OK, well, the OPT were made to the same specs , although later ones have secondary taps to 16 ohms while the earlier versions are tapped out to 32 ohms. In the picture the opt are EICO HF87 from a basket case that i bought awhile ago. The amp i made with them is a class A PP with a transformer phase splitter. The circuit is simply an "RH" type universal amp with the signal first undergoing a phase split before seperating into 4 rh circuits. My intentions were to test the effect of phase splitting on sound quality. I would say that even this type of phase splitting, as accurate as it may be, left a sonic fingerprint on the sound quality. There is a slight "haze" around the notes that are not present when the exact same circuit is used single ended. This is something that i now notice on every pp amp, instead of the sound being clean without artifacts. .So, if you want to buy these 2 transformers i would be willing to sell them but as a pair.
As far as EICO EL34 mono blocks they did have 2 models , afaik, one was the HF59 with a potted chicago trans, and the other the hf60, with the Acro OPT. So, for some reason they did not use the HF87 opt for a mono amp, afaik.
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