Bush TR82C - help request

[Mike Watterson]

Any Germanium diode. The 1N60 are good, common and cheap.

You can't reliably test in circuit. You need to disconnect one end. I did have a Decca portable with a diode gone high resistance, but otherwise it seems a rare fault.

[TinaRotator]

Thanks Mike, I will try to take the diode out and test it separately. I got some 1N60 for just in case, they were dirt cheap just as you said .

[TinaRotator]

Hi all,
I finally managed to get to the diode (CD1 OA70) and I tested it after taking it out of the circuit. My multimeter shows OL in both diode and resistance mode, measured both ways. I am waiting for the delivery of 1n60 diodes and will fit one once they arrive. In the IFT3 I also found a Hunts electrolytic (C20) which should measure 0.01 uF but my reading gives me 0.03 UF. I might replace it along with another Hunts and last electrolytic on the chassis - the C7 which should be 0.02uF but gives me 0.08uF.

Many thanks for your help,
TinaRotator

[ppppenguin]

"OL" on your meter literally means "overload" but in the contect of resistance means open circuit, or a higher resistance than the meter can measure. So the 0A70 is definitely duff.

A 0.01uF cap will never be an electrolytic. It will be a paper dielectric. Replace with a modern 0.01uF part. Commonly called 10nF these days. Any plastic dielectric (polyester, mylar etc) part will be fine. The high capacitance readings are caused by the caps being leaky. It's a side effect of the measurement method used in low cost meters that leakage shows up as high capacitance.

Rule of thumb: Most capacitors of 1uF and above will be electrolytic, most below that will not. The smallest electrolytics I can recall were 0.47uF which I would normally replace with plastic non-electrolytics. You can commonly get non-electrolytic caps up to 10uF. Even higher for some purposes.

[TinaRotator]

Thank you pppenguin and excuse my lack of knowledge! Funnily enough I have some new 0.01uF polyester at home from doing the record players, I should have remembered. Your explanation would have saved me a ton of time and ebay research last year. Thanks for taking your time and explaining this.

[ppppenguin]

The great thing is that you're happy to learn about these things.

The 0.02uF part can be repalced by a 0.022uF / 22nF modern part. Or a pair of 10n in parallel if that's what you have to hand.

If you're doing repair and restoration regularly you've probably worked out that it's useful to build up a stock of common components. An easy way to do this is to buy more than you immediately need of common parts. It's often inexpensive to buy 10, 25 or even 100. Then you need drawers or at least compartmented boxes to store them and suddenly you'll find that that you often have the parts you need already in stock.

[TinaRotator]

Hi all,

Pppenguin - thank you for the kind words of encouragement. I learned coding in a similar way, with one difference - I didn't have such a nice community to turn to.


I managed to fit the the new diode (IN60P) the same way the old diode was fitted. I replaced the Hunts capacitor inside IFT3 (0.01nF). I put the IFT3 back in and soldered in all the wires to the legs. I powered the radio and unfortunately nothing changed.

I could still do the same trick - connect the second tab of the volume potentiometer (RV1) to the legs 5 and 6 of the IFT3 and as a result get a very decent audio of BBC4, BBC Scotland and some other stations I didn't quite catch the names of.

I finally got hold of aligator clips so I could just leave them in and try to adjust volume etc. I noticed that the volume potentiometer seemed to cut off in the middle of the range as well as at both end. I found some spare brand new linear pot in my stuff and decided to replace it just to be certain that the issue isn't with the old potentiometer. The new pot is 10KOhm and the original one is 5KOhm so I put another 10KOhm resistor in parallel so that it's more like the original one. This didn't solve the problem either. I appreciate the difference in taper of those two pots and I am planning to order a 5KOhm log

I still needed to clip the 2nd tab of volume potentiometer to 5th and 6th leg of the IFT3 to hear the actual radio sound rather than just a very faint buzz. 

All the old electrolytics are gone now, I put a new diode. Why does the radio work when I clip those 3 points together but doesn't otherwise? How can I divide (and hopefuly conquer) this problem? Any hints will be appreciated again.

Have a good day,
TinaRotator

[Mike Watterson]

Check joint to joint with meter and set off to see is there a cracked track.
Re-flow joints with traditional tin/lead solder. Never lead free on vintage. Farnell sells it.