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Telefunken V-series questions

Discussion in 'Pro Audio Equipment' started by hollywood_steve, Sep 7, 2001.

  1. hollywood_steve

    hollywood_steve Active Member

    Joined:
    Jan 3, 2001
    I just received my V78 back from Tab-Funkenwerk where it was given a clean bill of health. Eventually, I want to get a 2nd V78 and rack mount them and my other Telefunken modules. But in the interim, I need some way to support the V78 module so its not just sitting loose on a shelf. I don't want to turn this into a complicated project, so I thought about just building a wood "lunchbox" to hold the module.

    Two questions:
    1. Do these units need the added shielding of a metal enclosure or will it work fine without it?

    2. How much air circulation do these things need? I have been in several studios that have one or two API or Neve modules in small, wood boxes, but the V78 puts out a lot more heat. Can I mount the unit in a small box, or does it need several inches of air space above the vent holes?

    I know that Oliver at Tab-F could answer these questions, but I hit him with enough questions concerning the work that he has performed on several of my modules. I was hoping that some other "end-user" might be able to answer these questions from his own experience.

    Thanks.

    Steve
    sjp@pacbell.net
     
  2. miketholen

    miketholen Guest

    wouldn't worry about shielding them any further than they already are(there's about 20 lbs. of Mu-Metal surrounding everything.
    You should leave a few inches of space for ventilation. I have several V modules and they are stacked side by side-never on top of each other.

    Did Ollie turn it into a V72?

    have fun! :D
     
  3. RandomGuest

    RandomGuest Guest

    Joined:
    Feb 10, 2001
    Originally posted by hollywood_steve:
    I need some way to support the V78 module so its not just sitting loose on a shelf.

    Then get some adhesive velcro, put a strip on the shelf, and a mating strip on the module, it's not going anywhere.


    I don't want to turn this into a complicated project, so I thought about just building a wood "lunchbox" to hold the module.

    That would work, but so would velcro, and you'll get better cooling if you don't add the 'wooden insulation'. The main reason these things fail is heat.

    Two questions:

    (which are actually 3 questions)

    1. Do these units need the added shielding of a metal enclosure

    No.

    or will it work fine without it?

    Yes.

    2. How much air circulation do these things need?

    Enough so they don't overheat. Not a whole lot, if you think about their original mounting frames, they were side by side [notice the latch on the front for locking it into an original frame]. I don't know how high they stacked them. In the REDD-37 desk [which was V-72S's, not too dissimilar from V-78's...at least heat dissapation wise], there wasn't a whole lot of 'breathing room' available to the modules. Then again, most of them required rebuilding when the desk came to our place.


    I have been in several studios that have one or two API or Neve modules in small, wood boxes, but the V78 puts out a lot more heat. Can I mount the unit in a small box, or does it need several inches of air space above the vent holes?

    Need, probably not. But those tubes are so ^#$%ing expensive, why risk shortening their life? It's not like they're getting any more plentiful as the days go on, nobody's made an EF 804 [I forget what the other one is, but it ain't cheap either] in years.
     
  4. Originally posted by Fletcher:


    Need, probably not. But those tubes are so ^#$%ing expensive, why risk shortening their life? It's not like they're getting any more plentiful as the days go on, nobody's made an EF 804 [I forget what the other one is, but it ain't cheap either] in years.


    I find that elevated line voltages will kill tubes faster than anything. The problem is caused by these modules have unregulated power supplies which means that the B+ and Heater voltages follow along with the wall voltages.

    It is *very* important to feed these modules exactly 220 volts. I use a variac in line with the wall voltage and into the step up transformer to exactly set the line voltage. Elevated heater voltages will kill tubes quickly. Happened to my BA6A, it killed a pair of v-mu tubes very quickly. I had to add a resistor to the heater voltage control pot inside the limiter to get the proper range of adjustment.
     
  5. hollywood_steve

    hollywood_steve Active Member

    Joined:
    Jan 3, 2001
    Thanks guys for all of the info. A couple of comments:

    1. The reason that I want to build some sort of enclosure is that I need to be able to move the modules around for some limited location recording. And I like the protection offered by even a simple wooden box.

    2. According to the schematics, the V78 takes two EF804S tubes and these suckers now run a minimum of $50ea; more like $100 for "sealed NOS." (maybe I should take a class in Glass Blowing at the local Arts & Crafts center.....)

    3. I'm hoping that the voltage fluctuation problem will not be an issue. The rental space I'm now looking at as possible home for the studio includes a fairly sophisticated power "conditioning" system according to the landlord. But I have no idea yet what that really means.

    I've finally had a chance to use the V78 since it was returned from its recent servicing. With a Royer R121 into the V78 and then straight to DAT, it sounded just like you would want a tube preamp to sound. nice, very nice.

    sjp@pacbell.net
     

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