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Thread: My new old Marconi Instruments signal generator

  1. #1
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

    Default My new old Marconi Instruments signal generator

    Well I saw this old TF1370A on the evil bay and put a daft bid in for it, thinking it may fetch £100+.... I won it for £7 Then saw it was "collection in person only"... In that London

    That is where AOS came into play "Edwardlon" kindly collected it for me and took it as far as Sheffield to Si (SQ) who brought it up to me with an amp he needs sorting on Saturday (he even cleaned it first!). Thanks guys!

    It's about the size of a microwave oven, weighs in at 37 Lbs and contains 13 valves! (rectifiers are SS so that's 12 "active" valves) My biggest fear was that the crop of Mullard and Brimar valves had been filched but this proved not to be the case

    I wound it up on a variac over a couple of hours and it worked... after a fashion... The regulated HT, from a full on complicated all valve voltage regulator with two ECC83's, 85A2 voltage reference and 6080 series pass valve, was found to be at 166V rather than the correct 285V! A 1M resistor open circuit and 0.5uF cap leaky were both replaced. This had the HT restored

    The heater supply is also regulated... using them new fangled transistor thingies... 3 of them with the output series pass on a nice sized heatsink. This seems to be spot on as delivered These are the only transistors in it but it uses several germanium diodes.

    The 10 and 30V outputs come via a 20dB amplifier and these were found to be giving a VERY distorted output... Also the square wave section isn't working....

    The output stage is a clever variant of the White cathode follower using two EL84's, one pentode connected as the follower and one triode connected as the active current sink. The pentode, being floated up at 200V above ground, has it's own floating heater supply to avoid cathode/heater shorts It can give 30V RMS into a 2K load @1MHz and 10V RMS to 10MHz!! A similar topology could make a stonking headphone amp!

    This was I guess around the time of the "last hurrah" for valve gear (manual dated 1965 and this one built late 1968) and uses some of the last and best valves to be made such as frame grid EF184's, E810F's and E88CC (yes gold pin Mullard!).

    The components used back then are crap compared to what we have today and I'm expecting to find more open circuit or 50%+ high resistors and several leaky caps yet before these sections are working correctly.

    One thing I did just notice in the schematics is the presence (not for much longer!) of a couple of 500V rated 1nF paper caps, one each from live and neutral to chassis!! They hadn't heard of "X" and "Y" rated caps back then and I don't fancy my chances of the one from live to chassis remaining a non conductor for long!

    Interesting to note that, as is often the case, the valves have outlived the resistors and capacitors!
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  2. #2
    Join Date: Jul 2016

    Location: Welsh Borders

    Posts: 283
    I'm Gary.

    Default

    Ah, the joys of playing with vintage kit! You sound properly made up.
    Of course 98% of your post is not understandable to me, but I know that feeling of mingled respect and pleasure from my own incompetent faffings-around with old four-wheeled stuff. Enjoy!
    IB

  3. #3
    Join Date: Mar 2010

    Location: Sheffield

    Posts: 2,898
    I'm Simon.

    Default



    She's a corker Jez. Make sure you save all that vintage 60's dust from inside. it'll be perfect for putting inside reconditioned mixing desks and the like for that authentic sound.
    Kuzma Stabi/S 12", (LP12-bastard) DC motor and optical tacho psu, Benz LP, Paradise (phonostage). MB-Pro, Brooklyn dac and psu, Bruno Putzeys balanced pre, mod86p dual mono amps, Yamaha NS1000m

  4. #4
    Join Date: Mar 2017

    Location: West Sūžsēaxe

    Posts: 2,015
    I'm Edward.

    Default

    Glad you now have it in your paws Jez.

    Of course I managed to follow every line in your post above - not.

    Will you get it working properly and will it be of any use? Or just nice to look at?

    E
    Current: [P20] Roon/Tidal > Custom PC> Chevron Paradox NDF16 > Phast Pre > Neuro. 686 > Tannoy Berkley (RFC tweaks)


  5. #5
    Join Date: Feb 2008

    Location: Middlesex, UK

    Posts: 4,481
    I'm Alex.

    Default

    I remember using either this or something like it in the 70's at college.

    Marconi Instruments made some good stuff.

    Later I worked for a branch of the Company and a load of our test equipment was calibrated by Marconi Instruments.
    Spendorman

  6. #6
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

    Default

    Quote Originally Posted by Edwardlon View Post
    Glad you now have it in your paws Jez.

    Of course I managed to follow every line in your post above - not.

    Will you get it working properly and will it be of any use? Or just nice to look at?

    E
    Oh it will be of use alright A practical classic still capable of paying its way. Quite a lot of my test gear is restored vintage stuff like this and generally, when we're talking Marconi Instruments, Racal, Hewlett Packard, Tektronix etc, these beasties cost more than a new car when they were new (in some cases more than a house when new!), were used at the time by the likes of Hawker Siddeley, NASA, MIT, The MOD, The GPO etc etc and still give superb performance that can be considered "par for the course" even when compared to the latest test gear.

    The big differences with today's gear are the obvious huge reduction in size and weight and that a lot of today's stuff is digital and has facility to store results, print out results via USB to PC and will often have "math functions" so it can, for example, calculate frequency response from impulse response via FFT etc. The ability of modern test gear to just take a measurement though has not improved much when compared to good quality old gear like this, and the old gear is usually vastly more intuitive to use and quicker to set up.

    It also has that all analogue "feel" where for example as you increase level on a rotary control and see it changing on the scope screen one may find a point in the output of an amplifier under test where it suddenly goes unstable. Now. with the old gear one can bring it up to just on the verge and back it off "just a midges" etc in a really intuitive way that is so much better than having to go through an on-screen menu and select "increase 1dB" !!

    For me though the real killer with modern gear is it generally can't be repaired by anyone but the manufacturer as it will be full of custom made IC's and have proprietary software held in ROM etc. So with modern good quality gear it cost's say £3000 to buy (the old gear more like £8000 in today's terms so test gear has come down in price in real terms), if it goes wrong it has to go back to the factory and they will charge something like £500+ to repair it, and once it's over say 10 years old it's no longer supported by the factory and it's land fill!
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  7. #7
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

    Default

    Quote Originally Posted by Infinitely Baffled View Post
    Ah, the joys of playing with vintage kit! You sound properly made up.
    Of course 98% of your post is not understandable to me, but I know that feeling of mingled respect and pleasure from my own incompetent faffings-around with old four-wheeled stuff. Enjoy!
    IB
    Very well put Gary!
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  8. #8
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

    Default

    All sorted Avoid Dubilier type 700 paper capacitors like the plague!! Every one tested was faulty!
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

  9. #9
    Join Date: Jan 2014

    Location: london se6

    Posts: 823
    I'm AndyElectroNumpty.

    Default

    I can picture Mr Arkless in full Dr Frankenstein mode, in the middle of an electrical storm , hair standing on end , turning dials and pulling levers on vintage test kit whilst souping up his latest box of tricks creation....

  10. #10
    Join Date: Oct 2012

    Location: NE England

    Posts: 4,173
    I'm Jez.

    Default

    Quote Originally Posted by smangus View Post
    I can picture Mr Arkless in full Dr Frankenstein mode, in the middle of an electrical storm , hair standing on end , turning dials and pulling levers on vintage test kit whilst souping up his latest box of tricks creation....
    So it was you hanging around the east wing of Castle Arkless the other night eh? If it wasn't for you meddling kids I would have gotten away with it!
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
    ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
    Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
    Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco

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