Bush TR90C Knob Removal? - UK Vintage Radio Repair and Restoration Discussion Forum

RadioRevival · 23rd Sep 2021, 4:28 pm

Hi All,
Have bought a Bush TR90C which I hope to restore, however, I'm struggling to remove the knobs to in turn remove the chassis. I cannot see any screws to remove the knobs and pulling gently is not doing anything...
Thanks

Paul_RK · 23rd Sep 2021, 6:42 pm

I've checked a current eBay listing for spare TR90 knobs which provides a clear photo confirming my memory that they're push-on types with the usual sort of clip. Probably not much for it, then, than to pull harder - the usual trick, at the risk of teaching granny to suck eggs, is to insert the edge of a piece of thin but strong cloth between knob and panel, going round the spindle about a turn and a half if possible, then bunch up the cloth and pull on that.

Paul

RadioRevival · 23rd Sep 2021, 11:18 pm

Thank you very much for that response! Unfortunately even with pulling harder (I was pulling as hard as I possible could!) they are still not budging...
I'm happy to upload an image of it if that helps?

crackle · 24th Sep 2021, 7:40 am

You don't need to remove the knobs to take the chassis out of the case.

Mike

RadioRevival · 24th Sep 2021, 8:14 am

Quote:

Originally Posted by crackle

You don't need to remove the knobs to take the chassis out of the case.

Mike

Sounds good I'll have a go at doing that!
What screws do I need to remove to loosen the chassis?

Nuvistor · 24th Sep 2021, 10:13 am

The service manual, available from the link at the top of the page states remove the knobs.
Note there are a few versions, slightly different manuals.

RadioRevival · 24th Sep 2021, 12:11 pm

Quote:

Originally Posted by Nuvistor

The service manual, available from the link at the top of the page states remove the knobs.
Note there are a few versions, slightly different manuals.

Ah brilliant! I've honestly tried pulling them really hard and the method used above with no luck... they still are firmly attached and not budging...

crackle · 24th Sep 2021, 12:36 pm

Quote:

Originally Posted by RadioRevivalism

Quote:

Originally Posted by crackle

You don't need to remove the knobs to take the chassis out of the case.

Mike

Sounds good I'll have a go at doing that!
What screws do I need to remove to loosen the chassis?

The big ones on the front and possibly on the back of the case.
Mike

Nuvistor · 24th Sep 2021, 1:26 pm

Hi Mike,
I am confused, nothing unusual, does the front and rear cabinet come away leaving the scale and knobs in place?

RadioRevival · 24th Sep 2021, 1:31 pm

As far as I can see there is only one screw on the external casing of the radio which opens up the top half. There doesn't appear to be any other ones?
As mentioned above the screws still don't budge... would any photos be of help?

Nuvistor · 24th Sep 2021, 1:40 pm

Photos may help, worth posting.

RadioRevival · 24th Sep 2021, 2:27 pm

Hope these help

Paul_RK · 24th Sep 2021, 3:01 pm

I've had this model in the past but don't have one now. Looking at a photo in the service manual, though, it appears that the two nuts mentioned in the post 6 attached image are near the top of the chassis - I think part of one is just visible above the tuning capacitor in your first photo, you may need a long spinner to turn it, and the other is to the right of the volume control spindle. The screw also mentioned looks to be at the bottom of the chassis, between an AF117 transistor and the lowest positioned IF transformer. According to the manual you do need to get the knobs off too, I'm puzzled why they're putting up so much resistance as it doesn't look as though they could be rusted on: then to fully remove the chassis the leads to speaker and earphone socket have to be unsoldered.

RadioRevival · 24th Sep 2021, 5:22 pm

All good!
I'm puzzled too? There does appear to be a light greenish tint on both of them (copper alloy corrosion?)
Would a very tiny amount of WD40 be recommended on it?
I'm determined to get them off!

Paul_RK · 24th Sep 2021, 6:43 pm

Couldn't do any harm if it doesn't get anywhere else, I think I'd make sure of that by spraying a drop on to the end of a screwdriver - or using a drop of penetrating oil the same way, or someone here may know something still more effective - then applying the screwdriver to the knob shaft / base of knob so the lubricant runs on and, with luck, in. Repeat once or twice if the amount seems minuscule the first time, leave it a while then give the knobs another go. Does seem very bad luck that both of them are proving really stubborn.

Nuvistor · 24th Sep 2021, 10:09 pm

Just to be sure, have you checked that grub screws covered with cream coloured wax are not holding the knobs on.
Even if there aren’t any I would rather ask to be sure.

Paul_RK · 24th Sep 2021, 10:57 pm

It did cross my mind that different knobs could have been substituted in the past, but a Google search for "TR90C knobs" leads directly to examples that can be viewed from above and below, they're the type I remember my own TR90Cs having, and those in the photos above are distinctly the same. That, and I don't think I've ever seen a battery transistor portable with grub screw holes filled with wax.

Paul

23rd Sep 2021, 4:28 pm	#1
RadioRevival Triode Join Date: Aug 2021 Location: Newcastle-upon-Tyne, Tyne and Wear, UK. Posts: 27	Bush TR90C Knob Removal? Hi All, Have bought a Bush TR90C which I hope to restore, however, I'm struggling to remove the knobs to in turn remove the chassis. I cannot see any screws to remove the knobs and pulling gently is not doing anything... Thanks

23rd Sep 2021, 6:42 pm	#2
Paul_RK Dekatron Join Date: Nov 2003 Location: Fakenham, Norfolk, UK. Posts: 4,255	Re: Bush TR90C Knob Removal? I've checked a current eBay listing for spare TR90 knobs which provides a clear photo confirming my memory that they're push-on types with the usual sort of clip. Probably not much for it, then, than to pull harder - the usual trick, at the risk of teaching granny to suck eggs, is to insert the edge of a piece of thin but strong cloth between knob and panel, going round the spindle about a turn and a half if possible, then bunch up the cloth and pull on that. Paul

23rd Sep 2021, 11:18 pm	#3
RadioRevival Triode Join Date: Aug 2021 Location: Newcastle-upon-Tyne, Tyne and Wear, UK. Posts: 27	Re: Bush TR90C Knob Removal? Thank you very much for that response! Unfortunately even with pulling harder (I was pulling as hard as I possible could!) they are still not budging... I'm happy to upload an image of it if that helps?

24th Sep 2021, 7:40 am	#4
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Bush TR90C Knob Removal? You don't need to remove the knobs to take the chassis out of the case. Mike

24th Sep 2021, 10:13 am	#6
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Bush TR90C Knob Removal? The service manual, available from the link at the top of the page states remove the knobs. Note there are a few versions, slightly different manuals. Attached Thumbnails __________________ Frank

24th Sep 2021, 1:26 pm	#9
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Bush TR90C Knob Removal? Hi Mike, I am confused, nothing unusual, does the front and rear cabinet come away leaving the scale and knobs in place? __________________ Frank

24th Sep 2021, 1:31 pm	#10
RadioRevival Triode Join Date: Aug 2021 Location: Newcastle-upon-Tyne, Tyne and Wear, UK. Posts: 27	Re: Bush TR90C Knob Removal? As far as I can see there is only one screw on the external casing of the radio which opens up the top half. There doesn't appear to be any other ones? As mentioned above the screws still don't budge... would any photos be of help?

24th Sep 2021, 1:40 pm	#11
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Bush TR90C Knob Removal? Photos may help, worth posting. __________________ Frank

24th Sep 2021, 2:27 pm	#12
RadioRevival Triode Join Date: Aug 2021 Location: Newcastle-upon-Tyne, Tyne and Wear, UK. Posts: 27	Re: Bush TR90C Knob Removal? Hope these help Attached Thumbnails

24th Sep 2021, 3:01 pm	#13
Paul_RK Dekatron Join Date: Nov 2003 Location: Fakenham, Norfolk, UK. Posts: 4,255	Re: Bush TR90C Knob Removal? I've had this model in the past but don't have one now. Looking at a photo in the service manual, though, it appears that the two nuts mentioned in the post 6 attached image are near the top of the chassis - I think part of one is just visible above the tuning capacitor in your first photo, you may need a long spinner to turn it, and the other is to the right of the volume control spindle. The screw also mentioned looks to be at the bottom of the chassis, between an AF117 transistor and the lowest positioned IF transformer. According to the manual you do need to get the knobs off too, I'm puzzled why they're putting up so much resistance as it doesn't look as though they could be rusted on: then to fully remove the chassis the leads to speaker and earphone socket have to be unsoldered.

24th Sep 2021, 5:22 pm	#14
RadioRevival Triode Join Date: Aug 2021 Location: Newcastle-upon-Tyne, Tyne and Wear, UK. Posts: 27	Re: Bush TR90C Knob Removal? All good! I'm puzzled too? There does appear to be a light greenish tint on both of them (copper alloy corrosion?) Would a very tiny amount of WD40 be recommended on it? I'm determined to get them off!

24th Sep 2021, 6:43 pm	#15
Paul_RK Dekatron Join Date: Nov 2003 Location: Fakenham, Norfolk, UK. Posts: 4,255	Re: Bush TR90C Knob Removal? Couldn't do any harm if it doesn't get anywhere else, I think I'd make sure of that by spraying a drop on to the end of a screwdriver - or using a drop of penetrating oil the same way, or someone here may know something still more effective - then applying the screwdriver to the knob shaft / base of knob so the lubricant runs on and, with luck, in. Repeat once or twice if the amount seems minuscule the first time, leave it a while then give the knobs another go. Does seem very bad luck that both of them are proving really stubborn.

24th Sep 2021, 10:09 pm	#16
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Bush TR90C Knob Removal? Just to be sure, have you checked that grub screws covered with cream coloured wax are not holding the knobs on. Even if there aren’t any I would rather ask to be sure. __________________ Frank

24th Sep 2021, 10:57 pm	#17
Paul_RK Dekatron Join Date: Nov 2003 Location: Fakenham, Norfolk, UK. Posts: 4,255	Re: Bush TR90C Knob Removal? It did cross my mind that different knobs could have been substituted in the past, but a Google search for "TR90C knobs" leads directly to examples that can be viewed from above and below, they're the type I remember my own TR90Cs having, and those in the photos above are distinctly the same. That, and I don't think I've ever seen a battery transistor portable with grub screw holes filled with wax. Paul