PP transformer for SE?? Help!

[ThSpeakerDude88]

I just ordered a Hammond 125C for a 2 watt single ended Guitar amp by mistake! They had the 125SE, and its not too late to let them know, but will the 125c work fine?

The 125c is for "general use for push pull amplifiers" and universal primary tap ( 1.2k-10k)

if its ok I'd just like to keep the 125c because it costs about $7 less. Will it work ok in single ended duty?

I need my primary to be 2.5k, and my secondary to have a tap for 4/8/16.

[andrew_whitham]

Push pull transformers are no good for SE. The standing current saturates the core.

...unless you use parafeed or other jiggery pokery.

Andy

[ray_moth]

You won't get what you want from a PP tranny. It's designed to be used with zero net direct current in the primary winding, because the opposing currents of the PP tubes cancel out. An SE tranny can tolerate net DC in the primary without the core saturating. You should order the correct tranny.

If you were stuck with the PP tranny, I would suggest trying to balance out the DC by imposing a dummy load on the unused end of the primary with a resistor to ground, which might work.

[JandG]

I have 6sn7 driving 6sn7 SET amp w/ NFB that is suppossedly using Pilot iron & looks it. But I am sure this can't be SE OT's, How did this guy use PP iron for this unit..? I do not have schematic as of yet, I am working on it. Amp is dead quiet & doesn't seem to do anything wierd, very relaxed sonics.. 250v on plates.. parralleled 6sn7 output, w/ 6sn7 ahead of that. I did not build the amp, but wonder why this dang thing sounds good..?It is not a stellar sounding amp as far as magic, but it is far from bad..I keep waiting for something bad to happen with it...might make a good tweater amp..

[andrew_whitham]

Originally posted by JandG
But I am sure this can't be SE OT's, How did this guy use PP iron for this unit..?

Ok so this is pre-morning coffee but

why are you sure they cant be SE OT's? am I missing something. they look massive for a 6sn7. (they are larger than the SE trafos on the kt88 one I have )

To put it another way I believe its possible to use a hugely oversized pp transformer In SE configuration most will withstand *some* DC offset

alternatively, its not parafeed or anything is it? I think I can only see a coupling cap tho'

generally for SE, people just use SE transformers, if theres a way of connecting P-P iron as SE it ain't generally publicised (and somewhere theres a boffin with a teeny little SE amp)

Andy

[JandG]

Yeah, I suppose it could be SE iron....but I am in seriouse dought. cap coupled it is,..I have had it full tilt volume all day & nothing has went amiss..mmmmmmIt doesn't like my low output by-passed output stage on my NOS DAC though, needs at least 1.5v he said for full output. I have my TVC almost maxed, but that is very loud..extremelly linear..no range sticks out like a sore thumb. Dang thing is way quiet, queitest amp I have..I supposed to get a schematic with it,, that is in the air...he was real fussy about that dang schematic..I will try my best to get it..it is sort of dual mono in the PS. What does saturated OT's sound like...?I hear no distortion.. my speakers are revieling as a mo-fo..Hopefully he e-mails me back soon with the schematic....but never know..I will hand do it if I have to...It is way differant than my other 6sn7 se amp,..smoother, I need more time with it..I have only seen PP Pilot iron so I don't know of a comparison..

[tubelab.com]

You can get away with using a oversized P-P OPT with SE if the current is low enough. A 6SN7 in SE isn't going to draw a lot of current. I have used an 80 watt P-P OPT in SE with a 45 tube at 30 mA (almost 2 watts). There was no obvious signs of saturation. The sound did improve once I restacked the laminations to create a gap.

What does saturated OT's sound like

Strong bass sounds gross, almost like a muted fart. The mids and highs may be unaffected unless accompanied by bass, in which case everything sounds bad. If you have OPT saturation, you will know it.

[andrew_whitham]

Originally posted by JandG
Yeah, I suppose it could be SE iron....but I am in seriouse dought. cap coupled it is,..

sounds like parafeed then - all bets off! The Sowter trafos Over here have Mumetal for 1/2 the core and should sound fantdangtastic and they're only diddy! The cap is supposed to boost the LF response whilst keeping the DC from the trafo. Sizing the cap between the output tube and the trafo though is allegedly a black art but when done "correctly"

depends if you wanna cross the void between science and art

speaking of which...

Originally posted by tubelab.com

Strong bass sounds gross, almost like a muted fart.

Or one could say BAD but you have captured the essence of the sound most effectively - now wipe....

As my mate once said NOISE! This from a guy who'd spent rather more than the record collection on the radio...

Andy

[ThSpeakerDude88]

Hey guys wanted to say thanks, I called antique electronic supply and got my order sorted out. I ordered the 125cse. I had originally ordered a small surplus 3 watt ot, because it was only 5 bucks. But then I noticed that the impeadance was 2.5k-8 ohms. Well I need a Jensen mod 6 inch in my amp for size reasons, and it only comes in 4 ohm. I also needed the option to plug into an external cab, thus I would need 8/16 ohm taps, so It makes sence for a larger ot.

I wanted to tell you guys what I am building. Essentially it is a Harmony H303A clone. While I know there are better ways to design a guitar amp than a 50c5 and 12au6, the harmony has a sound all of its own, and the 50c5 has its own sentimental reasons for me building this , as it was the first tube I ever played with when getting into tubes. I figured out a way to run the heaters off of a center tap. I am using a 120vct filiment trafo, and using the 60v tap to run the 50c5 and 12au6 in series. I would like to thank eveyone who has taught me many things here on DIY audio, particularly tubelab.com for having a lot of patience with me since my humble start in the hobby.

Now that I have my thanks out of the way..

I am wanting to add a triode/pentode switch to this amp as I did with my high octane, but since the 50c5's datasheet says nothing about running it in triode connection, I do not know if its ok to run the tube like this. I was planning on using a 2.2k resistor between the grid and the plate... Will this work ok?