Mullard Magic

Discussion in 'Shock Brother's DIY Amps' started by dougsta, Sep 26, 2020.

  1. dougsta

    dougsta TDPRI Member

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    Found an old reel to reel tape machine on ebay for £20 and scored some nice Mullards from 1959, inc a long plate ecc83 f92, but what to build?

    2 x EL84
    1 x ECC83
    1 x EF86
    1 x EZ90
    1 x EM84 IMG_7134.jpg
     
  2. Norris Vulcan

    Norris Vulcan Tele-Afflicted

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    An AC15 with EF86 channel ?
    Nice find, by the way. Enjoy !
     
  3. Norris Vulcan

    Norris Vulcan Tele-Afflicted

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    Or just plug in to the tape machine ? :lol:
     
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  4. dougsta

    dougsta TDPRI Member

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    I removed and replaced all the old caps in the tape machine and got it running, it's only a single speed 3 3/4 ips, not the best. I've put a mix of old/new tubes in it to test, Lorenz EM84, 2 russian el84s, a jj 12ax7, another EF86 I have (Mullard also) and a Mazda EZ80. EM84 looks good, esp with the lights dimmed and playing Dark Side of the Moon.
     
    Last edited: Sep 27, 2020
  5. dougsta

    dougsta TDPRI Member

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    I need a 1950s ECC82 to complete my collection... Screenshot 2020-09-26 at 19.05.49.png
     
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  6. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    Which factory are these from?
     
  7. trancedental

    trancedental Tele-Meister

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    Most of my Mullards & Brimars have Made in England on them. Don't know how old they are, they have the older badge & writing is usually white.

    I have a dozen or more military Brimar ECC81's some had the yellow triangle on 'em , 6060, CV4024 & other designations. I don't think I've ever bought a new 12AT7!

    I was checking out my old valve stash last night, after a quick bit of research it seems that new tubes are very expensive, as for old stuff most on Evilbay are priced too high especially to take a chance. Shipping charges from USA have also gone crazy.

    I used to pick up those old GE 6L6GC's for a few quid on Ebay, I know they aren't the best old 6L6 power tubes but they sound better than any new 6L6 to my ears. Plus I'm biased as I used to work for General Electric back in the day.

    Got maybe enough old tubes for 3/4 amp builds, after that I'm running out!
     
  8. dougsta

    dougsta TDPRI Member

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    Here's the info on the valves in the photo:

    The ECC83 has the codes f92 and B9I etched at the bottom near the British Made print, B9I = Blackburn factory 1959 September and the f92 is the manufacturing revision - long plate and a halo getter on a single post

    The EL84s have the codes rXI and R9H, R9H = Mitcham factory 1959 August and rXI is the manufacturing type.

    The EF86 and EZ80 are Blackburn factory 1959

    The tape recorder they came with has the date November 1959 stamped on the cabinet.

    I will dig out/dust down my Canon DSLR for some close-ups of the of the glass/internals

    I don't have a tube tester (I've ordered the parts for building the one by Grant Willis at ValveHeaven.com) so will be able to check mutual conductance at the data sheet voltages and compare how much they are off spec and if they are gassy.

    I can check the ECC83 gain, triode balance, noise and microphonics on my scope.

    A simple do they make any sound test is to run them in an amp, I have a Bugera v5 (12AX7-EL84 5 watter) and a Mike Soldano designed JCA22H p-p EL84 head.

    Doug
     
  9. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    Are the transformers up to snuff?

    If you have an ECC82 in your drawer of delights, EF86 feeding an ECC82 with the 'a' side being used as a cathode follower to drive a TMB ( or T-B with fixed mids ) and the 'b' for gain recovery. ECC83 LTP phase inverter. Cathode bias the EL84 pair. Or, EF86 -> ECC83'a' -> basic tone control -> ECC83'b' cathodyne -> EL84 goodness. Master volume if required.
    Instead of the usual gain control, vary the screen voltage of the EF86. It'll alter the gain, and also affect the compression.

    ps. My simple 'Do they make untoward noises' is a WF-55 and a JCA20H too. Simple and effective.
     
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  10. dougsta

    dougsta TDPRI Member

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    Thanks, interesting ideas. I'll wind some custom transformers and leave the tape recorder intact, it has heater current for about 3 amps worth but the HT wont be up to much current delivery.
    I don't have an ECC82, the closest I have is a couple of Westinghouse 5963, these were used in old computers, I've tried them in an amp and the sound ok. I was thinking of using them for a Robrob p-p micro.
     
  11. dougsta

    dougsta TDPRI Member

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    After a quick look thru my hoard, I have a couple of these interesting old Mullards, the ECC85, 6.3v filament on pins 4,5. mu=59 and a screen between the triodes at pin 9, it was designed for use in rf service. They sound great.
     
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