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Old 14th Oct 2019, 7:32 pm   #1
David Simpson
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Default Roberts Valve Tester

Folks,
Does anyone know anything about a "Roberts Valve & Circuit Analyser" made by LONDON - SOUND - LABS - LTD? My guess is post-war 40's or early 50's. Internal battery = flat 4.5V cycle torch battery. No mains supply, and just a lid with 7 pairs of 1" clips. Two 500uA fsd meters for amps, volts & ohms. Came with a lead with an IO plug one end & a strange 9 pin plug with a thin metal spade spigot at the other end. Nice clam-shell case, but not as sturdy as a CT160's.

Regards, David
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Old 14th Oct 2019, 7:54 pm   #2
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Default Re: Roberts Valve Tester

The links in the link below was all I could find the last time one of those was mentioned:

https://www.vintage-radio.net/forum/...d.php?t=154900

Lawrence.
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Old 14th Oct 2019, 9:22 pm   #3
David Simpson
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Default Re: Roberts Valve Tester

Thanks Lawrence. Yep I had seen those thread posts, but its now closed. What "Radio Wrangler" said might well be spot-on, with a set of jumper leads for all types of UK used valve holders. Possibly can read Ia, but maybe not Gm.
Would really like to get a copy of the handbook or manual.

Regards, David
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Old 22nd Oct 2019, 7:25 pm   #4
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Default Re: Roberts Valve Tester

I recall reading about these years ago and if the memory serves me correctly they came with a set of adaptors that plugged the unit into the place of where a valve was in the radio then that valve was plugged into the right holder on the unit. Then you could check the current and voltage of each electrode by using that rotary switch in the centre. I've never used, or even seen one in the flesh, but it sounds like it was a reasonable idea.
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Old 22nd Oct 2019, 7:49 pm   #5
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Default Re: Roberts Valve Tester

Hi David, I think I have one of these somewhere and may even have the instructions for it.

From memory they were not good to use and the stray capacity in the leads could cause high gain valves to "hoot"

Ed
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Old 23rd Oct 2019, 4:12 pm   #6
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Default Re: Roberts Valve Tester

Its no secret that I have more than a passing interest in valve testing & valve testers. Hence I wouldn't mind seeing how this Roberts' results compared to the results obtained from a more complicated VCM/Tester.
Myself & others have banged on at times about manufacturer's static tests for Gm etc. Whilst others have the view that a valve is best tested within the radio/equipment in which it is used. This Roberts would seem to be designed to satisfy both schools of thought. Perhaps the reason that myself & many others had never heard of them, unlike AVO, Mullard, Taylor, Hickok, etc., is the parasitic problem that Ed has mentioned. Hence London Sound Labs Ltd sold very few, and just had a short production run.
A nice wee winter project, me thinks.

Regards, David

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Old 27th Oct 2019, 10:54 am   #7
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Default Re: Roberts Valve Tester

Many thanks to Ed Dinning for posting a copy of the Instructions. Arrived yesterday & make some very interesting reading.

Regards, David
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Old 28th Dec 2019, 5:39 pm   #8
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Default Re: Roberts Valve Tester

The Roberts is now back on the bench for further delving. Still unable to locate a technical manual/handbook or circuit diagram. Just have the basic working instructions thank to Ed.
Are there any Audio/Recording folk out there who might have any info on the London Sound Labs Ltd from the 40's/50's onwards ? Were they absorbed into another company which might still hold archive material ?
I've discovered one drawback in its "in situ" function today. Using a known 6AU5, (and my DC Valve Tester as a substitute Rx chassis),which draws approx. 1A at 6.3V on the heater, the eventual heater voltage has dropped to approx. 4V after passing through the ext. cable & the tester's internal wiring to the IO base. Hence an Ia reading of 40mA as opposed to the approx.47mA produced separately by my DC Tester & AVO MK3. Thus the resultant Gm is lower(observed by monitoring the Ia's change when changing Vg). So perhaps this Roberts was only intended for use with just bog-standard simple domestic radios from the post-war years. Not O/P valves that give a bit of oomph.

Regards, David
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Old 29th Dec 2019, 12:01 am   #9
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Default Re: Roberts Valve Tester

Glad you're finding it interesting. If it turns out to be not worthwhile, at least it's a source of some bits and various valve holders.

Any joy with the TF2002 yet?

David
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Old 31st Dec 2019, 4:16 pm   #10
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Default Re: Roberts Valve Tester

Seemingly, the LONDON SOUND LABORITORIES LIMITED brought out the LSL Portable Analyser in Jan.1949 and the Sole Distributor was
Messr's Kerry's (Gt. Brit) Ltd. According to the London Gazette, LSL was "Struck Off" by Companies House on 10th Oct. 1958.
LSL's address back in 1949 was 40 South Molton Lane, Bond Street, London, W1(a prestigious address ?).
Kerry's was Warton Road, Stratford, London E15, and Branches.
There is, according to Google, a modern 21st century "London Sound Laboratory" which specialises in "Funky Junk". Yuck ! Kerry's was absorbed into a series of take-overs starting in 1968. SFA chance of any archive documentation being found now.
Maybe, & its a slight chance, there might be a Forum member who is acquainted with those London Boroughs, and might know of a local heritage society whome I could pester.
Aye David, I'll persevere with fault finding on the Roberts( hey - Roberts - there was a Roberts wireless manufacturing company many years ago). Re the Marconi TF2002, in an amazing coincidence, after stopping in a garage a bit down the road, met a chap who had been at the Moray Firth ARS Sale and who had seen the 2002 in the back of my Fabia. Wanted it, sight unseen, and promised to donate fifty quid to the ARS at the next sale in May. So felt magnanimous. Over the years I've donated stuff & cash to the ARS, its a worthy cause.

Regards, David
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Old 20th Jun 2020, 6:20 pm   #11
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Default Re: Roberts Valve Tester

Well, other projects sorted & "to do" shelf cleared, except for the Roberts. In fact, I now have two of the troublesome so & so's. Similar age, but with a full collection of extension leads. However, lacking a circuit diagram, unable to reverse trace it out due to mixture of seemingly random choice of coloured wiring, in looms, in both sets, and still both sets refusing to work - - me wonders what to do ? Hey, the concept of testing a valve inside its circuitry within a radio or equipment is jolly rare. However, I suspect, possibly 50 or 60 years ago, that someone well & truly phooked the cascade of W/W resistors & other circuitry whilst testing KT88's or the like. Also, London Sound Laboratories seem to have chosen cheapo multi-wafer switching, prone to nasty black contact corrosion which despite much spraying with jungle-juice cleanser, still gives poor circuitry contact.
Me thinks that, if I've to strip out the whole caboodle of circuitry in both testers to sort faults & then rebuild one good tester, then hey - why not build another homebrew DC Valve Tester. Put my money where my mouth is, so to speak having recently badgered Adrian & others to get stuck in. Again - I reckon with all the Robert's gubbins, plus T/F's, rectifier bridges, spare meters, switchgear, etc. - once again it'll cost under £200 I reckon, tops. Far less than AVO's range of pensioner VCM's, plus non of the fanny-fanny misleading AC circuitry.
Yep, I could greatly deplete my savings & get a 21st century RoeTest, or delve into modern mini electronics & build a Sussex. But hey - we're a Vintage Forum, and I'm a "Vintage" Analogue guy - so perhaps that's the road I'll follow.

Regards, David
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Old 22nd Jun 2020, 3:17 pm   #12
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Default Re: Roberts Valve Tester

Right, stripped down one of the ******'s & it doesn't look much at all, bits & bobs wise. Two decent 3.5" meters, 5 switches, 3 ancient rectifiers, 17 valve holders(needs a B9A), - about the same as an AVO VCM, a paxolin strip with a heap of winky wanky(some phooked) w/w resistors, a pot, & 5 manky waxies. The valve holders are all in good nick, but the hotch-potch of
different coloured wires follows no real colour code.
The top left "Adaptor" socket is just that, despite it looking exactly like an IO or MO valve holder, but has nine pins. There are two proper 9 pin holders(B9 & B9G), but only a loom of 8 interconnecting wires between all the holders & respective pin numbers. Number 9 pins are unconnected.
I've still feeders out to try & get a circuit diagram, but I'm pessimistic.

Regards, David
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Old 23rd Jun 2020, 12:03 pm   #13
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Default Re: Roberts Valve Tester

Aye, weel, Davie - if anybody can make anything of it, you're the Man!

Cheers,

Frank
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Old 27th Jun 2020, 4:33 pm   #14
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Me wonders if this Valve & Circuit Analyser was produced with Radio/TV shops, (who just sold Roberts Radios) in mind. As it was solely marketed by Kerry's, I also wonder if Roberts Radios were also solely distributed by Kerry's ? Hence the valve testing design might have been biased to Robert's range of domestic radios from 1932 to 1949 & the valves used therein ?
I've discovered that there is one simple flaw in its design which may have contributed to its short commercial lifespan. The interconnecting cable has 9 wires between the two 9pin adaptor plugs, but "wire nine" is only connected to the TC crock clip at one end, at the other end - only 8 pins are connected. Consequently, despite the valve holder panel part having a British B9 & a B9G valve holder - their pins9 are unconnected, and there is also no miniature B9A valve holder at all. But by the start of the 50's, B9A's & B7G's were becoming the valve base of choice for newer more compact domestic radios & TV's. Just a quick shufti through AVO's VDM - shows hundreds of valves where pin 9 can be used for any of the valve's electrodes. So - bye bye Roberts valve testers, and welcome AVO VCM's & Mullard HSVT's for many servicing shops & departments. Yep, it would work with IO's & MO's, and smaller pin configurations, but they were going out of fashion, domestic radio-wise. Me also thinks that the evidential damage to pokey wee shunts & multipliers was due to some ambitious phool trying his luck with big IO or UX7 power valves back in the 50's or 60's.

Regards, David
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Old 1st Jul 2020, 12:57 pm   #15
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Default Re: Roberts Valve Tester

If there is connection to Roberts radio, then one of them prettied up might be of value to some collector/museum of their things.

Otherwise you've got a bit of metal with a collection of valve sockets.

Anyway, You've got plenty of valve testers. How about something different? There are plenty of low frequency scopes cropping up for pennies.... how about a curve tracer?

David
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Old 1st Jul 2020, 3:27 pm   #16
David Simpson
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Default Re: Roberts Valve Tester

I'm afraid, David, that my suspicions of a link between the two "Roberts" companies were unfounded.
Perhaps I should follow your sentence 3's advice & look for a Curve Tracer to complement my main valve testing set-up.
The original concept of testing a valve within its radio's circuitry & power supplies is an interesting & novel one, but Roberts design was very limited. For it to be seriously modified & more likely hybridised involves decent metering, nine 1 pole/10 way break before make wafer switch assemblies, plus individual metering & circuitry for electrode's voltages, and Ia, plus a method of introducing delta Vg for calculating mA/V.
But, and its a big BUT, who the phook would want it ? My existing valve testing set-up has a MK3, my DC Tester & three external PSU's - that's me maxed out for space, as you've seen.
But there again - how much space would a reliable curve tracer take up ?
Seemingly TEK made one back in the 70's or 80's that's supposed to be the bee's knees? No doubt there are modern Chinko/Jappo ones out there, but costly, no doubt.
I've plenty of decent 2nd hand & NOS meters, and I'm still contemplating if I've enough wafer switches in my RS MAKA - Switch construction kit. But, it looks like an open s/b/s format will need to be used with the Roberts 3" deep clamshell casing, if everything is to be fitted.

Regards, David
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Old 2nd Jul 2020, 12:20 am   #17
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Default Re: Roberts Valve Tester

I think any valves in your vicinity are pretty well tested!

Valve testers are interesting machines in their own right, but maybe it's time to move on? I've got a little Taylor 45D in the attic which comes down when there's a need. Not as nice as an AVO, but does the job. I think it'll next get used to check a load of biscuit tins of valves at the radio club and see what's dross and what is worth finding a user for. It'll also be educational for some of the members to experience first hand how much labour is involved

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Old 2nd Jul 2020, 10:35 am   #18
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Default Re: Roberts Valve Tester

I'm surprised, David, that HP with all their expertise & up-market equipment, never built a valve tester. Something that could've wiped away AVO VCM's & Hickoks.
Good on you for encouraging young-uns to take an interest in valve technology.

Regards, David
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Old 26th Jul 2020, 3:06 pm   #19
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Default Re: Roberts Valve Tester

Well, after a long break, weeding, pruning & laying drains - now back to the Roberts project.
Bollox to fannying about with heaps of shunts & multipliers - hey - why not incorporate a trusty AVO 8? Panels all sized up & cut, except for bottom l/h/s which is a temp veneered hardboard one. Large sq c/r meter is for a radio's Vg, and the smaller round one is for applied delta Vg, (Read the change in Vg, whilst studying Ia's rise or drop - hence - - Gm). The AVO 8/6(nice & light) is essentially for Ia, but will also be able to read any valve pin's voltage plus T/C. The 10 miniature 2p/on-off-on toggle switches connect or disconnect valve pins & a T/C according to a Valve Data Book(or AVO's VDM if one is familiar with the thumbwheel codes).
Next - finish fitting all the rotary switches, etc., then wire everything up, then hope I haven't made an arris of it!
Apart from the doubled-up Roberts casing & a valve holder panel, only some of the original wafer switches will be used. A heap of Ferrite beads will be fitted in the valve holder circuitry.

Regards, David
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Old 26th Jul 2020, 5:03 pm   #20
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Default Re: Roberts Valve Tester

I love your re-imagining of vintage test equipment, I suppose the modern idiom would call it a mash up.
You have certainly inspired me to be somewhat less precious about re-purposing test equipment.
Nice job.

Peter
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