Usage of 1760E or 1760H with EL84 pair

[Leevi]

Is there experience of using these transformers with EL84 pair?


https://www.hammfg.com/files/parts/pdf/1760E.pdf

https://www.hammfg.com/files/parts/pdf/1760H.pdf

/Leevi

[kagliostro]

Ciao Risto

Unfortunately I've no experience with those OT

Perhaps I was considering this for a quartet (of el84)

https://www.tube-town.net/ttstore/hammond-1760j-for-fender-outputtransformer-125a6a-022848-upgrade-vibrolux.html


Franco

[Leevi]

Ciao Franco,
Yes, 1760J is optimal at least impedance wise for el84 quartet
Hammond's AC15 version is this:
https://www.hammfg.com/files/parts/pdf/1750Y.pdf
The primary impedance of 1760H does not differ much from the 1750Y but are
there some other things like winding or iron that should be taken in to consideration
when using 1760H?

/Leevi

[dwinstonwood]

Leevi, I'm using the 1750E in my AC15:
https://www.hammfg.com/files/parts/pdf/1750E.pdf

It looks to be identical to the 1760E in your first post minus the 4 & 16 Ohm secondaries.

[Leevi]

I'm using the 1750E in my AC15:

Do you like the sound?
/Leevi

[dwinstonwood]

Yes, I'm totally happy with it. But, I'm using a NOS Tesla EF86, and two NOS Reflektor 6n14n's. And, I've never tried a different OPT.

[edit: there was a mistake in the first schematic I posted. This one has been fixed.]

[Leevi]

Yes, I'm totally happy with it. But, I'm using a NOS Tesla EF86, and two NOS Reflektor 6n14n's. And, I've never tried a different OPT.

Thanks for the schematic. I can imagine your amp is pretty loud. There is not any voltage divider between vol and pi.


/Leevi

[dwinstonwood]

Thanks Leevi. There was a mistake in the schematic I uploaded in reply #5. I fixed it, and uploaded the correct one.

[Leevi]

I see the mistake now but I meant another issue. The similar EF86 preamps I have built have always been too loud if there is not any extra  damping after the volume pot. The 500K volume pot helps a bit but still... Matchless DC30 uses a 470K ground resistor after the 1M volume pot. In the last project I added a 100K/100K voltage divider and it was still very loud. Of course it also depends how you bias the EF86.


/Leevi

[dwinstonwood]

Hi Leevi, I guess it's loud.  It's based on the original design that has no voltage divider after the volume pot:

https://el34world.com/charts/Schematics/files/Vox/Vox_ac15.pdf

It would be easy enough to add in two resistors. In fact, my Musing amps have - at sluckey's recommendation - a 220K/220K divider right before the second volume/gain pot.

Thanks

[sluckey]

The volume control IS a very effective voltage divider for that circuit. 

[thetragichero]

whenever i make a pentode preamp amp i have a spot on the board before the volume pot for a 'tuning' resistor. i usually default to 10k but if it gets too nasty (we all like a little nasty) i can easily embiggen it

[dwinstonwood]

Also, I went through a few EF86's - Tung-Sol, EH, JJ, and finally a Tesla - before my amp sounded right to me. It's a funny tube type; I can really hear a difference between various ones. Not so much, if at all, with 12AX7's.