[ARC5] GO-9 Project: Why the Resistor?

[howard holden]

Yes. PA is on all the time only because the original scheme keyed the 
primaries to the HV transformers. With 1400V no load, about 1300V at 120 
mA load on the 803 plate and 350V on the screen, (I like conservative 
running) I run about 50 mA idling which is well within the 803 
dissipation, and about 110 watts out. The 803 tube I've been using now 
for many years, including leaving the GO on for days at a time with the 
idling current. No diminution in power. So I simply key the open end of 
R207 to ground. I use a simple one HV transistor switch to ensure 
positive consistent keying on that, because if the key contacts get 
flaky, so does the VFO. The key merely connects the transistor base to 
+voltage to close the  C-E and ground the keyline. No key, the battery 
line is open as well as the fil CT. The signal is quite good, chirp is 
all but non-existent. My VFO is stable within 20 Hz or so after about 30 
minutes, and drifts down perhaps 20-25 Hz over a few minute exchange. 
That might upset the DDS VFO boys but not me.


Howie WB2AWQ

On 10/22/2019 3:31 PM, David Stinson wrote:
> Thanks for writing, Howie.
> If you key R207 to ground, key-up the PA is running unbiased.
> This hasn't been a problem?
>
> On 10/22/2019 3:07 PM, howard holden wrote:
>>
>> I never paid much attention to that resistor, but I can tell you that 
>> for 10 years of heavy use my GO has used the same tube in the IPA, 
>> with no noticeable difference in performance. Maybe related to the 1K 
>> resistor in the filament CT R207? Dunno. B
>>
>>
>