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    6L6 IN ST120?



    Posts : 1292
    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

    Posts : 2382
    Join date : 2008-11-26
    Location : Massachusetts

    Re: 6L6 IN ST120?

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


     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 ...



    Posts : 1292
    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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