UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Closed Thread
 
Thread Tools
Old 4th Oct 2006, 9:48 pm   #1
tivo
Triode
 
Join Date: Aug 2006
Location: High Wycombe
Posts: 12
Default Peak atlas analyser readings - AF117 transistors

I have been searching for a serviceable replacement AF117 for a failed item in the mixer of one of my "patients". I have several donor boards and have been carefully de-soldering candidates and testing on a peak atlas component analyser.

All I have tried so far (4) show no shorts to screen but indicate a "Resistor shunt between B-E". None of these candidates help in making the mixer oscillate (but then again, neither does an OC71 in its place).

Has anyone measured a known working AF117 on the peak? If so does it indicate as expected or is this a feature of this transistor on this tester?

I am unclear as to whether all the items I have tested are genuinely faulty or, taking into account the test replacement by an OC71, there is a secondary problem in this area.
tivo is offline  
Old 5th Oct 2006, 6:57 am   #2
Pumpernickel
Triode
 
Join Date: Nov 2005
Location: Germany (in the south)
Posts: 6
Default Re: Peak atlas analyser readings - AF117 transistors

Hello Tivo,

the B-E-shunt may be a result of the leakage current of a Germanium type of transistor. That is probably normal.

What kind of cicuitry is that with the mixer? Maybe there is a different fault there.

Dieter
Pumpernickel is offline  
Old 5th Oct 2006, 9:34 am   #3
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 6,309
Default Re: Peak atlas analyser readings - AF117 transistors

Quote:
Originally Posted by tivo View Post
I have been searching for a serviceable replacement AF117

All I have tried so far (4) show no shorts to screen but indicate a "Resistor shunt between B-E". None of these candidates help in making the mixer oscillate (but then again, neither does an OC71 in its place).

taking into account the test replacement by an OC71, there is a secondary problem in this area.

The OC71 is an audio transistor and would not work as a replacement for an AF117. If you have an OC44, try that.


Rich.
__________________
On Spike Milligan's headstone......I told you I was ill...
Sideband is offline  
Old 5th Oct 2006, 6:31 pm   #4
tivo
Triode
 
Join Date: Aug 2006
Location: High Wycombe
Posts: 12
Default Re: Peak atlas analyser readings - AF117 transistors

Dieter, the Peak manages other Germanium's OK, it actually displays the type (Si/Ge) - the OC71, for instance, displays correcty. I am kind of hoping that the AF117 may be an exceptionally leaky Ge type giving this reading even if OK but it would be nice to confirm this absolutely.

Without going off topic I could mention that the mixer circuitry belongs to a Hacker Autocrat RP33 so fairly conventional front end and mixer if that helps.
tivo is offline  
Old 6th Oct 2006, 8:04 am   #5
Mike Phelan
Dekatron
 
Mike Phelan's Avatar
 
Join Date: Nov 2003
Location: Near Leeds, West Yorkshire, UK
Posts: 4,448
Default Re: Peak atlas analyser readings - AF117 transistors

Tivo
It may be worth measuring the b-e resistance (both ways) with a meter.
As long as it is more than a few hundred ohms reverse, it should not matter in a common-emitter stage, which it will be.
__________________
Mike.
Mike Phelan is offline  
Old 6th Oct 2006, 9:38 pm   #6
Hunts smoothing bomb
Octode
 
Hunts smoothing bomb's Avatar
 
Join Date: Oct 2005
Location: Wimborne, Dorset, UK.
Posts: 1,397
Default Re: Peak atlas analyser readings - AF117 transistors

hi Tivo,

I have just repaired my Murphy B485, the transistor at fault was sopposed to be an Ediswan PXA102 and someone had replaced it with an AF117, I also have the Peak Atlas analizer and it came up with the same result as you have described.

I have replaced my AF117 with a 2n2431 and the set seems to work perfectly, I also tried an AC126 (what I had in the scrap draw) and this worked but was down in gain.

I believe the resistor shunt (that the LCR specifies) is whiskers shorting between EB or C that have not quite fully developed and are still are of a fairly high resistance but of enough value to stop the stage working.
Also if someone previous has tried the cap clearing trick between screen and EBC, only between screen and EBC will be clear. (won't clear shorts between E,B or C)

I have measured other Ge transistors in my stock and they all test fine and the tester as said states weather they are Si or Ge as Tivo has said.

Regards
Lee
__________________
Lee
Hunts smoothing bomb is offline  
Old 7th Oct 2006, 6:12 pm   #7
tivo
Triode
 
Join Date: Aug 2006
Location: High Wycombe
Posts: 12
Default Re: Peak atlas analyser readings - AF117 transistors

Lee, glad to see someone else gets the same measurements. I don't think the AF117 is the reason the oscillator doesn't - I have temporarily removed one from a working radio and the results are the same!

Mike, I get what I find surprising resistance readings - 56K forward and around 3M reverse!

I believe that common wisdom is the "tin whiskers" grow from the case surface inwards. If this is the case, a whisker bridging emitter and base but not showing a screen short would probably be a very rare configuration.
tivo is offline  
Closed Thread

Thread Tools



All times are GMT. The time now is 12:26 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2021, Paul Stenning.