[Boatanchors] Heath Warrior bias supply (was WTB: 6.3VAC/20A and 10VAC/low current transformer)

[Gary Schafer]

Hi Rick,

I might do away with that bias circuit and put a 4.5 volt zener between the
filament center tap and ground for bias. (I think you said it needed 4.5
volts)
Then to put the amp in standby place a 50K resistor between the bottom end
of the zener to ground and short out the resistor with a relay to go to
transmit. Ground the grids directly. Now you have a well regulated bias
supply with the zener and no transformer needed.

In the old days these amps were called "class B" as they were run close to
plate cutoff but were/are really class AB2. You will see the same amplifier
configuration referred to as class AB2 in modern amplifiers.

73
Gary  K4FMX

> -----Original Message-----
> From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf
> Of Rick Poole WA1RKT
> Sent: Friday, November 21, 2014 11:30 AM
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Heath Warrior bias supply (was WTB:
> 6.3VAC/20A and 10VAC/low current transformer)
> 
> 
> From: "Ian Wilson" <ianmwilson73 at gmail.com>
> Sent: Friday, November 21, 2014 11:32:31 AM
> >>
> >> ...run a 120V/6.3V transformer backwards.
> 
> Good afternoon, Ian (and others who have made the same suggestion in
> this thread).
> 
> Heathkit claims that the bias circuit needs to provide 400 ma (?!?!?) so
> that it is "stiff" enough to handle the "large amounts of grid current
> drawn by the amplifier" (their words).  Seems rather bizarre for a bias
> circuit but that's their story and they're stickin' to it... maybe it's
> a characteristic of class B rather than class AB2.  So, using a reverse-
> connected 6.3VAC transformer would require that the 6.3 volt side be
> capable of 8 amps or better to provide enough current on the 120 volt
> side.
> 
> So yeah, that's a good thought if the bias circuit were more like what
> one might expect.
> 
> Rick WA1RKT
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