On 2020-05-20 10:40, Adrian Tuddenham wrote:
Brian Gregory wrote:

On 18/05/2020 12:59, Adrian Tuddenham wrote:
I have had some success with an Eddystone EB35 by replacing them with
silicon transistors and adjusting the base bias to get approximately the
same collector current.

And if something starts oscillating because you have too much gain with
the silicon replacements then adding a low value R in series with their
emitters will usually fix.

There are already emitter resistors, but they are bypassed, so adding
resistance in series with the bypass capacitors (or removing them
altogether) would be the way to go.

I used fairly mundane silicon transistors with a lowish cutoff frequency
and didn't have any trouble.


Retrofitting germanium transistor circuits can be tricky, especially the
ones where they rely on the apparent beta being negative, i.e. the CB
leakage being larger than I_C/(true beta).

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com