On Thu, 11 Sep 1997 17:13:02 EDT w7cs@juno.com (Chuck Smallhouse) writes:
>
>Phil et all,
>
>These MRI "driver" amps are also meant to be used with a 3CX800 in
>place of the 8874. The built in power supply has filament windings
>for either tube. The socket is pin for pin compatible for both tubes
>- all you need to do is to modify the silcon (typical ETO) rubber to
>accept the larger diameter anode of the 3CX800. Also you should
>change the meter multipliers to reflect the larger currents and power
>used in AB linear operation versus pulse operation (for either tube).
>
>The power xfrmr looks wimpy, and the HV does drop significantly under
>load, but mine with a 3CX800 in it puts out well over 1 kw. The built
>in RF switching relays should be replaced with external coax relays -
>the VSWR presented to an exciter is very high and the stock open frame
>relays have questionable efficiency ..
Many open frame relays work very well at 6M with negligible loss. They do
however present a bit of XL to the exciter. On the TX side the Pi-Net
does the work.
The easiest cure is to place a 20-100pf Arco trimmer from the thru
connection at the relay to ground. Tune for lowest VSWR, measure the
value and replace with a 500V silver mica or a 1KV NPO ceramic. You can
also just leave the trimmer in place; an Arco 406 will handle 100W with
ease.
At 6M the typical open frame relay found in amps will tune with 25-35pf.
Nearest standard value caps have always brought the "thru" VSWR to 1.2 or
less in the many 6M conversions I have built from HF amps.
Viva 6M !
73....Carl KM1H
>There is a lot of extraneous circuitry that can be pulled and tossed (
>computer interfaces for remote monitoring) etc. It is a very easy and
>pleasant amp to work on, as ever module is connectorized and easily
>removed/replaced even the power xfmr. In other words it's a" jewel in
>the not so rough".
>
>GL and
>73,
>Chuck, W7CS
>w7cs@juno.com
>
>On Wed, 10 Sep 1997 18:48:46 -0400 k6eid
><k6eid/pop.avana.net@tiger.avana.net> writes:
>>For Sale - ETO 6 meter desktop amp. Originally used as a driver for a
>
>>16 kW
>>RF power amp used in medical equipment. Uses single 8874. Covers 40
>to
>>70
>>MHz. Built in power supply. Has all controls and power meter mounted
>>on
>>front panel. Fully ready for 6 meter use (I used it to work Europeans
>
>>and
>>Africans in mid-1995). Have some technical data including schematics.
>
>>In
>>shielded cabinet mounted on a 19" rack panel. Asking $550 plus
>>shipping.
>>Prefer local pickup in Atlanta area as unit is heavy.
>>
>>Phil Finkle K6EID
>>k6eid@avana.net
>>
>>
>>------------------------------
>>Phil Finkle
>>
>> POLITICAL CORRECTNESS ISN'T!!!
>>Stop the insanity --- Support traditional values
>>
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>>
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