Tube amp design relative to tube manufacturers

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mbratch, May 3, 2008.

  1. mbratch

    mbratch Member

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    I was fussing over my Pro Reverb today with a few choices in 6L6 at my disposal. I have a set of old RCA 6L6 that are original to the amp. Unfortunately, one is a little loose mechanically inside. And I have a couple pair of Sovtek (6L6GB and 6L6WXT+) and pair of Fender labeled 6L6B GTs.

    I've tried each of these sets in the amp, did a bias adjustment each time.

    I have to tell you the RCA's earn their reputation for simply being sweet sounding. The other ones just sucked being more or less excessively cold, spikey, sterile, and/or brittle in varying degrees depending upon the tube. The RCAs went back in.

    This got me thinking, though...
    • Do the old tubes sound good in these old amps because that's what the designers had to work with when they designed these amps?
    • Do a lot of new builds sound better with NOS tubes because the designs are based mostly upon the old amp designs?
    • If a new amp design were developed around the characteristics of what are currently some "less desirable" tubes, would the new amp then sound great with this tube, and not as good with NOS tubes?
     
  2. SatelliteAmps

    SatelliteAmps Member

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    Some amps are very touchy about tubes. Most times when comparing vintage vs. new tubes, it is easy to tell a difference. If an amp sounds good with current tubes, it will almost always sound better with NOS tubes.

    Very few amp designers are thinking about specific tube brands when designing an amplifier. Those that do, usually suffer eventually when their personal supply of NOS tubes runs out. And most consumers don't like to be forced into buying expensive tubes all the time. And, new tubes and old tubes all have variations that make it difficult to apply specifically to a design.

    The differences in current made tubes are somewhat of a personal preference to the individual player. Some people love the sound of brand new cheap tubes.

    It has nothing to do with being a new or old design. Most amp designers today are putting their own spin on tube amp design and coming up with great stuff.
     
  3. groovy daddy

    groovy daddy Member

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    A good tech told me the old tubes used better metals and coatings and were better made internally. I have a set of RCA 6L6 1966 used a lot-still good. I wanted to save them so I called The Tube Store for replacements. I told them the amp (66 Bassman), type of music (old rock and roll). They recommended TAD 6L6WGC-STR. I don't know if they got lucky but these biased and balanced nearly identical to the old tubes. Don't sound exactly the same but very good-no complaints.
     
  4. mbetter

    mbetter Member

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    Wasn't the Dr.Z Z-28 designed around the EH 6V6?
     
  5. Blue Strat

    Blue Strat Member

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    Some amps are more responsive to tube changes than others. I've seen no correlation between amps that were "designed" around modern tubes (which I feel is complete BS) and those that weren't.

    The amps with the most minimal designs, which often sound the best, tend to be the ones that respond the most.

    YMMV.
     
  6. donnyjaguar

    donnyjaguar Member

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    I agree with Bluestrat's last sentence. A simple amplifier will have its gain optimized in the low-signal section and generally will be running no loop negative feedback. For these two reasons any variance in tubes will likely be noticeable.

    In all honesty, this is bad engineering. But its done to keep costs as low as possible. A good design will consider variances in components values so when they age it won't be as noticeable. NFB power amplifier design is a good example here, and 12AX7 tubes with 100k plate resistors. :)
     
  7. mbratch

    mbratch Member

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    I see what you mean, but I guess it depends on how you're defining "bad engineering".

    Good engineering means I designed something that meets my specifications. Specifications might or might not include working equally well with different tube manufacturers. It actually might not even include optimizing tube life. Thus, we get "badly engineered" amps that sound great because tube life, or resilience to tube brand were not significant requirements relative to sound/tone. What makes amp design life interesting I suppose is that requirements include subjective items, like tone, high on the list...
     
  8. mbratch

    mbratch Member

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    Mike, I guess the word I selected, "design", is too strong a word in my original quesition. And I hope I didn't suggest that amp makers "design" around modern tubes versus vintage.

    But when designing and building a new amp, there's a lot of experimenting and tweaking that goes on I would think, that lead to adjustment in component values, minor circuit adjustments, etc. When this test-tweak cycle is being done, would the results be somewhat different if new production tubes are used in the process versus NOS? In some cases (I think it was stated) amp makers try to tweak it "in the middle" to optimize the sound for both cases.
     
  9. jimkelly

    jimkelly Member

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    Wasn't the Dr.Z Z-28 designed around the EH 6V6?

    I like the EH 6V6. My '61 Ampeg Jet sounded better with the EH's than the original Sylvanias (could just be the Sylvanias were worn out) and definitely better than a new pair of matched Tung Sols.
     
  10. Blue Strat

    Blue Strat Member

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    Differences? Probably. Better or worse? Impossible to say.

    Anyone who's been hanging on this board for more than 10 minutes knows that there's no consensus on tone.

    Basically, this is a non-topic...or a topic that can only be addressed on a one by one basis. No one else's experience is likely to mirror yours.
     
  11. mbratch

    mbratch Member

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    Well, there does seem to be some consensus on tone, since most people who have tried NOS tubes in their amps rave about them. Which is what triggered my thinking and question to begin with.

    Non-topic? Aw now, Mike, don't tell me you don't find this discussion thought-provoking. ;)
     
  12. Blue Strat

    Blue Strat Member

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    We can think about it all we want but we'll never get closer to the truth than by actually experimenting to see what WE like;)
     
  13. Swarty

    Swarty Member

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    True for both preamp and power tubes.
     

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