4-6v6 OT?

[pgambon]

What would be a suitable off the shelf OT for a four 6v6 amp. I'm thinking of changing my Tweed twin to run 6v6's. Mercury makes a Jim Kelley OT, but its pretty costly. Thanks

[tubeswell]

For 4 x 6V6 PP (2 per side) running about between 340-390V on the plate, it will work okay with anything between a 2k5 - 5k reflected load, but will probably sound better between 3k2 - 4k IMHO. (So a Tweed Bassman OT with a 4k Pr and 2R secondary would want either 4 x 8R speakers in parallel or 2 x 4R speakers in parallel)

[Wakculloch]

AC30 or 50w marshall style will also both work well and should be easy to source.

[MWJB]

What kind of plate voltage do you have? You may need to run JJ/EH brands that will take typical Twin voltages, especially with the smaller current draw of the 6V6s.

If you use 2x16ohm speakers, in parallel, you don't need to change the OT. The JJ will even cope with mismatch, with stock 2x8ohm speakers.

[pgambon]

Thanks for the replies. I'm wondering... The PT has a dual voltage secondary. I believe it produces a B+ of 385v and 430v. I'm thinking if I used a 50wt Plexi OT I could run 4-6v6's at 386v or 2-EL-34's at 430v. Now that would be cool!

[stokes]

If you dont want to pay the prices for a Mercury,I personaly dont think they are worth it,check out Hammond,for about $100 you can get a 60watt push pull,with 4,8 and 16 ohm secondaries.I like to see closer to a 2.5k to 3k primary,but like tubeswell says 2k to 5k will be okay.

[Diablo]

I'm using a Heyboer HYO18343 OT in my Tweed Bassman and Tweed Twin. It's a 4K primary and 2-4-8 ohm secondary. It should do the job for you too with whatever speaker combination you intend to use. It's only $68 from here:

https://taweber.powweb.com/store/heyboer/hy_order.htm

[Diablo]

What would be a suitable off the shelf OT for a four 6v6 amp. I'm thinking of changing my Tweed twin to run 6v6's. Mercury makes a Jim Kelley OT, but its pretty costly. Thanks

The cheapest route is to just use the OT you have in the Tweed Twin. I think it calls for a 4K primary and 4 ohm secondary. If you have two 8-ohm speakers in parallel now, that's a 4-ohm load, and that also should work out fine if you sub in 4 6V6 tubes instead of the 2 6L6 tubes.

[pgambon]

It's a high power Tweed Twin. So, I believe the OT trans primary is about 2k. I'm actually running 4-6v6 JJ's now, and it works fine. My thought was to get the correct OT.

[tubeswell]

Look at a typical 6V6 tube datasheet. Most of them specify a plate-to-plate load resistance for Push Pull of 8k for two tubes. So 4 tubes is going to need about half of that. Sure, 2k will work, but you will be sacrificing output power. So with that 2k OT, if you wired the speakers so that their combined impedance going to the OT secondary is twice the nominal speaker load for that OT at 2k, then that will reflect a 4k load back to the tubes.

[Diablo]

It's a high power Tweed Twin. So, I believe the OT trans primary is about 2k. I'm actually running 4-6v6 JJ's now, and it works fine. My thought was to get the correct OT.

Oh, I assumed it was the low powered Tweed Twin. The high powered version looks just like an 80 watt Tweed Bassman to me.

[stokes]

Look at a typical 6V6 tube datasheet. Most of them specify a plate-to-plate load resistance for Push Pull of 8k for two tubes. So 4 tubes is going to need about half of that. Sure, 2k will work, but you will be sacrificing output power. So with that 2k OT, if you wired the speakers so that their combined impedance going to the OT secondary is twice the nominal speaker load for that OT at 2k, then that will reflect a 4k load back to the tubes.

Quite often what the datasheets say are different than what "works best" in guitar amps.Fender typically ran a pair of 6V6's at about 6k.I certainly cant argue with the fact that Fender had the "magic formula" for tone,so with a 4X6V6 output in the amps I've built I went for the 3k primary.I have to admit that I just happened to have a couple of OT's that fit the 3k criteria,if they were 4 or 5k I would have used them anyway.

[pgambon]

So, I'm going to use a 4K primary OT (JMP50) and run 4-6v6's with the option of 2-El-34's. Other than rebiasing is there any pitfalls I should watch out for?