BTH crystal Sets info wanted - UK Vintage Radio Repair and Restoration Discussion Forum

n_r_muir · 4th Feb 2019, 2:55 pm

Hi,

I have a BTH "Bijou" crystal set and another BTH one with the dual crystal set up. The "plastic" covers for the Cat's whisker on both these sets are heavily discolored.

I think I might just have discovered source of plastic tubing that might be a suitable replacements for these.

At the moment I am 6.000 miles away from these sets so could someone help me out with the dimensions of these covers please.

Dimensions in inches please.

Tube length,

Tube outside diameter,

Wall thickness of the tube, or the internal diameter of the tube.

Any help would be much appreciated.

Thanks Ross

hilitevr · 4th Feb 2019, 6:05 pm

Hi, Ross

I have the large BTH with doal crystals, dimentions as follows in inches.

Length 1.64"
Inside Diameter 1.76"
Outside Diameter 1.78"
Thickness 0.02"

Hope this helps.

60 oldjohn · 4th Feb 2019, 8:58 pm

Hi Ross, I will stick my neck out and say the BTH Bijou Type C form BB is a fairly rare set compared to the BTH Bijou Type C form B. The difference being the enclosed detector. So if anyone has one with an enclosed detector don't think some one else will measure theirs.
Are the enclosures actually some sort of plastic? I would have thought they were originally made of glass.

John.

n_r_muir · 5th Feb 2019, 7:46 am

Hi Trevor, thanks for the information regarding the twin crystal holder dimensions

Hi, 60 oldjohn The ones I have are definitely not glass, they are some type of plastic which has turned brown over the years.

Ross

Dave757 · 5th Feb 2019, 11:37 pm

Quote:

Originally Posted by hilitevr

Hi, Ross

I have the large BTH with doal crystals, dimentions as follows in inches.

Length 1.64"
Inside Diameter 1.76"
Outside Diameter 1.78"
Thickness 0.02"

Hope this helps.

Hi

Is not the thickness therefore 0.01"?

Kind regards
Dave

hilitevr · 6th Feb 2019, 11:45 am

Your probably correct, but I measured the thickness with micrometer and it said .02".

Dave757 · 6th Feb 2019, 11:52 am

Quote:

Originally Posted by hilitevr

Your probably correct, but I measured the thickness with micrometer and it said .02".

Hi,

Thinking about it, 20 thou (2/3 of a typical spark plug gap) does
sound much more realistic.

Kind regards
Dave

Paul_RK · 6th Feb 2019, 12:02 pm

Quote:

Originally Posted by 60 oldjohn

Are the enclosures actually some sort of plastic? I would have thought they were originally made of glass.

John.

Celluloid on my Type C Form A, well yellowed and a bit warped with the years but I'm not tempted to change it. I agree about the Bijou, it seems much more commonly found in its open detector form.

Paul

60 oldjohn · 6th Feb 2019, 5:11 pm

Quote:

Originally Posted by Dave757

Quote:

Originally Posted by hilitevr

Hi, Ross

I have the large BTH with doal crystals, dimentions as follows in inches.

Length 1.64"
Inside Diameter 1.76"
Outside Diameter 1.78"
Thickness 0.02"

Hope this helps.

Hi

Is not the thickness therefore 0.01"?

Kind regards
Dave

I agree with Dave, the maths don't add up. Maybe the tube is deformed, giving a misleading outer or inner measurement. Anyway its nice that someone has helped the OP.
If the OP is unable to get the right thickness which is the critical measurement ID, OD or is it both ?

John.

David G4EBT · 6th Feb 2019, 7:52 pm

If the O.D is 1.78" and the measured wall thickness is .02", the I.D. must be 1.78" less .04" = 1.74". A wall thickness of just 20 thou suggests that it's celluloid, (mainly nitrocellulose) which is unstable and distorts and discolours with age. As it's highly flammable it was replaced as film stock with acetate decades ago. I guess nowadays, to replace the tubes would call for clear acrylic ('Perspex'). 1.78" equates to 45.2mm diameter. It's widely available in 45mm OD with a wall thickness of 2mm, so 41mm I.D. You end up being caught between a rock and a hard place - either a length of at least 1 to 2 Metres at a reasonable price, but plus P&P, or a short length (EG 300mm), more expensive but inc post. EG:

45mm OD, 41MM ID (hence, 2mm wall thickness).

2m length £14.88 inc VAT. Will cut to length (up to ten cuts free) plus post:

https://www.theplasticshop.co.uk/acr...o-60mm-od.html

12” length 45/41mm £13.13 post free.

https://www.ebay.co.uk/itm/CLEAR-ACR...-/360795949871

Hope that might help a bit.

Paul_RK · 6th Feb 2019, 8:10 pm

Quote:

Originally Posted by 60 oldjohn

If the OP is unable to get the right thickness which is the critical measurement ID, OD or is it both ?

John.

I think only the inner dimension matters much - each end plate is flat but for a slightly raised circle which positions the tube.

Paul

n_r_muir · 7th Feb 2019, 1:01 pm

Thanks everyone for your help, especially David for the info on UK sources.
I have bought a 2 foot length of Perspex tube for $10 which will fit easily into my suitcase.

Thanks

Ross

4th Feb 2019, 2:55 pm	#1
n_r_muir Hexode Join Date: Jul 2007 Location: Edinburgh, UK. Posts: 344	BTH crystal Sets info wanted Hi, I have a BTH "Bijou" crystal set and another BTH one with the dual crystal set up. The "plastic" covers for the Cat's whisker on both these sets are heavily discolored. I think I might just have discovered source of plastic tubing that might be a suitable replacements for these. At the moment I am 6.000 miles away from these sets so could someone help me out with the dimensions of these covers please. Dimensions in inches please. Tube length, Tube outside diameter, Wall thickness of the tube, or the internal diameter of the tube. Any help would be much appreciated. Thanks Ross

4th Feb 2019, 6:05 pm	#2
hilitevr Pentode Join Date: Jul 2006 Location: Sidcup, Greater London, UK. Posts: 122	Re: BTH crystal Sets info wanted Hi, Ross I have the large BTH with doal crystals, dimentions as follows in inches. Length 1.64" Inside Diameter 1.76" Outside Diameter 1.78" Thickness 0.02" Hope this helps. __________________ Regards Trevor BVWS member

4th Feb 2019, 8:58 pm	#3
60 oldjohn Dekatron Join Date: Dec 2004 Location: East Yorkshire, UK. Posts: 3,988	Re: BTH crystal Sets info wanted Hi Ross, I will stick my neck out and say the BTH Bijou Type C form BB is a fairly rare set compared to the BTH Bijou Type C form B. The difference being the enclosed detector. So if anyone has one with an enclosed detector don't think some one else will measure theirs. Are the enclosures actually some sort of plastic? I would have thought they were originally made of glass. John.

5th Feb 2019, 7:46 am	#4
n_r_muir Hexode Join Date: Jul 2007 Location: Edinburgh, UK. Posts: 344	Re: BTH crystal Sets info wanted Hi Trevor, thanks for the information regarding the twin crystal holder dimensions Hi, 60 oldjohn The ones I have are definitely not glass, they are some type of plastic which has turned brown over the years. Ross

6th Feb 2019, 11:45 am	#6
hilitevr Pentode Join Date: Jul 2006 Location: Sidcup, Greater London, UK. Posts: 122	Re: BTH crystal Sets info wanted Your probably correct, but I measured the thickness with micrometer and it said .02". __________________ Regards Trevor BVWS member

6th Feb 2019, 7:52 pm	#10
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,763	Re: BTH crystal Sets info wanted If the O.D is 1.78" and the measured wall thickness is .02", the I.D. must be 1.78" less .04" = 1.74". A wall thickness of just 20 thou suggests that it's celluloid, (mainly nitrocellulose) which is unstable and distorts and discolours with age. As it's highly flammable it was replaced as film stock with acetate decades ago. I guess nowadays, to replace the tubes would call for clear acrylic ('Perspex'). 1.78" equates to 45.2mm diameter. It's widely available in 45mm OD with a wall thickness of 2mm, so 41mm I.D. You end up being caught between a rock and a hard place - either a length of at least 1 to 2 Metres at a reasonable price, but plus P&P, or a short length (EG 300mm), more expensive but inc post. EG: 45mm OD, 41MM ID (hence, 2mm wall thickness). 2m length £14.88 inc VAT. Will cut to length (up to ten cuts free) plus post: https://www.theplasticshop.co.uk/acr...o-60mm-od.html 12” length 45/41mm £13.13 post free. https://www.ebay.co.uk/itm/CLEAR-ACR...-/360795949871 Hope that might help a bit. __________________ David. BVWS Member. G-QRP Club member 1339.

7th Feb 2019, 1:01 pm	#12
n_r_muir Hexode Join Date: Jul 2007 Location: Edinburgh, UK. Posts: 344	Re: BTH crystal Sets info wanted Thanks everyone for your help, especially David for the info on UK sources. I have bought a 2 foot length of Perspex tube for $10 which will fit easily into my suitcase. Thanks Ross