UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Closed Thread
 
Thread Tools
Old 13th Nov 2017, 2:10 pm   #1
sunthaiboy
Tetrode
 
Join Date: Jun 2011
Location: Crew Green, Powys, Wales, UK.
Posts: 54
Default Monster Pantry Transmitter

I have just acquired a very interesting and well built "Pantry Transmitter" from the deceased estate of an EX BBC Engineer (David Dunmall). It has taken some time to identify the function of all of the valves and the unusual tuning arrangements. It is a wonder to behold, especially when powered up. HT 1000V+, a pair of VR150's for screen stabilization of the twin 807's plus a VR105 for the driver stage. It must use a linear class of O/P stage as there is no high level modulation. It radiates at a touch under 4 MHz (Xtal derived), so into a dummy load only. Not quite sure of the function of the jam-jars, they don't improve the safety aspects!

David will be much missed, he was a real character and top notch engineer who has provided other lovely items that are on display at Criggion MW Radio Station.
Attached Thumbnails
Click image for larger version

Name:	20171111_165136_resized.jpg
Views:	380
Size:	62.5 KB
ID:	152197   Click image for larger version

Name:	20171111_165236_resized.jpg
Views:	313
Size:	32.6 KB
ID:	152198   Click image for larger version

Name:	20171111_165309_resized.jpg
Views:	319
Size:	50.8 KB
ID:	152199  
sunthaiboy is offline  
Old 13th Nov 2017, 2:56 pm   #2
Colin G8TMV
Tetrode
 
Join Date: Apr 2013
Location: Cambridge, Cambs. UK.
Posts: 71
Default Re: Monster Pantry Transmitter

CW or AM?

It may be that the crystal has drifted with age and it was originally intended for the 80m band (3.5 to 3.8MHz)
Colin G8TMV is offline  
Old 13th Nov 2017, 2:58 pm   #3
M0FYA Andy
Octode
 
Join Date: May 2007
Location: Preston, Lancashire, UK.
Posts: 1,612
Default Re: Monster Pantry Transmitter

'Pantry Transmitter'? That would reach every pantry in the UK!!!
Andy
M0FYA Andy is offline  
Old 13th Nov 2017, 3:36 pm   #4
paulsherwin
Moderator
 
paulsherwin's Avatar
 
Join Date: Jun 2003
Location: Oxford, UK
Posts: 17,101
Default Re: Monster Pantry Transmitter

Just to be clear, it is not permissible to discuss the operation of this transmitter for unlicensed broadcasting
paulsherwin is offline  
Old 13th Nov 2017, 4:12 pm   #5
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 6,516
Default Re: Monster Pantry Transmitter

I recognise the style of ceramic tuned-circuit former used in the output-stage: I've got an identical one here [I guess it's an Eddystone item: Raymart/G5NI in Birmingham were advertising them in the WWII-era RSGB Radio Handbook supplement].

Mine happily handles 400W PEP as the base-loading coil for a 40M-band 22-foot vertical.

Some 'pantry' transmitter!
G6Tanuki is offline  
Old 13th Nov 2017, 4:37 pm   #6
astral highway
Nonode
 
astral highway's Avatar
 
Join Date: Nov 2006
Location: London, UK.
Posts: 2,742
Default Re: Monster Pantry Transmitter

Wonderful work, really ingenious modular and open-plan construction . Love it!! Thanks for sharing this find

Why is this being described as a pantry-transmitter, though? Other than as a joke, I mean ... It clearly never was that and with forum posts often returning at the top of search results, it will lead to a lot of disappointed traffic!!
__________________
Al
astral highway is offline  
Old 13th Nov 2017, 6:53 pm   #7
sunthaiboy
Tetrode
 
Join Date: Jun 2011
Location: Crew Green, Powys, Wales, UK.
Posts: 54
Default Re: Monster Pantry Transmitter

Thank you for the reminder about unauthorised emissions and duly noted. Fortunately it is not yet illegal to own such "emitting devices" of which I have several much larger, although I will not hold my breath on this point.

Criggion MW Radio Station and the VLF site 50m away broadcast field strengths high enough to burnt out the tops of trees and support posts that held the ground counterpoints in place. The stray emissions from the pantry transmitter tank coils inside a blast proof building are suitably attenuated and don't even false trigger my cardiac pacemaker. The same cannot be said from modern switch mode PSU's which radiate wonderfully at LF through mains wiring, which makes a super antenna. Criggion LF/MW prior to de-commissioning had a Marconi HS51 (30KW) and as everybody in the know knows the VLF Tx had a custom built PA stage that fed 600KW at 250KV into the hill mounted antenna and was initially used in CW and as such modulated the main 11KV EAS before the 33KV upgrade.

I have not yet studied the Xtal in detail which sits in a tobacco tin on the lower deck. I doubt it has drifted that far off. I don't think David was a Amateur Radio man, so that's why it has "Pantry" classification. David did work at Daventry in the late 50's and went on to work in Ascension so probably knew a thing or to about emissions. The mode of operation is A3E. There is magic eye indicator which monitors the modulation levels (alas not visible in my photo). IP's are suitably low as there is a 3 tap band pass filter between the lower deck and the upper (PA stage).

I am currently building a much larger one with a similar layout.......
sunthaiboy is offline  
Old 13th Nov 2017, 7:10 pm   #8
m0cemdave
Heptode
 
Join Date: Feb 2009
Location: Bletchley, Buckinghamshire, UK.
Posts: 595
Default Re: Monster Pantry Transmitter

That is quite a work of art. A modern take on 1920's Amateur transmitter construction. I wonder if it was built for an exhibition display or an apprentice project?

4MHz is in a broadcast band but it should be easy to change the crystal and tuning to 3.615 or 3.625 kHz, the commonly used frequencies for licensed amateur band AM.

It looks like the 807's are a broadcast style push-pull final amplifier, should happily do about 30 watts carrier on AM in AB1 linear service, or rather more in Class B ...
m0cemdave is offline  
Old 13th Nov 2017, 7:12 pm   #9
sunthaiboy
Tetrode
 
Join Date: Jun 2011
Location: Crew Green, Powys, Wales, UK.
Posts: 54
Default Re: Monster Pantry Transmitter

A correction to my last. Rugby Radio Station used Marconi HS 51's a 30KW short-wave transmitter. Criggion MW/LF used HS 81's a 40KW LF transmitter. Anybody who has any historic information (or photo's) on Criggion, I am eager to receive it.
sunthaiboy is offline  
Old 14th Nov 2017, 1:03 am   #10
Skywave
Dekatron
 
Skywave's Avatar
 
Join Date: Jun 2006
Location: Chard, south Somerset, UK.
Posts: 6,053
Arrow Re: Monster Pantry Transmitter

Quote:
Originally Posted by sunthaiboy View Post
It must use a linear class of O/P stage as there is no high level modulation.
It might use (what is commonly called) series-gate modulation: a derivation of the protective clamp valve cct. design for the RFPA stage.

Al.
__________________
"Your idea is crazy! But the question is this: is it crazy enough . . . . to be true?" (Niels Bohr)
Skywave is offline  
Old 14th Nov 2017, 6:20 am   #11
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 10,908
Default Re: Monster Pantry Transmitter

Is it a transmitter per se? It could have been intended as a driver for a higher power stage. 4MHz is a broadcast band, and a pair of 807s isn't really enough for broadcasting.

It could be a test transmitter for antenna tuning.

it looks like a lash-up, and its purpose may be to try out a circuit design rather than to be a piece of operational equipment. It may be the precursor to a version on a rack-mount chassis.

An engineer in a transmitting station with a small maintenance bench and a junk box of gash bits and time on his hands might be thinking about doing better than some bit of unreliable kit and doing a bit of investigation.

A good puzzle.

David

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 14th Nov 2017, 10:08 am   #12
sunthaiboy
Tetrode
 
Join Date: Jun 2011
Location: Crew Green, Powys, Wales, UK.
Posts: 54
Default Re: Monster Pantry Transmitter

I think the lower section was all that was intended, using mostly very early (1930's) valves. I will generate a valve line up when I get the chance. I suspect the top (PA) section was the RF equivalent to a slug of nitrous oxide...... I hope to come across the circuit diagram at some point....in David's vast shed of electronics. The RGD radiogram(s) he had covered 4megs on SW. The XLR (balanced audio) I/P points to a way of getting near Hi-Fi AM broadcasts (1950's style), if you have no regards to bandwidth or how many channels you use. It's probably a purely academic build as it cannot be used (as has already been pointed out), but then buying or restoring a classic car and looking at it (never driving it), is in the same vain. Mind you, you could probably use such a transmitter in Ascension as you would need something a little more powerful to receive a QSL.......and who would ever stop you if you were the senior communications controller?

I like to collect HF Military transmitters and build LF/HF amongst other things, which I cannot use, so I am probably cut from the same cloth.....Selling my house and buying a derelict, vandalised Ex MW Radio Station with no power, water or sewerage, sitting on a flood plane for use as a radio shack probably confirms my madness.

Last edited by sunthaiboy; 14th Nov 2017 at 10:13 am. Reason: words missing "if you"
sunthaiboy is offline  
Old 14th Nov 2017, 11:07 am   #13
cmjones01
Octode
 
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 1,810
Default Re: Monster Pantry Transmitter

It looks quite recently built to me. The 'chassis' looks like a repurposed shoe rack, and look at the PCBs (or are they just bits of fibreglass board?) holding the valveholders on the lower deck. The fan wafting over the 807s on the top doesn't look too vintage, either.

It's a lovely thing, anyway.

Chris
__________________
What's going on in the workshop? http://martin-jones.com/
cmjones01 is offline  
Old 15th Nov 2017, 12:48 am   #14
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 12,483
Default Re: Monster Pantry Transmitter

That tobacco tin is just the icing on the cake, I reckon!
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline  
Old 15th Nov 2017, 9:46 am   #15
Colin G8TMV
Tetrode
 
Join Date: Apr 2013
Location: Cambridge, Cambs. UK.
Posts: 71
Default Re: Monster Pantry Transmitter

Tobacco tins can contain many things, for example:

http://www.tuckley.org/qmite/

73, Colin G8TMV
Colin G8TMV is offline  
Old 15th Nov 2017, 11:42 am   #16
HamishBoxer
Dekatron
 
HamishBoxer's Avatar
 
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 6,155
Default Re: Monster Pantry Transmitter

I think it is a 80m transmitter.Certainly a lethal looking beast.
__________________
G8JET BVWS Member and V.M.A.R.S
HamishBoxer is offline  
Old 16th Nov 2017, 2:46 pm   #17
Neil Purling
Octode
 
Join Date: Jul 2005
Location: Hull, East Yorkshire, UK.
Posts: 1,913
Default Re: Monster Pantry Transmitter

This beast ought to be tested in a screened workshop where output power & frequency can be accurately measured.
You said the o/p frequency was a touch under 4Mhz.
As 80M is or was 3.5-3.8 Mhz.. What frequency is the crystal marked as being?
The Shack is sacred territory to a radio amateur & something like this would have sat brooding on a high shelf. Nobody would have been allowed near it.
It is a very odd method of construction. One would expect a aluminium chassis inside a aluminium case to prevent any RF escaping from any place but the proper output.
Neil Purling is offline  
Old 16th Nov 2017, 3:17 pm   #18
astral highway
Nonode
 
astral highway's Avatar
 
Join Date: Nov 2006
Location: London, UK.
Posts: 2,742
Default Re: Monster Pantry Transmitter

Quote:
Originally Posted by Neil Purling View Post
It is a very odd method of construction. One would expect a aluminium chassis inside a aluminium case to prevent any RF escaping from any place but the proper output.
And fire!

It's possibly simply because the builder didn't have the capacity to work metal - either the tools or the skills. Just conjecture, but for example, I would find it difficult if not impossible to work a metal chassis here. I barely have enough metalworking training, and I certainly don't have either the tools or the space to do a good job.

For a prototype, certainly, it is far easier to attach the various sub-assemblies that we see dotted around there. Nothing that I see there would cause me any problems to construct, and I'm not in the elite club of forum master-craftsmen!
__________________
Al
astral highway is offline  
Old 17th Nov 2017, 11:27 am   #19
sunthaiboy
Tetrode
 
Join Date: Jun 2011
Location: Crew Green, Powys, Wales, UK.
Posts: 54
Default Re: Monster Pantry Transmitter

As can be seen from the frequency counter, my touch under 4MHz = -2.5KHz (ish), not in the 80m band, but I'm sure tunable with the existing coils/caps. The Racal 835 is old but the frequency displayed is accurate although not correctly gated (sync via a 3-polled rubidium standard). Ignore the spectrum analyser frequency counter, it has its own ideas. 2nd harmonics are 30dB down

I will look inside the tobacco box and let you know what frequency the Xtal is. I suspect 3.975 MHz. (Please note....terminated into a 30dB atten and then the dreg's into my spec anny at 50 ohms)
Attached Thumbnails
Click image for larger version

Name:	20171111_165157_resized.jpg
Views:	63
Size:	56.2 KB
ID:	152370   Click image for larger version

Name:	20171111_165224_resized.jpg
Views:	54
Size:	41.2 KB
ID:	152371  
sunthaiboy is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 2:11 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.