[TenTec] CorsairII notch potentiometer

[Steve Hunt]

Jerry,

Yes - it was disappointing.

I can't think of any simple way of "fudging it". The Corsair filter 
circuit has them configured as variable resistors rather than 
potentiometers, so the usual trick of a fixed resistor from slider to 
one end wont work well. I tried some options using a spreadsheet; a 
2M2Ohm linear pot with a fixed 560 Ohm across it begins to look 
something like the correct shape, but I would think a dual gang 2M2 is 
pretty rare.

I may just fit the 220k linear version from the same company.

OT: Discovered a way to waste 2 hours!

1) While the Corsair is stripped down, check all the other controls for 
smooth operation
2) Notice that you only get 17W max power output with the Drive control 
fully CW; that on 80m - on other bands the PSU trips
3) Start fault finding around the Low-Level-Driver and PA areas
4) Decide it might be the 2N3866 on the LL Driver board - the output 
from that stage is only slightly more than the input
5) Change it for a new 2N3866 - clean off the heatsink compound from 
your shirt - find that there's no improvement in power output
6) Decide to give up and take a listen round 20m to de-stress
7) Notice that the antenna noise is barely above the Rx front-end noise
8) Waggle the temporary patch lead between the Corsair on the test bench 
and the station patch panel - Corsair bursts into life
9) Check the Tx operation - close to 100W on all bands
10) Confine patch lead to waste bin !!!!!!!!

73,
Steve G3TXQ



On 09/02/2011 17:19, Dr. Gerald N. Johnson wrote:
> Bummer. I had hoped for a better fit because the description said a
> quarter inch shaft and the drawing showed a 3/8" bushing with the
> quarter inch shaft. So I guess I won't order from Maplin.
>
> My scheme of shunt loading a linear pot probably isn't a lot better than
> the log pot, needing to be reverse log. Maybe using a series resistor on
> the wiper of would band spread the HF end better.
>
> Mouser offers a compact dual section linear pot that might make wiring
> easier.
>
> 73, Jerry, K0CQ
>