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-   -   Bush TR106GL (https://www.vintage-radio.net/forum/showthread.php?t=176894)

G8vsjDave 21st Feb 2021 3:37 pm

Bush TR106GL
 
Hi there, When I was a spotty teenager back in the sixties, I had a bush TR116 that I had great fun with. Unfortunately, I left my radio at my parents home after I left to go into big wide world and it got damaged and thrown away. For some time now, I have been been looking for out for a TR116 to add to my small collection of sixties transistor radios. Last week I found a TR106GL which has a similar look, but without short wave. The radio was complete, but filthy. A strip down and good clean had it looking great except for slight yellowing of the plastic. Now, this is where I need a little help. The radio basically works , but is somewhat unstable with distorted audio on strong signals. I get the impression that the problem is with the IF stage because SLIGHT adjustment to the IF transformers do effect the audio. Can anyone point me in direction of a circuit diagram please or give me any pointers. I have a DMM and scope for test gear but not a signal generator. Thanks - Dave

crackle 21st Feb 2021 3:43 pm

Re: Bush TR106GL
 
Some of the modern AM broadcasts these days do sound a little distorted on some radios.
But I would check out the caps on the AGC line, C30 & C8 & R2 (trader) and the electrolytics on the audio power supply and the RF/IF power supply. C24 & C39
Mike

Cobaltblue 21st Feb 2021 3:52 pm

Re: Bush TR106GL
 
Hi Dave

The circuit info is available top right (or follow the links below) for both the Bush TR106 and the TR116

TR106: https://www.service-data.com/product...49/1081/m10649

TR116: https://www.service-data.com/product...52/1084/m10652

Cheers

Mike T

G8vsjDave 21st Feb 2021 5:33 pm

Re: Bush TR106GL
 
Thanks Mike, I've down loaded it. Just got to do the fault finding now. Dave

G8vsjDave 23rd Feb 2021 11:17 am

Re: Bush TR106GL
 
1 Attachment(s)
Hi folks, well, I’m embarrassed to say I’m stuck on this one and could do with pointing in the right direction. The radio ‘works’ but the agc doesn’t seem to be doing its job properly. When a station is tuned in I get clipping like distortion on the audio and a scope on the collector of VT3 shows a clipped IF waveform of about 7volts p-p (full supply voltage) . Tune to one side of the carrier and the IF amplitude reduces and I get un-distorted audio. All the transistor voltages are about right (within 0.2 volt). C8 and C9 are both fine, I did find R5 was high at 140k but changing that made no difference. There is about a 1.5 volt change on C9, the agc smoothing capacitor and R10 is about right. Any advice welcome. Dave

ronbryan 23rd Feb 2021 11:21 pm

Re: Bush TR106GL
 
Diode CD1 is supposed to damp the primary of IFT1 for very strong signals. Have you checked CD1 and associated components?

Ron

G8vsjDave 24th Feb 2021 9:03 am

Re: Bush TR106GL
 
Hi Ron, thanks for the suggestion. Yes, I've checked the diode, it's series resistor and the capacitor - all fine. I've checked and replaced some R's that have gone high value - with no improvement. The manual suggests connecting a 8.2k R across C9 to reduce the sensitivity for alignment, and that seems to make the radio work Ok. The local oscillator waveform is not a good sine wave - is that a problem? - Dave

ronbryan 24th Feb 2021 9:38 am

Re: Bush TR106GL
 
As the 5k volume control is part of VT2 base bias network, has this gone up in value significantly?

I have always thought that a distorted oscillator waveform is more likely to generate spurious responses to out of band signals, rather than increase sensitivity. Higher than designed oscillator amplitude may improve the conversion gain of the mixer I suppose.

Ron

G8vsjDave 24th Feb 2021 12:28 pm

Re: Bush TR106GL
 
We are getting desperate now. No, the volume control is Ok. I think I'm just going to leave it with reduced sensitivity - it's working Ok and it looks good. I do feel I should carry on but I've already spent FAR more time on this than I should have. What has surprised me is that I have no leakage in any of the three AF117s (shield to EBC), but I guess, 'don't look a gift horse' eh. Thanks for your help. - Dave

ms660 24th Feb 2021 2:43 pm

Re: Bush TR106GL
 
What's the voltage across C8 when the signal is overloading?

Lawrence.

G8vsjDave 24th Feb 2021 3:48 pm

Re: Bush TR106GL
 
With normal, non overloaded signal and the 8.2K resistor disconnected the voltage across C8 is 6.8v. Overloaded the voltage drops to 5.5v - Thanks for your interest - Dave


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