Reinhardt Bias Instructions?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Phil M, Jul 19, 2008.

  1. Phil M

    Phil M Member

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    I didn't see this on the site and I know Bob stops in here sometimes, but here goes.

    My Reinhardt JKC33 has the external bias points and I want to check the bias on the amp. I have a cheap $30 RadioShack multimeter that I used to use for my Allen Old Flame. The Allen just had a simple knob and was very easy to bias, but the JKC33 has a dial with numbers on it and there is also a little number in a window that increases or decreases as you do full rotations (2, 3, 4, etc.). What do those numbers all mean?

    Anyway, when I set my multimeter to "2mA" I get a reading of .020. Am I supposed to be doing DC millivolts? At any rate, I have not changed the bias and have left it where it is so as not to damage the amp or tubes. I'm really not even sure where 6CA7s are supposed to bias.

    Here's some additional info. on the multimeter I've been using:

    "15-Range Digital Multimeter. Measures AC and DC voltage up to 500V, DC current up to 200mA and resistance up to 2MΩ"
     
    Last edited: Jul 19, 2008
  2. goneracin

    goneracin Member

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    The numbers in the little dial are meaningless. The dial is just a locking brake for the pot, so that you cant accidently turn the pot and change the bias setting. As far a your meter, set it on dc milivolts, or dc volts. If it reads MV, the reading is direct, IOW 35MV = 35MA bias. If it only reads volts, it will read .035 volts for the same 35 MA bias. The tip jacks are reading the voltage drop across a 1 ohm resistor, so you are getting the correct reading. Some inexpensive voltmeters do not have any amp or MA capabilities, so its easier for the end user to just get any voltmeter, and read it in MV. Hope that helps man, and let me know if there is any other info.

    Bob
     
  3. Phil M

    Phil M Member

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    ah ha, thanks. I just sent you a PM, but basically my meter is reading .020. Way low, huh? Should I just turn the dial until they both read .038?
     
  4. Phil M

    Phil M Member

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    OK, I went down and tried again. I get to about .024-.026 and the knob stops turning.

    I had a thought though. I have my multimeter set to 2 mA--so when it's reading ".020" per tube, is that really .040? If that's the case, I'd want to back the bias dial down to .019 (to be .038).

    Thanks for all the help.
     
  5. reaiken

    reaiken Member

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    Pardon me for butting in here....

    That's wrong - it must be set to a "mV" range, or a "volt" range, not a "mA" range, like Bob sez...

    Randall Aiken
     
  6. goneracin

    goneracin Member

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    yes. If you are reading it on the MA range on the meter, its not reading what its supposed to. set the meter on either the MV range, or DC volts range or whatever you have, not the MA range.
     
  7. Phil M

    Phil M Member

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    There's a "DCV" range with 500V, 200V, 20V and 2V settings. There's also a "DCA" range with 200mA, 20mA and 2mA settings.

    My first readings that I did this morning were in the DCV range on the 2V setting and the tubes read .002. I wouldn't give me more detailed readings than that (like .0025, etc.).
     
  8. Phil M

    Phil M Member

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    It's not butting in, IMO. It's helping, and I appreciate it.
     
  9. goneracin

    goneracin Member

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    if the tubes read .002 dcv, with it on the 2v range, they are way cold. it should read something like .035 in that range.
     
  10. Phil M

    Phil M Member

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    I'd better call you
     
  11. Phil M

    Phil M Member

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    Guys here's why I wasn't getting good readings when I initially tried DCV settings earlier this morning: I had the power-scaling on '0', just like all the other controls. I had learned to turn all controls to '0' when biasing my old Allen. But with power-scaling the level control should be full up. Once I did that, it was easy to get it to go up to .035.

    Bob, thanks a ton for taking a call from a nobody on a Saturday. I learned a bit and you did a great job trouble-shooting. AND, I like the amp better now that the bias is fixed. At some point I'd still like to try the winged =C= EL34s that you recommended to me awhile back but these Siemens 6CA7s sound better now.

    It's been a good week. Between the A2 Marshallhead that I put in my Les Paul, adjusting the bias and "discovering" the vintage/modern switch I'm getting better tones out of the JKC33. I'm glad I didn't have any takers when I offered this amp up a few weeks ago.

    Thanks again, Bob. I'll let you know whether I'll go with a headshell or a 1x12 extension.

    --Phil M.

    Just Killer Combo

    [​IMG]
     
    Last edited: Jul 20, 2008
  12. Figher53

    Figher53 Member

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    FWIW, I made the same mistake awhile ago. I had no idea the power scaling level knob had to be at 10 for biasing. I biased my Storm with the level control at 5 or 6 and then later fried a set of 6v6's when I turned it up to 10. Hope this thread will help others who are biasing their amps in the future.
     
  13. Phil M

    Phil M Member

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    OK, just a quick update. I got some Penta KT66es and biased them around 32, so a little colder than the 35 I had the Siemens at. I will not get a chance to crank the amp until later, but they sound WAY better at lower volumes. A bit less gain (tube or bias value?) and sizzle, but the sizzle was what was annoying me about the amp in the first place. Rebiasing last weekend helped, but the KT66es sound a little bigger and rounder with less distortion. I wouldn't think power tubes would make so much difference at low volumes--I would've sworn the sizzle was coming from the preamp.
     
  14. Ud Reks

    Ud Reks Member

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    I once had 8 amps around the house (now down to 2) and just got tired of using the cheapo volt meters. So I bought a Weber Bias Rite, and it's been great. Yes, you can find something else to spend your money on, but it's one of the better tools I own.

    Of course, now that I'm down to two amps, the thing hasn't seen the light of day in many many months, but it's nice to know that it's around.
     

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