Marconi TF2700

[synx508]

I've been threatening to pick one of these bridges for a while and the first rally of the year for me was the opportunity.

I had to rebuild the outer range multiplier selector knob as the plastic had crumbled around the centre. I had most of the pieces, as they'd been held captive by the design of the knob and the case so I reassembled the 3d jigsaw of plastic, superglued them in place and then poured a load of epoxy resin over the whole lot. I also lubricated and cleaned the switches, cleaned up the front panel a bit (not finished…). There was one switch contact that wasn't making but turning the switch with a little pressure applied to the back of the contact seems to have cleared it.
The only modification I did was to add a PP3 battery clip as the previous owner had soldered a PP3 to the power leads.
The amplifier board probably needs some new capacitors and has had a GET transistor replaced with an ACY type at some point but it all appears to work.



Why do I want this old and obsolete instrument? I wanted to sample the "fully manual" way of measuring parts, the switches and potentiometers are quite lovely to use and you don't get that with a T7-H

[EC8010]

The TF2700 is a lovely bit of kit; I had one for many years, and paid £70 for it in 1993. They go for peanuts now. I gave mine to a colleague when I replaced it with a computer controlled impedance analyser that could go to 200kHz. I've now replaced that with one that can go to 8MHz.

It was intended to run off a PP9 battery. You might want to go back to that as I have personally seen/heard three PP3 alkaline explode unprovoked. Not serious explosions, but it would be unfortunate if one destroyed an unobtainium transistor. PP9s still appear to be old-fashioned Leclanche cells made of six stacked cakes internally and don't even ooze, let alone explode.

You can significantly improve a TF2700 by replacing its main range resistors with 0.1% types (originally 0.5%), and the outer range switch resistors also with 0.1% types. If you now use the instrument to measure a stack of (say) 100k resistors with the range multiplier switch set to zero (forcing the measurement to be made by the inner potentiometer), you can plot the results, fit a straight line to it and determine by how much the inner dial needs to be rotated on its shaft. Doing all this can bring your uncertainties down to 0.25% or better.

If you need to measure decent capacitors (polystyrene, polypropylene, PTFE, air) accurately, a TF2700 is excellent. It's only when you start investigating lossy components that you need a fancy impedance analyser. Treasure your TF2700.

[tggzzz]

The only modification I did was to add a PP3 battery clip as the previous owner had soldered a PP3 to the power leads.

Zenith enabled me to not be able to pass one of these up at W-s-M rally a couple of years ago. Meter is a bit naff, but usable.

I just poke the PPx battery clips out of the back panel, and use croc clips to attach them to a bench PSU.

Crude? Of course!
Functional? Yes.
Reversible? Yes, in 30s.
Quick and simple? Yes.

Sufficient job done.

EC's concept of improving the resistors is tempting.

[Zenith]

Here is a photo of my example of this extremely fine classic instrument. Note the protective layer of dust, which keeps it in good condition.

DSCN4659.JPG

The small yellow thing at the side is a Peak LCR45, which is what I tend to reach for now, if a DMM isn't up to the job. I've found the probe on the Peak is rather delicate and has had to be repaired. The official replacement leads are pricey in my view. It also uses a 12V lithium battery, which is expensive if you buy them from a supermarket, but can be bought on ebay for a more reasonable price.

[AVGresponding]

Interesting. The DCA75 Pro uses a single AAA, and internal boost reg to get up to 15V (iirc) for curve tracing purposes.

I will agree that the clips seem fragile; I am super careful, I do not want to have to repair those.

[synx508]

Mine doesn't have the "mi" logo, so perhaps that makes it earlier. Marconi struck me as a company that wouldn't have taken to the idea of "branding" and "logotype" easily or quickly.

[Zenith]

I
I will agree that the clips seem fragile; I am super careful, I do not want to have to repair those.

They are high quality mini-grabbers. The connections are bound to wear out and need replacing eventually. It's not a difficult job, but you need to use very flexible instrument lead wire. I have a reel I bought years ago. It's blue. Similar wire is available in short lengths in various colours on ebay.

[EC8010]

Marconi struck me as a company that wouldn't have taken to the idea of "branding" and "logotype" easily or quickly.

Oh, they did. Just take a look at valves. Valves out of a single factory were branded Marconi, Marconi-Osram, MOV (Marconi-Osram Valve), GEC, Marconiphone, and all sorts. The shenanigans of the valve cartel was quite something.

[Zenith]

I didn't know GEC were part of Marconi. There were a number of valves sold as GEC which were not just renumbered versions of standard valves, they were different in construction and only appeared in GEC radios and TVs.

The BVA was the cartel, with most UK valve makers being members. Exceptions were HiVac, which specialised in sub-miniature valves, and Tungsram, which imported valves of standard types from Hungary. At one time the BVA had a rule that only one function could be included in an envelope, obviously intended for their benefit.

The whole industry became a complicated mess of patents, cross licensing, rebadging, and later rebadging imports.

[tggzzz]

I didn't know GEC were part of Marconi.

They weren't. GEC borged Marconi, and many many other companies - to the detriment of British industry.

When I was doing the "milk round" of interviews during my final year at university, I applied to 6 GEC companies and was offered 11 interviews. I even received one letter that I interpreted as "you can have a job without being interviewed". Some were looking for 200 graduates!! I went to several interviews, and decided I never wanted to work at a GEC company.

Arnold Weinstock was a superb financial engineer, and knew how to milk "cost plus" contracts for all they were worth, e.g. having 200 additional bums on seats. His successor was John Simpson, who sunk GEC with an elementary mistake: paying cash (not stock swap) for an American company that turned out to be fraudulent. (HP/Autonomy anyone?)

[EC8010]

The whole industry became a complicated mess of patents, cross licensing, rebadging, and later rebadging imports.

Yes, and Mullard kept very quiet at the time about the fact that Philips owned a large proportion of his company almost from day one, let alone later when they bought the remaining shares, making Mullard a non-UK company.

[Zenith]

I didn't know GEC were part of Marconi.

They weren't. GEC borged Marconi, and many many other companies - to the detriment of British industry.

When I was doing the "milk round" of interviews during my final year at university, I applied to 6 GEC companies and was offered 11 interviews. I even received one letter that I interpreted as "you can have a job without being interviewed". Some were looking for 200 graduates!! I went to several interviews, and decided I never wanted to work at a GEC company.

Arnold Weinstock was a superb financial engineer, and knew how to milk "cost plus" contracts for all they were worth, e.g. having 200 additional bums on seats. His successor was John Simpson, who sunk GEC with an elementary mistake: paying cash (not stock swap) for an American company that turned out to be fraudulent. (HP/Autonomy anyone?)

It's an incredibly convoluted story.

https://en.wikipedia.org/wiki/General_Electric_Company

In 1919, GEC merged its radio valve manufacturing interests with those of the Marconi Company to form the Marconi-Osram Valve Company.

But GEC was involved in the valve industry and marketed distinctive designs, so they must have retained a close relationship with M-O-V.

I had the impression that when Arnie was in control he ruled with a rod of iron and accumulated a tidy cash pile. When he retired around the time of the dot com boom, they spent money on all sorts of hare-brained schemes which ended in ruin.

Ferranti bought a US company that was more or less a fraud and caused their collapse. I don't believe Ferranti was part of GEC, but I wouldn't be surprised if GEC had one or more subsidiaries which bought US companies which were worthless.

Autonomy was the biggest of a long succession of disastrous acquisitions HP went in for. It was a shocking lack of due diligence.

[tggzzz]

I didn't know GEC were part of Marconi.

They weren't. GEC borged Marconi, and many many other companies - to the detriment of British industry.

When I was doing the "milk round" of interviews during my final year at university, I applied to 6 GEC companies and was offered 11 interviews. I even received one letter that I interpreted as "you can have a job without being interviewed". Some were looking for 200 graduates!! I went to several interviews, and decided I never wanted to work at a GEC company.

Arnold Weinstock was a superb financial engineer, and knew how to milk "cost plus" contracts for all they were worth, e.g. having 200 additional bums on seats. His successor was John Simpson, who sunk GEC with an elementary mistake: paying cash (not stock swap) for an American company that turned out to be fraudulent. (HP/Autonomy anyone?)

It's an incredibly convoluted story.

https://en.wikipedia.org/wiki/General_Electric_Company

From wackypedia, it seems I got most of it right...

During 1996, Lord Weinstock retired as GEC's managing director and was replaced by George Simpson. In July 1997 ... Simpson, along with finance director John Mayo, decided to pursue a risky strategy of pursuing fast growth via rapid acquisition of numerous other companies, particularly within the United States.
...
After most of its US acquisitions failed, GEC began to make a loss. The cash reserves that Lord Weinstock had built up during the 1980s and early 1990s had been all but depleted, and the company was heavily in debt.


.... but George/John, and I may have ?partially? conflated it with Ferranti.

I had the impression that when Arnie was in control he ruled with a rod of iron and accumulated a tidy cash pile. When he retired around the time of the dot com boom, they spent money on all sorts of hare-brained schemes which ended in ruin.

Profit was the be-all-and-end-all for Weinstock, and it showed.

Ferranti bought a US company that was more or less a fraud and caused their collapse. I don't believe Ferranti was part of GEC, but I wouldn't be surprised if GEC had one or more subsidiaries which bought US companies which were worthless.

Autonomy was the biggest of a long succession of disastrous acquisitions HP went in for. It was a shocking lack of due diligence.

When the gossip was that the HP MBAs wanted a "50-50 company" ($50e6, 50e3 employees), and thought it cheaper to buy a successful $1e9 company than pay for HP Labs, I knew it was time to leave. (Plus I had personal reasons!) I've never found reason to change that opinion

[Zenith]

The whole industry became a complicated mess of patents, cross licensing, rebadging, and later rebadging imports.

Yes, and Mullard kept very quiet at the time about the fact that Philips owned a large proportion of his company almost from day one, let alone later when they bought the remaining shares, making Mullard a non-UK company.

It was founded in 1920. In 1923 Mullard sold half the company to Philips. By 1927 he'd sold the rest. For years it was a close secret even within the company.

"Mullard the Master Valve".

[Zenith]

I had the impression that when Arnie was in control he ruled with a rod of iron and accumulated a tidy cash pile. When he retired around the time of the dot com boom, they spent money on all sorts of hare-brained schemes which ended in ruin.

Profit was the be-all-and-end-all for Weinstock, and it showed.

A view of the world with obvious defects, but I'd argue healthier than, "Whee, we've got all this money to spend on all sorts of exciting concepts and fads. We don't understand them but they are damned exciting."

I heard a story that Arnie was due to visit a GEC plant that was in a tatty condition, not having seen a lick of paint since it was built. So they redecorated, but only the bits within sight from Arnie's route. This included painting a wall which a stairway ran against, but only halfway up, because that was as much as was visible from the corridor Arnie was set to walk along.

I feel sure that had Arnie found out he would have pretended to be annoyed, but actually thoroughly approved.

Ferranti bought a US company that was more or less a fraud and caused their collapse. I don't believe Ferranti was part of GEC, but I wouldn't be surprised if GEC had one or more subsidiaries which bought US companies which were worthless.

Autonomy was the biggest of a long succession of disastrous acquisitions HP went in for. It was a shocking lack of due diligence.

The multinational corporate version of "It was a job lot I bought from an Irishman in a pub. He dropped it off on my driveway in the middle of the night and I paid him cash".

When the gossip was that the HP MBAs wanted a "50-50 company" ($50e6, 50e3 employees), and thought it cheaper to buy a successful $1e9 company than pay for HP Labs, I knew it was time to leave. (Plus I had personal reasons!) I've never found reason to change that opinion

I'd had enough by 1999, just before the arrival of Kali, the Goddess of Destruction. Nothing I heard later caused me to regret it.

[tggzzz]

When the gossip was that the HP MBAs wanted a "50-50 company" ($50e6, 50e3 employees), and thought it cheaper to buy a successful $1e9 company than pay for HP Labs, I knew it was time to leave. (Plus I had personal reasons!) I've never found reason to change that opinion

I'd had enough by 1999, just before the arrival of Kali, the Goddess of Destruction. Nothing I heard later caused me to regret it.

Oh, yes, Princess Fiorina had - ahem - arm'ed my logic analyser and it was waiting for the trigger to arrive.

I remember seeing her perform in the canteen, and not understanding the words she was using: something about "double downing" on something or other. All the previous CEOs had made simple, understandable and (somewhat!) actionable statements.

[Zenith]

The rot had started before then. Lew Platt had a mission to shake every employee's hand. Our version was also performed in the canteen, after his ranconteur performance . To my shame I partook, but it happened so fast it barely registered. On mature reflection I should have held myself aloof, but it was fascinating to see a human hand move so fast and not fly apart because of the G forces.

[synx508]

Just done a three-way test-off with the modern T7-H tester, a Wayne Kerr B424 component tester and the Marconi TF2700. First I tried a NOS 68µF 63V Philips. This showed up as 75µF on the T7-H, but with 1Ω ESR. The Marconi indicated 34.3µF and 34µF on the 1,000µF range as a confidence test. It seemed pretty sure and that's quite a difference. The Wayne Kerr took its time to warm up but once it did it was showing 33µF, which is close enough to an agreement with the Marconi.
With a 220µF 16V Philips of a similar age the T7-H was showing 250µF, the Wayne Kerr 241µF and the Marconi 222µF. ESR was better on this one, so I suppose with electrolytics I should test that first.