PT question from an ST 70

[nj pheonix]

I'm not sure if this is known. If you look at the schematic of an ST 70, The 2 6v windings (filaments) Greens and browns.
The greens carry 6 tubes and the pilot light. The brown, 5 tubes.
Would it be a fair assumption that the brown winding would have the same capacity or would one have a higher current rating than the other (to keep costs down.)?

 

[nerdorama]

I'd say it's quite likely. Do you have a way to measure low resistances to compare the two windings?

 

[RWood]

If you were really curious you could also measure and compare the current going through those windings.

The earlier ST70s used a smaller PT than the later. I have had both and there is a noticeable difference in height (I used to have a picture). As I understand it, the filament windings on the earlier ones were prone to failure and then they beefed them up. Sure enough, the smaller PT of mine had a blown filament winding.

 

[nj pheonix]

I appreciate the input.
I've been a little caught up. The victim (er, I mean donor isn t whole.
Not sure I want to repair just to gut.
Project will require an additional PT anyway, I was just trying to see my options.
Would you know offhand (or would you be able to see the part # of the earlier or later versions?

 

[nerdorama]

I think Heyboer can make you a new power transformer to your specs. They need to know the mounting bolt pattern, whether standup or laydown style, and the voltage and current requirements. They may already have made an Eico ST-70 replacement. I had them make a power transformer to match the physical size of the ST-70 transformer but with a different B+ voltage. It was just a bit over $100 as I remember.
John

 

[nj pheonix]

I think you misunderstand. I was harvesting all the iron out of this. My intention is to build the (or a reasonable facsimile) of
http://audiokarma.org/forums/index....ign-custom-power-amp-with-6550s-kt88s.825888/

It is somewhat back burnered now. i do anticipated getting into it before spring though.

 

[GordonW]

In my experience- there's no difference between the green and brown heater windings. Put the same number and type of tubes on them, and you get the same heater voltage.

Mind you- as I mentioned in the thread about building the amp- there's not enough available heater current on them, even combined, to drive all four KT88s. I usually put two KT88s (both on one channel) on a separate 4 amp (or more) heater transformer, and run everything else off of the original Eico heater windings (one KT88, one 6SN7 and the 12AX7 on one, and the remaining KT88 and 6SN7 on the other).

Regards,
Gordon.

 

[nj pheonix]

Thanks Gordon

Project is somewhat on hold though I sourced separate filament transformers a while back.
Thread was sort of old. I'm wondering how it popped up on your radar now?