[ARC5] Considering GO-9 Transmitter Power Options.

[J Mcvey]

 Yeah, it may be that the 813  on hand.
Looks like you are stuck with using two filament transformers with that design (or  one that has double CT windings) 

Since the poor thing is so modified and missing parts, etc,  a mod to make things easier should not be discounted.
Other than stablizing the VFO voltage, why not leave it on rather than keyed and just key the PA and output? Less chirp? Although the PA keying will draw from the osc a bit since they share the bias resistor.
I wonder how fast those grids float to cutoff?

    On Sunday, September 1, 2019, 5:59:03 PM EDT, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:  
 
 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
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