[Amps] 4CX250 IMD

[jeremy-ca]

----- Original Message ----- 
From: "Steve Thompson" <g8gsq at eltac.co.uk>
To: <amps at contesting.com>
Sent: Friday, September 28, 2007 5:45 AM
Subject: Re: [Amps] 4CX250 IMD


>
>
> jeremy-ca wrote:
>
>> In any case the -23/27 is what Ive experienced with that tube at 2KV in
>> a 2M amp before building the 3CX1000A7 and the generic 250 is a bit
>> worse. This was in the dark days and I used VR tubes for screen
>> regulation.
>
> Looking at GW4FRX's measurements, I wonder if the IMD you measured owed
> more to the screen supply than to the tubes themselves?

Looking at the Eimac data it doesnt appear that the VR tubes had much effect 
but that was back in my BC days. Im guessing that they did their 
measurements with VR tubes also. Later testing did show improvements with 
Ian's circuit.


>
>  The old
>> xvtr was replaced about 15 years ago by a MM unit from your side of the
>> pond that I improved the RX a bit.
> Was that the new version or the older one in the diecast box?

The diecast. I have them for 144, 220(222), 432, and 1296. They became dirt 
cheap when improved devices/xvtrs came along. Working in a microwave lab at 
the time with access to the latest and greatest GaAsFets I did my own 
upgrades and NF/IMD optimization.

Carl
KM1H