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 13th Jul 2017, 12:21 pm   #1
Oldelectronics
Heptode
 
Join Date: Jan 2016
Location: Nottinghamshire, UK.
Posts: 676
Default AF125 versus GT322B

I recently bought a couple of Hacker Heralds A VHF set in red and a MW/LW set in black (I have run out of room for the 50s valve sets I like!)I was totally amazed by the VHF sets performance. The MW/LW set just hisses a bit!I can see that the screen lead on at least one AF117 has been cut so I think the problem is with the AF117s? I have some AF125s and some Russian GT322Bs. Does anyone have a recommendation as to which is the best replacement for this job Any other hints would also be much appreciated.

Regards

Kev
Oldelectronics is offline  
Old 13th Jul 2017, 12:47 pm   #2
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
Default Re: AF125 versus GT322B

The AF125 is a direct equivalent in a different package. The GT322B looks slightly different on paper but works fine in practice. Each has a different pinout from the AF117 and each other.


https://www.vintage-radio.net/forum/...5&postcount=36

The MW/LW set will likely take any old RF/IF Ge transistor or even Si but the VHF one may be a bit more fussy.
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline  
Old 13th Jul 2017, 1:04 pm   #3
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
Default Re: AF125 versus GT322B

Chris has said it all.
paulsherwin is online now  
Old 13th Jul 2017, 1:44 pm   #4
mhennessy
Dekatron
 
Join Date: Jul 2007
Location: Evesham, Worcestershire, UK.
Posts: 4,241
Default Re: AF125 versus GT322B

Luckily, the only Ge in the VHF Herald is in the audio amplifier.
mhennessy is online now  
Old 13th Jul 2017, 2:05 pm   #5
Boater Sam
Banned
 
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
Default Re: AF125 versus GT322B

The only critical possition I have found is the frequency changer, just about most general purpose RF transistors Ge and Si seem to work in the other possitions.

Sam.
Boater Sam is offline  
Old 13th Jul 2017, 4:09 pm   #6
camtechman
Nonode
 
camtechman's Avatar
 
Join Date: Jan 2008
Location: Milton Keynes, Bucks. UK.
Posts: 2,552
Default Re: AF125 versus GT322B

The AF125 is a direct equivalent in a different package.

I thought the AF127 is the direct equivalent to the AF117
__________________
When I die, please don't let my Wife sell my collection for the amount I told her I paid for it!
camtechman is offline  
Old 13th Jul 2017, 4:16 pm   #7
mhennessy
Dekatron
 
Join Date: Jul 2007
Location: Evesham, Worcestershire, UK.
Posts: 4,241
Default Re: AF125 versus GT322B

They're all the same bit of Ge.

It's possible that they were selected and "binned" according to some aspect of their performance (standard practice in the semiconductor industry), but it's also possible that they were simply labelled up according to what Sales wanted. Certainly, no data sheet I've ever seen lists any material difference between them.
mhennessy is online now  
Old 13th Jul 2017, 7:48 pm   #8
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
Default Re: AF125 versus GT322B

The Mullard data books quote different parameters for each transistor to imply that they are optimised for different functions, but a quick look in Towers reveals the truth.
paulsherwin is online now  
Old 13th Jul 2017, 8:11 pm   #9
mhennessy
Dekatron
 
Join Date: Jul 2007
Location: Evesham, Worcestershire, UK.
Posts: 4,241
Default Re: AF125 versus GT322B

Yes, looking in my Mullard 1971/2 data book, the only difference between them is Cob. It's 2.5pF for the AF114 and AF115, 3.5pF for the AF116 and 4pF for the AF117. All other parameters are identical.

Meanwhile, Towers lists 3pF for all of them. I wonder where they got that from?

Either way, 2.5pF to 4pF - if we believe Mullard - is a pretty small change in reality. And there will be a tolerance associated with that. So as I say, I've yet to discover a material change. Was this just Marketing, or do any insiders remember anything?
mhennessy is online now  
Old 13th Jul 2017, 8:50 pm   #10
Oldelectronics
Heptode
 
Join Date: Jan 2016
Location: Nottinghamshire, UK.
Posts: 676
Default Re: AF125 versus GT322B

Thank you for the input guys very much appreciated.

regards

Kev
Oldelectronics is offline  
Old 13th Jul 2017, 10:40 pm   #11
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: AF125 versus GT322B

The electrical properties of the AF124-7 are fine to replace the AF11X series or OC169 series transistors, which all need replacing because of the tin whiskers...But they are what I regard as a poor physical replacement. Part of the charm of radios of this era, like the Hackers and the Eddystone EC10 was the large cased transistors, and the AF 125's just don't look good and are sometimes difficult to wire in without cumbersome lead wire extensions. They just don't have "That look"

In the past I researched the options and found three types that are suitable (Photo attached)

The AF178 is nearly ideal with better specs, the AF185 is good too, but unlike the AF178 it has become more difficult to get. The American 2N2084 is excellent and comes with long lead wires which can be very helpful. The third option is the resin filled Tesla OC169 & OC170, these are the bees knees as the linear pin out array matches the AF115 series.
Attached Thumbnails
Click image for larger version

Name:	AF1XX.jpg
Views:	944
Size:	56.3 KB
ID:	146163  
Argus25 is offline  
Old 13th Jul 2017, 11:03 pm   #12
'LIVEWIRE?'
Rest in Peace
 
'LIVEWIRE?''s Avatar
 
Join Date: Mar 2006
Location: N.W. Oxfordshire(Chipping Norton)
Posts: 7,306
Default Re: AF125 versus GT322B

I've not come across the Tesla OC169/OC170, but I'd guess they're less likely to suffer from the 'Tin Whisker' problem due to their being resin filled. Presumably any available are NOS by now, given that they use the OC numbering system, which predates the Pro-Electron (AF) system. Regarding the use of AF12x/178, etc., transistors, I've sometimes mounted them upside down to enable the leads to reach the appropriate holes in a PCB designed for AF11x types, though I agree they can be a pain to fit. The long leads of the GT322B are the main reason, apart from cost, why I prefer to use those nowadays.
'LIVEWIRE?' is offline  
Old 13th Jul 2017, 11:14 pm   #13
Oldelectronics
Heptode
 
Join Date: Jan 2016
Location: Nottinghamshire, UK.
Posts: 676
Default Re: AF125 versus GT322B

Just a quick look ones that look NOS are about £7 each.

Last edited by Oldelectronics; 13th Jul 2017 at 11:19 pm.
Oldelectronics is offline  
Old 13th Jul 2017, 11:27 pm   #14
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: AF125 versus GT322B

I know there are rules for links to ebay addresses etc, but the fact is that this seller in Slovakia, not only has these Tesla transistors but they are all pre-tested before he sends them. Yes the Tesla OC170's come up on uk ebay.

My advice would be stock up on these, while you can, something like this is unlikely to last. They are about 7 GBP, but they are worth it.
Argus25 is offline  
Old 13th Jul 2017, 11:37 pm   #15
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: AF125 versus GT322B

Quote:
Originally Posted by 'LIVEWIRE?' View Post
I've not come across the Tesla OC169/OC170, but I'd guess they're less likely to suffer from the 'Tin Whisker' problem due to their being resin filled.
Yes, resin filled transistors are free from the tin whisker effect.
Argus25 is offline  
Old 13th Jul 2017, 11:48 pm   #16
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
Default Re: AF125 versus GT322B

Hmm, £7 a pop is quite a lot to replace an AF11x. These 1960s domestic RF/IF circuits are very tolerant of transistor types, perhaps because there was so much production variation anyway. It's possible to mount a replacement transistor inside an old AF11x can if internal appearance is important, though I do take the point about the leadouts.

The last set of AF11xs I replaced were in a TR82C and I used ex equipment 2N1307s, which have a TO5 case and didn't look out of place. These wouldn't be suitable for an FM set though.
paulsherwin is online now  
Old 14th Jul 2017, 1:05 am   #17
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: AF125 versus GT322B

Quote:
Originally Posted by paulsherwin View Post
Hmm, £7 a pop is quite a lot to replace an AF11x.
That is true and I guess if this was for a radio service job where the customer had no interest in the physical appearance of the transistors and pcb, it would be totally out of the question. But for your own prized and loved radios, it then becomes worth it I think.
Argus25 is offline  
Old 14th Jul 2017, 10:33 pm   #18
Oldelectronics
Heptode
 
Join Date: Jan 2016
Location: Nottinghamshire, UK.
Posts: 676
Default Re: AF125 versus GT322B

Slightly off topic I am cleaning etc a Roberts R200 which - touchwood - sounds great but has the AF117s fitted (Mullard). Is failure inevitable or do some go on and on? While it's working the way it is, my instinct is to leave well alone.

Kev
Oldelectronics is offline  
Old 15th Jul 2017, 12:29 am   #19
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
Default Re: AF125 versus GT322B

Failure is effectively inevitable, but the existing transistors may soldier on for decades. It's really a personal choice to replace working AF11x transistors. The R200 isn't very fussy about transistor types and I would change them, but I have a number of suitable replacements to hand. It's a perfectly valid choice to leave the originals in place.
paulsherwin is online now  
Old 15th Jul 2017, 10:40 am   #20
Oldelectronics
Heptode
 
Join Date: Jan 2016
Location: Nottinghamshire, UK.
Posts: 676
Default Re: AF125 versus GT322B

Thanks Paul.

Kev
Oldelectronics is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 7:09 pm.


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 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.