push pull ot in a single ended amp

[TUBEDUDE]

Thanx, I'll have to try a slice of Pi. I have over 280uF now, to little effect. I'll have to find some chassis space for a 193H I have laying around. I should have tried that. It'll be good to dust off and finish that project.

[Mr. Lime]

Sorry for digging up this old thread but it fits so well.

I have an 125E PP OT left over and would like to use it for "Ghetto UL".
Some EL84s and EL34s are in my drawer as well and I wonder if an EL34 could replace the KT66 in the Hoso56?

Kevin O'Connor has a chapter in his TUT book series called "Champ" where he explains that different tubes can be used with the 125E.
Prim. impedance for the EL34 might be 3k5?

Is it safe with this OT or shall i better try the EL84 with prim. 4-5k?
Some say 50% OT tap is fine for the EL84, some don't.
El34 seem to work fine with 43-50% according to other threads..

I'm still in research what fits best..

Looking forward for your opinions!
Thanks

[martin manning]

See page two for EL84 DL operation: https://frank.pocnet.net/sheets/129/e/EL84.pdf

[Mr. Lime]

Thanks Martin!

Seems like ~50% tap leads to reduction in distortion while 20% help to reach the maximum output?
Thinking about a clean channel, decreasing distortion of the EL84 might be an object..

Still wondering if the EL34 SE can be combined with a 125E OT?

[Mr. Lime]

Nobody's having an idea if a 125E works sufficient with an EL34?

How about reducing the B+ in the power amp to be safe?
Can anyone suggest me a range, like 250V or lower?

Should keep the OT core from saturating I would guess..

[Colossal]

Nobody's having an idea if a 125E works sufficient with an EL34?

How about reducing the B+ in the power amp to be safe?
Can anyone suggest me a range, like 250V or lower?

Should keep the OT core from saturating I would guess..

300V on the plate for an EL34 is a great target and can sound killer with a 3k primary. As mentioned earlier though, it's best to get the right OT for the job. A single ended OT is gapped because of the magnetizing voltage generated by the DC bias current. As Martin said, you may "get away with it" because of the mass of the PP transformer you plan to use.

[martin manning]

You could do low voltage p-p EL34 with 125E. 240V plate, 230V screen, 4k2 primary (8Ω speaker). I'm assuming you have 125E push-pull OT there. That would be right around 15W output power, matching the OT spec.

[Mr. Lime]

Thanks again Martin and Colossal!

I have so many PP amps and I want to try something different on a budget.
Some unmatched EL34 are laying around and I like the idea of UL SE with that 125E OT.
A new SE OT with UL is way to expensive for this project.

Alright so I will target about 300V on the plate. That's about 50V less than FogHorn had tried in post #4 with a KT66.

[martin manning]

I had to go back to the top of this thread to understand what you are proposing, which I believe is using a PP OT as a UL SE. You can try that at 300V with 4k2 primary for one EL34, but the idle current may be an issue for that transformer. It is spec'd at 60 mA, but that is for PP.