Another Bush DAC 10 - Page 4 - UK Vintage Radio Repair and Restoration Discussion Forum

DonaldStott · 7th Jun 2020, 10:27 am

Quote:

Originally Posted by ms660

Check the coil.

Lawrence.

I checked the coils as best as I could with the Tuning Unit still in place - you're not going to like it (coil numbers as per the Trader Sheet): -

Push Button No.1 (L5) - 0.5 ohms
Push Button No.2 (L4) - 4.9 ohms
Push Button No.3 (L3) - 4.7 ohms

I also noticed that the winding on L4 has started to unravel!

I still have: -

Push Button 1 - BBC Radio 4 LW (1500 Metres)
Push Button 3 - Clyde 2 MW (261 Metres)

So it's decision time - do I just leave things as they are with two of the Pre-set Push Buttons working along with LW and MW Manual Tuning - Pre-set Push Button 2 is still not working - or do I remove the Tuning Unit to get at the coils in the rear!

What are my chances of finding replacements or having these rewound??

ms660 · 7th Jun 2020, 10:48 am

I suspect your measurements are in error, measuring low values can be difficult.

I would also make sure that C29 is being switched into circuit and that it's not leaking or short circuit.

If the circuit looks to be in order I would check the alignment, remember that the coils selected on preset are connected across the LW oscillator coil.

Lawrence.

DonaldStott · 7th Jun 2020, 1:31 pm

Quote:

Originally Posted by ms660

I suspect your measurements are in error, measuring low values can be difficult.

I agree - must do better!

Quote:

Originally Posted by ms660

I would also make sure that C29 is being switched into circuit and that it's not leaking or short circuit.

Looking at the Erratum to the Bush Radio Service Instructions it states: -

TC4 - 100-450 mmfd (picoFarads)
TC3 - 100-450 mmfd (picoFarads)
TC2 - 25-150 mmfd (picoFarads)

What I'm measuring: -

TC4 - 302 picoFarads

TC3 - 45 nanoFarads (45,000 picoFarads)

TC2 - 80 picoFarads

So unless my measurements are wrong (again?) there seems to be something "not quite right" with TC3 (C39)!

Quote:

Originally Posted by ms660

If the circuit looks to be in order I would check the alignment, remember that the coils selected on preset are connected across the LW oscillator coil.

Check the alignment - easy for you to say!

DonaldStott · 7th Jun 2020, 9:29 pm

So before I go rushing off and Post in the Wanted section for a 100-450 mmfd (picoFarads) trimmer from a Bush DAC10 Tuning Unit I really need to know if its easy to replace such a component and what's involved after that in terms of alignment??

Or just leave it and walk away ...?

electrogram · 7th Jun 2020, 10:22 pm

Will tc3 not be in parallel with the AvC decoupling cap (0.05uf) , via the aeriel coil, when it's button is pressed ?

DonaldStott · 8th Jun 2020, 9:48 am

Quote:

Originally Posted by electrogram

Will tc3 not be in parallel with the AvC decoupling cap (0.05uf) , via the aeriel coil, when it's button is pressed ?

Thanks electrogram, of course it will be - I should have noticed that Push Button No.2 was pressed when I took my readings!

With no buttons pressed I'm now measuring 395pF for TC3 - that's more like it as it's within the expected range for that trimmer.

DonaldStott · 11th Jun 2020, 9:52 am

Today is the Last Chance Salon for Push Button 2 ...

I managed to disassemble the supporting strip for the trimmers from the Tuning Unit and there doesn't appear to be much wrong here. This also allowed a closer look at the coils and once again nothing untoward to the untrained eye.

I measured the full range of trimmer TC3 and it is 33.5pF - 424pF ?

The oscillator coil associated with TC3 is L2 in Bush Radio Service Instructions and this has the range 550-350 Metres. So BBC Radio Scotland MW (370 Metres) should fall within the range covered by this Push Button but it's nowhere to be found?

I know that Push Button 2 is set by adjusting the oscillator coil (L2) followed by the aerial trimmer (TC3) to get the best signal. All I can get on Push Button 2 is two very, very faint stations both badly distorted, neither of which is BBC Radio Scotland?

All switch contacts have been cleaned once again!

Four out of the five Push Buttons are working and two of those are the LW and MW manual tuning Buttons, so not much lost apart from the convenience of one Push Button!

So unless someone has any further ideas or insights then the chassis is going back in the case today and this restoration is finished - hurrah!

ms660 · 11th Jun 2020, 10:01 am

I'd check the alignment if possible, you don't have to tweek anything in the receiver to do that.

Lawrence.

7th Jun 2020, 10:48 am	#62
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Another Bush DAC 10 I suspect your measurements are in error, measuring low values can be difficult. I would also make sure that C29 is being switched into circuit and that it's not leaking or short circuit. If the circuit looks to be in order I would check the alignment, remember that the coils selected on preset are connected across the LW oscillator coil. Lawrence. Last edited by ms660; 7th Jun 2020 at 11:03 am. Reason: extra info

7th Jun 2020, 9:29 pm	#64
DonaldStott Octode Join Date: Aug 2015 Location: Glasgow, UK. Posts: 1,842	Re: Another Bush DAC 10 So before I go rushing off and Post in the Wanted section for a 100-450 mmfd (picoFarads) trimmer from a Bush DAC10 Tuning Unit I really need to know if its easy to replace such a component and what's involved after that in terms of alignment?? Or just leave it and walk away ...? __________________ BVWS Member

7th Jun 2020, 10:22 pm	#65
electrogram Heptode Join Date: Jul 2008 Location: Hereford, UK. Posts: 719	Re: Another Bush DAC 10 Will tc3 not be in parallel with the AvC decoupling cap (0.05uf) , via the aeriel coil, when it's button is pressed ?

11th Jun 2020, 9:52 am	#67
DonaldStott Octode Join Date: Aug 2015 Location: Glasgow, UK. Posts: 1,842	Re: Another Bush DAC 10 Today is the Last Chance Salon for Push Button 2 ... I managed to disassemble the supporting strip for the trimmers from the Tuning Unit and there doesn't appear to be much wrong here. This also allowed a closer look at the coils and once again nothing untoward to the untrained eye. I measured the full range of trimmer TC3 and it is 33.5pF - 424pF ? The oscillator coil associated with TC3 is L2 in Bush Radio Service Instructions and this has the range 550-350 Metres. So BBC Radio Scotland MW (370 Metres) should fall within the range covered by this Push Button but it's nowhere to be found? I know that Push Button 2 is set by adjusting the oscillator coil (L2) followed by the aerial trimmer (TC3) to get the best signal. All I can get on Push Button 2 is two very, very faint stations both badly distorted, neither of which is BBC Radio Scotland? All switch contacts have been cleaned once again! Four out of the five Push Buttons are working and two of those are the LW and MW manual tuning Buttons, so not much lost apart from the convenience of one Push Button! So unless someone has any further ideas or insights then the chassis is going back in the case today and this restoration is finished - hurrah! __________________ BVWS Member

11th Jun 2020, 10:01 am	#68
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Another Bush DAC 10 I'd check the alignment if possible, you don't have to tweek anything in the receiver to do that. Lawrence.