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lowering 5f1 voltages

Discussion in 'Amp Tech Center' started by Ronno25, Feb 10, 2021.

  1. Ronno25

    Ronno25 TDPRI Member

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    I just built a 5f1 from some organ transformers. It sounds pretty cool. The voltages are high when compared to expected voltages for a 5f1. I used a 340-0-340 power transformer so this isn't a surprise. I understand there are two methods most people use for lowering voltages: Zener diodes or a high wattage resistor. I'm hoping for some guidance on which method to use, why, and how to do it. Some specifics would go a long way to helping me out. Thanks!

    unnamed-1.jpg unnamed-2.jpg
     
  2. Jon Snell

    Jon Snell Tele-Holic

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    Resistors reduce the current and Zenor Diodes shunt or drop the voltage across them.
    Neither is a good idea in my opinion but if you placed a Zenor in series with each of the 340v feeds to the rectifier, that will drop some voltage.
    A pair of 47v 5W Zenors on heat sinks may do the job.
     
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  3. 2L man

    2L man Tele-Meister

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    Very good regulation comes using a FET circuit and it improves filtering too and it is easy to make adjustable as well. HiFi tube builders use it more than instrument amp builders but I have seen few documented uses on guitar amps. I think you find info searching "variable voltage regulation guitar amp" or hifi amp

    Installing a Choke is one method to lower operative voltage and improve filtering and it is called LC filter

    Installing more RC filters is easiest method to lower voltage and improve filtering and for a Single Ended amp it should work fine because its operative current change less than a PP amp. When a rectifier tube is used installing Current Limiter Resistors to rectifier anodes should be first step and if there are CLR changing them bigger is good when it improves rectifier tube life too.

    For me who has learned and worked with electronics 42 years I found new and interesting way to do filtering is using RCR where resistor is also installed to the beginning of the Ground Bus. Valve Wizard has wrote it shortly here in this grounding article link. I will test that on my 10W SE build which turrett board will be drilled in few days.

    http://www.valvewizard.co.uk/Grounding.html
     
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  4. D'tar

    D'tar Friend of Leo's

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    your heater voltage is spot on in your build thread.... I would throw a JJ in there and have fun playing. Tons of champ circuits burning hot out there!!!
     
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  5. Axis29

    Axis29 Poster Extraordinaire Silver Supporter

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    Try a Copper Cap Rectifier with a higher voltage drop. Easy, relatively inexpensive and safe.... Oh, and reversible if you don't like it simply by plugging your tube rectifier back in.

    I use 5w4 copper caps in my two big tweed amps, which usually take GZ34 tube rectifiers. The voltage drop is about 67 volts and puts all the other voltages inside my amp almost exactly in line with those on the vintage schematics. I love what it does for my tone in these two amps. Makes them sound 'right'.

    If your transformers support them, you can use different tubes instead of going to a solid state rectifier (It's about filament voltages). My two amps might... But, I couldn't be certain from the bit of research I had done, so I stayed on the safe side of things.
     
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  6. timfred

    timfred Tele-Meister

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    Play it for a while.

    Then if you still want to tinker here’s one trick if you are only worried about the power tube:

    Add a second 470 Ohm 5w power resistor between your cathode resistor and ground. The junction between them is an elevated ground that drops effective plate voltage by 20V or so. Connect the grid leak resistor to this new elevated ground. Keep the bypass cap connected to the actual ground.
     
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  7. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    +1
    Play it awhile.
     
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  8. Ronno25

    Ronno25 TDPRI Member

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    Alright guys I'm gonna play it for a while. I'm also going to pick up a JJ 6v6s. Euro Tubes is in town so I can swing by there and get one today. This tinkering thing is addictive and I get pretty curious about how things will sound with lower voltages aside from the reduced plate dissipation on the 6v6. I'm probably going to add a switchable NFB or a switchable value on the V1 bypass cap. I drilled an extra hole for it in the chassis to give me the option. Haven't yet decided what choice would be the better mod but I don't have space for both.

    Out of curiosity, why is neither a good idea?
     
  9. Commodore 64

    Commodore 64 Friend of Leo's

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    Assume you are already using a 5Y3?
     
  10. Ronno25

    Ronno25 TDPRI Member

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    I picked up an old Tung Sol 5y3 with the radio/record player I got the transformers out of. In fact all three tubes in there are old Tung Sols right now.
     
  11. Spats Davenport

    Spats Davenport TDPRI Member

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    I did this a long time ago, I think it involved a zener between the centre tap and ground.
     
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  12. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Another thought is a bucking transformer. It would knock down the wall voltage to around 110VAC. The lower voltage on the primary would drop the secondary voltages of the PT.
     
  13. akuster777

    akuster777 TDPRI Member

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    try different old 5y3 rectifier tubes, then measure voltages and listen for what you like
     
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  14. Ronno25

    Ronno25 TDPRI Member

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    So I went out and got a JJ. I have to say the sound is better with the Tung Sol. The JJ sounds okay, the low end is a bit tighter (which is nice), the highs a bit shriller, and the cleans less sweet. It sounds more generic for lack of a better way of putting it. I have swapped out tubes in other amps and haven't noticed much of a difference so this 5f1 must be sensitive to tube changes.

    I snapped some pics of the Tung Sol lit up. Can you guys tell if it's red plating from the pics?

    627c7b3f-d79d-45d1-a833-9956bed437a5.jpg abdaccb3-6ebf-4598-b32c-94a77ed41f78.jpg
     
  15. sudogeek

    sudogeek Tele-Meister

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    I’ve played around with champ circuits for years and, when I build one and in my current CLO (Champ-like object), I recommend an additional filter stage. Add a 16-22 uf cap and a 100–1000R resistor in front of the regular filter caps. I usually use cap cans so this is easy. Anyway, much less noise and really no sonic difference from a regular vintage circuit. You can size the dropping resistor to taste to achieve whatever your target voltage is.

    But actually, if it sounds good and is not on fire (at the present moment), play it and enjoy it.
     
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  16. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Nice description of the sound difference with the JJ. I have never been able to articulate it but imo you hit the nail on the head. That is the way they sound to me.

    Redplating. Look up this on youtube:
    Red Plating Power Tubes Fix - 1966 Fender Blackface Bassman
    Start watching at 24:26
     
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  17. Ronno25

    Ronno25 TDPRI Member

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    This is super helpful. Okay, well then my tubes are definitely NOT red plating.
     
  18. Ronno25

    Ronno25 TDPRI Member

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    I took some voltage readings with three different 5y3's I had in other amps - 2 RCA's and a Sylvania 5y3WGTB. Pretty interesting.

    Here are the specs:

    Both RCA's were virtually identical:

    B+1 386
    B+2 350
    B+3 306
    V2 p8 22.4
    NFB 1.42
    V1p6 203
    V1p1 207
    V1p3 1.45

    The Sylvania was a B+ of 387 and then consistent thereafter relative to the RCA's.

    I also took the readings again with the Tung Sol and they dropped to about a B+ of 395 since my initial reading.

    Sonically I couldn't tell any difference between any rectifier changes, despite that drop in voltage of about 10.


    Edit*** I found another Sylvania 5y3. Voltages were just below the RCA's:

    B+1 385
    B+2 348
    B+3 305
    V2 p8 22.3
    NFB 1.41
    V1p6 202
    V1p1 206
    V1p3 1.44
     
    Last edited: Feb 10, 2021
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  19. Ronno25

    Ronno25 TDPRI Member

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    Well, despite the higher voltages I've decided to keep the Tung Sol 5y3 in there. It could be my imagination (and probably is) but it feels like it gives the amp a touch more character - it sounds a little nastier (maybe this is the difference of 10 additional voltages), which is good for the little champ that could get overly mushy and mellow.
     
  20. Commodore 64

    Commodore 64 Friend of Leo's

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    OK, I wish I'd have seen your voltages before. Your first post, why are there no voltages?

    Your cathode is what? 20ish volts? Your Plate voltage is then, about 360-370?

    There's nothing wrong. Put whatever tubes you want in there and make sure it ain't redplating (set the bias). There is not, and never has been, an issue here.
     
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