Bush DAC90A can't get tuning knob off - UK Vintage Radio Repair and Restoration Discussion Forum

Steve1952 · 22nd Aug 2021, 9:54 am

Hello; decided to start a "new" hobby, well since 1964 and the school radio society. Friend gave me a Bush DAC90a which I plugged in (know now I shouldn't have) and it worked, sort of for a bit with distant Radio 4. Seems to be an older restoration judging by the dust inside.

Problem is, the band change and volume knobs are secured by grub screws as per advice in this site, but the tuning knob (which looks original, with felt disc and broken perspex collar) doesn't have a screw securing it but what seems like an oddly shaped metal bush on the shaft as seen from the inspection hole underneath. I can't work out what this is or how to get it off to get at the chassis. Can anyone help? Otherwise my new hobby seems to be dead in the water.

Thanks

Herald1360 · 22nd Aug 2021, 10:15 am

That doesn't sound original. The tuning and volume knobs should be the same.

The collar is a retaining clip on a push on knob from somewhere else. Judicious application of Plus Gas, gentle heat and brute force is likely to be needed. The knob's not right anyway, so.....

SiriusHardware · 22nd Aug 2021, 10:25 am

It looks to me like a 'Horseshoe' spring, made from spring steel. Others will hopefully confirm but I think you just have to prise it open at the gap shown in the second picture until the gap is wide enough to let the spring come off the shaft.

Of course it may be rusted onto the shaft, which could complicate things a bit.

ms660 · 22nd Aug 2021, 10:33 am

The knob would normally just pull off complete with the "D" clip.

Lawrence.

slidertogrid · 22nd Aug 2021, 10:49 am

As Lawrence said the knob should just pull off.
See if you can carefully ease the clip off the back of the knob using a long screwdriver through the hole. Then as suggested apply some release agent to the back of the knob you may be able to get it to run down the control shaft and into the back of the knob.
Once it has had time to soak in wriggle the knob carefully and push and pull at the same time. It should give in. The clip is easily refitted once the knob is off.
Before you refit the knobs apply a little grease or Petroleum Jelly to the control shafts this will make refitting and future removal easier.
If you have one front knob held with a screw and one with a clip one of the knobs is wrong for the set. Only the later versions had knobs held with clips, earlier had screws. A picture of the set and knobs would help identify which knob is the wrong one for the set if that is the case.
Rich.

Steve1952 · 23rd Aug 2021, 9:50 pm

Many thanks to all, will have a go if I understand the advice correctly. Yes the two knobs are different, different sizes, the tuning one looks original. Will let you know how I get on

dj_Keet · 25th Aug 2021, 12:52 am

Yeah it does look like its on the wrong way round try using flat head screw driver through the hole push in a sliding motion (with the screwdriver still straight) against the area marked by the red arrow try not to use the hole as leverage as you will damage that area of the case if your not sure/confident put cardboard around the hole but a touch of force and a bit of technique will get it off take your time and think it through

Colin Boggis · 25th Aug 2021, 11:42 am

Plus gas on the shaft and leave radio face down so it soaks in - always worked for me. I also find a lever each side of the knob helps once the plus gas has had some time.

Steve1952 · 6th Sep 2021, 12:33 pm

Thanks all especially DJ Keet, I used the plus gas and flathead screwdriver approach and it came off - turns out it was not a metal bush but part of the bakelite knob. Still I now have a chassis free and ready to replace the caps, living and learning in this great hobby.

Graham G3ZVT · 6th Sep 2021, 5:14 pm

Surely the two knobs must have looked different, you even mention a Perspex collar on the wrong one.

bobhowe · 6th Sep 2021, 6:08 pm

Quote:

Originally Posted by Steve1952

Thanks all especially DJ Keet, I used the plus gas and flathead screwdriver approach and it came off - turns out it was not a metal bush but part of the bakelite knob. Still I now have a chassis free and ready to replace the caps, living and learning in this great hobby.

Hi Steve glad you got this set please be aware that this set has no mains transformer and depending which way the mains lead is connected the chassis becomes live and have you got the service sheet ? you can buy it on this forum for £1.99 kind regards Bob

Steve1952 · 7th Sep 2021, 3:24 pm

Yes thanks to all I have got the service sheet and am aware of live chassis (potentially). Will be very careful when it comes to testing.

bobhowe · 7th Sep 2021, 5:11 pm

Hi Steve please post some pictures of the set before & during replacing capacitors kind regards Bob

Radio Tech · 8th Sep 2021, 4:55 pm

Steve

If you want electrolytics you can get them from Jellyfish Audio at very reasonable prices

Ken

Bob_Moss · 8th Sep 2021, 7:38 pm

Does it need new electrolytics? My DAC10 is working fine on the original from 1952!

Station X · 8th Sep 2021, 9:24 pm

Indeed.

Electrolytics in Bush DAC90A's seem to be a cut above the rest. I've never had to replace a smoothing can in one.

bobhowe · 9th Sep 2021, 12:01 am

Quote:

Originally Posted by Station X

Indeed.

Electrolytics in Bush DAC90A's seem to be a cut above the rest. I've never had to replace a smoothing can in one.

Yes I second that I have not had to replace a smoothing can on a DAC90A or DAC90. Kind regards, Bob.

60 oldjohn · 9th Sep 2021, 9:08 pm

After about 3 years of use, my restored DAC90 electrolytic caps failed. I wish I had changed it when I restored the radio, it would have saved a run around thinking it was an intermittent valve fault.

John.

bobhowe · 9th Sep 2021, 11:19 pm

Quote:

Originally Posted by 60 oldjohn

After about 3 years of use, my restored DAC90 electrolytic caps failed. I wish I had changed it when I restored the radio, it would have saved a run around thinking it was an intermittent valve fault.

John.

Hi John was it the main ht capacitor that had failed ? & what was the make kind regards Bob

60 oldjohn · 9th Sep 2021, 11:44 pm

Hi Bob, I will check tomorrow.

John.

22nd Aug 2021, 9:54 am	#1
Steve1952 Diode Join Date: Aug 2021 Location: Sheffield, South Yorkshire, UK. Posts: 7	Bush DAC90A can't get tuning knob off Hello; decided to start a "new" hobby, well since 1964 and the school radio society. Friend gave me a Bush DAC90a which I plugged in (know now I shouldn't have) and it worked, sort of for a bit with distant Radio 4. Seems to be an older restoration judging by the dust inside. Problem is, the band change and volume knobs are secured by grub screws as per advice in this site, but the tuning knob (which looks original, with felt disc and broken perspex collar) doesn't have a screw securing it but what seems like an oddly shaped metal bush on the shaft as seen from the inspection hole underneath. I can't work out what this is or how to get it off to get at the chassis. Can anyone help? Otherwise my new hobby seems to be dead in the water. Thanks Attached Thumbnails

22nd Aug 2021, 10:15 am	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Bush DAC90a can't get tuning knob off That doesn't sound original. The tuning and volume knobs should be the same. The collar is a retaining clip on a push on knob from somewhere else. Judicious application of Plus Gas, gentle heat and brute force is likely to be needed. The knob's not right anyway, so..... __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

22nd Aug 2021, 10:25 am	#3
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,560	Re: Bush DAC90a can't get tuning knob off It looks to me like a 'Horseshoe' spring, made from spring steel. Others will hopefully confirm but I think you just have to prise it open at the gap shown in the second picture until the gap is wide enough to let the spring come off the shaft. Of course it may be rusted onto the shaft, which could complicate things a bit.

22nd Aug 2021, 10:33 am	#4
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Bush DAC90a can't get tuning knob off The knob would normally just pull off complete with the "D" clip. Lawrence.

22nd Aug 2021, 10:49 am	#5
slidertogrid Octode Join Date: Apr 2005 Location: Peterborough, Cambridgeshire, UK. Posts: 1,898	Re: Bush DAC90A can't get tuning knob off As Lawrence said the knob should just pull off. See if you can carefully ease the clip off the back of the knob using a long screwdriver through the hole. Then as suggested apply some release agent to the back of the knob you may be able to get it to run down the control shaft and into the back of the knob. Once it has had time to soak in wriggle the knob carefully and push and pull at the same time. It should give in. The clip is easily refitted once the knob is off. Before you refit the knobs apply a little grease or Petroleum Jelly to the control shafts this will make refitting and future removal easier. If you have one front knob held with a screw and one with a clip one of the knobs is wrong for the set. Only the later versions had knobs held with clips, earlier had screws. A picture of the set and knobs would help identify which knob is the wrong one for the set if that is the case. Rich. __________________ The rotation of the earth really makes my day... Last edited by slidertogrid; 22nd Aug 2021 at 10:57 am. Reason: correction and clarification

23rd Aug 2021, 9:50 pm	#6
Steve1952 Diode Join Date: Aug 2021 Location: Sheffield, South Yorkshire, UK. Posts: 7	Re: Bush DAC90A can't get tuning knob off Many thanks to all, will have a go if I understand the advice correctly. Yes the two knobs are different, different sizes, the tuning one looks original. Will let you know how I get on

25th Aug 2021, 12:52 am	#7
dj_Keet Triode Join Date: May 2017 Location: West Midlands, UK. Posts: 21	Re: Bush DAC90A can't get tuning knob off Yeah it does look like its on the wrong way round try using flat head screw driver through the hole push in a sliding motion (with the screwdriver still straight) against the area marked by the red arrow try not to use the hole as leverage as you will damage that area of the case if your not sure/confident put cardboard around the hole but a touch of force and a bit of technique will get it off take your time and think it through Attached Thumbnails

25th Aug 2021, 11:42 am	#8
Colin Boggis Pentode Join Date: Jun 2008 Location: Christchurch, Dorset, UK. Posts: 237	Re: Bush DAC90A can't get tuning knob off Plus gas on the shaft and leave radio face down so it soaks in - always worked for me. I also find a lever each side of the knob helps once the plus gas has had some time.

6th Sep 2021, 12:33 pm	#9
Steve1952 Diode Join Date: Aug 2021 Location: Sheffield, South Yorkshire, UK. Posts: 7	Re: Bush DAC90A can't get tuning knob off Thanks all especially DJ Keet, I used the plus gas and flathead screwdriver approach and it came off - turns out it was not a metal bush but part of the bakelite knob. Still I now have a chassis free and ready to replace the caps, living and learning in this great hobby.

6th Sep 2021, 5:14 pm	#10
Graham G3ZVT Dekatron Join Date: May 2010 Location: Greater Manchester, UK. Posts: 18,715	Re: Bush DAC90A can't get tuning knob off Surely the two knobs must have looked different, you even mention a Perspex collar on the wrong one. __________________ -- Graham. G3ZVT

7th Sep 2021, 3:24 pm	#12
Steve1952 Diode Join Date: Aug 2021 Location: Sheffield, South Yorkshire, UK. Posts: 7	Re: Bush DAC90A can't get tuning knob off Yes thanks to all I have got the service sheet and am aware of live chassis (potentially). Will be very careful when it comes to testing.

7th Sep 2021, 5:11 pm	#13
bobhowe Heptode Join Date: Jun 2005 Location: Sunderland, Tyne and Wear, UK. Posts: 661	Re: Bush DAC90A can't get tuning knob off Hi Steve please post some pictures of the set before & during replacing capacitors kind regards Bob

8th Sep 2021, 4:55 pm	#14
Radio Tech Nonode Join Date: Dec 2012 Location: Bocking, near Braintree, Essex, UK. Posts: 2,071	Re: Bush DAC90A can't get tuning knob off Steve If you want electrolytics you can get them from Jellyfish Audio at very reasonable prices Ken

8th Sep 2021, 7:38 pm	#15
Bob_Moss Pentode Join Date: Mar 2003 Location: Mansfield Woodhouse, Nottinghamshire, UK. Posts: 216	Re: Bush DAC90A can't get tuning knob off Does it need new electrolytics? My DAC10 is working fine on the original from 1952! __________________ I was so upset that I cried all the way to the chip shop.

8th Sep 2021, 9:24 pm	#16
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Bush DAC90A can't get tuning knob off Indeed. Electrolytics in Bush DAC90A's seem to be a cut above the rest. I've never had to replace a smoothing can in one. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

9th Sep 2021, 9:08 pm	#18
60 oldjohn Dekatron Join Date: Dec 2004 Location: East Yorkshire, UK. Posts: 3,987	Re: Bush DAC90A can't get tuning knob off After about 3 years of use, my restored DAC90 electrolytic caps failed. I wish I had changed it when I restored the radio, it would have saved a run around thinking it was an intermittent valve fault. John. __________________ My favourite text message "I'll be there in five minutes, if not read again"

9th Sep 2021, 11:44 pm	#20
60 oldjohn Dekatron Join Date: Dec 2004 Location: East Yorkshire, UK. Posts: 3,987	Re: Bush DAC90A can't get tuning knob off Hi Bob, I will check tomorrow. John. __________________ My favourite text message "I'll be there in five minutes, if not read again"