Quote:
Originally Posted by dieseljeep
My Zenith chairside has the same chassis. That chassis uses the direct coupled triode driver and 6AC5 triode output. Why????? most of the other Zeniths used penthodes.
Mine came with, probably the last 6X5GT's made. It has the small internal structure like the 6X4. I'll leave it!  |
I wondered this as well and looked at a book I just got "understanding hi-fi circuits" by Norman Crowhurst. What I took away was this:
The triode output versus the pentode has lower harmonic distortion but the plate efficiency is also much lower, reducing output power. Additionally, the handling of varying plate load, due to output transformer and speaker reactance across the frequency spectrum is improved with the triode. It is likely a tradeoff that Zenith accepted in exchange for better fidelity.
This odd feature of the Zeniths is motivation enough to recap (and replace the tranny) and give it a serious listen.