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 > Success Stories

Notices

Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

Closed Thread
 
Thread Tools
Old 12th Jun 2004, 7:04 pm   #1
Richard_vmt
Guest
 
Posts: n/a
Default Success with Telefunken Bajazzo

At least moderate success. Owing to absence of a good replacement whip antenna shortwave reception is spotty but it presents no mystery and the set proves itself capable of excellent reception when a good replacemenyt can be found.
I bought the set cheaply on Ebay. The appearance was as poor as the seller claimed but the vinyl cleaned up with elbow grease and vinyl restorer. I replaced the AD 155 output transistors in the mistaken belief they were faulty. I also reconnected a lead from the thermistor which protects the output transistors, and a lead to a coil in the rf section. With the latter the radio played but very low. My opinion the output transistors were faulty was based on a test by shorting the emitter to base and the collector current was supposed to rise to nearly the supply voltage. Apparently this test was not reliable because taken out of circuit both transistors were okay--although I can say they were anything but a good match (the bad old days? I remember to emphasis of solid heat sink technology related to the use of germanium transistors and the baajazzo uses the speaker frame as heat sink--very formidable).
However in the long run the culprit was a defective earphone outlet. However, with a replacement there was an unexplainable shorting of the subframe to the speaker frame which was causing a putt-putt feedback. I never figured it out but replaced the scres with nylong screws and forever ended the unwanted feedback. The sound is very clear and powerful. Must now conclude with thanks to all who helped.---Richard
 
Old 12th Jun 2004, 10:38 pm   #2
Sideband
Dekatron
 
Sideband's Avatar
 
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,550
Default Re: Success with Telefunken Bajazzo

Hi Richard.

Just for the record I would say that it is not good practice to short transistor electrodes together. To turn a transistor 'ON' the base potential should be taken slightly towards collector potential. For germanium transistors you should measure about .2 volts between base and emitter. For silicon it's about .7 volts between base and emitter.

Shorting base to emitter as you did would turn the transistor off and theoretically it should not draw any current at all (and shouldn't do the transistor any harm) but NEVER short base to collector. You should always be extra carefull with DC coupled stages as a short in one area can cause a disaster elsewhere!

Rich.
__________________
There are lots of brilliant keyboard players and then there is Rick Wakeman.....
Sideband is offline  
Old 14th Nov 2004, 11:17 pm   #3
davew
Tetrode
 
davew's Avatar
 
Join Date: Feb 2004
Location: Deal, Kent, UK.
Posts: 74
Default Re: Success with Telefunken Bajazzo

The forum helps me out again I recently picked up a bajazzo de luxe 101 cheaply which worked perfectly except for this really annoying occasional motorboating which you've just solved for me - Thanks Richard.
The set really is well built and sounds great from a surprisely small speaker - Also nice to see proper power transistors on a heatsink. Doubt if I'd find many of those in my Morphy Richards Companion!
Funny how the Telefunkens seem to go for far less than Grundigs - Best 12 quid I've spent for a while

Dave
davew is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 1:34 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.