Traynor YBA-1 at high plate voltage

Posted on Feb 6, 2014

As some of you know, the Traynor YBA-1 is a very close derivative of the classic Bassman/JTM-45 circuit. I recently picked up a spectacularly clean `67 copy that was all original with the exception of a rather `crappy` fully reversible master volume mod and unfortunately a burnt Power Transformer. This is the version that has the SS rectifier and

Traynor YBA-1 at high plate voltage
Click here to download the full size of the above Circuit.

choke and is exactly like the schematic that can be found here: I spent quite a bit of time trying to locate a period correct PT, with no luck. these things were built like tanks and over engineered wrt the power circuits, hence, not many really bite the bullet. I finally ended up using the failed unit as a reference for locating a current production similar sized Hammond PT, which I found in the 278CX. Ironically, the form factor and mounting scheme was exactly alike, so all good there. Except - and this is a pretty big *except* - the secondary is wired for 800V center tapped. My calculations put the B+ at well over 500V. I have no idea what the specs are for the original, Hammond doesn`t have a clue, as these were specially produced for Traynor in the mid-60`s, and emails with Traynor came up short - apparently they don`t keep records that long either. So off I go. The original tube chart calls for 7027A power tubes, which were rated north of 500V on the plates and 450V on the screens. So I bought some of the CP JJ 7027A`s, which are really just larger bottled 6L6GC`s (I have found out), and installed the 278CX. While waiting on the PT to arrive I also did a bit of maintenance, 3-prong power w/death cap removal, cleaning the pots, replacing all the Electrolytics, checking the main coupling caps for DC leakage, installing a variable bias adjust pot/1-ohm 1% resistors off the cathodes, verifying and replacing key resistors...

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