Bogen J330 Output Transformer T261

[Nichesound]

Greetings
I have a nice Bogen 6L6 octal tube amp that is a J330 which I will use to build an octal based amp. I am leaning towards a bassman type design or layout but using 6SL7's and those 5691's I have. I know about the 6SL7's tendencies to be microphonic, but I am not too worried.

My question concerns the connections to the output transformer for this amp. It says T261 on it, has 10 connection points, and the #10 lug has the choke attached to it, which goes to a huge wirewound, then the middle lug of the resistor goes to the screens of the 6L6. What is this connection point for the transformer? There is 3K ohms going to the screens on this huge 100watt I believe resistor. It has one lug, the #2 which goes to ground, so I wonder if that #10 connection then is the center tap point of the output transformer? Any help in determining this would be great, otherwise I am forced to buy the schematic online, which I can do, though I thought I may bring this up here. I will show results once I get started on this project.
Have a great V-day....johnne in seattle

[Structo]

The first thing I would do is get a schematic for the amp so you know how everything should be connected.
There may be information about the amp.
Or try to find the manual for the amp as they usually have the schematic and also other pertinent information.

[tweedeluxe]

Looks like the same scheme as the J130 I worked on. B+ Voltage divider for the screens and PI/preamp. B+ was around 510V, the divider dropped the screens to around 350V.

[Phil_S]

I can usually "borrow" a Sam's Photofact from the local public library. Apparently, they subscribe for nuts like me. In actuality, a librarian will usually scan it an email it to me. It's free. You just have to be patient. Your library may not be quite that helpful, but it is a great resource.

[Cliff Schecht]

I'm a project lab advisor up at school for a student working on a Bogen 6V6 amp conversion project. From what I've studied in the schematic and in the actual chassis, I've recommended he gut the amplifier entirely and start from scratch. I don't trust these PA's as far as I can throw them and they almost always have been modified somehow internally already. The one my advisee is working on had the fuse holder jumpered over with a TINY piece of speaker wire, for example..

Figuring out that transformer is as easy as grabbing an Ohm meter and doing a bit of napkin math to figure out the ratios. Two almost equally large resistances is two sides center tapped and the secondary side has progresively smaller resistance from about 2 Ohms (16 Ohm tap) to about .8 Ohms (4 Ohm tap).

That resistor is definitely not 100W, closer to 30W IIRC.

[mumford]

I'm a project lab advisor up at school for a student working on a Bogen 6V6 amp conversion project. From what I've studied in the schematic and in the actual chassis, I've recommended he gut the amplifier entirely and start from scratch. I don't trust these PA's as far as I can throw them and they almost always have been modified somehow internally already.

This was my experience as well. It was a serious rat's nest in mine, and there were broken connections all over the place. Mine had a few random mods, too. In the end, I decided to gut it and use the transformers/chassis.

[Nichesound]

Last night after looking at this one more time, I realized that the center tap is number 10 lug on the transformer. This amp is in really great shape. I took off all the PA wiring, resistors, caps, and will layout for the amp this week. There is so much info out there to digest and since this will be my 4th amp, I am looking forward to hearing the fatter tube sound thru this old amp...thanks for listening.
johnnne

[Nichesound]

this resistor is about 3 inches long and 1 inch across, also it is a 30K ohm resistor, and is 3K ohm between the end lug and next lug

[tweedeluxe]

the big resistor is the voltage divider for the screens/preamp

[Nichesound]

yep, figured that out, just that the resistor is so huge, compared to the ones I worked with on my Traynor YGM4 and Fender Deluxe I rebuilt/built...onward.

[tweedeluxe]

Sorry - I misread your first post, thought you were asking about the resistor.

With the J130 I rebuilt, I did an all 6SL7 preamp and KT66 outputs. AC30-ish. Sounded really good.

[Nichesound]

TweedDeluxe, would you have any pdf file of your amp setup?

I have been drawing up my schematics in autocad. this amp has a bunch of octal tube sockets, so I am taking my time in figuring out what direction I want to go...maybe your design can give me some ideas...anyway these tubes are addicting..