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Wartime GEC ? Miniscope





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 GEC Miniscope

Made for ultra portability fits in an 8x12x 2.5 inch case when the thyratron and vibrator are removed from the chassis and stowed near the hinge. What war time use was there for such a small 'scope, with in-the-field 12V supply capability? Thinking of ultra - almost as though it was for SOE use, repairing behind the lines radio transmitters. War finish presumably means the off white enamel rather than black crackle finish. Does war finish mean whatever remnant pots of paint were around got mixed in together ? Plate on the brown casing lid
Miniscope
Miniature C/R oscilloscope
Pattern No 53259
Stencilled labels on the case are
R.L.4 and No 1 Presumably somewhere would have info on the pattern number. Even using "-dr who" googling does not find anything on Miniscope or that pattern number, 6K25 thyratron , 9 pin VR91, 10E/92 and 9 pin CRT VCR 522, 10E/787, Design Inspected CRT 4 (shattered probably when the shoulder carrying strap broke and corner brace broke off and split occured in the "suitcase" ) no other valves, also Masteradio G650 12V vibrator, military trident symbol in a couple of places , after an A on the VR91 and before a Z on the CRT side panels and one knob missing, someone has crudely bodged in a pot where a pin had broken off the Sync pot.
 GEC Miniscope

 GEC Miniscope

 GEC Miniscope
The skew aluminium cased pot is one of the things a previous owner had done probably in 60s or 70s . He probably added the 2 Si diodes then. The genuine pots are very small and the original one, still in place is broken, functionally replaced with that one , presumably the smallest he could find but too large to fit in place. He must have given up when the carrying strap broke and CRT cracked.
 GEC Miniscope
specs etc on hinge-down, prop-up plate
 GEC Miniscope

 GEC Miniscope

 GEC Miniscope

VR91 would seem a pentode http://www.radiomuseum.org/tubes/tube_vr91.html CRT some info www.radiomuseum.org/tubes/tube_vcr522.html apparently equivalent to CV1522 or related E4103/B/4 / CV320 / CV967 / CV335
I picked it up at a "silent key" disposal at a carboot sale. Inheritors had no knowldege about it. The valves etc may not be what was originally in there of course.
http://www.thevalvepage.com/testeq/gec/miniscope/miniscope.htm GEC one looks very similar externally, especially the prop plate The chassis dimensions are similar, this one 8 x 6.5 x 2.25 inches but valves and internals look earlier and no built in 12V option.
I downloaded the GEC schematic from http://www.thevalvepage.com/ but substantially different, except 4V and 6.3V heaters agree with VCR 522 and VR91, and the aircraft power supply option, so transformer may be similar.
Of course a broken CRT makes it easy to determine pinning. As broke unpowered the heater is still there, all 4 X,Y plates exposed and A3 so just leaves A2 and grid undetermined without destroying the envelope more. 155mm long, 1.5 in diam, and 7 out of 9 pins agrees with GEC E4103/B/4 with 1.1KV pda and 4V heater. And I have the pinning for the 6K25 and pentode. I have scanned in the board edges, as is with, and add interconnect labels , and multi-photo before undoing and trying to unravel the schematic while trying to find out about its likely in service use. The black cable extending out may not be original , DC supply.
I'd thought of contacting Kew ,PRO, national archives, but the Imperial War Museum makes sense as well. I'm a bit concerned with the use of the word pattern before the number 53259 in that it may relate to the "samsonite" case rather than scope although etched on to the metal plate refering to C/R oscilloscope. Perhaps there is a GEC archive somewhere other than Kew and the war museum.
No laboratory equipment would be made deliberately too small, requiring the removal of parts before placing in a protective housing. This was made to be ultra-portable, the smallest possible carrying case for discretion, airbourne use, or covert reason, I would suggest. Routine military equiptment is not made for the effete to carry around. Come to think of it wartime airbourne radios etc were not made deliberately light or compact. There was no original probes just some home-brew croc-lead things from the 60s or 70s , of much the same date as the bodged pot. Tested the 6K25 and the VR91 as EF50 settings and ok Testing a Thyratron. New one to me. 6K25 tested on an Avo CT160. Data for 30mA, 100V settings is , under mA/V column 2K ohm. neg grid voltage is undoubtably 4.1V, above that and meter swings below 0 and below 4.1V it swings over fsd. What is the 2K figure, do you have to take and graph out values around the "flash over" point ? I should say I started with setting of 40V then 60, then 75, 90 and finally 100V. Didn't note it but the -4.1V trigger voltage appeared at 60V , I think, and hardly changed. Just for the archives - as thyratron testing is not very kind to test-sets. I could not decide whether to start with lower current setting , but decided to set at the data criterion of 30mA and vary the anode volts. Switching to test and back as quick as possible to save the meter movement.
An email response from the guy at the valvepage site Yes that GEC is internally quite different to mine, and the use of bigger valves suggests an earlier design. The catch on that case looks very un-military-like as it and the case look so fragile. Maybe the crt broke when the chap in the aircraft got fed up and threw the darn thing out of the aircraft - the shaped controls on mine are still fiddly, yet the controls on the front of yours would I think be impossible to use with gloves on ! Also, where on earth do the valves go ? There doesn't seem to be any space, and I also can't spot any ht rectifier. I've seen quite a few of the GEC scopes like mine but not encountered any like yours before so I can't really add any information. Perhaps you could let me know if you find out more. Also, could I scrounge a couple of pics for my website ? Just a small pic of the front and one of the side, just enough so if a visitor sees my page they'll think "that looks just like mine" and they can then follow a link to your page.
END

I found 2 unlabelled black painted glass Si diodes of the 70s , not original for the added reason that 2 solder points were to wires and not tag board tags. Se rectifiers been around since earlier than 1933 but where was there space for any. Even if the vibrator was originally synchronous type , would it be possible to use such a vibrator to rectifierless feed mains in , via the transformer to such a vibrator, to allow 12V and 180/230V ac use? The mains cable seems to go to the output side of the vibrator, with no mechanical interlock to lockout other than someone remembering to unplug the vibrator, or does it matter ?. For the 4 pin vibrator, that came with it, gum on Masteradio label is bad and original un-re-badged label under is Mallory G650 Indianapolis Ind Made in USA Anyone have specs for the G650 ? or even whether synchronous types could be in only 4 pin format Anyone care to decode the knob legends
Vc,Vf,F,C,A,S
Vc was on the 6 way timebase switch, I am assuming it was moved from the least used or easiest to turn without a knob Gueses S for Sync, A for attenuation, F for Fine, C for Coarse , Vf for focus but Vc ?
Someone else's guess Vc is cathode voltage - probably the brilliance control Agree Vf for focus. F could be (timebase) Frequency?
This is the preliminary node map for the scope http://www.diverse.4mg.com/miniscope_node_map2.jpg Scanner does not like full A4 useage. Letters E, K and C along the top 2 tag boards running vertical, numbered from bottom S (16) and R (16) then P (11) and Q (11), colours match major component pinning numbers to node numbers. ground lines not added and some components around the front panel pots, switches and 2 3.5 mm i/p sockets (feintly marked as worn off , maybe read INVERT and GAIN not readable on the earlier pics) not transcribed. Some unplaced loose wires and 2 caps covered in laquered cloth so left in place as unknown values and puffy cap values are assumed , ignoring the green and yellow "multiplier" dots that are probably temp or tolerance values. polarised caps marked with a - . QQ is unkown function as knob missing and other Q pot functions as letters on the knobs, as found. There are bound to be still more errors, I've just noticed the 22K resistor apparently going to doubley N/C K6, maybe used as a tag. M & VIB wiring and power select shorting plug arrangement is probably much like the valvepage schematic including the vib, for the later miniscope. Power cable wiring Y,R,B is the same in both cases Next intermediary schematic is placing the valves etc into the optimum coloured nodes and un-knotting to a certain extent. Nothing powered up so far, a few volts from variac may resolve a few problems, and valves not tested yet. Primary of M is probably ok , selecting 230V is 129 ohm and 180V is 75 ohm The socket for the vib is badly fixed , one bolt is skew as it interferes with something else on the chassis. So maybe not original vib type but I don't see how a synchronous type could have made it Si diode rectifierless. What were the smallest Se rectifiers available in the 1940s for this sort of application ? As a circuit guide , 6K25 thyratron used in a TV frame oscillator Ultra model V815 of 1953 and EF50 pentode in 1953 Beethoven A1188 and small CRT in Mullard 6800 with ECR36 , Cossor 1039M with 23D and the later GEC miniscope. What about small Selenium rectifiers that could have fitted in the space either side of the pentode. I have a data book , printed in 1933 Westinghouse "the all-metal way" metal rectifiers , how to build High Tension battery eliminators and battery chargers. A 300V , 60mA Westinghouse one in 1933 was about 3x3x5 inches, no mention of Selenium, trade secret then ?. The pic http://www.diverse.4mg.com/Se_R.jpg Shows on the right a disassemled one from a 1959 Dansette, one of the two , 8 layer blocks is shown, removed, on end near the ruler (0.1 inch) Single element rectifier Siemens lazy S logo Made in Germany E 250c50 Kc 0.6e 11/16 1979 Siemens databook and E250C50 were still listed, rating 200V, 20mA The book page is from 1967 catalogue. Would the English military have had access to these size and sort of ratings, of the later rectifiers, in 1940s, they could have been heatsinked. I'm trying to find if any sort of (presumably) non-thermionic rectifier could fit in a space 95x70x12 mm in the 1940s. 2 Selenium rectifier trade names of the right sort of specs, of the early 1950s, were Westinghouse Westalite and STC SenTerCel for which the earliest reference I've found is 1951. according to ebay http://i16.ebayimg.com/05/i/000/88/e0/2dc0_2.JPG is a WAR DEPT!! WESTALITE RECTIFIER,NORTON, TRIUMPH, MATCHLESS etc... Straight from the War Department. Genuine NOS Military parts removed from 'jungle paper' Rectifier Made in England By Westinghouse Brake & Signal Co Ltd. Pat 620102 & others. Cat No. 2L 985. Positive Case. 98mm x 98mm x 12mm. When did "war dept" cease ? http://www.wikipatents.com/gb/0620102.html for UK patent 620102, 1947, is about rectifier construction/gaskets but refers to "well known selenium type" So compact , presumably low V, high A for motorcycle use in war time but what about high V, low A , compact multiplate rectifier in early 1940s ?
Another example of early miniaturisation , from Germany The Minifon P55 wire recorder with 5 hours record possibility, uses 2x DF67 and a DL67 apparently "Walkman" Size 1 9/16 x 3 15/16 x 6 11/16 inches , 2 lbs Scanned in image from the 1956 version of the book in the heading, with preceeding lines inserted over the top, correction 3 batteries http://www.diverse.4mg.com/minifon.jpg
preliminary schematic
 GEC Miniscope

Will have to check the top left HT rail cap wiring, noticed since plotting out. Anyone know of an E4103/B/4 or compatible CRT around the UK ? I quite often see similar at radio rallies. Will make do with a 2 inch one , Telefunken DG 7 32 strangely maybe the same as Mullard DG7 32, poking out the front From someone at the Defence Electronics History Society ,Shrivenham , 180v 500Hz is a standard Navy power cct for Navy not the RAF.
Update August 2009
Ron in Lancashire picked up a complete one at a radio rally. One of the side panels has the circuit diagram and parts list etched on, of which he sent me a pic
 GEC Miniscope
negative version which is clearer to read. Includes 2 Selenium rod type HT rectifiers "H55" ? (no info found on H55, H10 were metal rectifiers made by Westinghouse probably no more than 100V rating, available about 1943 to 1947 ) , one of them shown here
 GEC Miniscope
His also has the brown carrying case. From his researches "it (this miniscope) was used in the Royal Navy/ Fleet Air Arm in connection with tone modulation frequency tests on sonobuoys that were dropped and then monitored by Fairey Gannet aircraft. This was an anti submarine operation until superseded by helicopters and their dipping listening devices." From his contacting the journal, there will be a future item published in Practical Wireless (sometime after September 2009).

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