Magnificent crystal - UK Vintage Radio Repair and Restoration Discussion Forum

John_BS · 16th Mar 2012, 9:05 pm

Hows about we start a "Miss Silica" beauty pageant for quartz crystals?

Here's my entry: I know it was used in a medium-wave transmitter drive, and I strongly suspect it might have been employed as a high-stability carrier-reference crystal for one of a group of synchronised transmitters used in WW2 ("Group H", 1474kHz). It's 70mm diameter x 50mm tall, weighing in at 666g!

John

PS if anyone has any more information relating to this, I'd be most grateful

16th Mar 2012, 9:42 pm

Sex on a stick, super!

ITAM805 · 16th Mar 2012, 10:17 pm

Quite beautiful. Why am I reminded of a wheel bearing...

Alistair D · 16th Mar 2012, 10:34 pm

A co-axial crystal? I wonder if it was driven at higher power and the outer casing was used as a heatsink. Only surmising.

Al

16th Mar 2012, 11:12 pm

I think the crystal per se is in the (rather pretty) box.

John_BS · 16th Mar 2012, 11:53 pm

The actual quartz crystal is a square slab sat below the central stud: you can see the corners in the second photo. I think the gubbins below might be some kind of sophisticated support structure which holds the crystal under constant pressure irrespective of temperature changes etc.?

ronbryan · 17th Mar 2012, 12:07 am

There was one just like it on a stall next to the stage at the BVWS meeting at Harpenden a couple of weeks ago. It might have been Jon Weller's stall.

Ron

AVO_VCM163 · 17th Mar 2012, 1:11 am

This is, I believe a Post Office crystal type 6B.

It was used by the BBC to ensure frequency stability between the groups of stations. At the outset of hostilities in 1939 the long wave transmitter was switched off as this could have afforded navigational aid over long distances. By rearranging and synchronising the MW broadcast frequencies, this aid was inhibited.

This scheme had been devised by the BBC engineering staff well ahead of September 1939 and the PO crystal units were used to achieve the necessary frequency accuracy and stability.

The crystal is therefore of historic interest.
Roy

davidw · 17th Mar 2012, 9:39 am

Referred to here http://www.bbceng.info/Technical%20R...ott-drives.pdf paragraph 2 Wartime broadcasting.
A lovely looking bit of precision engineering.

John_BS · 17th Mar 2012, 4:57 pm

David:

That's an excellent article, and not one I'd managed to unearth. I did think, however, that the design was by Gouriet: he's got a Wiki entry

http://en.wikipedia.org/wiki/Geoffrey_G._Gouriet

Current attempts to measure the crystal parameters are proving tricky: it seems to have a resistance of 200 ohms @ 736.946kHz series-resonance (at room temperature), which confirms that these crystals were oven-operated. The static holder capacitance is about 11.5pF.

John

John_BS · 14th Jan 2015, 4:42 pm

Update:

Just found Chapter & Verse on the oscillator / drive: the BBC wrote one of their excellent Techical Instructions (this one is TT2) describing in great detail both the actual design and design philosophy. The drive occupied an entire 19 inch rack!

John

http://www.bbceng.info/ti/early/TT2_...0Equipment.pdf

16th Mar 2012, 9:05 pm	#1
John_BS Octode Join Date: Dec 2008 Location: Wincanton, Somerset, UK. Posts: 1,784	Magnificent crystal Hows about we start a "Miss Silica" beauty pageant for quartz crystals? Here's my entry: I know it was used in a medium-wave transmitter drive, and I strongly suspect it might have been employed as a high-stability carrier-reference crystal for one of a group of synchronised transmitters used in WW2 ("Group H", 1474kHz). It's 70mm diameter x 50mm tall, weighing in at 666g! John PS if anyone has any more information relating to this, I'd be most grateful Attached Thumbnails

16th Mar 2012, 9:42 pm	#2
Guest Guest Posts: n/a	Re: Magnificent crystal Sex on a stick, super!

16th Mar 2012, 10:17 pm	#3
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: Magnificent crystal Quite beautiful. Why am I reminded of a wheel bearing...

16th Mar 2012, 10:34 pm	#4
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: Magnificent crystal A co-axial crystal? I wonder if it was driven at higher power and the outer casing was used as a heatsink. Only surmising. Al __________________ I won't tell you how I discovered that.

16th Mar 2012, 11:12 pm	#5
Guest Guest Posts: n/a	Re: Magnificent crystal I think the crystal per se is in the (rather pretty) box.

16th Mar 2012, 11:53 pm	#6
John_BS Octode Join Date: Dec 2008 Location: Wincanton, Somerset, UK. Posts: 1,784	Re: Magnificent crystal The actual quartz crystal is a square slab sat below the central stud: you can see the corners in the second photo. I think the gubbins below might be some kind of sophisticated support structure which holds the crystal under constant pressure irrespective of temperature changes etc.?

17th Mar 2012, 12:07 am	#7
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Magnificent crystal There was one just like it on a stall next to the stage at the BVWS meeting at Harpenden a couple of weeks ago. It might have been Jon Weller's stall. Ron

17th Mar 2012, 1:11 am	#8
AVO_VCM163 Retired Dormant Member Join Date: Mar 2008 Location: Hampshire, UK. Posts: 297	Re: Magnificent crystal This is, I believe a Post Office crystal type 6B. It was used by the BBC to ensure frequency stability between the groups of stations. At the outset of hostilities in 1939 the long wave transmitter was switched off as this could have afforded navigational aid over long distances. By rearranging and synchronising the MW broadcast frequencies, this aid was inhibited. This scheme had been devised by the BBC engineering staff well ahead of September 1939 and the PO crystal units were used to achieve the necessary frequency accuracy and stability. The crystal is therefore of historic interest. Roy

17th Mar 2012, 9:39 am	#9
davidw Heptode Join Date: Sep 2006 Location: Woodbridge, Suffolk, UK. Posts: 643	Re: Magnificent crystal Referred to here http://www.bbceng.info/Technical%20R...ott-drives.pdf paragraph 2 Wartime broadcasting. A lovely looking bit of precision engineering. __________________ Dave G1AGK. My perception is my reality!

17th Mar 2012, 4:57 pm	#10
John_BS Octode Join Date: Dec 2008 Location: Wincanton, Somerset, UK. Posts: 1,784	Re: Magnificent crystal David: That's an excellent article, and not one I'd managed to unearth. I did think, however, that the design was by Gouriet: he's got a Wiki entry http://en.wikipedia.org/wiki/Geoffrey_G._Gouriet Current attempts to measure the crystal parameters are proving tricky: it seems to have a resistance of 200 ohms @ 736.946kHz series-resonance (at room temperature), which confirms that these crystals were oven-operated. The static holder capacitance is about 11.5pF. John

14th Jan 2015, 4:42 pm	#11
John_BS Octode Join Date: Dec 2008 Location: Wincanton, Somerset, UK. Posts: 1,784	Re: Magnificent crystal Update: Just found Chapter & Verse on the oscillator / drive: the BBC wrote one of their excellent Techical Instructions (this one is TT2) describing in great detail both the actual design and design philosophy. The drive occupied an entire 19 inch rack! John http://www.bbceng.info/ti/early/TT2_...0Equipment.pdf