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RE: Oh wow! So I could do that too with my ST-70?

174.18.9.42

In Reply to: RE: Oh wow! So I could do that too with my ST-70? posted by Cougar on March 15, 2023 at 12:40:22

I've had a VTA (or Bob Latino at the time) ST70 for over a decade. This amp came stock with the 12AT7 board. Fortunately at least in my case, I've been quite happy with the 12AT7. Another friend who has the ST120 recently had the 6SN7 board installed. This replaced his 12AU7 board. Although he wasn't unhappy with the 12AU7 board, he says the 6SN7 board and companion 6SN7's of course have been a noticeable improvement. He had bought a 6SN7 adapter, but opted instead to do the entire board. So using a 6SN7 adapter in the middle position of the 12AU board seems to be a good inexpensive option to try for either the ST70 or ST120. Some may later opt for the entire board or be perfectly happy with just the adapter. Regardless, I think the VTA amps are some of the best value tube amps out there. I never tire of listening to mine even though I've got another P-P tube amp that lists for 2.5X
the cost of the ST70.

Follow Ups:

RE: " he says the 6SN7 board have been a noticeable improvement" - 1973shovel 16:08:39 03/15/23 (6)
According to Roy Mottram, on the VTA forum, about 90% of his customers who tried both the 12AU7 and 6SN7 board, prefer the 6SN7 version.
I only wish I'd tried the 12AU7 socket to 6SN7 tube adapter in the gain section years sooner than I did. The improvement took my ST-70 with the VTA board from an amp that almost never left storage, to one I can now enjoy listening to.
Oh, and for the record, according to Bob Latino himself on the VTA forum, the amps aren't, and have never been "Bob Latino" amps, as shown above.

Edits: 03/16/23
- Thanks, and one clarification question - JoshT 07:29:25 03/16/23 (5)
  Are you continuing to use single 12AU7 socket to 6SN7 tube adapter or was that just a stepping stone for swapping in a new board?
  
  I've emailed Roy and he confirmed the single tube approach works, but I get the sense many people do that as an interim step to confirm its an improvement before replacing the entire board. I'd really rather not replace the entire board because it's a new amp and I am already enjoying it as is.
  
  Thanks!
  ___
  "If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."
  - I continue to use the adapter - 1973shovel 08:21:37 03/16/23 (4)
    ...but that's only because this ST-70 with the VTA driver board is one of my back-up amps, and only sees occasional use. If it were my main, best sounding amp, I'd opt for the octal board over the noval.
    
    Regarding tube adapters in general, Jim McShane told me that they can sometimes cause somewhat diminished highs, depending on the particular tube and circuit. I didn't notice that in my system. but eliminating them with the proper octal socket(s) for the 6SN7(s) would really be the best way to go.
    - I ordered an adapter - JoshT 06:48:56 03/17/23 (3)
      I bought one based on a link from Roy and received an email from the seller - screen shot below.
      
      Is this just a generic warning about putting a 6 volt tube in a 12 volt tube socket? I assume it would be a concern if I were replacing all three tubes but isn't where I'm just replacing the center tube?
      
      Thanks for your input on this.
      
      ___
      "If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."
      - RE: I ordered an adapter - 1973shovel 07:33:19 03/17/23 (2)
        
        In Reply to: RE: I ordered an adapter posted by JoshT on March 17, 2023 at 06:48:56
        
        All tube filaments in a Dynaco ST-70 (including the VTA version) use 6.3 VAC, other than the 5AR4 rectifier. So the 6.3 V adapter is the one you want, even if you were adapting all three driver tubes.
        
        Continuity meter - 1973shovel 08:07:54 03/17/23 (1)
        
        In Reply to: RE: I ordered an adapter posted by 1973shovel on March 17, 2023 at 07:33:19
        
        I'm going to assume that you have a continuity function on the meter you use to check tube bias. If so, above is a crosscheck I came up with from the data sheets of the two tubes, to be certain that the adapter is wired correctly before you use it in your amp. I wasn't willing to leave the adapter to "It's probably OK", and it only took a minute to test.
        
        The column on the left are the 12AU7 pins, and on the right are the corresponding 6SN7 sockets.
        
        Good luck with it, and I strongly suspect you'll soon be a member of the 90% Club (who prefer the 6SN7 over the 12AU7 in the VTA). Please keep us posted.
        
        Thanks again! - JoshT 10:57:10 03/17/23 (0)
        
        In Reply to: RE: Continuity meter posted by 1973shovel on March 17, 2023 at 08:07:54
        
        Now to order a tube, most likely from Jim, Brent or the Tube Depot. Or an Inmate, lol. I've had good luck in the past with all four sources. :-)
        ___
        "If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."

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