Rectifier Tube

Discussion in 'Tube Audio' started by canton, May 17, 2018 at 1:13 PM.

  1. canton

    canton Active Member

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    Need to buy a pair of rectifier tubes for a pair of Dynaco MK IV amps never had to pick them up before anyhow any thoughts on what ones to get, like I said never paid much attention to those tubes just seemed to last forever any help apprecitated.
    Canton
     

     

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  2. primosounds

    primosounds Parallel single ended EL84 ,EDCOR OPT

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    well, unfortunately, if you are going to use 5ar4 the new production are not the equal of the vintage units. You might have to do a hybrid SS/tube mod to make the rectifier reliable.
     
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  3. triode17

    triode17 Well-Known Member

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    I still like the Chinese One Electron brand 5AR4s. Have one in a Scott LK48 for about 100 hours now, without any problems. The Sovteks' are good too. Or spend big money on Mullard 4 notch or 9 notch rectifiers. The communist countries are probably the most experienced at making vacuum tubes because they never stopped, like western countries did 30 years ago.
     
  4. whoaru99

    whoaru99 Epic Member

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    I bought some new production Tung Sol on Jim McShanes recommendation for decent, reasonably priced 5AR4s.

    They're still in the boxes though as I've not finished the amp builds.
     
  5. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    To lump all NON DOMESTIC or EURO 5ar4's(ie: Russian and Chinese) into one grouping is UNFAIR! Medicine is the same way. Each individual is different and it's not fair to them to lump them automatically into one group of patients. I've got a Sovtek 5ar4 in my Fisher TA-600 Receiver and it hasn't had a problem in 6 years. I'm also running Tung-Sol Russian's in my X-101-B and X-202 Amplifiers. Absolutely no problems. Voltages are nominal with schematics and voltage droop is minimal with all 3. The Russian Rectifiers have improved in the last 5 years while the Chinese rectumfriers are still a crap shoot. I can't afford Old Stock Tubes so I tend to Russians for the most part and they do just fine.

    To the OP. Contact Jim McShane and ask him what he recommends for the MKIV's. His testing of Rectifiers exceed the Voltage and Current requirements of practically any amp made (except those Wildly expensive that have 4-6 rectfier tubes and 36 or more output tubes that run B+ voltages in the KV range.)
     
    Last edited: May 17, 2018 at 6:23 PM
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  6. Brice

    Brice AK Subscriber Subscriber

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    I second that. I use Sovtek 5AR4 and so far so good.
    I would trust them as much as I would trust a NOS.
     

     

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  7. sKiZo

    sKiZo Hates received: 8641 Subscriber

    EDIT >> A GZ37 draws near the operating limit if you're still using the stock PA-060 power transformer. Even a GZ34 (5AR4) will push the OEM iron hard enough to cause some concern as these amps age. The gurus lean towards setting the bias to no more than 40mV per tube (1.25VDC per bank) if you haven't yet upgrade the iron to avoid rectifier meltdowns - highly recommended if you want to keep these old gems singing.

    Then again, if you can score a couple of the old Mullard GZ37's ... nudge nudge ... know what I mean? ;-}

    [​IMG]
     
    Last edited: May 19, 2018 at 3:19 PM
  8. gadget73

    gadget73 junk junkie Subscriber

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    I have a couple of Sovtek 5AR4's in service as well as Tung-Sol. Can't really tell the difference other than the T-S has a brown base and a slightly higher price tag. The T-S is in my Magnavox 9300, but it was doing service in my Fisher TA-600 before I got a screaming deal on an oddly branded Mullard. The Sovteks are in my Bogen DS-225, which uses a very unconventional dual rectifier arrangement. They run in series rather than parallel though, the "lower" rectifier carries the full load, plus the load of the lower voltage section it feeds.
     
  9. Palustris

    Palustris Well-Known Member

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    I suppose it is worth repeating the rectifier tube has a specific voltage and current rating for the heater. The Dynaco specifies a 5AR4 with a 5V 2A rating for the heater secondary of the power transformer. Personally, I use the 5V3A/5AU4 ($15) rectifier whenever possible since it is a more robust replacement for the 5U4GB with extra current and voltage capabilities. However, this tube uses 3.75 A of current so could overload the Dynaco power transformer which are notoriously under spec already. The GZ37 draws 2.8A of current while the transformer secondary is rated at 2A; so not as egregious as the 5V3A/5AU4, it still will overload an already stressed transformer. At the very least if you use a GZ37 measure the heater voltage to ensure it is a full 5V and not loaded down by the GZ37. The GZ37 is a good robust rectifier: I bought 8 at $12 each back in the 1980s from Ned Carlson for my Quicksilver monoblocks. They are still in their original boxes because I find the internal impedance drops too much B+.
     
  10. Lavane

    Lavane AK Subscriber Subscriber

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    The GZ37 should be ok to use in the VTA ST-70's, no?
     
  11. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    You could buy cheap plug in SS replacement.
    Add a 50 ohm 10w resistor to compensate for the lower v drop and a current in rush device .
    If you have stock PS caps (read that as original , 50?YO caps , not new original value) that might push them over the edge.
    If you go this route, it frees the 5v PT winding to act as a bucking transformer.
     
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  12. Palustris

    Palustris Well-Known Member

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    Check the power transformer secondary. Is it rated at 2A for a 5AR4 or 3A for a 5U4GB?
     
  13. gadget73

    gadget73 junk junkie Subscriber

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    The Mark IV is fine with a 5AR4. Consider its half an ST-70, but using the same rectifier. You won't need any special super duty rectifier in this application.
     
  14. sKiZo

    sKiZo Hates received: 8641 Subscriber

    The Mark IV used the exact same A470 power transformer as the ST70 ...

    Hadn't really thought of that though - my Latino kit has much stronger iron than the OEM Dynacos did. Tube complement includes the GZ37, a quad of KT120's, and three drivers, including a 6SN7 center. I also lose some B+ dropping the line voltage to around 117vac and that takes a slight hit from an inline thermistor as well. Several years now since the build with no issues ...

    (I also drive the amp to relatively insane levels ... ) ;-}
     
    Last edited: May 18, 2018 at 5:08 PM
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  15. Retrovert

    Retrovert AK Subscriber Subscriber

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    Adding solid-state rectifier diodes (I suggest low-Qrr) to the base of the rectifier reduce the stress of inverse voltage on the tube and improves its lifespan. This still delivers the B+ delay to ensure the cathodes are hot before B+ can flow.
     
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  16. gadget73

    gadget73 junk junkie Subscriber

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    There is that, but more importantly the forward current required for a Mark IV is within what a 5AR4 is capable of doing reliably. Between the diodes and reasonable current draw you should have no issues.
     

     

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  17. Lavane

    Lavane AK Subscriber Subscriber

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    5ar4 is what is recommended with the kit.
     
  18. Lavane

    Lavane AK Subscriber Subscriber

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    That's why i was wondering if the beefier ST-70 power trany could handle the GZ37.
     
  19. sKiZo

    sKiZo Hates received: 8641 Subscriber

    Did some digging ...

    The rectifier line on the OEM PA-060 power transformer is rated at 4 amps and a GZ37 draws 3 amps. A GZ34 draws less than two. The original PT was marginal when pushed and designed to minimum standards so that the amp could be sold at a price point. Truth be told, a lot of folk figure the GZ34 was too much of a load, especially as the iron ages.

    ** The Dynaco gurus recommend you set bias to 40mV per tube (1.25VDC per channel). This leaves enough reserve to comfortably handle the drivers as well.

    PS ... edited my original post on the GZ37 to recommend that ONLY if the iron's been upgraded.
     
    Last edited: May 18, 2018 at 10:36 PM
  20. canton

    canton Active Member

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    Thanks all for the info. The MK IVs are 90% compleat don't want to jinx them now. I will post the final results and what was done with them. I feel they are a pair of excellent amps. Now they are close to being compleatly rebuilt. This is very exciting to be at this point. I have a Pas 3X pre amp that is going to be used with them. I have other older pre amps that i would like to kick around as to what would match up well with them. Like I said exciting times for me.
    Canton
     

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