EMI 806 mic amps (REDD style)

Discussion in 'Tech Talk - Electronic Repair Modifications DIY' started by synthpunk, Jul 29, 2003.

  • AT5047

    The New AT5047 Premier Studio Microphone Purity Transformed

  1. Russell

    Russell Active Member

    Jul 9, 2011

    Dear Brian

    Thanks for reading my entry in "RECORDING ORG" on the 806 mic preamp

    During 1953 to 1959 I was employed at EMI under their training scheme at EMIED, EMI Engineering Development. We trainees worked in different laboratories for 4 month sessions, or if we were required to do so this was sometimes extended by a further 4 months.

    I did know Dr Dutton
    I did a lot of of early stereo experimental work during my 8 months in Dr Geoffrey F Dutton's Tape laboratory in the Research Building.
    I designed and manufactured a special switching unit (including the wafer switch) which enabled Geoffrey to demonstrate at his lectures on Stereo the different complex sounds that were available from the two channel source from a stereo recording, with just a simple rotory switch giving following
    Stereo to both channels
    Sum (Left plus Right = mono) both channels
    Difference (Left minus Right = stereo information) both channels
    Left only
    Right only

    The above selected onto either
    Both channels
    Left only
    Right only

    We also made up all of the special motor/generator equipment to operate the recording machines from car batteries to record trains on Hayes station for the EMI stereo Demonstration disc.
    Peter Dix (who came from Goodmans Loudspeakers) also worked in this lab, where we made up the monitor loudspeakers for the studios at Abbey Road. These were powered by Leak TL10 amplifiers that had special feedback applied to enable the cabinets to be individually equalised for a flat response.

    Philip B Vanderlyn also was in this section, where work was being carried out to attempt the job of sending out stereo information on FM radio without using the GE multiplex patent. Peter was trying to steer a mono signal using the difference channel information, but the results were not really that impressive.

    Henry A M Clarke was in the EMI International Division, I was there for 8 months.

    BED under Felix Trott
    When I joined the Broadcast Equipment Division (which covered Television and Audio) in 1958 to help with mic preamp design under Philip P D R Marks in the Studio Sound section, we were not only were designing the pre-amp to replace the Seimans Halske V72 and the new desk , together with the Studio Talk Back Amplifiers, but we were fitting out a complete mobile van for the Australian Broadcast Company. I believe the mixing desk that used the 806 series went into the van first, and then when being specially painted for Joe Meek at Landsdown Studios (to record I believe Acker Bilk initially) in Red, instead of the normal EMI green. The studios naturally had them to try out initially.
    The 806 mic amp went out as EMI Studio Sound whilst I was there.

    When Marks asked me to move this huge outside broadcast vehicle, I stated it should have some windows in the sides of left and right foot wells, to enable safer manoeuvring. So Marks asked me to cut out the sides out and make up some curved formed Perspex clear windows. This was possibly the first vehicle to have these side observation windows.

    As regards to Philip P D R Marks, he designed the 806 completely from scratch as well as the drawings for the cabinet. I did all of the prototype metal work, which was before the REDD. In fact, when we wound the special input and output transformers, we did not want our competitors to cut through them to see our special windings layout, so Marks had then potted not only in Araldite, but with very fine sand added to the mix

    In actual fact, it was quite a task trying to improve on the V72 specification initially, but we managed it and produced a very low noise pre-amp for that time, with good bandwidth and transient response.
  2. Brian_G

    Brian_G Active Member

    Aug 11, 2011
    Hi again Russell,

    This is such an interesting subject to me.

    I too was an EMI Apprentice, although from a slightly later era.
    I joined Hayes in 1962 as a "Student Engineer" and we did a day release course (ONC then HNC) at Southall Technical College. I too, went through the 4 months rotation through various departments, although my chief interests were sound recording and reproduction. I'd been building amplifiers and tape recorders when I was at school, mainly from designs published in "Practical Wireless" magazine. After I finished my Apprenticeship I managed to secure a job in the tech department at Abbey Road, where I worked for over 30 years.
    Since leaving Abbey Road I have continued to work as a frelance tech, specialising (for obvious reasons) in old EMI equipment.
    I met the other Brian posting here (BrianK) during the course of he and his partners research for their book entitled "Recording the Beatles" and I have continued my interest in the subject of EMI's audio history. In 2004/5 I landed the job of restoring the EMI REDD51 mixing console that was originally in EMI's studio in Milan.
    One of my other customers has a rack of the 806 Mic amps which started this discussion thread, although unfortunately they are in storage and I do not have access to them at the moment.
    You mentioned a number of names from Hayes, some of whom I also knew.
    Dr Dutton's department that I knew was actually EMI Research Laboratories, who developed the TG12345 transistorised mixer (1967), that replaced the REDD consoles.
    The designer of the TG desk was Mike Batchelor and some of the other people I knew from that project were Mike Terry, who was in overall charge of the TG development, Gerry Kelly, Don Paine, Katie Phillips and Dave Browning. Other members of Research included Peter Dix, whom I knew very well although he was involved with speakers and microphones. He used the large anechoic chamber located next to the Research building. Another name from Research was Reg Willard. EMI International was run by Wally Rand.
    I wonder if you recall any of these people?

    REDD was formed under the auspices of Len Page in 1955/56 for the purpose of developing stereo recording equipment for use within EMI's studio network. One of the first REDD products was the REDD17 (1956) which was developed in conjunction with EMI/Electrola in Germany, and used the Siemens-Halske V72 amplifiers.
    I was interested by your statement that the 806 was developed to replace the V72. Was this for a specific console or just as a general purpose amplifier?
    The V72 is not specifically a Mic amplifier like the 806, and is really a fixed gain modular "building block" that can be used in a number of ways.
    I'm not really surprised you could not match the V72 since they are a masterpiece of miniaturisation, particularly integrating the power supply in such a small package.
    The REDD47 was the REDD replacement for the V72, but it was not as reliable, although the performance is really good. Keeping up with replacing the EF86 first stage valves can be a bit of a chore since they go noisy with boring regularity.

    I was going to send you a personal email to discuss these things further if that's OK with you.

  3. Russell

    Russell Active Member

    Jul 9, 2011
    Dear Brian_G

    I have posted a private message for you.

    We certainly have a lot in common.

    Kind regards

  • AT5047

    The New AT5047 Premier Studio Microphone Purity Transformed

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