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    That Good Old Rectifier Sound

    MarcVBelgium
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    • Post n°51

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    Post by MarcVBelgium Tue Nov 18, 2014 11:49 am

    sKiZo wrote:Somebody refresh my memory ... will the 5U4 family work in an ST120? Electronically similar, but the 5U4's are direct heated instead of the indirect heat of a 5AR4 or GZ34 (or GZ37) ... best I can tell, that's internal, and the pin outs are identical?

    Major concern I understand would be "cathode stripping" on the power tubes, as they'll be getting full DC way before they're ready ... indirect heating avoids that by ramping current up slowly. You can get 5U4's on the cheap, but I suppose not a good trade off if you're saving money on a rectifier only to shorten PT life.

    Then again, that could be compensated for by adding a slow start board?

    PS ... I notice the TAD KT88STR's I just got heat up a LOT faster than the KT120's using the Mullard GZ37. I still give them a good five minutes warm up before jamming ... no big rush here.


    Hi Skizo, my ST-120 is running on 5U4GB (NOS Sylvania), TAD 12BH7 and TAD 6550 STR's...... it does have the TDR board.
    Sound is terrific ! No problemo whatsoever.
    Marc
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    sKiZo
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    • Post n°52

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    Post by sKiZo Wed Nov 19, 2014 2:32 pm

    Good to know ... I'll keep that in mind for my "tweak" list.

    I just purchased insurance for my current GZ37 rectifier ... as in, buying a good spare. Now that I've got another one, the original will probably never die ...  clown

    It's a NATO military version by Mullard, circa 1960's. $50 used, but not abused. Doesn't have the pretty Mullard shield on it, but I can live with that.

    That Good Old Rectifier Sound - Page 3 Cv378-british-military

    If it ...

    - gets here in one piece
    - Actually works

    ... I think I done good ...
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    mantha3
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    • Post n°53

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    Post by mantha3 Wed Nov 19, 2014 2:55 pm

    Not to cause trouble... But... For an ST120... Is a Mullard GZ33 better than a GZ37? I thought these were rated higher and would not be pushed as hard as a gz37...
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    • Post n°54

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    Post by sKiZo Wed Nov 19, 2014 3:25 pm

    From what I gather, the GZ37 has a higher voltage drop and uses higher heater voltage, but can push more current. The GZ33 is less picky about input caps, but that doesn't seem to be a problem. The ST120 can handle the drop, and for me, the current reserve is where it's at driving low efficiency speakers with a quad of KT120s. I also go strong on bass using a sub synthesizer, and like it loud, so it's pushed hard ... deep and hard ...

    Been running one here for maybe six months now. Haven't blown anything up yet anyway, and the system sounds choice.


    Last edited by sKiZo on Wed Nov 19, 2014 3:39 pm; edited 2 times in total
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    mantha3
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    • Post n°55

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    Post by mantha3 Wed Nov 19, 2014 3:30 pm

    Ah, ok,

    I've had a hard time knowing what would be better between a GZ37 and a GZ33. Thanks sKiZo! the current reserve makes sense
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    • Post n°56

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    Post by deepee99 Wed Nov 19, 2014 3:50 pm

    mantha3 wrote:Ah, ok,

    I've had a hard time knowing what would be better between a GZ37 and a GZ33.  Thanks sKiZo!  the current reserve makes sense

    The old Mullard GZ-33 is the bad-boy of the crowd. You could do an ice-bucket challenge on them while they're hot and they'd survivie.
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    • Post n°57

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    Post by Bob Latino Wed Nov 19, 2014 4:16 pm

    deepee99 wrote:
    mantha3 wrote:Ah, ok,

    I've had a hard time knowing what would be better between a GZ37 and a GZ33.  Thanks sKiZo!  the current reserve makes sense

    The old Mullard GZ-33 is the bad-boy of the crowd. You could do an ice-bucket challenge on them while they're hot and they'd survivie.

    In reality, EITHER the GZ33 or GZ37 may be used in the VTA ST-120 or M-125 monoblocks. There may be some minor differences in the specs between these two tube rectifiers but I have listened to both and I find no difference in sound quality between the two.

    If you want to save a few bucks, just use the Weber WZ68 SS rectifier. At $22 each they are lot cheaper than the Mullard GZ33 or GZ37 and will flow more current (450 milliamps) than either the GZ33 or GZ37.

    Bob
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    • Post n°58

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    Post by sKiZo Wed Nov 19, 2014 5:31 pm

    Which closes the circle ...

    Which sounds better? Either? N/or?

    The GZ37 presents a different mechanical load to the amp than a GZ33, which could/not make it sound different. Can't answer that as I haven't done a head to head test. Even then, I've made some changes to the basic amp here that might/not affect the sonics.

    There ... I hope that's clear/not enough ... Wink

    PS ... given the 5AR4 (GZ34) as the basic rectifier the amp is designed to use, the GZ33 is a closer electronic equivalent.
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    • Post n°59

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    Post by zx Wed Nov 19, 2014 8:41 pm

    For about a year now i have been runing a pr of my MK3s with out a choke.... i can tell the diff in evey rectifier tube i put in....great tone...I put a 1mf Vcap right on pin 8...i never new how much diff there was in tube rectifiers....the one that sounded best with the Choke in.... sound way diff with out the choke!
    More time an $$ need to be put in to these chokes.... from what i am hearing.. were loseing a lot of the tube tone an sweenes ..the main reason we are into tubes.....even these SS rectifiers sound vary close to tubes with the choke out....
    These chokes are ringing an adding a sound of there own.......Lot great old tube amps out there..Eico for one...that have no chokes......................Have fun with tube sound
    Ck this choke maker............hehe

    https://youtu.be/AmA-b8I3ThY




    Thanks for the site Bob...............


    Last edited by zx on Thu Nov 20, 2014 6:39 am; edited 1 time in total
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    • Post n°60

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    Post by kaner Wed Nov 19, 2014 11:09 pm

    Perfect discussion of sag.  I think the distinction between guitar amps and audio amps is hugely important.  I'll throw my 2 cents in from a guitar player's perspective.  Sag in a guitar amp is the sweet spot between pushing your amp too hard and not hard enough.  But that moment when the drive from my guitar pushes an amp to the point where it strains to keep up is the perfect tonal definition of sag.  The amp becomes part of the guitar and the guitar sings through the amp.  Use the sag as part of the sound.  Whether sag exists or not is not even a question.  It does.

    Jim Marshall and Leo Fender both understood that and designed power supplies to help players push that edge.  The amp becomes part of the sound.  

    When it comes to audio amplification, the amp should be reproducing the sound that was recorded. It should not introduce its own version of sag.  BUT, an amp that is an extension of the original recording rather than a perfect, digital reproduction is also an extension of the sound.  When Jimmy Page, David Gilmour, and Eric Clapton listened to their recordings and blessed what would ultimately become an album they did so through audio amplifiers.

    That's what we're looking for.  Our living room version of what they wanted us to hear.  SO, a tube rectifier, a tube amplifier with a bit of its own sag and vacuum tubes with their own harmonic distortions are exactly what they wanted us to hear.

    Sag, harmonic distortion, analog reproduction.
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    • Post n°61

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    Post by zx Thu Nov 20, 2014 10:31 am

    I gess not using a choke on any rectifier tube ...... Gives massive Sag, harmonic distortion...
    in analog reproduction.....................................................Yesss........... Less
    is more
    Just have fun with tube sound in 2014............still





    Thanks for the site Bob...................
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    Post by sKiZo Thu Nov 20, 2014 2:24 pm

    Trade off is a higher VAC component in the signal line?

    I went with the larger chokes in my custom build, so I should sag even less ...

    That Good Old Rectifier Sound - Page 3 Compare-chokes

    Didn't really put much thought into it - just figured as long as I had the room, why not? If anything, I expected the larger structure to help with heat dissipation. Come to find out, there may actually be some additional benefit as well ... kewl! I do know the amp can produce massive amounts of SPLs - some might say dangerous levels - before I hear any distortion, and even then, it's minimal.

    PS ... in case anyone's wondering, the Triad C17x chokes that I used won't even come close to fitting in a stock chassis.
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    Post by zx Thu Nov 20, 2014 5:33 pm

    Looks too me like you would have been a two choke guy......Stereo two ch amp an all??
    as for more SPL..
    That the frist thing i notest when i pulled the cokes....sounded like thay had more power...
    thay definitely sounded like thay had better bandwidth.....thats why i have not put the chokers back..
    or Maybe i just been choket a neff....or Mybe not a nuff...




    Thanks for the site Bob...................
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    Post by evgenibgr Thu Nov 20, 2014 6:02 pm

    sKiZo wrote:Trade off is a higher VAC component in the signal line?

    I went with the larger chokes in my custom build, so I should sag even less ...

    Didn't really put much thought into it - just figured as long as I had the room, why not? If anything, I expected the larger structure to help with heat dissipation. Come to find out, there may actually be some additional benefit as well ... kewl! I do know the amp can produce massive amounts of SPLs - some might say dangerous levels - before I hear any distortion, and even then, it's minimal.

    PS ... in case anyone's wondering, the Triad C17x chokes that I used won't even come close to fitting in a stock chassis.

    Because here talking about chokes, it's my decision. The good news is that on the front choke is not visible. It is worth.

    That Good Old Rectifier Sound - Page 3 EQE7ueU6WcQO4k32yNTQAmUuT359_ympksNI8yenMnI=w701-h526

    That Good Old Rectifier Sound - Page 3 -4KLJxtBb1wFR2Pyk54iNkTXY-cZeHO3lQDqjmMQrWg=w701-h526
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    Post by sKiZo Thu Nov 20, 2014 6:36 pm

    zx wrote:Looks too me like you would have been a two choke guy......Stereo two ch amp an all??

    Ahem ...

    That Good Old Rectifier Sound - Page 3 Wiring-done-003

    Two, two, two chokes in one!! cheers
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    Post by sKiZo Thu Nov 20, 2014 7:25 pm

    evgenibgr wrote:
    That Good Old Rectifier Sound - Page 3 EQE7ueU6WcQO4k32yNTQAmUuT359_ympksNI8yenMnI=w701-h526

    The Lundahl outputs are a nice touch. Off the shelf or custom wound?
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    Post by zx Thu Nov 20, 2014 7:28 pm

    I gess i miss the other choke.............Did you ever use just one?
    Dose it drop B+??...when you go from one two, two....Hehe
    An yes from What i hear.... Biger choking..... is much better for Big Tone...
    I spoke to Mr Handson...from the SS Ayre Audio fame....i ask him... what gave his SS amps the tube like sweet tone... all were freaking about..an still are....
    He said other amp makers were not using a over 100hy choke in there SS amps B+.....an yes only one in his Stereo Amp.... One of a kind sound....well to me anyway..



    Thanks for the Site Bob.....
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    Post by sKiZo Thu Nov 20, 2014 11:35 pm

    B+ tested steady at 507 (ooPs!) 407 with the larger rectifier when I ran the numbers on the bench after firing it up, so that would put it smack dab in the middle of the recommended range. The Chinese 5AR4 could only give me around 470, downhill with a good wind at it's back  ... clown

    The Triad C17x rates 60mA higher than the stock C24x which I expect would explain the difference ... As I mentioned, my goal was mostly to reduce heat buildup under stress by using the larger components.

    And I do so like to apply stress ...  Twisted Evil

    Can't say it's any better sounding than it would have been with the stock chokes as I built it with the larger ones. All I can say is it IS a really good sounding amp.

    ** Worth mentioning - I also use a C90 thermister on the AC line that would account for some additional drop. I also drop the wall current to around 117vac average using a bucker. Amp seems to be quite happy in that range.


    Last edited by sKiZo on Sun Nov 23, 2014 7:01 pm; edited 1 time in total
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    Post by evgenibgr Fri Nov 21, 2014 4:14 am

    sKiZo wrote:

    The Lundahl outputs are a nice touch. Off the shelf or custom wound?

    Output transformers are LL1663PP/AM amorphous core 5 kOhms/8Ohms. Sound is completely different than conventional transformers. There is much more information in the high frequencies. Now playing as a single-ended amplifier.

    Choke is LL1638 / 4 H, Recommended DC current 400ma, Saturating current 575 mA, DC resistance 36 Ohms

    In my Dynaco i don't use negative feedback and with this choke bass control is superb.
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    Post by zx Fri Nov 21, 2014 4:38 am

    sKIZo..almost 510 on the b+..........Wow...and with all the drop you have ...i say yes.. you have HIGH SpL.....with the KT120s.........well i gess any tube with 510...B+
    Well you should have....
    Can you say what your heaters are runing at??
    I say close to 7...or less i hope....
    So i gess with the nom...5AR4 these amp heaters at 120-125 Ac.. coming from the wall... the heaters well be even higher??
    how about the 5V AC for the rectifier tube....is it higher than 6 ACv??
    Thanks for the info......


    evgenibgr....i like your Choke setup...4hy got sound better than the stock 1.5hy....an you did what ever it tuck to get it in...it all about the sound..an yes i bet the output tran. sound great..thanks for the pic...




    Thanks for the site Bob..............................
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    Post by evgenibgr Fri Nov 21, 2014 5:58 am

    zx wrote:

    evgenibgr....i like your Choke setup...4hy got sound better than the stock 1.5hy....an you did what ever it tuck to get it in...it all about the sound..an yes i bet the output tran. sound great..thanks for the pic...


    I made a lot of changes in my Dynaco ST70. If you're interested, here's 2 pictures more. With these scan speak speakers sound is great.

    That Good Old Rectifier Sound - Page 3 3b4KttrQXm55wKRBm44ak_x2DvcF5fGmnrsAnxwt-ac=w701-h526

    That Good Old Rectifier Sound - Page 3 OelJaHYgsCiZnJYWMlxjvsWmNzxGU6zUJ_TNBH0MnyE=w722-h526

    I am very interested in someone to share their experiences with Genalex Gold Lion GZ34 vs vintage Mullard GZ34.
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    Post by poconoman Sun Nov 23, 2014 2:16 pm

    sKiZo wrote:I run my GZ37 full time here. Gonna find out just how bulletproof they really are.

    Keeping an eye out for a good spare, but right now it's not even breathing hard driving the new TAD KT88STR's ...

    Which btw are sounding better all the time. He shoots ... he scores!!    cheers

    Can a GZ37 be a drop in for any amp using a GZ34?

    Thanks.
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    Post by sKiZo Sun Nov 23, 2014 6:03 pm

    I'll let Bob & Co assume the liability and answer that one ... Wink

    IMHO ... the GZ33 or GZ37 both draw too much power for the stock iron on the older Dynacos. Not an issue with the ST120 and new monoblocks as that has a LOT more iron. I don't figure the old monoblocks with stock iron would have any problems. Not sure about the new production smaller amps.

    PS ... proof positive all rectifiers aren't created equal, even from the same company. The "new" Mullard NATO issue CV378 (circa 1962) I just got as a spare biased up at 40mV each tube using the same pot settings that gave me 55mV on the Mullard GZ37 (circa 1968) I've been using. Tubes look identical except for the base color and I don't see any difference in the internal structure. Both are "O" getters. The '68 I've been using is a "real" Mullard with the shield.

    Not losing any sleep over it ... the "new" rectifier biased the amp up nice with plenty of room to spare on the pots, and it's been holding rock steady. I'll stash the other one for now and see how this one handles the amp long term.
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    Post by sKiZo Sun Nov 23, 2014 6:54 pm

    zx wrote:sKIZo..almost 510 on the b+..........Wow...

    First off, I goofed ... I fat fingered what should have been 407 ... my bad. I edited the original ooPs!

    Second ... thanx for making me look! I went to double check the B+ just now and it was reading 378 ... short of low recommended range, but not so much that it'd be an issue.

    But wait ... there's more!

    Checked the AC line voltage, and it's at 119.5 today. Aha! Took the bucker out of line, and B+ jumped back up to a comfortable 410 at rectifier pin #4 ... back in tolerance. Tested with all tubes in and biased up.

    One thing I plan to check next time I get under the hood is the voltage before and after the CL90 thermister I have on the AC line in. Move one wire is all it would take.

    That Good Old Rectifier Sound - Page 3 Cl90-002

    (for you observant types, I DID move the blue wire under the thermister after the pic was taken. Those things get HOT ... )

    That gives me a softer start, but it also drops the line voltage 1-2vac. Bypass that, and I expect I'll end up right back in the middle of the B+ recommended range.

    PS ... heater seems to be pretty consistent at 6.5 no matter what.
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    Post by sKiZo Sun Nov 23, 2014 7:26 pm

    evgenibgr wrote:

    That Good Old Rectifier Sound - Page 3 3b4KttrQXm55wKRBm44ak_x2DvcF5fGmnrsAnxwt-ac=w701-h526

    Ever think about adding some extra legs to help support all those MCaps on that driver board? lol!
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