Thank you.
In the meantime I built a prototype along the lines of the original paper but with the balancing issues resolved differently.
Some more changes:
Result:
In the meantime I built a prototype along the lines of the original paper but with the balancing issues resolved differently.
Some more changes:
- overall gain reduced to 22dB
- output pentodes from 4 x 38HK7 sweep tubes cathode biased to dissipate 12W idle
- balancing issues resolved as shown in a reader's letter 1995: https://www.diyaudio.com/community/...-jeff-macaulays-hybrid-amplifier-jpg.1166051/
- unorthodox power supply runs from a single isolation transformer 115+115V
- uses 4 x booster diodes from 38HK7 (2 per channel) as rectifiers in voltage multiplier configuration
- series heater chains from same 115V transformer windings as B+ as well as opamp ps
- multipliers and heater chains are half wave but connect to the transformer halfs in pairs so that DC cancels
Result:
- not very efficient (160W from mains)
- output 20W max with 1V line input
- output impedance about 1 Ohm
- unexpectedly quiet despite the half wave multiplier rectifiers running in the same bottle as the outputs
- sounds good enough for me
Attachments
Sorento, have you measured the distortion of the assembled amplifier? I would be very interested to see the results.