Push-pull OT for 12AT7

[GibsonLover]

Do any of you guys have a favorite P-P OT used for a flea-powered output? I want to use one for a P-P reverb driver using a 12AT7. I'd prefer one spec'ed for the purpose than screwing with a Universal (like Hammond 125A). Nothing against Hammond, lust lookiing for a more finished, designed-in look, preferably with end bells.

[Suusi M]

Do any of you guys have a favorite P-P OT used for a flea-powered output? I want to use one for a P-P reverb driver using a 12AT7. I'd prefer one spec'ed for the purpose than screwing with a Universal (like Hammond 125A). Nothing against Hammond, lust lookiing for a more finished, designed-in look, preferably with end bells.

We are talking push pull reverb driver?

Why?

Why not get a fender single ended reverb driver transformer, which is normally driven by a paralleled 12AT7 its off the shelf and its cheap

OK if you insist. I do not think that anyone can help until you specify the R Plate to Plate and the output impedance of the output, and the power out required.

Without that no one can calculate the windings required

[Enzo]

I don't think he wants to custom wind. If I read him right, he wants to use what someone might use in a 1 watt guitar amp. Are ther any existing nice looking transformers that fit the bill? After all, a reverb driver is nothing more than a tiny power amp.

[Chuck H]

You might do dome searching over at the AX84 forum. They have a couple of miniwatt type projects like the Moonlight. Find out what those guys are using.

Chuck

[Bruce / Mission Amps]

I wonder if something like this Hammond 125A OT would work OK... Kinda pricey at $40.00

http://www.tubesandmore.com/scripts/...P?item=P-T125A

[Steve Conner]

In England, RS sell a little universal OPT that can be used for push-pull. (When we talk about RS it's not Rat Shack, it's these guys http://rswww.com )

I used it for a push-pull reverb driver and have posted about it here in the past, search the archives for my Ninja Deluxe project.

I ended up using a 12AU7 in self-split, and I clocked it at about 0.8W before clipping. It actually sounded quite good driving the speaker directly :-)

It has no end bells, to get that designed-in look I wrapped it in electrical tape :-)

[GibsonLover]

It may have been the AX84 site I found the "Decimator", using a P-P 12AU7
and spec'ing the Hammond 125A. Given the connections shown and looking at the tranny spec, the plate to plate resistance is ~5600. I didn't realize the 12AT7 was so much higher, 20K+ plate to plate. Steve may be on to something using the 12AU7. The push-pull is more efficient than SE, and I figure maybe requiring less gain of the stage, or less drive to run it, to those wondering "why". Another merit is the noise cancellation feature of push-pull. More to the point, 'why not'? We can recycle Fender to death, but I've been there.

[Suusi M]

fair enough, and an excellent answer. I like people who like challenges.


R U going to run in on a spice simulator before building it ? or build and go?


Edit:

there is no reason you couldnt use a low voltage mains transformer with two 120 volt windings as the primary, long as the windings ratio is ok

[tbryanh]

You might be able to combine two single-ended transformers to make one push-pull transformer.

-Bryan

[johan]

I've been trying to build a tiny amp for some time too...and just a few days ago came to realize, I really dont like single ended amps when they clipp, so back to drawing board..

what I ended up with was a small PP amp built around a tiny power-toroid fed by a 12au7..sounds great..its just a small ( 7va) dual primary(2x115) and 9volt secondary...with a 8ohm load I get 5200 ohm anod to anode...a little low perhaps, but it sounds great and has been powered up for several days straight now without even geting hot

..search for talema 70001k for the part I used...much sheaper than a hammond...but please note, it will work for a small push/pull amp( like a 12au7), but will saturate badly if you try to operate it single ended

johan

[stingray_65]

FWIW

I've just built a couple IPod docking stations with just 12AX7's

for the OT I used a SPECO 20 w line matching transformer and the sound is AMAZING

I'm working from memory but the multitap primary has 8,000 ohm 6,000 4,000 2,000 and common

I used the 8000 and common with the 4000 as a ct

has 4 and 8 ohm out

not pretty transformers but for $10 and a frequency responce of 40 - 20,000 hz I 'm not complaining

[loudthud]

Do the math. The 2000 is the CT. The 4 ohms tap is the CT of a 16 ohm secondary.

[Merlinb]

I generally use a 100V line mathching (PA) transformer. The Common - 0.25W-1W taps work fine for mini PP power amps.