Pam TB77 - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

jonnybear · 16th Mar 2016, 1:00 pm

Hi John
It seems there are several different manufacturers of the AC142 transistor and as a consequence connections may differ looking at my towers, jaeger, and eca books. Have you a analogue meter of any type?, as I find it easier to check a transistor with one of these. If you disconnect the leads from the transistor
looking at the transistor leads at the base connections are emitter, base, collector, with meter set to ohms x 10, place the red probe on the base lead, black probe on the emitter and then the collector, you should have a reading, then place the black lead on the base lead and then the red probe on the emitter and the the collector there should be no reading. check this and get back.
John

crackle · 16th Mar 2016, 6:02 pm

The noise you describe before in post 11 could be "motorboating" have you checked C20 100uf electrolytic?

Mike

longneck90 · 19th Mar 2016, 5:34 pm

Hello to all. The Pam TB77 is now going and power output section stabilised. I changed all 'wax' capacitors, removed the AC142s and installed AC188s in their place. Thanks to everyone on the Forum for their help and information. All the best. John.

? I have only just now, seen 'reply posts' from John (jonnybear) and Mike (crackle). C20 was first capacitor I changed. I check ? all transistors before installing them. Being used to valves, transistors lead to much head scratching for the unwary such as I. Thanks again. John.

16th Mar 2016, 1:00 pm	#21
jonnybear Octode Join Date: Nov 2010 Location: Cullompton, Devon, UK. Posts: 1,435	Re: Pam TB77 Hi John It seems there are several different manufacturers of the AC142 transistor and as a consequence connections may differ looking at my towers, jaeger, and eca books. Have you a analogue meter of any type?, as I find it easier to check a transistor with one of these. If you disconnect the leads from the transistor looking at the transistor leads at the base connections are emitter, base, collector, with meter set to ohms x 10, place the red probe on the base lead, black probe on the emitter and then the collector, you should have a reading, then place the black lead on the base lead and then the red probe on the emitter and the the collector there should be no reading. check this and get back. John Attached Thumbnails

16th Mar 2016, 6:02 pm	#22
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Pam TB77 The noise you describe before in post 11 could be "motorboating" have you checked C20 100uf electrolytic? Mike

19th Mar 2016, 5:34 pm	#23
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	Re: Pam TB77 Hello to all. The Pam TB77 is now going and power output section stabilised. I changed all 'wax' capacitors, removed the AC142s and installed AC188s in their place. Thanks to everyone on the Forum for their help and information. All the best. John. ? I have only just now, seen 'reply posts' from John (jonnybear) and Mike (crackle). C20 was first capacitor I changed. I check ? all transistors before installing them. Being used to valves, transistors lead to much head scratching for the unwary such as I. Thanks again. John. Last edited by longneck90; 19th Mar 2016 at 5:57 pm.