The Dynaco Tube Audio Forum

Would you like to react to this message? Create an account in a few clicks or log in to continue.
The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


+37
fedoragent
Dale Stevens
KenGaler
Wharfcreek
Tubes4ever
Peter W.
deepee99
rjpjnk
ejc
Dave_in_Va
GreggW
gener8r
neali
Jim McShane
Pat R.
heyraz
GP49
dmtparker
arledgsc
MexicoMike
stewdan
Ed Rosenberger
telefunking
scottlowe
guentherj2
ricohman
corndog71
sKiZo
Maintarget
poconoman
burnedfingers
Feistygoat
mantha3
Bob Latino
anbitet66
pmit2188
Roy Mottram
41 posters

    tube rectifier "yellow sheet" diode mod

    avatar
    rjpjnk


    Posts : 262
    Join date : 2018-07-18

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by rjpjnk Mon Jan 14, 2019 2:01 pm

    I may be wrong, but here is my thinking.

    The specified peak reverse voltage of a high quality vintage 5AR4 is 1500v,

    https://drtube.com/datasheets/5ar4-amperex1958.pdf

    but I've heard it said that the new copies by Chinese and Sovetek might have much lover PIV limits before they self destruct.

    It seems that in normal operation the tube will have  PIV equal to the difference between the B+ DC in the filter caps and the negative peaks in the transformer secondary. So this is about 800v right? I guess the thinking is that some of the newer tubes even 800v might be unhealthy.

    The addition of the diodes removes the negative from the plates so the tubes don't see a high peak inverse voltage.

    Yes, the diodes alone would work just fine. The tube is mostly there to slow the rise time of the B+.
    deepee99
    deepee99


    Posts : 2244
    Join date : 2012-05-23
    Location : Wallace, Idaho

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by deepee99 Mon Jan 14, 2019 8:00 pm

    Just break down and buy a genuine, NOS Mullard GZ-33. Your problems will be over. Did everything I could to ruin mine; nothing worked.
    avatar
    rjpjnk


    Posts : 262
    Join date : 2018-07-18

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by rjpjnk Tue Jan 15, 2019 1:15 pm

    Is the GZ-33 a drop-in substitution for 5AR4?
    deepee99
    deepee99


    Posts : 2244
    Join date : 2012-05-23
    Location : Wallace, Idaho

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by deepee99 Tue Jan 15, 2019 1:21 pm

    rjpjnk wrote:Is the GZ-33 a drop-in substitution for 5AR4?
    http://antiqueradios.com/forums/viewtopic.php?f=13&t=276422
    Peter W.
    Peter W.


    Posts : 1351
    Join date : 2016-08-07
    Location : Melrose Park, PA

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by Peter W. Tue Jan 15, 2019 3:19 pm

    I have been sitting on my fingers, and I will continue to do so. But the nature of filaments, hot and cold, clearly needs to be better understood.
    Tubes4ever
    Tubes4ever


    Posts : 167
    Join date : 2015-07-14
    Location : Star, Idaho

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by Tubes4ever Wed Jan 16, 2019 8:47 pm

    rjpjnk wrote:Is the GZ-33 a drop-in substitution for 5AR4?

    I discovered that it is. I have an ST70. I substituted a NOS GZ-33 in place of my 5AR4 and I didn't even need to rebias the tubes! That's how close the voltage drops of both tubes are. The GZ-33 is definitely a much more robust tube and looks much better!
    deepee99
    deepee99


    Posts : 2244
    Join date : 2012-05-23
    Location : Wallace, Idaho

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by deepee99 Wed Jan 16, 2019 10:48 pm

    Tubes4ever wrote:
    rjpjnk wrote:Is the GZ-33 a drop-in substitution for 5AR4?

    I discovered that it is.  I have an ST70.  I substituted a NOS GZ-33 in place of my 5AR4 and I didn't even need to rebias the tubes! That's how close the voltage drops of both tubes are.  The GZ-33 is definitely a much more robust tube and looks much better!
    It's the "studliest" tube for audio applications since the Great War! And for our purposes, the pin-out's the same as a 5AR4. Light a pair of genuine GZ-33s up in a dark room and pretty and otherwise reserved women will disrobe at the sight.
    avatar
    Wharfcreek


    Posts : 45
    Join date : 2017-07-15

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by Wharfcreek Wed Aug 28, 2019 9:38 pm

    Don't know why I'm chiming in on this subject now, but I guess that little 'teaser' thing that pops up on email is directing me here........so.....here's my comment: I've been using this diode mod for years. As stated in prior posts, the Inverse Voltage protection aspect seems to be a reality, as I don't believe I've had one episode of an arcing rectifier tube since. I guess it's pretty safe to say: It works at some level. Is it infallible? Probably not! But, does is it worth a few cents and a few minutes of time of protect a tube rectifier? Yes! I know when this thread was started the figure of $30 was mentioned as 'cost' of a rectifier tube. Since I see some 5AR4/GZ34 tubes now selling for upwards of $100 or more......seems like a couple of $0.15 diodes is worth the investment. So, I do this mod on virtually every tube amp I own. One thing I didn't read in all this was the fact that when doing this 'diode mod', the tube rectifier itself still acts like it did without the diode mod. By that, what I'm referring to is the fact that it still has to warm up prior to passing current. So, not only does the diode mod protect the tube, but the tube still acts to provide the 'slow start' function it was designed for. I consider that a 'win-win'.
    KenGaler
    KenGaler


    Posts : 76
    Join date : 2019-10-11

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Alternate diode

    Post by KenGaler Mon Oct 21, 2019 12:39 pm

    At the risk of flogging this dead horse.. This is a good choice for a diode also. Yes, it's overkill but that's the mode we're in anyway. Same forward voltage drop as the 1N4007 so it will dissipate the same power but because the case is larger the temp rise will be slightly lower. I plan on using them in a M-125.

    https://is.gd/qsjSYX

    Regards,
    Ken
    KenGaler
    KenGaler


    Posts : 76
    Join date : 2019-10-11

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Power fail latch

    Post by KenGaler Tue Oct 22, 2019 12:30 pm

    I'm not sure what happens either if the power is lost then restored within a few seconds but this relay trick will make sure it doesn't happen.  When the Power switch is turned
    ON (or AC is restored with the power switch in the ON position) the relay is not energized until the momentary Start button is pushed.  When pushed, the relay switches and latches itself ON and supplies AC out.  When power is lost for more then about a cycle or two, the relay opens.  Considering that we're running non-critical equipment such as stereo amplifiers this seems to be a good solution.  

    tube rectifier "yellow sheet" diode mod - Page 4 AC-Input
    Dave_in_Va
    Dave_in_Va


    Posts : 445
    Join date : 2013-04-02
    Location : Mid. VA

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by Dave_in_Va Tue Oct 22, 2019 1:59 pm

    KenGaler
    KenGaler


    Posts : 76
    Join date : 2019-10-11

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by KenGaler Tue Oct 22, 2019 2:05 pm

    I think that trips on a ground fault, not a power loss. But, I'm not sure.
    avatar
    Dale Stevens


    Posts : 203
    Join date : 2014-07-06
    Age : 75
    Location : Loris, SC

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by Dale Stevens Tue Oct 22, 2019 2:09 pm

    manual reset is required after GFCI trip and ( power outage ) .
    Dave_in_Va
    Dave_in_Va


    Posts : 445
    Join date : 2013-04-02
    Location : Mid. VA

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by Dave_in_Va Tue Oct 22, 2019 2:33 pm

    As Dale said, it trips out with a power outage and you have to manually reset it.
    Look back at posts numbers 72 and 73 in this thread.
    (Currently listed at $14.00.)
    avatar
    rjpjnk


    Posts : 262
    Join date : 2018-07-18

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by rjpjnk Sun Jul 05, 2020 8:48 pm


    This is a really cool little device. I had no idea there were devices designed to trip upon power outage. I read the full description on the amazon link and there is no mention of it. Only in the reviews and questions did I find it discussed. Yes, everyone says it trips. I wonder why the listing doesn't advertise this very useful functionality? Perhaps they are not confident it will always work this way?

    avatar
    fedoragent


    Posts : 57
    Join date : 2013-09-14

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by fedoragent Fri Mar 12, 2021 3:59 pm

    Bob Latino wrote:Those diodes will look at about 360 VAC. Either the 1N4007 or the 1N4005 should work fine .. Since the 1N4007 is 1000 volt rated, I would probably use the 1N4007 ... Another diagram below of this mod.

    Bob


    tube rectifier "yellow sheet" diode mod - Page 4 Rectifier-diode-mod

    Bob,

    I'm going to figure that this was just to account for regular rectifiers, but would absolutely not apply to the SS rectifier (Copper top) some of us are guying from the nice gent in the Southeast right?

    Thanks,

    FG/Jon
    avatar
    rebellovw


    Posts : 78
    Join date : 2022-01-23

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by rebellovw Sun Jan 23, 2022 12:54 pm

    Quick question - I've added this mod to my VTA amp a while ago - and today the amp went belly up - playing fine- then burning smell - and the Mullard Rectifier tube - bright red - why didn't the diode's do their thing?  I'm concerned I've just blown the rectifier and was under the impression the diodes would have acted like a fuse - in this case they didn't - the amp just red plated.

    Very surprised.

    Edit:

    Update - I moved the GZ37 to the other working amp - and it started just fine and the bias is staying put. Man these are tough rectifiers.

    I'm not sure what happened or even if this mod helped - but I'm sure glad my Mullard GZ37 is working.

    Could the mod have prevented something even worse from happening? Did it likely help in any way?
    avatar
    New2Tubez


    Posts : 184
    Join date : 2018-03-20
    Location : NY

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by New2Tubez Tue Jan 25, 2022 1:50 am

    "Quick question - I've added this mod to my VTA amp a while ago - and today the amp went belly up - playing fine- then burning smell - and the Mullard Rectifier tube - bright red - why didn't the diode's do their thing?  I'm concerned I've just blown the rectifier and was under the impression the diodes would have acted like a fuse - in this case they didn't - the amp just red plated."

    That's not what they do. They protect the rectifier if the amp powers down and back up in too short a time. Diodes are like oneway check valves. They prevent the charged caps from discharging back into the rectifier.

    Your issue sounds like something else.

    rebellovw likes this post

    avatar
    rebellovw


    Posts : 78
    Join date : 2022-01-23

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by rebellovw Tue Jan 25, 2022 10:17 am

    New2Tubez wrote:"Quick question - I've added this mod to my VTA amp a while ago - and today the amp went belly up - playing fine- then burning smell - and the Mullard Rectifier tube - bright red - why didn't the diode's do their thing?  I'm concerned I've just blown the rectifier and was under the impression the diodes would have acted like a fuse - in this case they didn't - the amp just red plated."

    That's not what they do. They protect the rectifier if the amp powers down and back up in too short a time. Diodes are like oneway check valves. They prevent the charged caps from discharging back into the rectifier.

    Your issue sounds like something else.

    Thanks that makes sense and helps me understand it better.
    avatar
    Sichum


    Posts : 5
    Join date : 2021-01-16

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by Sichum Mon Feb 14, 2022 7:37 pm

    please excuse my ignorant of the topic. Will I still need this mod with VTA Octal in place of the original PC3? Thanks
    corndog71
    corndog71


    Posts : 840
    Join date : 2013-03-19
    Location : It can get windy here

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by corndog71 Mon Feb 14, 2022 10:02 pm

    Sichum wrote:please excuse my ignorant of the topic. Will I still need this mod with VTA Octal in place of the original PC3? Thanks

    I would still recommend it.

    Sichum likes this post

    Seamus
    Seamus


    Posts : 86
    Join date : 2020-03-17

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by Seamus Fri Feb 16, 2024 6:11 pm

    The mod's purpose is to stop the capacitors from discharging through the power transformer secondary in the event of a tube rectifier failure.

    [Tube rectifiers are great for MI, not so much for HiFi - from an electronics engineer's point of view.]

    The mod can be implemented with one 1N5407 between the capacitors and the rectifier output.
    Fewer components and connections are generally more reliable.

    tube rectifier "yellow sheet" diode mod - Page 4 YellowSheetImproved
    Roy Mottram
    Roy Mottram
    Admin


    Posts : 1839
    Join date : 2008-11-30

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by Roy Mottram Fri Feb 16, 2024 9:03 pm

    the original yellow sheet mod (see up half page post 91) will work much better than just one isolation diode as Seamus has shown.
    The two diodes will do half the work of the rectifier tube and thus it will only need to rectify the upper half of the AC input voltage,
    rather than deal with all of it. Much better protection for the rectifier tube itself !!

    rebellovw likes this post

    Seamus
    Seamus


    Posts : 86
    Join date : 2020-03-17

    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by Seamus Sat Feb 17, 2024 11:41 am

    The 3A diode has more than double the capacity of 2x 1N4007.
    As far as the upper half of the AC voltage, the single diode works on the DC component to protect the power transformer.
    Two diodes in the original apply DC to the tube rectifier, essentially negating its function.

    As Einstein is purported to have said: "As simple as possible and no simpler." Cool

    Sponsored content


    tube rectifier "yellow sheet" diode mod - Page 4 Empty Re: tube rectifier "yellow sheet" diode mod

    Post by Sponsored content


      Current date/time is Wed Oct 09, 2024 2:37 am