Converting EL84 to 6V6 or vice versa?

Discussion in 'Amp Tech Center' started by schmee, May 30, 2019.

  1. schmee

    schmee Poster Extraordinaire

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    So I've been thinking about this, mostly for giggles. I once had a Carmen Ghia that I made 6V6 converters for. It sounded like crap.
    It's possible I did something wrong, but been afraid to try since. So here's my question:
    What things might need to be changed to convert an amp? I'm not talking big things like transformers etc as those should work out in many cases, but talking about more subtle things, resistor values etc.
    Any thoughts on what might need to be tweeked to do this ?
    Say you are going to convert a BF Princeton to EL84's.... it seems in theory it should be easy ... but... Do the tube adaptors you can buy do other things than just make the correct pin outs?
     
  2. JD0x0

    JD0x0 Poster Extraordinaire

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    You probably didn't factor in a ton of things like operating points of the tube and the output transformer's primary resistance. IIRC the yellow jacket converters run the EL84's in cathode bias and also limit the voltage and current the tubes are seeing. They aren't simply a pin out converter. It's very very unlikely that'd work out well.
     
  3. schmee

    schmee Poster Extraordinaire

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    Yeah, the voltages and primary OT were ok. Many Transformers are compatible with both 6V6 and EL84 usage. I noticed comparing the Tremolux 6G9 (EL84) to the 6G9B (6L6) versions the short lived 6G9 (and Fender's only vintage amp with EL84's) has a few subtle differences. Throughout the board actually. But it was so short lived I don't know if those were necessary things or just experiments on Fender's behalf as they didnt know EL84 amps. :>)
    I wonder if people who have had the 6G9 liked the sound, or if they even worked properly and consistently?
     
    Last edited: May 30, 2019
  4. VintageSG

    VintageSG Friend of Leo's

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    I've got a plug in converter to allow me to run an EL84 in place of a 6V6 in my Champ-a-like. Meh. Ideally, a resistor change is needed. I 'croc-clipped' another 470r in parallel and frankly, until the amp was really being worked hard, it sounded pretty much the same. Sure, there were a few differences. The EL84 had better treble response, the 6V6 better bass. Bear in mind I'm using better in a very loose way here, not an accurate way at all. Nothing an EQ pedal wouldn't solve. As the volume rose, the changes became more pronounced. Maybe the EL84 chimed and sparkled, while the 6V6 growled and rumbled?. The 6V6 had girth while the EL84 had projection. I doubt I could consistently tell the difference at anything other than high volume levels. At low, clean levels?, I wouldn't stand a chance. I get more changes from altering picking dynamics and position.

    http://www.ampmaker.com/infocentre/thread-120.html

    The link takes you to a schematic for an amplifier that can use either an EL84 or a 6V6 ( a 6L6 is on the cards too ). It shows how much needs to be altered in a simple, single ended amplifier. When Barry gets back from walkabout ( or whatever he's doing ) and re-opens Ampmaker for sales, I think I'll build one. It looks interesting.
     
  5. gusfinley

    gusfinley Tele-Holic

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    The bias voltage is higher on the 6V6 vs the EL84. Other than that they are considered "electrically equivalent."

    I once built a champ-style amp with two output sockets - one for EL84, one for 6V6. With only one tube plugged in, everything was electrically correct. I did some side-by-side testing and did not notice a difference in tone between the two.
     
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  6. schmee

    schmee Poster Extraordinaire

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    Interestingly though, Dr Z has made a revolution out of high voltage on EL 84's. My Ghia ran 450 plate volts and I've never heard an EL84 amp sound so glorious.! I wonder how that relates to bias voltage?
     
  7. Andy B

    Andy B Tele-Afflicted Gold Supporter

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    I converted one of my Blues Jr’s to 6V6’s. Had to change the bias setting. I also changed the screen and control grid resistors to Fender values of 470 & 1500 ohms. I also had to tweak the tone stack. I like the sound better with the 6V6’s.
     
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  8. dan40

    dan40 Tele-Afflicted Silver Supporter

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    As Gus mentioned, the el84 requires less bias voltage which means it also takes less signal to push the el84's into clipping than it does the 6v6's. You may need to alter some values in the PI to adjust for the differences.
     
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  9. gusfinley

    gusfinley Tele-Holic

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    The ultimate consideration is plate power disippation. This is plate voltage multiplied by plate current - in simplest terms. If you run the voltage high, you have to bias the tubes for less plate current to keep the dissipation in levels that don't exceed the tubes specs. There are also specs for maximum voltage. Both the specs for maximum plate power dissipation and maximum voltages are often pushed past their published "maximums." This is where watching for red-plating comes in handy.
     
  10. JeffBlue

    JeffBlue Tele-Afflicted

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    .......not trying to hijack the thread, I have a Carvin Bel Air and the board with the EL84 power tubes arced and damaged. I punched the chassis and hard mounted 4 octal sockets and wired it all up. Of course it isn't correctly working until I change the resistor values for 6V6s. Can someone please give me some direction? Thanks. I figure a Carvin Bel Air with four 6V6s would sound really good.
     
  11. gusfinley

    gusfinley Tele-Holic

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    Based on the REV E1 schematic you may need to adjust the voltage divider on your bias circuit. Measure across the bias voltage cap ( C38 ) to see what bias range you have already. I'm having a hard time find typical Class AB bias voltages for 6V6s at the moments, but they are typically a little higher than EL84 * which are around -14VDC). You may have enough range to run them as is.
     
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  12. uriah1

    uriah1 Doctor of Teleocity Ad Free Member

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    Tried a few of those converters in my day.
    All sounded thin and lifeless.
     
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  13. schmee

    schmee Poster Extraordinaire

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    Question: Has anyone here ever actually had a 6G9 Tremolux (el84) amp?
    How did the EL84's work in that Fender BF style circuit?
    Did Fender abandon it because it sounded crappy or other reasons?
    Inquiring minds want to know.... layout comparison:
    [​IMG]
     
    Last edited: Jun 1, 2019
  14. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    Okay, I finally have an opportunity to tell everyone about one of my infamous childhood electronic technician moments. I was about 14 and my friend Joe was about 12. This was back in the 80's, and he had an old TV at his house that was inoperable and we decided we were going to fix it. We took the back cover off and powered it up - noticed that one of the tubes was not glowing (whether or not it was supposed to is irrelevant), so we pulled a tube out of another TV he had to replace it. Well, the new tube had too many pins for the socket, so I took a pair of pliers and bent the "extra" pins out of the way, and forced it in the socket. To be safe (see? We were thinking about safety!), we turned a table on its side and hid behind it, then powered up the TV using an extension cord that we plugged into the wall from our safe location.

    It made a noise like a firecracker and smoke came out of the TV so we unplugged it.
     
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  15. JD0x0

    JD0x0 Poster Extraordinaire

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    No screen grid resistors, and I'm assuming they ran the plate and screen voltage kind of high, especially if they used the same PT. I'm assuming eating tubes and lack of a source of cheap 6BQ5's for fender making the change.
     
  16. schmee

    schmee Poster Extraordinaire

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    Yeah I noticed the lack of screen grids....
     
  17. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    I have 18w Marshall clones in both stock el84 and also one with 6v6 power tubes.
    Really not much difference, but I love access to all the vintage American 6v6 tubes, and sometimes notice more difference from one set of 6v6 to another, than from the el84 amp to the 6v6 amp.
    Like Ken Rad and Philips black plate 6v6 are more glassy, bassy and bright, than any other 6v6.
    All will be drawing slightly different current also, but most seem to be running well and not hot or cold.
    I think comparing an el84 Tremolux to a 6L6 Tremolux has just too much else going on to hear the tubes.

    Converters, may not be fair comparison, IDK.
    Tilting at windmills but fun nonetheless...
     
  18. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    Jim Kelley did the same with 6v6 but ran a less successful business.

    I doubt it was the tube type!

    Edit: note also that when Dr Z built a Plexi he chose 6v6.
     
  19. schmee

    schmee Poster Extraordinaire

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    Really? I can tell an EL84 amp right off. Has that high end fizzy kind of EQ in the mix. 6V6's are my hands down favorites too.
     
  20. telemnemonics

    telemnemonics Doctor of Teleocity Ad Free Member

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    Comparing different amp circuits?
    Seems fizzy is what designers assume buyers associate with el84 amps.
    Same with Plexi pedals, they sound fizzy like JCM800 circuits despite real Plexi amps sounding more creamy.
    My stereo amp has el84 and doesn’t sound fizzy.
    And neither of my 18w sound fizzy.
    Blues jr sounds kinda fizzy but orange OR 15 doesn’t.


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