UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio 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.

Reply
 
Thread Tools
Old 23rd Apr 2019, 8:56 pm   #1
Steve G4WCS
Pentode
 
Steve G4WCS's Avatar
 
Join Date: Sep 2004
Location: Preston, Lancashire, UK.
Posts: 223
Default RF power transistor testing

Picked this bargain/money pit up for less than the price of the heatsink. Someones gone to a lot of thought with this then spoilt it by tacking bits on like an afterthought
I'm going to give it a full rebuild. I don't like the rats nest biasing circuits, and I'm thinking of using the LM723 bias circuit as per the Motorola application note.

I'm hoping the power transistors aren't fried but I'm working on the assumption that they are.
What's the recommended way to test them, just checking for shorts/open circuits and checking the diode junctions, any precautions etc?

Thanks
Attached Thumbnails
Click image for larger version

Name:	1570FE4B-15C8-4E26-A0DE-3C9E23F52055.jpg
Views:	155
Size:	45.7 KB
ID:	181737   Click image for larger version

Name:	0076A745-19B7-4C19-9F78-C8C7F1271713.jpg
Views:	141
Size:	74.2 KB
ID:	181738   Click image for larger version

Name:	53E85F9D-C1F3-431A-88EB-D8BEE4833971.jpg
Views:	155
Size:	60.8 KB
ID:	181739  
Steve G4WCS is offline   Reply With Quote
Old 23rd Apr 2019, 10:10 pm   #2
Steve G4WCS
Pentode
 
Steve G4WCS's Avatar
 
Join Date: Sep 2004
Location: Preston, Lancashire, UK.
Posts: 223
Default Re: RF power transistor testing

Made a start. Cif bathroom cleaner. Never known anything like it to lift dirt.
Also isn't the internet wonderful. Couldnt' find any info on it so googled 140 watt push pull amplifier and found this.
Attached Thumbnails
Click image for larger version

Name:	5437CC9B-8D04-4F90-83E4-12BB09850BC6.jpg
Views:	84
Size:	43.3 KB
ID:	181746   Click image for larger version

Name:	EFB37EA1-14A8-4C13-AD7D-1239473DD8A0.jpg
Views:	80
Size:	43.5 KB
ID:	181747   Click image for larger version

Name:	3E26C792-EBF8-4846-8ED3-DA18BCFB8B7C.jpg
Views:	86
Size:	42.0 KB
ID:	181748  
Steve G4WCS is offline   Reply With Quote
Old 23rd Apr 2019, 10:48 pm   #3
Steve G4WCS
Pentode
 
Steve G4WCS's Avatar
 
Join Date: Sep 2004
Location: Preston, Lancashire, UK.
Posts: 223
Default Re: RF power transistor testing

Thinking about it after a beer, should I just reassemble it as is first off then give it a sniff of rf and see what it's doing or not ?
Steve G4WCS is offline   Reply With Quote
Old 24th Apr 2019, 3:53 am   #4
Terry_VK5TM
Heptode
 
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 820
Default Re: RF power transistor testing

I found what I think is the original auction listing for it - definitely says not working, so another beer and a bit more thinking may be in order.

That amp is probably straight out of one of Motorola's app notes if you can find it.
__________________
Terry VK5TM
https://www.vk5tm.com/
Terry_VK5TM is offline   Reply With Quote
Old 24th Apr 2019, 9:21 pm   #5
Steve G4WCS
Pentode
 
Steve G4WCS's Avatar
 
Join Date: Sep 2004
Location: Preston, Lancashire, UK.
Posts: 223
Default Re: RF power transistor testing

Terry. Over here most radio/cb type equipment is listed as not working to cover the sellers from bad selling experiences. The last cb linear I bought as a non worker was fine when tested.

Stripped it down and these are the components that will be changed as a matter of course. I can now get at it to perform resistance and voltage checks. Nothing appears to have let magic smoke out
The heatsink has been snook into the dishwasher.
Attached Thumbnails
Click image for larger version

Name:	9B46111C-E755-42FC-92B3-AACF6778A9C2.jpg
Views:	64
Size:	59.2 KB
ID:	181797   Click image for larger version

Name:	77BCB360-E1D2-4F44-B2B0-EC430B8805E2.jpg
Views:	70
Size:	62.3 KB
ID:	181798   Click image for larger version

Name:	BAE7F836-E8F2-4012-BF0A-EA6F9508E12E.jpg
Views:	66
Size:	42.3 KB
ID:	181799  

Last edited by Steve G4WCS; 24th Apr 2019 at 9:41 pm.
Steve G4WCS is offline   Reply With Quote
Old 29th Apr 2019, 4:40 am   #6
Argus25
Nonode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,170
Default Re: RF power transistor testing

Quote:
Originally Posted by Steve G4WCS View Post
The heatsink has been snook into the dishwasher.
........hmmm I thought I read on a thread somewhere that somebody else did this, perhaps they had a lot of, or a high concentration, dish wash powder (which is very alkaline and attacks anodizing and aluminium) and it spoiled the nice black anodizing on the heatsink. But you may be ok if the solution is weaker and/or temperature lower and not get any issues. It might be better to do it by hand with a trace of the friendly hand dish wash and a small soft brush.


I found the thread:

https://www.vintage-radio.net/forum/...d.php?t=139689

Last edited by Argus25; 29th Apr 2019 at 4:48 am. Reason: add link
Argus25 is offline   Reply With Quote
Old 29th Apr 2019, 12:47 pm   #7
Steve G4WCS
Pentode
 
Steve G4WCS's Avatar
 
Join Date: Sep 2004
Location: Preston, Lancashire, UK.
Posts: 223
Default Re: RF power transistor testing

It survived the dishwasher, but has had a coat of satin black anyway
Attached Thumbnails
Click image for larger version

Name:	455EDDCA-1C3B-4F3C-BFFB-60AD23611CB3.jpg
Views:	35
Size:	90.7 KB
ID:	182096   Click image for larger version

Name:	7D5494B4-65CB-4823-B7DD-9D3CBAFC4DEA.jpg
Views:	38
Size:	44.1 KB
ID:	182097  
Steve G4WCS is offline   Reply With Quote
Old 29th Apr 2019, 1:11 pm   #8
Argus25
Nonode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,170
Default Re: RF power transistor testing

......just a thought possibly not a wonderful idea to spray the surface where the transistors screw down with spray paint, as it is not a wonderful thermal conductor.

Was the anodized finish damaged at all in the dishwasher ?
Argus25 is offline   Reply With Quote
Old 29th Apr 2019, 1:29 pm   #9
Steve G4WCS
Pentode
 
Steve G4WCS's Avatar
 
Join Date: Sep 2004
Location: Preston, Lancashire, UK.
Posts: 223
Default Re: RF power transistor testing

Quote:
Originally Posted by Argus25 View Post
......just a thought possibly not a wonderful idea to spray the surface where the transistors screw down with spray paint, as it is not a wonderful thermal conductor.

Was the anodized finish damaged at all in the dishwasher ?
I haven't, I've only painted the visible elements, and no.
Steve G4WCS is offline   Reply With Quote
Old 3rd May 2019, 11:15 pm   #10
Steve G4WCS
Pentode
 
Steve G4WCS's Avatar
 
Join Date: Sep 2004
Location: Preston, Lancashire, UK.
Posts: 223
Default Re: RF power transistor testing

rebuild started. Old tantalums and elecs are going. A couple of old 15 ohm carbons have drifted away so will be replaced.
Attached Thumbnails
Click image for larger version

Name:	C7599ED2-3FA7-4922-83CF-27F10DF780EE.jpg
Views:	26
Size:	86.2 KB
ID:	182409   Click image for larger version

Name:	7B509F58-355F-45E2-BF11-8BE08DDC893A.jpg
Views:	28
Size:	57.8 KB
ID:	182410   Click image for larger version

Name:	5B82F622-9C6A-4C37-B5D7-D1F62A9B6896.jpg
Views:	29
Size:	60.8 KB
ID:	182411  
Steve G4WCS is offline   Reply With Quote
Old 3rd May 2019, 11:43 pm   #11
Oldcodger
Octode
 
Join Date: Oct 2014
Location: West Midlands, UK.
Posts: 1,288
Default Re: RF power transistor testing

Quote:
Originally Posted by Steve G4WCS View Post

I'm hoping the power transistors aren't fried but I'm working on the assumption that they are.
What's the recommended way to test them, just checking for shorts/open circuits and checking the diode junctions, any precautions etc ?

Thanks
AVO on ohms . Junction test/DVM on diode test. if inconclusive, isolate base ( if possible ) for further testing.
Oldcodger is offline   Reply With Quote
Old 4th May 2019, 10:42 pm   #12
Steve G4WCS
Pentode
 
Steve G4WCS's Avatar
 
Join Date: Sep 2004
Location: Preston, Lancashire, UK.
Posts: 223
Default Re: RF power transistor testing

Pet hate 1. Untidy wiring
Pet hate 2. Non flux removal
Attached Thumbnails
Click image for larger version

Name:	FB4963CC-925F-4020-AAA4-C05695D4BE84.jpg
Views:	40
Size:	95.4 KB
ID:	182486   Click image for larger version

Name:	957166D2-46A3-44F1-854A-70C152A64428.jpg
Views:	38
Size:	112.9 KB
ID:	182487   Click image for larger version

Name:	77AF7A76-F5A8-4C4E-8507-8F49D8C8169D.jpg
Views:	38
Size:	52.5 KB
ID:	182488   Click image for larger version

Name:	8BCE0F1B-D94F-4F80-8F39-36959C906D6B.jpg
Views:	31
Size:	50.6 KB
ID:	182489  
Steve G4WCS is offline   Reply With Quote
Old 17th May 2019, 11:03 am   #13
Steve G4WCS
Pentode
 
Steve G4WCS's Avatar
 
Join Date: Sep 2004
Location: Preston, Lancashire, UK.
Posts: 223
Default Re: RF power transistor testing

It lives.

Haven't tried it at full power levels as I hadn't put thermal compound on the power transistors

https://youtu.be/Dy_cqqq89xI

I've added a small computer fan to it as there are some parts inside that get warm and aren't heatsinked, I used a riding helmet bag for filter material as it's very breathable

It's quiet enough

https://youtu.be/WT7t1fq6Kc8

Plan is to use it with the IC-251 which has a Mutek front end.
Should make quite a good setup
Attached Thumbnails
Click image for larger version

Name:	AB590873-E5B2-438E-AB30-ADFE2AF8FF6B.jpg
Views:	22
Size:	59.4 KB
ID:	183266   Click image for larger version

Name:	695A2FE9-27C2-48BF-816F-5C4EB575B467.jpg
Views:	20
Size:	41.1 KB
ID:	183267   Click image for larger version

Name:	EE1FF966-F8F4-4A47-AED5-41229B992AA1.jpg
Views:	18
Size:	77.7 KB
ID:	183268   Click image for larger version

Name:	44D29179-028F-408A-8DB8-D77624038DC6.jpg
Views:	21
Size:	97.6 KB
ID:	183269   Click image for larger version

Name:	9A001DB7-2493-4351-9244-F26BE7FB6E97.jpg
Views:	15
Size:	45.8 KB
ID:	183270  

Steve G4WCS is offline   Reply With Quote
Old 17th May 2019, 12:03 pm   #14
Refugee
Dekatron
 
Refugee's Avatar
 
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 4,117
Default Re: RF power transistor testing

A riding helmet bag sounds expensive.
I normally use a vacuum cleaner motor filter. They are made to be cut to size.
I just linked to the first one on a search. Wilco stopped stocking them for some reason.
https://www.amazon.co.uk/Universal-V.../dp/B004A8JMSE
A cheaper one.
https://www.amazon.co.uk/dp/B078VTCW79/ref=dp_cerb_1

Last edited by Refugee; 17th May 2019 at 12:06 pm. Reason: Cheaper one added
Refugee is offline   Reply With Quote
Old 17th May 2019, 12:15 pm   #15
Steve G4WCS
Pentode
 
Steve G4WCS's Avatar
 
Join Date: Sep 2004
Location: Preston, Lancashire, UK.
Posts: 223
Default Re: RF power transistor testing

Quote:
Originally Posted by Refugee View Post
A riding helmet bag sounds expensive.
I normally use a vacuum cleaner motor filter. They are made to be cut to size.
I just linked to the first one on a search. Wilco stopped stocking them for some reason.
https://www.amazon.co.uk/Universal-V.../dp/B004A8JMSE
A cheaper one.
https://www.amazon.co.uk/dp/B078VTCW79/ref=dp_cerb_1
good shout.

the helmet bag was being cleared out anyway but I spotted its potential
Steve G4WCS is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 7:49 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 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.