[Boatanchors] Heath Warrior - Class B??

[Gary Peterson]

Rick,

I think you are confusing a class B, push-pull modulator with a class B, RF amplifier.  The modulator is really a specialized audio frequency (AF) amplifier and each tube supplies half of the output waveform, as you stated.  Actually, most “class B” modulators are really running class AB2, to avoid a type of distortion that would occur if each tube was biased precisely to cutoff.  Class B modulators usually have a small amount of idling current, with no signal applied to the grids.

On the other hand, a class B, RF amplifier can be single-ended, as the tank circuit, acting as a flywheel, completes the RF waveform.  There are plenty of class B, linear RF amplifiers around - for instance the Ameritron AL-80, with a single 3-500Z.  I think the Heathkit engineers knew what they were doing.

73,

Gary, KØCX
      


“The Heath HA-10 Warrior amplifier, using four 811A tubes, is described as a Class B single-ended (all four tubes are in parallel).
I gotta say I haven't ever seen a single-ended Class B RF power amp before, at least not so I'd notice... seems like Class B has always been push-pull to amplify both sides of the waveform.
If I'm reading all of this correctly... any idea what the Heath engineers were thinking when they made this thing run at Class B?
Since I have to redesign/rebuild the bias supply circuit anyway (to incorporate internal cut-off bias), wondering if I should convert this to Class AB2, maybe redesign the whole bias circuit to look more like the Collins 30L-1.
Thoughts?
Rick WA1RKT”