout problem w/ab763 build

[six el six]

My OT will not fit above the speaker in the combo cab I intended to put this amp in. It is a deluxe reverb size cab w/a standard ab763 chassis.

So, can I put the OT over where the cap can normally goes and put the cap can where the OT would be?

I've heard putting the OT by the preamp could be bad (hum). Any thoughts/experience?

Gracias!

[phsyconoodler]

Just move the OT closer to the back panel.You can move it closer to the preamp side but keep it rearward of the inputs.

[jim]

In my DR I moved the choke close to the back panel betweel the PI and power tubes and could squeeze the new larger OT behind it  close to the PT (about 3/4" apart).  As long as the OT does not phsically touch the speaker basket you are OK.  Mine are 1 mm apart.
Jim

[Willabe]

Or, you can make a new baffle and move the speaker. The speaker does not have to be centered on the baffle.

I had to do this once on a 5E3 I built when I changed the speaker to a ceramic mag. I had enough clearance, but the speaker mag. was so close to the output tubes, they light up (white) like a light bulb.       Worked great.


            Brad     

[six el six]

Thanks for the tips.

This OT will not fit in the normal position on BFDR under any circumstance. It's huge.

So, if I'm going to use it on this build it 's either Willabee's idea of a new baffle, in which case I'll be working on my cabinetry skills (and grill cloth applications) OR move it to the preamp side.

If I move it to the preamp side it will still be close to the inputs. Like I said, she's a brick (du- nu- nuh- nuh) house!

And here's my question: How much noise, trouble, hum am I going to get into if I decide to put it to that side? Is it really a big deal?

I may bail on this OT and use the Heyboer I have. I really just wanted to try the bigger OT w/6,600 primary impedance. I want a clean toned BF (think super/twin reverb).

[PRR]

Running the primary leads from output tubes to OT _past_ preamp tubes or pots is sure to make trouble, mostly squeal/howl from the 400V plate signal leaking into 0.1V preamp stages.

On one build I ran the primary wires outside the chassis, but they have to be VERY well insulated so nobody gets shocked. And the distance you propose to run may mean splicing the factory OT leads, givig more chance for shock.

Does the OT really need to be so big?

[eleventeen]

I have done two variations of what you speak of. I modded a Princeton Reverb using Dynaco ST-35 power and output trannies, changing the tubes to 6L6. The PT went about where the original PT went, but the OT is all the way at the other end of the chassis. I ran the leads to the OT (HV and speaker) outside the chassis, because even back then (I did this over 30 years ago) as little as I knew, it made no sense to run those leads through the preamp section. Yes, I insulated the bloody hell out of them. Of course there was a wire splice 4-5" away from the OT on every lead. Those got tubing, plus I insulated almost all the rest of the wires with more tubing. It's been working for 30 years.

The second variation was to mod a Deluxe Reverb to 4 (yes 4) 6L6. Hey, we wanted watts back then, and a Deluxe Reverb was not a rare thing at all. This one, a Twin Reverb OT went in place of the original. It was ultimately necessary to remake the baffle board and carefully rotate the speaker so that the tallish OT poked down between spokes in the speaker. This used an Altec 417-8H which is a deep (NOT like a JBL D-120) speaker with four spokes. Goofy, but it worked. That one still works, too, though I have taken out 2x 6L6 and downgraded the OT. Still have the power transformer from 4 x 6L6 power which weighs a ton, but I just didn't want to mess with it.

[jim]

Which OT are you using there?  If you're amp has an alnico speaker, you can also remove the magnet cover. Perhaps you could rotate the speaker if you are not bumping on the magnet.  You are going to alot of trouble for a small improvement.  Jim