[ARC5] Considering GO-9 Transmitter Power Options.

[Kenneth G. Gordon]

On 1 Sep 2019 at 14:28, David Stinson wrote:

> I still don't understand replacing the 803 with 
> the 813.

Me either. Kinda dumb in my opinion.

> 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.

I would definitely go with blocked-grid keying, which is essentially "cut-off bias" keying.

> 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.

First of all, what is the value of R-207? That resistor obviously biases the filament and 
cathode above ground. I suspect R-207 provides operating bias for the oscialltor, and the 
buffer is not effected since its cathode is direcly grounded.

R-303 and R-313, and L-302 and L-303 with C-307 and C-308 are most likely filters to keep 
the 800 Hz AC from modulating the VFO.

>From the circuit designations, BOTH sets of filaments are fed from the same transformer 
T-202, so T-202 must be a multi-winding transformer having a 12.6 V winding for the 837s 
and a 10 V winding for the 803.

Now...I don't see a problem with operating the filaments from DC, but I think you would have 
to be careful concerning what side of the filament is the + side. Maybe not.

And the 10 VDC applied to the 803 would, I would think, require you to adjust the value of 
R-310 to compensate for the change in bias voltage.

In like manner you would have to adjust the value of R-207 to make the bias on the VFO 
tube the same as when it is operating on AC.

Why do you want to operate the filaments from DC?

Ken W7EKB