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

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

  1. MilwMark

    MilwMark Poster Extraordinaire Ad Free Member

    Apr 29, 2013
    near Arnold's
    Ok, where are folks finding these rubes, er, "knowledgeable buyers" who are forking out $900 or $775 for a '65 DRRI or PRRI in a private sale?

    And even if they were, why would a shop ascribe $900 in value to one, used? I would expect a shop to give maybe $400-500 credit towards getting a deal done, tops. They regularly sell them for $600-700 (if they are lucky) and have to carry them in the meantime. Maybe sitting next to a new one that can be had for $900 if Fender allows them to "demo" it because it's been sitting.

    @theprofessor - I do trade deals all the time. And I'm a cheap so-and-so. But time is money and lack of dealing with selling stuff directly has value apart from that to me as well.
     

  2. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    That's me, too.
     

  3. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    OK. I got that 5U4BG in today, and I subbed it out for the Groove Tubes GZ34 that was in there (by the way, this was not a Sovtek, which GT has been re-branding recently; it says made in USA, and it's clearly an older tube; what is that?). I kept the JJ's in. The plate voltage went from about 450-455 to about 437. I biased the JJ's at the same point as before (70% mpd, which sounded good to me), and I noticed that the tone was definitely sweeter. The voltage drop (of only about 18 volts or so) had knocked a lot of the "edge" off the sound. Voltage makes a big difference in sound to me. I think I've noticed a difference before with as little as 8 volts difference, but 20 volts is a no-brainer. Is it enough for me to buy a Brown Box for $350? No, but I would absolutely use one if I had it.

    Then I switched out the JJ's with my matched pair of Tung-Sol black glass 6V6GT's. Have I ever said how much I love those tubes? I think so. Anyway, they sounded best to me right at about 70%. (Note to self: at 437 plate volts, my "Motorola"-labeled one was at about 19.2 mA, and my "Delco"-labeled one was at about 19.0 mA.)

    The switch from the JJ's to the Tung-Sol brought a noticeable change in bass response (not nearly as much with the Tung-Sols, which I appreciate). I was having a "boomy bass" problem with the JJ6V6S's, at least in my home. I had to keep the bass pot on "1" with the JJ's. With the Tung-Sols, the pot is actually usable now. Additionally, there was an increase in mid-range response. It sounded a lot more like a BF DR than before. (I thought it sounded like a mini-Twin with the JJ's and GZ34.) And I like that. I noticed that these tubes at this voltage and plate current draw made me want to play more delicately and with more touch. The JJ's make me want to pound something out--to cut through. In the change, I also believe I found that one of the JJ's was rattly. I thought this might have been coming from the baffle, but hopefully it was just a rattly power tube, since the rattle disappeared after I swapped to the old Tung-Sols.

    The JJ's have always made my amps sound "juiced." The certainly give more volume, but they also give a lot of punch and cut. Since that is the case, I would not hesitate to use them if I were clubbin'. They make the amp sound like it's on steroids, or like there's a slight boost on. To me, it is a more modern sound for a DR. If I were thinking about putting 6L6 tubes or 5881's in a SFDR, I would first try out these JJ 6V6S's with a GZ34 rectifier. As long as the voltages aren't outrageously high, I think this setup can offer some great service and a 6L6-like sound without the risk that using 6L6 tubes in a SFDR might cause for the output transformer. (Gerald Weber has a good discussion on all this, and all the things you'd need to consider if thinking of running 6L6's in a SFDR. See A Desktop Reference of Hip Vintage Guitar Amps, p. 201, and Tube Amp Talk for the Guitarist and Tech, p. 378)

    But for me, a more traditional, lower-powered sound is better. It just sounds "right." I'm already running at about 440 plate volts with the stock rectifier (5U4GB). That outlet was drawing right at 120ac today, so that would be about 430 plate volts in 1976, where the wall actually gave you 110ac or so. If I understand correctly, this higher-than-spec voltage is par for the course with SF Deluxe Reverbs and the like, so it seems like I'm in good shape. It seems to me like the difference between the GZ34 I had in there and the 5U4GB I just put in is not nearly as great as expected (only 15-20 volts), but I suppose that's because the GZ34 was an older tube, whereas the 5U4GB is truly NOS and tested at 100%+.
     
    Last edited: May 19, 2017

  4. moosie

    moosie Poster Extraordinaire

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    On TGP. Guy pretty much like many of us. Visible history. Asked very smart questions prior to deal.

    The amp was truly mint, even though my son and I (separately) had played it for a couple years. Recently serviced, with records, new power tubes, biased, etc. Guy was thrilled.

    Maybe that seems like an outlier situation to you, but that has not been my experience.
     

  5. moosie

    moosie Poster Extraordinaire

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    @theprofessor, you'll see a lot of USA Groove Tube markings on those 70s amps. I do, anyway. I think I figured out the stenciling one time meant that the ones I had anyway, were ... well, I forget now. But one of the four. RCA, Sylvania, GE, Philips. There, that was helpful, huh. :rolleyes::oops::lol:

    I hear ya about the voltage. I'd use a regulator if I had one, too.

    My blackfaced and tuned '77 is running a pair of TADs with a NOS JAN-Philips 5U4GB. 68%, or average 21.4mA, well-matched. Plates are running at 447. Yup. I questioned it, and got some experts here telling me it wasn't that unusual for these amps.

    The amp sounds great, even without the JBL :twisted:
     

  6. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    I don't know the history of Groove Tubes. Were they already around and re-badging tubes in the mid- to late-70's? If that's the case, my GZ34 might be pretty old (1980's or 90's?). At any rate, it's certainly not a recent one. I like any of those four American companies better than the recent Sovtek stuff!

    Yes, I've read on some old threads here about SF amps running at higher voltages. It sounds like at some point Fender changed the power transformer but kept the same part number. So they provide higher voltage. @SoK66 says in a post from several years back that his SF Deluxe Reverb runs at above 450 plate volts, even with the spec 5U4GB in there. I can't remember which thread it was in, or I'd cite it. That matches yours, which runs at just below 450 with a 5U4GB. Mine is at about 437 or 438 plate volts.

    It may be that I'm not "supposed" to like that JBL D-series in your 77 DR either, but I do. It sounds great. But when you say that it sounds great, even without the JBL, does that mean the JBL is not in there anymore? Or just that it sounds fantastic without it (but even more fantastic with it)?
     

  7. moosie

    moosie Poster Extraordinaire

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    I don't know the whole story of GT either, but yes, they've been around, rebadging, a long time.

    It means I really like the JBL in there, that's all.

    Remember that plate voltages changes inversely with bias point, so just talking about plate voltage, without specifying bias, won't be a proper comparison. When I was 'rolling' bias settings, to see what I preferred in that amp, the bias points (albeit sometimes with different tubes) covered the range from 47% to 75%. The plate voltages ran from 457 down to 442.

    I wonder why Fender changed the PT? And why didn't they change the darn part number... :mad:
     

  8. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    When you're at 68% on those TAD's in your DR, what is the plate current reading for the pair? Mine ends up at about 19 mA. I've been reading a good bit in Gerald Weber's books, and he recommends biasing the 6V6 tubes in a DR up to 30 mA, or until the plate voltage is no more than 425 volts. I wonder about that. That sounds like a lot more plate current than I'm running currently, and about 12-15 plate volts less.
     

  9. slider313

    slider313 Tele-Holic

    Age:
    60
    914
    Jan 6, 2011
    NC
    I'm not a fan of Gerald Weber's book. There's some good info but there's also some pretty bad info too. 70% should be a maximum guideline in a fixed bias amp. I usually keep mine in the 65% range, depending on the brand and how they sound at certain bias points.
     
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  10. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    Thanks very much, slider313. I have three of them: A Desktop Reference of Hip Vintage Guitar Amps; Tube Amp Talk for the Guitarist and Tech; and Tube Guitar Amplifier Essentials. I am no expert; I don't know enough other than to read the information he presents there as information presented by "an expert." I am a researcher and teacher by trade (in my real life), however, so I know enough to know that everything--everything--is contested. That said, are there other spots in his writings where you think the information is particularly bad or misleading? I'd love to hear your opinion about that, especially as it pertains to Deluxe Reverbs, if applicable.

    Also: I asked you some time ago about a speaker for this SF DR. One of your recommendations was an Eminence GA-64. To my ears (listening online), that sounds the most like what I take to be the defining qualities of a vintage C12N of anything I've heard. So if I change speakers down the road, I'm going with that one. However, I really, really like this big alnico (Blackhawk HP) I have in there now, and I see no reason to change at this point. Thanks for the tip.

    Oh, and I've been meaning to tell you: I like your Fender replacement knobs on that new DeArmond single-ended amp better than the original skirted ones.
     

  11. slider313

    slider313 Tele-Holic

    Age:
    60
    914
    Jan 6, 2011
    NC
    Professor: I learned much of what I know from a real good tech in NY. It's excessive current that kills power tubes, in a fixed bias circuit. If you take the datasheets for the 6V6GTA it show a max of 285v in an AB1 push pull circuit. That would mean every 6V6GTA used by Fender would have a very short life in the Deluxe Reverb. As time has proven, there are still some original RCA 6V6GTA's working in old Fenders. Jim Kelly amps run a quad of 6V6's upwards of 460v plate! The higher ac voltages we have today bring some Deluxe Reverb's B+ voltages up to a point where the plate voltages look like they would in an amp running 6L6's. IMO, the higher plate voltages with 6V6's make the amp brittle and strident. A GZ34 rectifier in the original blackface DR exasperates the effect. I've found, with my personal amp, that it sounds better when the plate voltages are in the 435v range or less. I'm using a 5R4GYB and getting 415v-420v running a pair of RCA 6V6GTA's just under 22ma.

    If the Blackhawk sounds good, then leave it in there!

    Thanks, I like the white/cream knobs also!
     
    Last edited: May 20, 2017
    theprofessor likes this.

  12. moosie

    moosie Poster Extraordinaire

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Yep. I went to 75% as an extreme, for testing. 70% is the highest I go in my SFs. Unless I really hate my tubes.

    My DR is currently set like this (with the TAD 6V6GT-STRs and NOS Jan-Philips 5U4GB):

    BIAS 68%
    Plates @ 447v; Avg Current 21.8 mA

    Actual per-tube current is 21.4mA and 22.2mA.

    (I know I said 21.4 avg earlier. Either I was mistaken, or my current and testing spreadsheets are out of sync. Thing is, measure in an hour, wall voltage fluctuates a bit, and the numbers change slightly. So both were true at some point.)

    30mA on a 6V6 sounds ridiculous, as far as I'm aware (I'm no expert). You sure he wasn't talking about 6L6s?

    @slider313, I was running a 5Y3 in my DR at one point, and I didn't like it at all. But, I have learned a lot since then, meaning I'm not sure what the bias was set at, and I wasn't trying to reduce voltage on purpose. I was just trying a tube, without much thought. Based on your comments, I might throw one in and take some measurements, and see if I can get it sounding good.

    I agree about the brittle and strident comment. My amp sounds good now, running pretty high voltages, but I guess I'm not sure why. If indeed I have one of those transformers with the higher voltage, there's no way I'm getting it down a whole lot, at least not with a 5U4 or a GZ34.
     

  13. slider313

    slider313 Tele-Holic

    Age:
    60
    914
    Jan 6, 2011
    NC
    Moosie, it could be the TAD 6V6's smoothing things out. They work well in some amps.

    I'm using a 6087/5Y3WGTB in my brown '61 Deluxe. This amp calls for a GZ34 but the plate voltage would be in the 460+v range. I believe it's running 425v with a pair of GE blackplate, smoked glass, 6V6GT's at 19ma each; and it sounds really good.
     
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  14. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    That's what I thought. That's why what he said didn't make sense to me.

    I agree. Even with my DRRI, I took out the GZ34 and used a 5V4. I put a 5U4GB in my SF DR yesterday, instead of the GZ34 that was in there when I bought it, and I really liked the results. (That's not surprising, since a 5U4GB is spec for a SF DR.) But it still only got the plate volts down to about 440. I wonder now about putting another rectifier in there that would drop the voltage even more. But as I understand it, you need a rectifier with the same or less filament current draw than the spec 5U4GB, as well as the same or more plate current rating. While both a 5Y3 and 5R4 qualify on the first score, both have a lower plate current rating.

    I've found that lowering voltages even by 15 volts had more of an effect than changing types of power tubes.

    Cool. That sounds about right.
     
    Last edited: May 20, 2017

  15. moosie

    moosie Poster Extraordinaire

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    You need to watch the input capacitance spec of your chosen rectifier. The 5U4GB is 40 uF, and say, a 5Y3, is only 20. People use 'em, but in theory, it don't work for long. And if it fails to work, I think you might risk a transformer. Not sure. The 5V4 is very low, if I recall, on the order of 5 or 10 uF.

    The tube datasheets are all googlable.
     

  16. slider313

    slider313 Tele-Holic

    Age:
    60
    914
    Jan 6, 2011
    NC
    The affect of using a rectifier with a lower peak output current, like going from a 5U4GB to a 5R4 or a 5Y3, would be more compression and sag under load. Tube data sheets were on the conservative side and listed the parameters for optimum working conditions, performance and long life. DeArmond/Rowe used a 5Y3 with 40uf of filtering in the Martin 112 and DeArmond R15, with no ill affects.

    As for the 5Y3 not working long in my DeArmond with 40uf of filtering; it's not the case. I've done dozens of gigs with the amp and the rectifier is still doing its job. Not a theory, just a real world example.

    FYI: the DeArmond R5T uses a 6X4 rectifier with 40uf of filtering!

    On the other side of the spectrum: Ampeg went to 7591's in the Reverberocket R12R-A, using a 5Y3 with 60uf of filtering. This model was very short lived for this reason; the 60uf was burning up the 5Y3's. The R12R-B went to diode rectification and was the longest production model of all the original top loaded Reverberockets.
     
    Last edited: May 20, 2017

  17. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    Interesting! I didn't even know about input capacitance vis-a-vis rectifiers. My choice of a 5V4 instead of a GZ34 came out of some conversations I had with @Opaltone . He suggested that I could try one. He also suggested that I could try a 5R4 as a more suitable substitute, but that I might not like the amount of voltage drop it brought. Furthermore, both tubes have a 2 amp filament current rating (whereas the spec of a GZ34 [in a DRRI] has a 1.9 amp filament current rating). The reason he said that the 5R4 is a more suitable substitute, I suppose, is that it is rated for 250 mA of plate current, just like the GZ34. The 5V4 is only rated for 175 mA of plate current, but it was fine in the DRRI for a good while.

    This and all the above I typed in response to @moosie 's post makes me think that it may be doable to try a 5R4 as a sub for the 5U4GB in my SF DR. That would give even more voltage drop and sag. Is that possible, slider313?

    For my reference (not for your benefit) I'm posting this here:
    RectifierTubesVoltageDrop.png
     

  18. adjason

    adjason Friend of Leo's

    Jan 9, 2010
    virginia
    great amp- I think your trades were justified and certainly not worth $1800 had you sold that stuff. I totally agree-buy local, try the item first and respect someone who runs a solid business. Great amp!
     
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  19. slider313

    slider313 Tele-Holic

    Age:
    60
    914
    Jan 6, 2011
    NC
    That chart is more than a bit off, in my experience. I've noted an 8v-10v drop when going from a GZ34 to a 5V4. I've also noted only a 4v-6v drop when going from a 5U4GB to a 5R4GYB. This is with a bias adjustment, so the tubes are drawing the same amount of current with each rectifier. YMMV
     
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  20. theprofessor

    theprofessor Tele-Afflicted

    Aug 8, 2016
    Chattanooga, TN
    Thanks very much, slider. I also noticed about an 8-volt drop when changing from a GZ34 to a 5V4. Interesting that you noticed only a 4-6 volt drop from a 5U4GB to 5R4GYB. That doesn't sound like a change that's really worth it, at least to me. I'll think on it. Thanks again.
     
    Last edited: May 20, 2017

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