Output transformers from Hammond AO-70

[Matt D]

I have a Hammond AO-70 with three output transformers. This amp ran 3 pairs of tubes in a push/pull arrangement.

2 pairs of EL84's separately powered two 8 ohm 8" speakers through two small output transformers.

Another pair of 7591's powered a 4 ohm 15" through a very substantial OT.

On the schematic I have the ratios are 200 ohms to .6 ohms for the smaller OTs and 130 ohms to .5 ohms for the large one.

If my math is right that means the large OT is only about 1k into 4 ohms. That seems really low.

The smaller ones would be 2.6k into 8ohms. Also seems low for the two pairs of el84's.

Would any of you guys mind checking the schematic below for me and tell me if I'm missing something? It's a little hard to read but the ratios can be made out if you enlarge the image.

Thanks

[rdjones]

The readings noted on the schematic are DC resistance measurements used for troubleshooting, not impedance ratings, and cannot be used to compute ratio.

Does the chassis looks like this (below) ?
I got this off eBay for the 6BQ5 OTs.
I think they are 7,500 ohm primary - 8 ohm secondary.
I'm missing the 7591 OT but those tubes seem to like a fairly high primary impedance (compared to 6L6s, for example) so is probably in the 6,600 - 9,000 ohm range."

"RedDog" Steve

[Matt D]

Thanks Steve,
That's the one. It came from the Salvation Army chocked full of fancy European tubes!

I appreciate the help.