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Converting Revox B77 MkII to HS IEC

Discussion in 'Tape' started by euromut, Oct 24, 2018.

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  1. euromut

    euromut Active Member

    Messages:
    125
    I am trying to collect all the bits necessary to convert my Revox B77 MkII 2 Track standard into a HS. Not worried about the face or anything like that.

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    So far, I have acquired a 1.177.233 Record Amplifier board, and a 1.021.302 HS Motor assembly.

    I believe,

    1.177.250 Reproduce amplifier, needs to have R1, R9, R17, and R22 (Left) and R27, R30, R42, and R43 (Right) values changed to make it the same as a 1.177.253. (Section 7/53 & 57 In Circuit Diagrams)

    1.177.135 Tape Tension Switch, Needs R3, R4, R5, and R6 values changed to make it the same as a 1.177.137.(Section 7/16 In Circuit Diagrams)

    Both Std and HS use the 1.177.325 Speed Control.

    I am still scouring the schematics. I am sure I've missed something. Has anyone done this?

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  2. kfalls

    kfalls Super Member

    Messages:
    1,106
    Location:
    Dennison, Illinois
    My company has two low-speed versions. Not a bad player to work on. W/F is, of course, terrible on the low speed. Otherwise a very nice player.
     
  3. euromut

    euromut Active Member

    Messages:
    125
    I can imagine the low speed machines are a not nearly as nice to listen to. This machine is nice as a 2 Track 3-1/4, 7-1/2 machine. Hopefully even better as a full serviced 15ips.
     
  4. Chip Chester

    Chip Chester Super Member

    Messages:
    1,986
    Location:
    Central Ohio
    They are the bees knees when tuned up. Used a brand-new one back in college (late '70s.) My previous portable recorder work had all been with tube-encrusted Magnecords. Twice as thick, twice as heavy (but still had a handle on top!) Usually twice as noisy.
     
  5. twiiii

    twiiii Addicted Member

    Messages:
    6,349
    Location:
    west Texas
    I found a hard wired speed controller for the B-77 so I can chose speeds from less than 1 its to over 15 its. You'll have change the EQ curves to use IEC. I have a B-77 manual some where. I guess I'll have crawl in the attic and pull down the B-77 and see if it packed with my Machine some day. I'm sure you can find one on the internet. I googled there manual and got a Buch of reply. Is your machine a MK I or II. That makes some difference I suppose.
     
  6. GPS16

    GPS16 Well-Known Member

    Messages:
    699
    Location:
    UK Manchester
    Hi Euromut,

    there will be Resistor/Capacitor changes to shift from NAB to IEC. Keep an eye out on the auction sites as the Rec/Play PCBs come up quite often. It would be nice to be able to revert back with not too much bother.

    The capstan rotation speed is the same for 3.75/7.5 and 7.5/15 IPS. The diameter of the capstan shaft doubles. Take note of the mounting holes drilled in the motor housing. They look to have been badly machined. They have not. As the moving surface of the capstan shaft has moved, the mounting position of the motor is shifted in the opposite direction to compensate. If this was not done, the tape would be rubbing against the rotating capstan when the machine was in STOP.

    The resistors on the Speed Change PCB modify the high power pulse width of the Take Up Motor when play is initiated. These are important to reduce startup snatches of the tape when Play/Rec is initiated.

    I have a HS NAB Revox C270 which was ex studio but looked after as the Master Machine. I then got hold of a dog which was intended for spares. In reality it just wanted a service and some TLC. So I started to convert it from 2 Track IEC 7.5/15 IPS to 4 Track NAB 3.75/7.5 IPS. This required the plug in daughter PCBs on the Rec and Play Amps to be re populated. The speed change was a shift in a DIL Switch which is checked on power up. I now wonder if I have the only NS NAB 4 Track C270 on the planet!!! I do hope so!!!

    If you and Twiiii PM me I will pass on the ftp:// download site. I am not sure if I would be in trouble to give it here!!! All Studer and Revox Manuals are available here.

    When serviced and properly set up these machines are performers!!! I still have my NS NAB 4 Track B77 which I got to replace a worn out Pioneer RT707. This is the machine I cut my "Revox" teeth on so to speak. I now have 1 B77, 2 A700s and 2 C270 machines. They are all runners!!

    Cheers.

    GPS16
     

     

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  7. euromut

    euromut Active Member

    Messages:
    125
    I love this machine in its current form, and cant wait to get it upgraded. I've collected all the different resistor values for the conversion.

    The motor pictured above is a smooth running HS original. So that's easy.

    While I'm in there, Ill be replacing all the Electrolytic caps with Nichicon Fine Golds, the pots with Pihers, and all the Poly caps with WIMAs. I have also stocked up on the needed transistors in case I come across any out of spec. My soldering station will be getting a work out.

    Its also getting Ceramic Hybrid bearings in the spool motors and tape guides.

    And I scored a NOS HS face plate.

    I have a local audio restoration shop who specializes in RtoRs. They will go through and do the calibration once I've completed the electronic restore.

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    And I am making side panels for the case from this Brazillian Rosewood.
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    I kinda want it to match or at least compliment my Thorens.
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  8. GPS16

    GPS16 Well-Known Member

    Messages:
    699
    Location:
    UK Manchester
    Hi Euromut,

    a nice project for the winter months.

    The side panels should look great. They do add to the appeal of the A700s.

    Like the turntable. I have a TD150 Mk II with a SME M2-9 and Shure V15-VxMR on the end. No lack of analogue in my house!!!

    I have had the kits of bearings and PDP65/GLY2100 from the guy in Australia, so my machines are now all set, mechanically, for the next few years.

    Keep up the good work.

    GPS16
     
  9. euromut

    euromut Active Member

    Messages:
    125
    Well, I'm getting closer. I went through the machine last night. Verified the board versions, and confirmed my parts stock. Also double checked the pin spacing for some of the WIMA film cap replacements I have. Everything looks to be in order.

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    I also had a very plesant stop at a local repair shop. Turns out he had NOS 2 Track heads. He wasn't sure what they were for, so I was able to pick them up reasonably. I've never been so tempted to rip open a parts bag before. But I'll leave the 027 in there till I need it.

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    GPS16 and damacman like this.
  10. damacman

    damacman Blown and Injected Subscriber

    Messages:
    8,795
    Location:
    Gilbert, AZ
    Definitely following this one with interest!
     
  11. euromut

    euromut Active Member

    Messages:
    125
    Finished up the first board. Plenty more to go.

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    GPS16 likes this.

     

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