[Milsurplus] [MMRCG] Considering GO-9 Transmitter Power Options.

[B. Smith]

After fooling around with several keying circuits I finally cheated and 
used a vacuum relay to key the HV to the screen and plates of the early 
stages and the screen of the final PA tube and 803. The   relay contacts 
from  ePay were rated at 12,000 volts. Then on to the next project.
k4che

On 9/1/2019 8:35 PM, Ray Fantini wrote:
> The original 800 cycle power supply keying was very stiff for the day with little variation between key up and key down.  Building a modern supply at 60 cycles results in having to use larger filter capacitors and a very annoying chirp along with a mysterious chirp after letting the key up. I had to use -120 volts where the red circle is shown to cut off the tube when the key is let up. Very similar to what goes on in the TDE; always thought the TBW/GO was a striped down TDE, wonder what came first?
>
> Ray F/KA3EKH
> ________________________________________
> From: MMRCG at groups.io <MMRCG at groups.io> on behalf of David Stinson via Groups.Io <arc5=ix.netcom.com at groups.io>
> Sent: Sunday, September 1, 2019 3:28 PM
> To: ARC-5; milsurplus at mailman
> Subject: [MMRCG] Considering GO-9 Transmitter Power Options.
>
> 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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