[Central-Electronics] CE-20A

[Jim Candela]

Donovan,

     Running a 20A barefoot pretty much minimizes the problems of poor carrier suppression, poor unwanted sideband rejection, and a frequency that often drifts. Once you amplify that signal up with the big boys you will stand out like a sore thumb. Consider that on 40m the VFO is tripled, and on 160m it is doubled. This magnifies the drift. Running on 80 or 20m is better. The 9000 Khz crystal in the rig moves around quite a bit too; several hundred hz over the first hour is common.

   I have been posting on this forum since 2003. I have taken stabs at all the issues mentioned, and I think have made some good progress to the point I can check into a net or have SSB QSO's without worry. I had too many episodes of , "your drifting out of the band man." These days anything beyond 50 hz drift is likely to get a comment. Also the SDR Flex boys will look at you in Frequency Domain and comment about the poor sideband rejection. This stuff is all fixable.

  My good friend George, W1LSB has made the suggestion about an intermediate amplifier to boost the signal to 80-100W. I've given that some thought; that seems workable. Staying with tubes could use a single 811 in G-G with maybe 800v plate. Maybe a passive input an pi-net output.

  If you have followed any of my posts, I chose another route. I have addressed the issues mentioned above, and at the same time undertook the challenge of boosting the 20A output to 80W PEP. This requires major surgery, and engineering effort. The good news is the stock power transformer can handle it. I've done this three times now. My 80W rig uses a pair of 7591 finals with 560v plate, 375 (reg) screen. Another one uses a single E34L (EL34 variant) for ~ 55-60W with 700V plate.

The downside of the QRO mods is that you lose 15-10m, and have to deal with some stability issues (especially on 40m). But for 160, 80, and 20m it works pretty well.

Jim
WD5JKO



________________________________
From: Donovan W. Case <dwcase at nb.sympatico.ca>
To: Central-Electronics at mailman.qth.net
Sent: Saturday, October 22, 2011 7:27 AM
Subject: [Central-Electronics] CE-20A

Folks,



I want to ask if anyone in the group ever tried using a 20A to drive a
Collins 30S-1?  I think the 30S-1 requires about 70-100 watts to get the
full output, but I wondered what might be had with the 20A's output, and
perhaps any technical challenges faced.



Best Regards

Donovan

VE1BDC

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