EDAboard.com | EDAboard.de | EDAboard.co.uk | WTWH Media

Looking to replace Germanium power transistors with Silicon

Ask a question - edaboard.com

elektroda.net NewsGroups Forum Index - Repair Electronics - Looking to replace Germanium power transistors with Silicon

Goto page Previous  1, 2

Jeff Urban
Guest

Sat Apr 18, 2020 9:45 am   



>Indeed, my mistake

Well thank you very much.

Looks like your best bet is to just put some silicon (diode) in series with CR107. I would recommend a pot for R127 so you can trim the bias. Forget specs just make it the same as the other channel.

And that is 47 volts supply ? That means 23.5 split. I wouldn't even bother with the MJ15023s, it is not worth it. The MJ2955 will handle that application no sweat. Just give it bias. Newark has then for like a buck and a quarter.

Of course check the drove circuitry first. To do that put 100 ohm resistors across the B and E of the outputs. The circuit should stabilise ad actually amplify but DO NOT put a load on it. Once it does that THEN you put the outputs in. Always on a DBY first.

John Robertson
Guest

Tue Apr 21, 2020 7:45 pm   



On 2020/04/18 1:00 a.m., Jeff Urban wrote:
Quote:
Indeed, my mistake

Well thank you very much.

Looks like your best bet is to just put some silicon (diode) in series with CR107. I would recommend a pot for R127 so you can trim the bias. Forget specs just make it the same as the other channel.


There was a 75R pot added in later amps of the same series with R127
reduced slightly in value. I am considering that.

Any particular silicon diodes?

Quote:

And that is 47 volts supply ? That means 23.5 split. I wouldn't even bother with the MJ15023s, it is not worth it. The MJ2955 will handle that application no sweat. Just give it bias. Newark has then for like a buck and a quarter.


I have some MJ2955s in stock.

Quote:

Of course check the drove circuitry first. To do that put 100 ohm resistors across the B and E of the outputs. The circuit should stabilise ad actually amplify but DO NOT put a load on it. Once it does that THEN you put the outputs in. Always on a DBY first.


I'll put up the schematic of the model I am looking to upgrade to with
my notes...past this model they changed the specs on the other
pre-driver germanium transistors which would require a bit more changes
to get the bias correct I suspect.

What is a "DBY"? Normally I use a series 40 to 60W lamp with the line
when doing test to current limit.


John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

Fox's Mercantile
Guest

Tue Apr 21, 2020 8:45 pm   



On 4/21/20 1:27 PM, John Robertson wrote:
Quote:
What is a "DBY"? Normally I use a series 40 to 60W lamp with the line
when doing test to current limit.


Jeff is hard pressed to spell anything.
DBY = DBT, Dim Bulb Tester.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

whit3rd
Guest

Wed Apr 22, 2020 6:45 am   



On Tuesday, April 21, 2020 at 11:27:45 AM UTC-7, John Robertson wrote:
Quote:
On 2020/04/18 1:00 a.m., Jeff Urban wrote:

Looks like your best bet is to just put some silicon (diode) in series with CR107. I would recommend a pot for R127 so you can trim the bias. Forget specs just make it the same as the other channel.

There was a 75R pot added in later amps of the same series with R127
reduced slightly in value. I am considering that.

Any particular silicon diodes?


To be careful, diode-test a good Ge transistor and its associated diode, and
try to get the same voltage-offset (transistor BE drop minus diode drop). Within 20 mV
would be good.

As I read the schematics, the pulldown output drive transistor has an emitter resistor
and base-negative pulldown resistor; you might want to change the base pulldown
resistor, too, to bias the emitter current the same as the original.

Goto page Previous  1, 2

elektroda.net NewsGroups Forum Index - Repair Electronics - Looking to replace Germanium power transistors with Silicon

Ask a question - edaboard.com

Arabic version Bulgarian version Catalan version Czech version Danish version German version Greek version English version Spanish version Finnish version French version Hindi version Croatian version Indonesian version Italian version Hebrew version Japanese version Korean version Lithuanian version Latvian version Dutch version Norwegian version Polish version Portuguese version Romanian version Russian version Slovak version Slovenian version Serbian version Swedish version Tagalog version Ukrainian version Vietnamese version Chinese version Turkish version
EDAboard.com map