[time-nuts] RF isolation amplifier question

[Mike Feher]

Corby -

 

>From the schematic it does not look like anything special but only a 50 ohm
in and out circuit with fairly high isolation due to the common base of the
second BFT66. You may be able to simply use a newer MMIC from one of the
many sources to replace the assembly if you know the gain. Get one with more
gain than needed and then use a resistive attenuator for additional
isolation. I did not see the variable Johanson on the schematic and there
are no tuned circuits that I can see, at least not LC wise. I would think
you could measure the Johanson by removing it from the board. Since I do not
know the exact purpose of the amp I do not really understand why it has to
be so critical. Regards - Mike 

 

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

848-245-9115

 

-----Original Message-----
From: time-nuts <time-nuts-bounces at lists.febo.com> On Behalf Of
cdelect at juno.com
Sent: Sunday, October 14, 2018 11:55 AM
To: time-nuts at lists.febo.com
Subject: [time-nuts] RF isolation amplifier question

 

Hi,

 

I removed this amp from the EFOS2 Maser as it was intermittent.

 

Of course now I can't get it to fail on the bench!

 

I have fabricated a new PC board to replace it and have the components on
hand.

 

Note the 12pfd cap on the collector .

 

Some notes I have indicate is select at test and that is it a glass
capacitor.

 

The as built unit has a johansen 50pf that looks to be an early version of
surface mount with leads soldered on.

 

How do I determine what value to install on the new amplifier?

 

Cheers,

 

Corby