[Milsurplus] Considering GO-9 Transmitter Power Options.

[David Stinson]

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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