[ARC5] ARC-5 on 20 meters

[MICHAEL ST ANGELO]

I searched for ARC-5 in the QST archive and found an article in the June 1948 issues of QST "ARC-5 Transmitter Modifications".


Even though the title says ARC-5 the article discusses two ways to modify the BC-459-A for 14 MHZ (or as they said back then 14-Mc.).


Both methods involve modifying the output to a PA doubler.


The first  mod is simple but you lose the PA and Oscillator condenser (capacitor) tracking. remove the C67 padding cap and C65 PA tuning cap from the circuit and replacing with a 75 uufd (pF) variable.


The second mod preserves tracking and improves doubling efficiency.


- Remove the C67 padding condenser and replace with a 35uufd variable.

- Remove 10 rotor plates from the PA tuning condenser.

- The plate coil is pruned down to 5 1/2 turns.


Plate-circuit tracking is adjusted with the new variable and by positioning the top turn on the coil.


To increase the doubling efficiency


- The tap of the grid leak R74 and grid leak bypass condenser C58 is moved  to the bottom of the grid coil.

- The  value of the grid leak bypass condenser is changed from 0.05 ufd to 0.00025 ufd.

- Remove the fixed neutralizing condenser C62.


Mike N2MS


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> On December 29, 2016 at 12:42 PM Dennis Monticelli <dennis.monticelli at gmail.com> wrote:
> 
>     What I especially like about the ARC-5 is it's natural ability to do push-push doubling because of the center tapped secondary on the osc coil.  The ARC designers used it for neutralization but that function can be eliminated in doubling service and the secondary re-purposed to independently drive the 1625's in push-push for greater efficiency.
> 
>     Dennis AE6C
> 
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