[ARC5] Considering GO-9 Transmitter Power Options.

[AKLDGUY .]

Changed to 813 because the 803 is scarce? Non-existent in ZL, never seen
one offered for sale in 50 years.
Neil ZL1ANM

On Mon, Sep 2, 2019 at 7:30 AM David Stinson <arc5 at ix.netcom.com> wrote:

> Been considering how to revive the GO-9 HF transmitter.   The original
> power supply has been stripped, so that's a good reason to go with a new
> 60-cycle supply.  The transmitter module itself has been somewhat
> modified, but recoverably.  The "Man With the Golden Screwdriver"
> removed the 803 and socket, replacing them with an 813 PA.  Simplifed
> original-circuit schematic attached.
>
> Left Red Circle:
> K201 on the left is a relay contact in the original power supply. In the
> original design, when the radio is keyed, this contact is grounded to
> complete the grid circuits of the MO and the Buffer, turning them on.  A
> relay contact in the power supply then keys the B+ and B++ to the
> transmitter.
>
> Right Red Circle:
> In the modded circuit, he lifted the PA grid ground connection at the
> ground end of Grid Current meter M502, opening the PA grid circuit, then
> connected these two "red" points together.
>
> In original configuration, when the transmitter is keyed, both these
> points are grounded and the PA's bias is developed from drive.   In the
> modded version, the most likely idea was to apply -250V +/-  bias
> voltage to cut the tubes off on key-up, and ground them for normal
> operation on key-down.  This isn't necessarily a bad idea; many transmit
> circuits work that way.  I still don't understand replacing the 803 with
> the 813.  The 540V supplied to the PA Screen is well above the 813's
> rated maximum of 400V.  The 803 Screen can take up to 600V.   The 803
> suppressor requires about +40V or so.  The 813 is a beam power tube, so
> that's kinda weird.   The 813 can deliver a little bit more power for a
> given power supply, but not enough to foozle-around with the design.
> With 1900V B++, the 803 should deliver about 200W.  With the 813,
> assuming the circuit will work with it, about 250W; not enough
> additional to justify the mod, IMHO.
>
> To key the circuit as originally intended,  we'd need to switch the 540V
> and the 1900 V.  This is not hard anymore- there are MOSFETs
> off-the-shelf that can switch 3000V, even 4000V at Amps for $14-$15
> these days which are plenty fast to cover CW. Regulating the 540V to
> stabilize the MO is child's play now.  I have NOS 803 and socket, so
> putting that back original is a given.
> Your opinions, please:  Key the B+, or cut-off bias keying? Keying the
> bias can also be done with FETs, so we don't have a fraction of a second
> of unbiased tubes during the relay's throw-time.
>
> The Green Circles:
> These are the isolated filament circuits for MO/Buffer and for the PA.
> The transformers in the diagram were actually located in the seperate
> power supply module; not the transmtter itself.  I don't see any way to
> wire these to a common DC filament source, do you? I can provide both
> correct-voltage/current transformers, but it's always nice to condense
> and eliminate extra power busses when possible.
>
> TNX ES GL OM DE Dave AB5S
>
>
>
>
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