DRRI Replacement PT

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by pt ray, Feb 28, 2012.

  1. pt ray

    pt ray Member

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    I'm looking at converting my 65 Deluxe Reverb RI over to PTP and was going to use different trannies. However, the bolt pattern on the DRRI PT is not traditional and is actually the same as used on the Vibrolux (3-1/8X2-1/2). The secondary voltages for a DR and Vibrolux are almost identical (650v vs. 660v) but wanted to make sure I'm not missing something why this wouldn't work.

    DR PT
    Vibrolux PT
     
  2. SatelliteAmps

    SatelliteAmps Member

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    The only issue I see is that your heaters will run a bit on the high side, due to having extra current available. Its not a deal breaker though. Should work fine.
     
  3. pt ray

    pt ray Member

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    Thanks. I also noticed Allens advertises their Vibrolux PT as being a DRRI replacement. Looks like I wasn't too far off with my thinking.
     
  4. guitarcapo

    guitarcapo Senior Member

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    Why would the heaters run any different? Same voltage to the secondary to the same
    tubes.
     
  5. Prattacaster

    Prattacaster Member

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    Heater secondary current capability. However that problem is a small one and is worth working with if the Allen PT has the same mounting holes.

    To drop the heater voltage by .5 to .7vac do this:http://s1122.photobucket.com/albums/l530/Prattacaster/?action=view&current=Diodearrangement.gif

    I should clarify we are adding TWO opposite facing diodes to one side of the heater secondary. Install the pair of diodes on only one side of the heater secondary...so not exactly like the schematic above. This schematic above will drop about 1vac to 1.4vac since the diode pairs are on BOTH sides of the heater secondary. So if your heaters are running close to 7.0vac then one pair should drop the voltage to 6.3vac.

    Since they are facing in opposite direction and parallel the voltage is still AC. Very easy to implement.
     
  6. diagrammatiks

    diagrammatiks Member

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    you don't need to go through all that trouble.

    the classictones are rated with fairly good regulation.
     
  7. SatelliteAmps

    SatelliteAmps Member

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    It doesn't have to do with regulation or manufacturer. If you have more current supply than needed, then the voltage will run high, as Pratt explained above.
     
  8. guitarcapo

    guitarcapo Senior Member

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    I googled this term for an explanation of this phenomenon and google provided me this very thread.
     
  9. Prattacaster

    Prattacaster Member

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    Heater secondary is the term, current capability is the explaination. I hope for the OP that the heater voltage is not too high. Sometimes it is, and the method I posted is far better than adding series resistance. If your heater voltage is 6.7vac or more then add the diodes.
     
  10. pt ray

    pt ray Member

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    I'll keep that in mind.

    It looks like my question has already been discussed back in Sept. 2011. Google pulls it up but the link doesn't work nor can I manually go through the TGP archive and find it.

    I'll probably shoot Magnetic Components (Classic Tone) an email and see what they say on the topic. Not that I question anyone's input, just curious.
     
  11. guitarcapo

    guitarcapo Senior Member

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    Is there any place you can steer me as to why a capability to handle more current would raise voltages? I'm having trouble getting any explanation online.
     
  12. SatelliteAmps

    SatelliteAmps Member

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    I=e/r

    Ohms law. If current (i) goes down (less tubes) and no change in resistance (r) then volts (e) has to go up.
     
  13. guitarcapo

    guitarcapo Senior Member

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    I would think it would be more like a fixed (constant) secondary voltage based on the transformer winding ratio. Reducing resistance or impedance (less tubes) would result in reduced current utilized.

    I'm mostly interested in how the voltage on the secondary is going up simply due to a capability (or capacity) to handle more current being there. Is it due to some transformer imperfections?

    Also if "I" goes down and r is constant...why does "e" go up? Doesn't seem to make sense algebraically.
     
    Last edited: Feb 29, 2012
  14. pt ray

    pt ray Member

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    I understand why the voltage would go up but the Vibrolux has 2 less tubes (pre-amp) then the Deluxe Reverb.
     
  15. phsyconoodler

    phsyconoodler Member

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    Vibrolux REVERB.Has the same number of tubes,however,it uses 6L6 tubes that draw more heater current.The vibrolux PT can handle 4 amps of heater current and the Deluxe can do 3 amps.
    that means that it 'MIGHT' make the heaters draw less that the PT is spec'd for,meaning that the current would allow the PT t6o supply slightly higher heater voltages because it doesn't draw the PT down.
    Guitarcapo is thinking it doesn't matter,but it does because transformer windings are not regulated and the rely on the current draw they were designed for.
    In a perfect world they would have lots of capability and be regulated.In the flawed world of guitar amps,they only put enough windings in the transformer to handle the design.No more,no less.
     
  16. guitarcapo

    guitarcapo Senior Member

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    Well that's why I asked if it was due to some transformer imperfections. I didn't say it didn't matter, I was more interested in the mechanism of why it WOULD matter. Now I'm off to google this "regulation" business......
     
  17. pt ray

    pt ray Member

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    I know but the Vibrolux with or w/o reverb still uses the same power tranny. I speculate that the requirements for a DR and a V a close enough that the PT can be interchanged without issue. I can see issues if swapping between a Deluxe non-reverb and a Vibrolux reverb being that the requirements between the two are much greater. Again, speculation since I haven't crunched the numbers.
     
  18. guitarcapo

    guitarcapo Senior Member

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    Here's a good article:

    http://www.allaboutcircuits.com/vol_2/chpt_9/6.html

    Seems to me from the article that this would only be a problem if the transformer wasn't very good quality, especially given the small difference in current consumption involved. It mentions a type of transformer that's very well regulated called a Ferroresonant transformer...I wonder if there's any audio applications for these.
     
  19. phsyconoodler

    phsyconoodler Member

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    I've used overspec tranny's in lots of amps with no issues with heater voltages.However.....it's irresponsible for an amp tech to tell someone that it's ok to use something that may or may not be right for the job,in fact it's out duty as professionals to point out the differences and you guys can make the decisions you want.
    It's better to know the options first.
    FYI lots of higher-end audiophile equipment is regulated heavily.Not necessarily the transformers themselves but external regulator circuitry.
     
  20. guitarcapo

    guitarcapo Senior Member

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