Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Baguette on July 25, 2015, 10:38:29 am

Title: Making a PP OT out of 2 SE OT
Post by: Baguette on July 25, 2015, 10:38:29 am: Hello,

So I've got a slew of little 5W Champ style OTs and would like to use two of them to make a PP OT for a Tweed Deluxe type amp.
The SE transformers are 5K to 8ohm.
- Would it give satisfactory results?
- How should I wire the two of them together? (an equivalent 10K to 8ohm PP transformer would be fine).

Thanks for the answers and all the very best.
Title: Re: Making a PP OT out of 2 SE OT
Post by: shooter on July 25, 2015, 12:58:20 pm: search this forum, there's some good threads on the pros n cons.
Title: Re: Making a PP OT out of 2 SE OT
Post by: kagliostro on July 25, 2015, 01:09:00 pm: It may work, but isn't the best

in a PP amp there is cancellation of noise because of the two opposite signals

using 2 x SE OT as to recreate a virtual PP OT didn't cancel noise

I've the example of an old Corland, italian guitar amp that a friend restored

(http://i.imgur.com/WcChocD.jpg)

(http://i.imgur.com/dpibunU.jpg)

He tried a single PP OT and was happy to leave it in the amp

K
Title: Re: Making a PP OT out of 2 SE OT
Post by: Baguette on July 26, 2015, 09:25:29 am: Hello,

I did a search and came up with nothing.
Do you have some useful links?

Thanks for the schemo. So the prims are in series and the secs are paralleled.
How should I do with mine to achieve the desired 10k to 8ohm ratio?

Thanks!
Title: Re: Making a PP OT out of 2 SE OT
Post by: jeff on July 27, 2015, 12:17:49 am: The primaries aren't really in series.

The primary of one goes from B+ to one tube's plate, while the primary of the other goes from B+ to the other tube's plate.

Each tube is connected to it's own transformer and the outputs of both transformers are in parallel. So it's like you have a "push" transformer and a "pull" transformer. One tube/transformer is handling mostly the positive part of the signal and the other tube/transformer is handling mostly the negative and you're combining both outputs for the full (push pull) signal to the speaker(assuming it's biased class AB)
Title: Re: Making a PP OT out of 2 SE OT
Post by: jazbo8 on July 27, 2015, 02:54:06 am: I think the calculation was shown in one of kagliostro's threads, it is also a bad idea to use two perfectly good SE OPT's for a PP amp. I would save them for other SE projects, and buy yourself a proper PP...