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Crack;Bottlehead OTL

Discussion in 'Headphone Amps (full-size)' started by ironbut, Mar 9, 2010.
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  1. L0rdGwyn
    That is SHARP. Love it, nice attention to detail. Enjoy the amp!
    Wes S likes this.
  2. audiowize
    In the output stage, the output tube sees a certain amount of bias voltage at its grids (from the first stage), the B+ voltage, and the load under its cathodes. When you use a 5998, the magnitude of the grid to cathode voltage drops a bit, but that change is inconsequential for proper amplifier operation. The cathode follower also doesn't have any voltage gain, so the mu of the tube isn't a problematic parameter.
    cddc likes this.
  3. cddc
    @audiowize, thanks a lot for explaining the theory behind it. :thumbsup:
    Last edited: Jul 21, 2019
  4. cddc
    I second it. Great work from PB!
  5. cddc
  6. audiowize
    The 6SL7 is absolutely not at all acceptable for use in the Crack. With the Speedball, the plate voltage on the 6SL7 will not drop much below the B+, so the 6080 will have absolutely no voltage to work with and the current sink under the 6080 cathodes would end up dissipating way too much heat if it did. If any signal managed to squeeze its way out of the amp, it would be horrendously distorted.

    With the stock circuit, the situation is only 99% as bad as the situation above. The amp would still be useless in this configuration.

    The 6SL7 also has a very high amplification factor, and maybe one or two people in 13 years have asked for a Crack with more gain. The 6SL7 is also the most microphonic indirectly heated tube I've ever used, which is another attribute nobody is looking for.

    The 6SN7 will work just fine in a well made adapter though.
    Darthpool and cddc like this.
  7. cddc

    Great, learned a lot here before making any mistakes. Much appreciate it!

    6SL7 has an amplification factor of 70, which could be too high for Crack I guess (similar to the 12AX7 case discussed earlier)
    Last edited: Jul 31, 2019
  8. Wes S
    One can go to the bottlehead forum and the Crack tube rolling thread, has all the acceptable tubes listed.
    cddc and Darthpool like this.
  9. cddc
    Thanks a lot, mate! I read the list before, somehow the list is incomplete.

    I like tube rolling...Bottlehead Crack /w Speedball is a wonderful tube amp to me in that it offers lots of fun rolling tubes and sounds sublime...I wish it came with a 6.3V to 12V heater switch someday...LOL
    Wes S likes this.
  10. Wes S
    There are tons of rolling options for the power and driver tubes, and the fact you only need one of each, really makes it fun and easy to find good tubes. I am loving my BHC, and just rolled a new tube combo, that has me stunned. I rolled in a Bendix 6080wb slotted plate/copper grid post and Sylvania gold brand 5814a triple mica grey plate and all I can say is WOW!
    cddc likes this.
  11. cddc

    Indeed, a matched pair is always overpriced and harder to find compared to 2 singles...I think BHC is better than other tube amps for people who love tube rolling, coz it takes only one single driver tube and one single power tube. It makes rolling much easier.

    Bendix 6080WB slotted graphite plates is one of the top 6080's...glad you enjoy it.:)
    Last edited: Aug 1, 2019
    Wes S likes this.
  12. Wes S
    Yes sir, a tube rollers dream amp, for sure! The Bendix is a killer power tube, and I have tried several of the top tier power tubes, including the Tung Sol 5998, and the Bendix 6080wb is king.

    My next roll, is the famous driver tube, the Amperex 7316 long plate, which should arrive tomorrow and we will see if it can dethrone the Sylvania 5814a triple mica. The Sylvania dethroned the famous Mullard ECC82 long plate square getter, and that says a lot.

    Happy tube rolling!
    Last edited: Aug 1, 2019
    cddc likes this.
  13. audiowize
    This sounds like a good idea until you run the amp with the switch on 12V and a 6V tube installed. Either you destroy the tube or the power transformer.
  14. cddc

    That won't happen.....hahah:ksc75smile:....won't run a 6V tube over 12V socket, or vice versa
    Last edited: Aug 4, 2019
  15. m17xr2b
    My stock bottlehead crack rebuild is finished. Next up, another one but overbuilt with speedball

    20190807_211920.jpg 20190807_211927.jpg 20190807_211943.jpg 20190807_212307.jpg
    cddc, DavidA, LikeABell and 5 others like this.
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