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New 5e3 kit build

Discussion in 'Shock Brother's DIY Amps' started by Romartin, Oct 16, 2017.

  1. Wyatt

    Wyatt Tele-Afflicted

    Nov 3, 2004
    What is the voltage between Pin 3 to Pin 8?...Should be around 350VDC (plate minus cathode)? That's the "actual" plate voltage in a cathode-biased amp for bias calculations.
     
    Last edited: Dec 18, 2017

  2. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    His math is right. That one tube, at least, is idling stupid hot - something like 15W. We might end up at something like 470r, or using a zener diode to pull down the B+ voltage some.
     

  3. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    The zener stack has been popular lately:)
     

  4. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Yeah, let's give dropping resistors equal time! :) Just kidding, mostly, but to be fair, putting a 470 5w wirewound between rectifier and first filter cap in my Vibro Champ was trivially easy and got my B+ totally in line. In my kindergarten understanding, a resistor does the same thing to B+ and generates the same heat as an equivalent zener stack; the difference is it adds some sag and bloom. I happen to like that in a vintage amp -- my VC sounds about as sweet as an amp can sound.

    Edit: Maybe you experts can comment. I had the impression that adding either zeners or a dropping resistor as above has some advantages over altering the cathode resistor, which can drop B+ but have effects on other downstream voltages. Am I even close?

    Also, I lost track, Romartin, but have you tried other 6V6s? I'm often amazed how variable power tubes can be as to plate and bias voltages.
     
    Last edited: Dec 18, 2017

  5. Romartin

    Romartin TDPRI Member

    Age:
    33
    68
    Aug 7, 2017
    USA
    So where did you put the resistor? Do you have any pics of this? I would love it if all i had to do was add a resistor to drop the voltage.
     

  6. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    You're right, it's pretty easy. BTW while you were typing, I edited my prior post with a question for you and one for the smart guys.

    I was gonna find a pic, but the layout of a VC with a cap can and all that space in the tray chassis won't be that helpful when you're looking at a 5e3. You just plunk the resistor into the wire run that goes from pin 8 of the *rectifier* to the first filter cap, the wire where the red star is...

    Layout 5e3 B+ R copy.png
     

  7. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY

  8. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Adjusting the bias resistor most likely will end up leaving 400+vdc on the 6v6 plates when you achieve proper dissipation. Adding the resistor before B+ node one will work, may change character I can't speek from experience there. The zener stack can be added to reach your desired goals and leave the circuit at stock values. I am surprised at your experience with the nos 5y3 rectifier.
     
    King Fan likes this.

  9. Romartin

    Romartin TDPRI Member

    Age:
    33
    68
    Aug 7, 2017
    USA
    Same here, I was very disappointed that the nos 5y3 was higher than the JJ 5y3. Ive read that the zener stack needs to have a heat sink etc due to excess heat. Does anyone on here have a good tutorial on this? Im really just considering ordering a different power transformer with lower output.
     

  10. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    For a good zener experience with no heat-sinks, see the recent 5F2a build thread by @theprofessor ...
     

  11. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    Yes, all I did was use two alligator clips--one on each lead of the zener--as small heat sinks, just like I did with other components on the board. I don't think anything else is necessary. I could be wrong, but it worked well in my case!
     

  12. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    mount them as shown above. no extra heat sink required. use heat sink while soldering then remove. Leave air gap/space around the diodes.

    $0.47 ea, much cheaper than a new PT
     

  13. theprofessor

    theprofessor Friend of Leo's

    Aug 8, 2016
    Chattanooga, TN
    I mounted mine between two terminal lug strips that I elevated off the chassis with a nylon washer (just to make extra sure that the grounding lug didn't ground out the setup in any way). You see the red-and-yellow wire (the PT's center tap) in the picture coming into the first zener's anode side. Then you have the zig-zag of the three zeners. Then there's another red-and-yellow wire that comes off of the last zener's cathode side. That wire is grounded together with the B+ wire through a ring terminal that is attached to the chassis.

    Be sure the zeners you use are rated at 5W. I used a 14V (5W), then two 12V (5W) ones. 38V volts of zeners dropped my B+1 32 volts, from 391V to 359V.

    IMG_9598.JPG IMG_9599.JPG
     

  14. Romartin

    Romartin TDPRI Member

    Age:
    33
    68
    Aug 7, 2017
    USA
    Thank you all for the responses, I really appreciate the info! I guess now what I need to do is figure out how much voltage I need to drop. Ill keep you updated. @theprofessor, @King Fan, @D’tar
     

  15. tombob

    tombob Tele-Holic

    Age:
    45
    573
    Jun 25, 2010
    Sonora, TX
    image.jpeg image.jpeg

    I finished my 5e3 build! I'm still unsure why the kit I bought came with a 5ar4 rectifier. I was getting 17 watts (!!) dissipation with it and started redplating my (14w) EH 6V6s. I have a nos Tung-Sol 5y3 that brought everything down to where it needed to be though. I'm really surprised to hear you got more voltage drop with a new JJ 5y3 than a nos. They must have made 10 million 5y3 tubes in the USA though, good NOS ones can be found cheaper than new production in most cases. I have tried the 5AR4 with 5881s and it works great and the PT stays cool enough to hold my hand on it. My 5e3 has a 25 watt OT so with the 5AR4/5881 setup it's very loud and has a lot of headroom (for a tweed Deluxe) it stays clean over half way up the volume range (tweed "clean" that is, like a slightly hairy clean). I have a NFB switch, PI grid resistor and screen resistors on the output tubes now. I also did a improved grounding bus with single point ground. I want to get a 1M push/pull audio pot the next time I order electronic parts and add the Framus type Mid Control. I'm thinking I might order a concentric 1M pot for the volume pots so I will have volumes/tone/mid control instead of volume/volume/tone. I'm really happy with it. Now I need to start thinking on cab/speaker options.

    I got a lot of inspiration watching your build Romartin and really appreciate you sharing your experiences with yours. Thanks for your openness and willingness to discuss your experiences good and bad!
     
    robrob likes this.

  16. Romartin

    Romartin TDPRI Member

    Age:
    33
    68
    Aug 7, 2017
    USA
    Wow,that is so awesome! Congratulations on the new build, it looks very nice! What is your plate dissipation with the nos 5y3? Let me know which cab and speaker you end up with. I’m still waiting on my cabinet to be finished. Once I have it though, I’ll post some pics. I ordered a MOSFET and Zener diode setup today, from Grangeramp, to try and bring my B+ down 30 volts or so. Ill post the results once I have it finished.
     

  17. tombob

    tombob Tele-Holic

    Age:
    45
    573
    Jun 25, 2010
    Sonora, TX
    I'm showing close to 13 watts with 5y3, I really think that's a bit higher than what it's doing from the sound (I usually end up using my ears as much as my multimeter when I bias a amp anyway). I use the current across the cathode resistor method to check it which isn't very accurate. I would change the 240r cathode R to a 270-300r if I was going to run 6V6s all the time but it's good now as long as I stick with EHX or JJs but I have decided to run a 5881/5AR4 setup. It's doing 17.5 watts with the 5AR4 and 5881s and with the 25 watt OT it's loud and has lots of headroom. I found another poster on here using the same kit with 6L6s for gigs where it's on for hours and he hasn't had any PT problems. Mine hasn't gotten very hot with them either. If I decide to go to 6V6s all or even most of the time in the future I'll bump up the cathode resistor but I think it's going to be the perfect club 5e3 with the 5881s.
    I have a couple of solid pine speaker cabs I built a while back. I haven't made my mind up for sure yet but I'm thinking about converting one of them into a combo cab then use the other for a matching ext cab. I like the idea of a 2x10 amp with a 1x15 ext. I've always been a fan of the 10/15 mix.
     

  18. jjmantele

    jjmantele Tele-Holic

    985
    Aug 23, 2003
    New Jersey
    I keep a selection of 5wt resistors from 150R to 2k so I'm ready for cathode biased outputs and screens. With all the variables involved, having good results from the one cathode resistor value provided in a kit is a crap-shoot. I guess some kits out there might include a few values. My guess is most probably provide the "vintage" value which is often not the best today. Just like providing the vintage 2-wire power cord setup would be unsafe and wrong today.
     

  19. tombob

    tombob Tele-Holic

    Age:
    45
    573
    Jun 25, 2010
    Sonora, TX
    There's too many variables for a single value bias resistor to always work. The vintage values were based on 110v wall voltage too, now 120-125v is closer to usual. One big thing, at least I would think is the fact that the voltage dividers, dropping resistors, etc. are rated to be within 5% or even 10% of the ratings. By the time you get all the way from the PT to the output tubes that could be a fair amount of fluctuation. With modern wall voltage 270-300r should be more of the standard anyway. I'm not sure why someone like Weber hasn't started selling a 500r, 8 to 10 watt wire wound adjustable rheostat. An adjustable cathode bias resistor would be great to have.
     

  20. tombob

    tombob Tele-Holic

    Age:
    45
    573
    Jun 25, 2010
    Sonora, TX
    Romartin I never seen you say anything about trying another pair of output tubes and seeing how they show their bias. I was going to mention that for this purpose you can stick a matched pair of 5881 or 6L6GCs in there if you don't have another pair of 6V6s. They're not going to sound their best since the bias will be cold but they should dissipate about the same wattage as the 6V6s (in other words they should show the same bias) and you can tell if one tube running hotter is a problem in the amp or a tube. I'm just talking about putting them in long enough to check the bias with them in and once you know if you have a unbalanced set of 6Vs or not you can put yours back/get a better matched pair of 6Vs.
    By the way, I'm really tempted to pick up a JJ 5Y3 to have after your results. I'd like to see how the JJ compares to the US made Tung-Sol 5Y3 NOS I have now.
     

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