Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

The pearl of great price... NAD: 1976 Deluxe Reverb

Discussion in 'Glowing Bottle Tube Amp Forum' started by theprofessor, May 12, 2017.

  1. moosie

    moosie Poster Extraordinaire Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    No, sorry, didn't mean to say it that way. I should have said, I've never understood why it works when it's so far out of spec. I know they're overbuilt / conservative spec, but a 5V4 at 10uF, filling the shoes of a 5U4GB?

    The 5R4 is rated 4uF....
     

  2. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    @moosie - If you try this with your 77 DR, let us know what you think. I'm curious to know.
     

  3. moosie

    moosie Poster Extraordinaire Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Will do.
     

  4. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    Hey @slider313 and @moosie : Can you explain this input capacitance for rectifiers to me? I've decided to give a 5R4GYB a try after all. It's a lot cheaper than the other options, which is to pay about $175 for one of these (http://www.vintagesoundworkbench.com/Amp_Preserver.html) or even more for an Amprx Brown Box or whatever. I emailed Mike Kropotkin this morning about whether a switch from a 5U4GB in this amp to a 5R4 might get me closer to my target of ca. 430 volts. He said that it would get me closer, but that he couldn't tell me exactly how close. I mentioned input capacitance and asked if there were any issues with such a swap, but he didn't mention that in his response. So I assume it's okay?

    Can you explain these filtering specs to me, and what they mean? @moosie looked up the data and posted it on this thread: The spec 5U4GB is rated for 40uF, while a 5R4 is rated at 4uF. Any issues here?
     
    Last edited: May 21, 2017

  5. slider313

    slider313 Tele-Holic

    Age:
    60
    916
    Jan 6, 2011
    NC
    Going from a 5U4 to a 5V4 will raise the voltage, not lower it.

    You'll have to try a 5R4 or a 5Y3.
     

  6. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    Right! Sorry. Just a typo. I meant 5R4. I went back and edited the above post to that effect.
     

  7. moosie

    moosie Poster Extraordinaire Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    I found the issue of input capacitance on my own, reading data sheets. Posted it on the forum, and I recall Wally was interested - as in thought perhaps it wasn't nothing, but knew it was ignored all the time, and couldn't recall why things worked in the face of the data. That's what I recall, anyway. I think slider was on the thread, so maybe he remembers differently.

    Either in that thread, or with my own emails to Mike at KCA, can't recall which, I learned that Mike has no concerns with the deviation from spec, not even on a 5R4.

    So, perhaps I'm the only "sky is falling" person here, and I know very little. But WTF? "Overbuilt", is the only reason I've got, I think. It's entirely possible it's been explained and went so far over my head that I wasn't aware it was an explanation.

    But 40 vs 4, or 10, seems just... I mean, why have a spec at all, if it really matters so little? I dunno.
     

  8. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    Yes, for real. 10x the spec of the other on input capacitance, but no problem interchanging them?! I went back to an old thread of mine when I was thinking of running a 5V4 in my DRRI instead of a 5AR4 (which I eventually did) where @Wally mentions input capacitance: http://www.tdpri.com/threads/question-about-5v4-in-a-drri.688637/#post-7302271

    And just to drop another link here for my reference and yours, this is the page of tube data sheets that @Wally pointed me to in that thread:

    https://frank.pocnet.net/sheets52.html

    So: input capacitance numbers:
    GZ34: 60 microfarads
    5V4: 10 microfarads
    5U4: 40 microfarads
    5Y3: 20 microfarads
    5R4: 4 microfarads

    I used a 5V4 (10 uF capacitance) for a good while in a DRRI in place of a GZ34 (60 uF capacitance) with no issues at all, so why not a 5R4 (4 uF capacitance) in place of a 5U4 (40 uF capacitance)? Seriously: WTF?
     
    moosie likes this.

  9. moosie

    moosie Poster Extraordinaire Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Yeah, already got that datasheet list bookmarked, thanks :) Good resource.

    That's a 5U4GB that's 40uF. Here's a Brimar 5U4G (from that list site) that lists 32uF.

    Looks like the actual reservoir capacitance of the DRRI is around 40uF. So, the GZ34 works, with room to spare. The 5U4GB works (at least as far as capacitance goes), and the 5Y3GT is only 100% too small, not 200% :lol:
     

  10. moosie

    moosie Poster Extraordinaire Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut

  11. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    Alright @slider313 and @moosie : I got in my RCA 5R4GYB from KCA NOS Tubes today, and I tried it out.
    IMG_2938.JPG IMG_2939.JPG

    Earlier in the day I set a baseline with my 5U4GB in there. It was a higher voltage day around here: 122 v. AC from the line. I was putting 452 volts on the plates of those old Tung-Sol 6V6GT's with them biased at 68% mpd, or 18 mA.

    I put in the 5R4GYB, which immediately dropped my bias down to 15.6 mA. So I adjusted it to 68% mpd as I had done with the 5U4GB in there. I biased it to 18.2 mA, and the plate voltage went down to 444. So with the plate current on the tubes at the same spot, I moved about 7-8 volts off the plates.

    I noticed that the sound was definitely "browner" and thicker. The treble was not as high (one could also say less sparkly), and there was less definition between the notes. The bass notes started to get fat and break up earlier on the dial. If all I was playing was blues, and I had no pedals, this might be a good sound for me. But I prefer the sound with the 5U4GB. So I put it back in.

    So now I have a ANOS (used for 5 minutes) as-new in box RCA 5R4GYB that I'm not using. Bummer. But I'm glad I found out what I liked. If I don't like the sound with a 5R4, I suppose I wouldn't like the sound of the amp with a Brown Box or whatever, either. So this was a less expensive experiment than if I had bought one of those. I'll just have to live with the higher voltage on the plates of these 6V6's.

    I really do like the way it sounds with the spec rectifier. More pop and definition and sparkle. I thought the 5R4GYB made it a little more "woofy" in the bass. It's a lot tighter with the 5U4GB. So back to the 1962 GE 5U4GB.
    IMG_2941.JPG IMG_2942.JPG
     
    Last edited: May 24, 2017
    moosie likes this.

  12. moosie

    moosie Poster Extraordinaire Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Yeah, I pretty much came to the conclusion that I may not understand why my DR operates so out of academic spec, but it always has, and sounds great. Not a great learning experience, but that's all...
     

  13. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    It may not be so unusual, since we're not the only ones with SF DR's with plate voltage at about 450 or above on high voltage days. That sounds really common. And as far as being out of spec: even without the issue of increased line voltage, there's the fact that even on the AB868 schematic, it notes that the voltages are 20% tolerance. The first note in the top right-hand corner says, "Voltages read to ground with electronic voltmeter. Values shown + or - 20%"

    At the same time, I want to know why Gerald Weber makes such a big deal of keeping the plate current on 6V6's at 425 or below that he's willing to suggest biasing them at 30 mA and working from there (a true 6V6 at 425 plate volts with a 30 mA current draw is at 106% mpd!). And on Mike Kropotkin's KCA page, he says that the plate voltage should not exceed 430 volts on 6V6's. So what's the deal? Sounds like almost everybody is doing it, as long as they're not using JJ's (which are not 12 watt tubes, anyway).
     

IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.