Tubes Asylum

Mac 240 with GL reissue KT66 . What is your take.......

70.68.3.104

bouncy ball

My friend has a mac 240, he wants to retube it. I have read about using GL reissue KT66, can anyone share your experience with such combination?
I like the reissue kt66 as much as those grey bottle KT66 but have no experience with 240, your info is much appreciated.
thanks

Follow Ups:

RE: Mac 240 with GL reissue KT66 . What is your take....... - Jim McShane 16:49:37 04/11/14 (8)
Can the Mac provide the additional heater current required - about .35 amps per tube, that's the question...

If so, I'd recommend it but I'm not sure of the power trafo's capability.
- Yes,they can take the KT66s and here is why. - Michael Samra 19:07:17 04/11/14 (4)
  Jim and Walter.
  Notice that the Mc240 like other Mac amps and other vintage amps of the day have octal sockets on the front that power the Mac C8 mono preamps in the case of the Mac that each have three 12AX7s,a total six tubes that the amp would have to power along with its existing tube lineup in the amp.The 12AX7s in the preamp are running at 6.3vac where each tube draws 3/10 of an amp filament current,so you at least have 1.8 extra amps of filament current as long as you don't plug the C8 preamps into the amp.
  
  Always remember tho,and it is very easy to test whether or not you have enough juice to drive tubes with higher filament current..Simply plug the prospective tubes in and take a reading between pins 2 and 7 of the octal socket..It if reads between 6.2 and 6.4vac,you are not hurting your power trafo one iota because you are well within tolerance of the ratings.
  
  Honest amplification is better than excessive 2nd order distortion anytime.
  
  Edits: 04/11/14 04/11/14
  - RE: Yes,they can take the KT66s and here is why. - Jim McShane 09:35:10 04/12/14 (1)
    Mikey,
    
    Thanks for clarifying!
    - RE: Yes,they can take the KT66s and here is why. - catama 10:48:57 04/17/14 (0)
      What about Valve Art 350B's? Could they be used in the 240?
  - Mike, what do you bias these new KT-66's to? - FenderLover 02:01:31 04/12/14 (1)
    Same as NOS ones? Like 60-70% of 35 watt max per tube. Class AB1, push-pull?
    
    �Gracias tanto, para su conocimiento abundante!
    
    8^)
    - RE: Mike, what do you bias these new KT-66's to? - Michael Samra 03:06:55 04/12/14 (0)
      Steve
      That would be about right at 70% of 35 watts but lets make it easier and treat it as a 25 watt tube and bias it like a 6L6GC at about 45MA to 55ma at 425vdc
      
      Honest amplification is better than excessive 2nd order distortion anytime.
- Thanks Jim. That's my concern but I had read some stated no issue by doing so. (nt) - bouncy ball 17:09:06 04/11/14 (2)
  .
  - yes, they are reissue. thanks Mike, also when you have time - bouncy ball 19:32:38 04/11/14 (0)
    can you drop me a call or email. thanks
  - Are those reissues something or what? - Michael Samra 19:17:42 04/11/14 (0)
    They got that tube so perfect that I don't see how it can be bettered.Anyway,McShane that Mc240 with the Citation 2 kit and and change couplers and you will be flying high with that amp..It makes a huge improvement..You will be fine running KT66s as I do that in both of my Mc240s.
    
    Honest amplification is better than excessive 2nd order distortion anytime.

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