G'day,

I have modified valve receivers in the past by using dual gate
mosfets. In my parts drawer now, I still have a couple of MFE131s,
but any dual gate mosfet should work OK although now they are usually
only available in surface mount.

I also used single gate juunction fets for the oscillator and BFO.
The ones I have left are MPF102.

Fets work OK in valve receivers as RF ampliiers, but not well as IF
amplifiers where the primary of the IF tramsformer is shunted by the
low output impedance of the fet.

Your B40 circuit looks a little tricky to use. Probably a resitive
load for the second RF amplifier would be OK (about 1K?) and I think
some experimenting with the oscillator circuit would be necessary to
find a satifactory arrangement.

Good luck. I reckon you'll be busy for a while!

73, Ric, VK7RO.

On Wed, 13 Mar 2013 16:20:23 +0000, richard8123
wrote:


I have a turret drum that came from an old boatanchor (Murphy B40D).

Here is the front-end schematic:

http://www.portabletubes.co.uk/boats/schem1.jpg

I want to use this drum, but I want to employ transistors not valves.

Now today, I presume we can select a transistor to replace a valve, and
it will be as good as, if not better than the old valve.

Any recommendations for suitable transistors for the local oscillator
and the rf amplifiers? I'm trying not to have to modify the circuitry
inside the drum.
Thanks.

Edit1: I'm thinking of using the hollow state circuitry after the
Front-End. Best way to maintain the excellent audio of this receiver.

Edit2: I probably should draw out the tuned circuits only that are in
the drum, post a link, and draw comments from that. Hopefully then a
solid-state circuit can be built up.




--
richard8123