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    6L6 IN ST120?

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    sKiZo

    Posts : 1310
    Join date : 2013-04-01
    Location : Michigan USA

    6L6 IN ST120?

    Post by sKiZo on Thu Feb 06, 2014 3:00 pm



    Title says it all ... I've seen some real raves about the sound of the 6L6 variants, and the TungSol new issues (6L6GC-SCR) look like an outstanding deal as well. They certainly do cram a lot of plate inside the bottle, and it looks to have some interesting kinks in the structure as well.



    Cathode type: Indirectly heated
    Heater voltage: 6.3
    Heater current: 900 mA
    Max dissipation Watts: 30
    Max voltage: 500

    I expect there'd be some power loss for total output, but not sure how all that would work or whether these would bias up  properly. Real world experience?

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: 6L6 IN ST120?

    Post by Bob Latino on Thu Feb 06, 2014 4:43 pm

    SKiZo,

     You could do it BUT ....

    1. The VTA ST-120 runs a B+ of just about 500 volts. The MAXIMUM DC voltage recomended on the plates for these tubes is 500 VDC. I don't feel that the tubes would last long looking at the maximum recommended voltage. In short > Tube life would be short running the tubes this hard ...

    2. I don't think that the VTA ST-120 would reach it's power rating with 6L6's in the amp. (you did mention this in your post)

    3. The bias sytem on the VTA ST-120 is for KT88's, 6550's or KT120's. It is posssible that 6L6's won't bias properly in the VTA ST-120. If they do bias OK, they will probably do it way over to one side of the bias pot's range. You could get around this by adding a resistor of 1K to maybe 3K for R39 on the bottom of the board. Right now R39 is a jumper wire on the VTA ST-120.

    The 6L6GC STR would (IMHO) probably be a great tube in the VTA ST-70. The VTA ST-70 runs 435 - 445 VDC on the plates and those Tung-Sol 6L6GC's would not be stressed out as much ...

    Bob

    sKiZo

    Posts : 1310
    Join date : 2013-04-01
    Location : Michigan USA

    Re: 6L6 IN ST120?

    Post by sKiZo on Thu Feb 06, 2014 4:55 pm

    Ah yes, R39 ... the mystery resistor!

    About as I figured though. I've seen them for $75 for a matched quad, and figured if anything, they might work out as a decent backup set.

    Have to keep them in mind for an ST70 - I keep eyeing one to power up the rear channels on my quad ... Not sure if I ever mentioned it, but the ST120 does that for the front speakers. That's why I did the dual jacks on the back so I could tie it into a tape loop as my Sansui QRX doesn't have pre out.



    Basic "Y" connection, only this one's an "innie" ...  clown

    PS ... I imagine the concerns about the B+ would be compounded even more with the high VAC line power I got here at the house. Reminded me that I did find a nice transformer to build a bucker and drop that.



    124 in with a 6.3 secondary should be just about perfect. Not sure about the rating, but it does weigh in at around 4 pounds, so I expect it can handle it ...

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