[MrFixr55]

I think that the Heathkit "Williamson" amps, popular in the mid to late 50s had "ultra-linear" output transformers with separate primaries like this, which were tied together at the B+ lead. I need to rebuid these but I have a WA-P5 (bad output tranny, 2 WA-P4s (one looks like a good homebrew) and a WA-P3. I believe that between these, I have 2 good Acrosound TO300 output transformers.

Other than the phase invertor circuit, the Eico seems very straightforward. Interesting that it uses cathode bias as most HiFi high powered amps use fixed bias. Interesting also that they allow a choice between 6L6 and EL34s. Seems that if they jumpered pins 1 and 8, they would be an even swap (assuming pentode operation and that the bias voltage is similar between the 2 tubes.

The Mac is a total monster, what with pro 70V line outputs for PA work, the KT88s / 6550s in the output stage, etc. Same type of phase invertor as the Eico, but I don't get the setup for the 70V line. I can't see the same amount of power being delivered by the 70V circuit as is available from the output transformer.

Generally speaking, in building a HiFi amp, a ground "mecca" is a good idea. this is often done with a piece of wire much bigger in diameter than needed for the B return for all loads. The "mecca" is grounded to the chassis at only one point. I believe that this nis at the input jacks. I have a 1947 Philharmonic AM radio and 78 RPM changer, an AA5 radio where they actually did this.