Bush DAC 90a poor reception - UK Vintage Radio Repair and Restoration Discussion Forum

harbottle · 7th Aug 2005, 11:45 pm

Hi
I have a Bush DAC90a but it will only pick up two stations, talk sport and radio 5 live. Both these stations are loud and clear and the radio runs for hours with no obvious other problems. Could anyone tell me how I can improve the reception on this radio?

Thanks

avro · 8th Aug 2005, 7:08 am

I have two DAC90As and the reception was good on one and terrible on the other. I had them restored by Steve Ostler and Radiocraft and the reception improved dramatically. Each day I listen to the World Service and R4 on one of them.

Turning the set does help a lot due to the aerial arrangement.

Avro

Aerodyne · 8th Aug 2005, 11:32 am

I'd suspect valve emission. Low emission will cause the kind of problem you are describing. That's a 'probable.' Truthfully though, there's lots of 'possibles' - low HT level, faults with the IF transformers, alignment off, etc. Valves first, though. Certainly check the output valve, although you might not think it would affect signal reception.
Yes, rotating the set will allow the directional properties of the inbuilt frame aerial to be maximised - but these sets are usually very sensitive anyway.
Good luck.
-Tony

Alf · 8th Aug 2005, 12:24 pm

I've experienced similar conditions with a DAC90A, it was caused by wrongly rated dial lamps being fitted, once the correct rated bulbs were fitted the set sprung to life, the effect of the wrong bulbs being fitted was of low emission by the valves, from memory I think they're 3.5v @ 150mA, worth checking before doing anything else.

Alf · 8th Aug 2005, 1:52 pm

From what I can remember, and it was some time ago, R5L and Talk Sport were receivable but hardly anything either side of them, on long wave there was hardly any reception at all, I remember checking the valves by trying them in another radio, no problems with them. I can't remember the voltage or current that the fitted dial lamps were except to say they weren't the ones specified in the circuit, I suppose it was really by accident that the fault was cured but it's one I'll never forget.

Aerodyne · 8th Aug 2005, 7:37 pm

It's a good point, Alf. The bulbs are 3.5V at 10.15A (according to the Trader sheet). As they are in series with the valves, wrongly rated current types could conceivably limit the valve heater current, creating just the effect you describe, even though there is (or should be) a parallel path through a lamp shunt resistor.

One to watch for, I think!
-Tony

mickjjo · 8th Aug 2005, 7:49 pm

Quote:

Originally Posted by Aerodyne

The bulbs are 3.5V at 10.15A

I expect Tony meant to say 3.5V at 0.15A ,

.

Regards, Mick.

Aerodyne · 9th Aug 2005, 5:28 pm

Oops....

-Tony
p.s. mind you, 10.15 amp lamps would be interesting in their own right. Or maybe not (said he, squirming with embarrassment. Bl***dy computers.)

Hoveradio · 10th Aug 2005, 3:13 pm

Hi,I've recently had this problem on two dac90a's that I have restored.

On the first one I discovered that the i.f. wouldn't tune up on the primary of the second i.f. coil(bottom adjustment screw I think).I soldered a 68pf cap across the top and bottom of the coil and hey presto it set up and an immediate improvement in reception.
The second one which I did just this morning had a similar problem,but it was on the primary of the first i.f. coil.This time I happened to have a 100pf cap to hand and soldered this in place and again it set up a treat and now reception is great.
I assume that the original caps(110pf) have lost their capacitance as I have left them in place.They can be got at but it means removing the coil from the set and bending the two aluminium tags back and removing the coils from the can.The waxy mica cap can then be removed.Hopefully if you have a similar problem to mine you can just get away with soldering a replacement to the outside.
I hope this is of some help to you and I'd be interested to know if other forum members have had a similar problem.
Best Regards John.

harbottle · 10th Aug 2005, 8:03 pm

Hi
Thanks for all the suggestions. I have started with what looks like the easiest thing first, the lamps. When I removed them they fell to bits so I reckon they must be original. I couldn't get 3.5v 150ma lamps so I have fitted 3.5v 200ma (I have the correct ones on order). This seems to have made a slight improvement, I can now pick up one ore two other stations but not very well. Also the lamps are very dim. The stations that I can get sound as if they are also being picked up a little further down the scale. The radio has also had some new capacitors fitted at some time.
It must be obvious that I know nowt about radio's but I am keen to learn and have a go.
Thanks once again
Tony

Sideband · 10th Aug 2005, 9:26 pm

Quote:

Originally Posted by harbottle

It must be obvious that I know nowt about radio's but I am keen to learn and have a go.

Then it will do no harm to advise you that this set uses the AC/DC technique (no mains transformer) and the chassis is potentially 'live'. If you do not have a mains isolating transformer you must make sure that the chassis is connected to mains neutral if you intend to do any work on the set. There has been much debate on the safety aspect of radio's in these forums over the last few days and it will do you no harm to read them. It WILL do you harm if you just 'dive in' without being aware of the possible dangers.

With regard to stations being in the wrong place, it could be that the 'phantom twiddler' has been at work and the set needs some re-alignment. This can be done without signal generators but requires some experience

Rich.

G0PKH - Pete · 11th Aug 2005, 12:19 pm

Hi.

It would also perhaps be worth checking the tightness of the windings on the
frame aerial.
The last one I restored had very loose windings (almost falling of the former).

Rewinding the aerial made a massive difference to sensitivity

Pete

Heatercathodeshort · 11th Aug 2005, 7:39 pm

Great advice from Richard in his thread Tony. Please don't be put off by our comments. We are not being 'stuffy' with guys that are new to old technology. There are rules that MUST be adhered to when working on valve receivers especially the 'universal' AC/DC receivers. The are safe to work on if you have the basic knowledge but like any technology, can be dangerous if misunderstood. Try to obtain some 1950's copies of the old 'PRACTICAL WIRELESS'. They often ran articles for readers that were new to the hobby and are first class articles. You don't need to get 'too deep' to get the basic idea. Any queries you may encounter will be well answered on this site! Regards. JOHN.

harbottle · 11th Aug 2005, 10:35 pm

Thanks John and Rich for your words of warning.
I am well aware of the dangers of working on these radios, I am a maintenance electrician with thirty years experience working in the manufacturing industry so I do know my a.c. from my d.c. and I am very aware of the safety aspects, I just know almost nothing about radios so I am very gratefull for the advice from the experts .

Thanks
Tony

7th Aug 2005, 11:45 pm	#1
harbottle Retired Dormant Member Join Date: Aug 2005 Posts: 3	Bush DAC 90a poor reception Hi I have a Bush DAC90a but it will only pick up two stations, talk sport and radio 5 live. Both these stations are loud and clear and the radio runs for hours with no obvious other problems. Could anyone tell me how I can improve the reception on this radio? Thanks

8th Aug 2005, 7:08 am	#2
avro Heptode Join Date: Jun 2003 Location: Kapellen, Belgium Posts: 656	Re: Bush DAC 90a poor reception I have two DAC90As and the reception was good on one and terrible on the other. I had them restored by Steve Ostler and Radiocraft and the reception improved dramatically. Each day I listen to the World Service and R4 on one of them. Turning the set does help a lot due to the aerial arrangement. Avro

8th Aug 2005, 11:32 am	#3
Aerodyne Octode Join Date: Jun 2004 Location: Hampton Vale, Peterborough, UK. Posts: 1,698	Re: Bush DAC 90a poor reception I'd suspect valve emission. Low emission will cause the kind of problem you are describing. That's a 'probable.' Truthfully though, there's lots of 'possibles' - low HT level, faults with the IF transformers, alignment off, etc. Valves first, though. Certainly check the output valve, although you might not think it would affect signal reception. Yes, rotating the set will allow the directional properties of the inbuilt frame aerial to be maximised - but these sets are usually very sensitive anyway. Good luck. -Tony

8th Aug 2005, 12:24 pm	#4
Alf Hexode Join Date: May 2005 Location: Wigan, Greater Manchester, UK. Posts: 479	Re: Bush DAC 90a poor reception I've experienced similar conditions with a DAC90A, it was caused by wrongly rated dial lamps being fitted, once the correct rated bulbs were fitted the set sprung to life, the effect of the wrong bulbs being fitted was of low emission by the valves, from memory I think they're 3.5v @ 150mA, worth checking before doing anything else.

8th Aug 2005, 1:52 pm	#5
Alf Hexode Join Date: May 2005 Location: Wigan, Greater Manchester, UK. Posts: 479	Re: Bush DAC 90a poor reception From what I can remember, and it was some time ago, R5L and Talk Sport were receivable but hardly anything either side of them, on long wave there was hardly any reception at all, I remember checking the valves by trying them in another radio, no problems with them. I can't remember the voltage or current that the fitted dial lamps were except to say they weren't the ones specified in the circuit, I suppose it was really by accident that the fault was cured but it's one I'll never forget.

8th Aug 2005, 7:37 pm	#6
Aerodyne Octode Join Date: Jun 2004 Location: Hampton Vale, Peterborough, UK. Posts: 1,698	Re: Bush DAC 90a poor reception It's a good point, Alf. The bulbs are 3.5V at 10.15A (according to the Trader sheet). As they are in series with the valves, wrongly rated current types could conceivably limit the valve heater current, creating just the effect you describe, even though there is (or should be) a parallel path through a lamp shunt resistor. One to watch for, I think! -Tony

9th Aug 2005, 5:28 pm	#8
Aerodyne Octode Join Date: Jun 2004 Location: Hampton Vale, Peterborough, UK. Posts: 1,698	Re: Bush DAC 90a poor reception Oops.... -Tony p.s. mind you, 10.15 amp lamps would be interesting in their own right. Or maybe not (said he, squirming with embarrassment. Bl***dy computers.)

10th Aug 2005, 3:13 pm	#9
Hoveradio Pentode Join Date: Jan 2005 Location: Pant-y-Dwr, Powys, UK. Posts: 134	Re: Bush DAC 90a poor reception Hi,I've recently had this problem on two dac90a's that I have restored. On the first one I discovered that the i.f. wouldn't tune up on the primary of the second i.f. coil(bottom adjustment screw I think).I soldered a 68pf cap across the top and bottom of the coil and hey presto it set up and an immediate improvement in reception. The second one which I did just this morning had a similar problem,but it was on the primary of the first i.f. coil.This time I happened to have a 100pf cap to hand and soldered this in place and again it set up a treat and now reception is great. I assume that the original caps(110pf) have lost their capacitance as I have left them in place.They can be got at but it means removing the coil from the set and bending the two aluminium tags back and removing the coils from the can.The waxy mica cap can then be removed.Hopefully if you have a similar problem to mine you can just get away with soldering a replacement to the outside. I hope this is of some help to you and I'd be interested to know if other forum members have had a similar problem. Best Regards John.

10th Aug 2005, 8:03 pm	#10
harbottle Retired Dormant Member Join Date: Aug 2005 Posts: 3	Re: Bush DAC 90a poor reception Hi Thanks for all the suggestions. I have started with what looks like the easiest thing first, the lamps. When I removed them they fell to bits so I reckon they must be original. I couldn't get 3.5v 150ma lamps so I have fitted 3.5v 200ma (I have the correct ones on order). This seems to have made a slight improvement, I can now pick up one ore two other stations but not very well. Also the lamps are very dim. The stations that I can get sound as if they are also being picked up a little further down the scale. The radio has also had some new capacitors fitted at some time. It must be obvious that I know nowt about radio's but I am keen to learn and have a go. Thanks once again Tony

11th Aug 2005, 12:19 pm	#12
G0PKH - Pete Retired Dormant Member Join Date: Aug 2003 Location: Stansted Essex Posts: 263	Re: Bush DAC 90a poor reception Hi. It would also perhaps be worth checking the tightness of the windings on the frame aerial. The last one I restored had very loose windings (almost falling of the former). Rewinding the aerial made a massive difference to sensitivity Pete

11th Aug 2005, 7:39 pm	#13
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Bush DAC 90a poor reception Great advice from Richard in his thread Tony. Please don't be put off by our comments. We are not being 'stuffy' with guys that are new to old technology. There are rules that MUST be adhered to when working on valve receivers especially the 'universal' AC/DC receivers. The are safe to work on if you have the basic knowledge but like any technology, can be dangerous if misunderstood. Try to obtain some 1950's copies of the old 'PRACTICAL WIRELESS'. They often ran articles for readers that were new to the hobby and are first class articles. You don't need to get 'too deep' to get the basic idea. Any queries you may encounter will be well answered on this site! Regards. JOHN.

11th Aug 2005, 10:35 pm	#14
harbottle Retired Dormant Member Join Date: Aug 2005 Posts: 3	Re: Bush DAC 90a poor reception Thanks John and Rich for your words of warning. I am well aware of the dangers of working on these radios, I am a maintenance electrician with thirty years experience working in the manufacturing industry so I do know my a.c. from my d.c. and I am very aware of the safety aspects, I just know almost nothing about radios so I am very gratefull for the advice from the experts . Thanks Tony