Dino
I built a 6 meter 2 4CX250B amplifier using the Ed Tilton W1HDQ design found
in the February 1964 QST, The VHF Handbook (ARRL) and reprint pdf's on the
web. I used 2 tubes where W1HDQ used 3. Tubes are plentiful and either
free or cheap. 4X150, 7034, 4CX250B or the 26.5 volt filament versions all
work well. My filament supply was built to handle either 6 or 26.5 volt
types, such as 4X150F, 8621 or 4CX250F/G. I used Eimac SK-600 series
sockets and SK-606 chimneys picked up at ham fests for $5 to $10 each. A
Daton 60 CFM blower connected to the RF deck with VW heater hose supplied
more than enough cooling. A free 97 lb plate transformer supplied 2200 volts
under a 500 ma load. Anything Peter Dahl if you want to spend or otherwise
that will give you 2000 VDC under a 500 ma load will work. Peter Dahl is on
the web for his transformer specs. I used a 400 VDC screen supply, shunt
regulated with 4 100 v 50 watt zeniors series connected. A variable bias
supply of about -50 VDC at zero current to set the zero signal anode current
for class AB1 completes the power supply line up. The grid tank is link
coupled split stator capacitor for neutralization and the plate tank is a
pi. The plate tune cap is home made two 3 inch aluminum disks but a small
vacuum variable 30 pf maximum should work fine. A little more plate C is
needed if only 2 tubes are used. The plate inductor is 1/4" copper tubing
about 2" inside diameter as per article. Drive for 1 KW PEP input with
the circuit is less than 10 watt PEP. I could switch to class C and plate
modulate with a pair of 811As in class B, but that is an old story.
Drive for the GS-35B, which is a high mu triode run in grounded grid, is
much higher. Also cost of the tube and the required custom socket will
probably be much higher for the 1500 watt anode dissipation and legal limit
output advantage. You question was about 2 4CX250s.
John WA4EPI
----- Original Message ----- > Date: Wed, 11 May 2005 08:47:58 -0700
(GMT-07:00)
> From: Dino Darling <k6rix@earthlink.net>
> Subject: [Amps] Pair of 4CX250s on 6-meters...
> To: Amps@contesting.com
> Message-ID:
> <7421068.1115826479254.JavaMail.root@beaker.psp.pas.earthlink.net>
> Content-Type: text/plain; charset=us-ascii
>
> Speaking of a pair of 4CX250s... I'd like to build a SSB mono band amp
for 6-meters using a pair of 4CX250B's. I have the cabinets I want to use
(separate RF and power supply decks).
>
> I've browsed different 6-meter designs on the web and asking if anyone
here has their favorites?!
>
> I'm a novice at building an amplifier and need to learn what parts to buy.
Example:
>
> I know I need two tubes, sockets, and chimneys. But what Peter Dahl
transformers do I need to properly feed two 4CX250Bs? How much CFM does the
fan need to be? What variable capacitors should I get (I am leaning towards
the vacuum capacitors).
>
> Any hints or outright shopping list would be appreciated!
>
> Dino - K6RIX
>
> -----Original Message-----
> From: k7fm <k7fm@teleport.com>
> Sent: May 11, 2005 7:59 AM
> To: Amps@contesting.com
> Subject: KLM KT34a tribander for sale
>
> Does this have 2 x 4CX250 tubes mounted in the boom?
>
> Colin K7FM
>
>
>
>
> ------------------------------
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|