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Tube Selection for 5F6A Bassman

Discussion in 'Amp Central Station' started by vonasemj, Jul 8, 2013.

  1. vonasemj

    vonasemj Tele-Meister

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    I finished building a Bassman clone with PPIMV mod last month, and did all my startup procedures with JJ tubes. I have a 5751 in V1, 12ax7's in V2 & V3, 6L6's in V4 & V5, and a GZ34 rectifier. I tried both 12ay7 and 12ax7 tubes in V1, but found that I like a 5751 best. I like the tone from the amp, but feel like I could get smoother gain and better harmonics from different tubes, specifically NOS that everyone insists are better. I do use the amp as a practice amp sometimes, so with the master turned down I am looking for good preamp distortion as well. If you had say $150 budgeted for new tubes, what would you get? I have been looking at KCA NOS and Hi Test Tubes, and I certainly wouldn't be able to get all new tubes for $150, but it would buy me a couple. My first instinct would be to replace V1 and V3 since I've heard that V1 and the PI make the biggest difference. Are there any particular tubes that really standout as a best buy for the money? Also, would it be worth it to think about Tung Sol 5881's in the future? My amp has around 450-460 volts at the plates. I play mostly classic rock and blues.
     
  2. bluesky636

    bluesky636 Tele-Holic

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  3. Minivan Megafun

    Minivan Megafun Tele-Holic Gold Supporter

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    Wait, did you say "master" as in master volume? The 5F6A Bassman does not have a master volume so you cannot turn it down and still drive the preamp.
     
  4. SoK66

    SoK66 Tele-Afflicted

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    If your clone has a voltage compensated PT (tuned to modern line voltages) try running a set of NOS Tung-Sol 5881s for power tubes. Try a good quality GZ34 in the rectifier socket, too. 5881s do just fine up to around 450vdc on the plates, but a bit less, in the range of the 5F6-A's 440-ish spec, is best. Pair those with some quality old production 12AX7s in V2 & V3, and kick it off with a good 12AY7, or your 5751 in V1 and you'll be in the pocket.
     
  5. vonasemj

    vonasemj Tele-Meister

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    Yes, there is a LarMar Post Phase Inverter Master Volume installed in my amp.
     
  6. vonasemj

    vonasemj Tele-Meister

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    I have a Classic Tone PT and I get around 460 volts at the plates with 121VAC from the wall. I know a 5R4 rectifier will drop around 30 volts. They are only about $25 for NOS RCA, so I'm thinking that might be worth a try. Will a $155 Mullard GZ34 make a big difference over the JJ, or is it more of just a reliability issue that people decide to go with the Mullard's?
     
  7. dmagalhaes

    dmagalhaes TDPRI Member

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    I have RCA 5881's and a 5R4 in mine with a 6072 and 2 12ax7's in the preamp. The secret weapon for these amps is a 5R4 rectifier. The amp will give it up much earlier. You could also try 6L6WGB's as they are essentially the same as a USA 5881. I've stocked up with 5 pairs.
     
  8. Gringo13

    Gringo13 Tele-Holic

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    I run the same tube line-up, except I use modern Tung Sol 5881. I agree that the 5R4 makes makes a world of difference. I love this amp.

    I sometimes alternate between 12ay7 and 5751 inV1 and used to run 12ax7 there but don't like it as much.

    The modern Tung Sol 5881 are actually great tubes and worth trying.
     
  9. Inventour

    Inventour Tele-Holic

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    ___________

    I am into the Bassman Twin 5F circuit, I took my 1958 Bassman out of the amp and made a new 4x12 cab out of maple for the Celestion Blue ALNiCO,
    now this amp is one of the most amazing I have played in a 40 watt class.

    You will lose some tone with the Lar/mar, you may be better off returning the amp back to stock, change the NFB Resistor from 27k to either 47k or 56k and see how you like that. The nice thing about this amp is you mcan constantly tweek and tune it up. I have these really strong alligator clips and I solder a resistor to the two clips so I can add to the NFB Resistor to do a quick test, this way I can find the tone I'm looking for.

    Here is my 4x12 Bassman.

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  10. CyanideJunkie

    CyanideJunkie Tele-Holic

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    A good NOS 5751 would fit just fine in V1 for your application. As for V3, I've had great results with the Sovtek 12AX7LPS. Most have had good experiences with the JJ ECC803S for a PI tube as well, but I've never tried one for myself. Make sure you have a strong, hardy tube for your V2 cathode follower. If you're going modern glass, stay away from tubes with a spiral filament.

    As for your power tubes, it would depend on your taste. 5881s would lower your total output, allowing your amp to break up easier. 6L6s would give you better headroom. The original 5F6-A circuit calls for 5881s so if you're going vintage-accurate, that would be your pick. I use Tung Sol 6L6GC-STRs which are kind of an in-between tube. Try it out and see for yourself. Don't forget to re-bias though!
     
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