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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


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Tom
nmchiefsfan
Dale Stevens
Rec
BryceJ
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    Switch from 5AR4 to 5U4 Rectifier

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    BryceJ


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    Post by BryceJ Sun May 29, 2022 3:49 am

    I was just looking at the tubes4hifi website and I notice that the ST120 and M-125 amps have switch to the 5U4 rectifier from the 5AR4. What is the reason for the change? It is a supply issue, for are there performance reasons?
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    Rec


    Posts : 43
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    Post by Rec Sun May 29, 2022 3:33 pm

    Current handling. M125 , 4 power tubes at 1v bias can be tough on 5AR4.

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    Dale Stevens


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    Post by Dale Stevens Fri Jun 03, 2022 10:29 am

    Rec, what about the ST120? Can you explain? Thx, Dale
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    nmchiefsfan


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    Post by nmchiefsfan Fri Jun 03, 2022 12:14 pm

    Dale, the exact same reason as the M-125. The ST-120 creates 120 - 130 total watts of output power but only has 1 power supply so the rectifier has to deliver essentially the same amount of bias current in the ST-120 and the M-125.

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    Tom


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    Post by Tom Wed Jun 15, 2022 1:49 pm

    So, by that logic, running my M-125s with only two KT-120s each, I'm good using my existing 5AR4s. Right?

    So much good info here, thanks all!
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    Rec


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    Post by Rec Thu Jun 16, 2022 9:36 am

    Sure. You can also still run the 5ar4 with 4 tubes, suggest you just bias at .9 bs 1v to lower stress on the rectifier, I’ve found that the m125 at 1v pushes rectifiers and have blown my share of 5ar4s.. Ultimately you will have longer life with diodes or a 5u4 for all reasons above.
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    yel17


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    Post by yel17 Fri Jun 17, 2022 7:26 am

    The 5V3A rectifier is rated at 415 mA, which is even higher than the 5U4 variants. It should be much more reliable than 5AR4 and 5U4 types.
    Bob Latino
    Bob Latino
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    Post by Bob Latino Fri Jun 17, 2022 8:41 am

    The nice thing about using a 5U4 or a 5V3 rectifier is that you can still get older USA made (RCA, GE or Sylvania) versions of these two tubes on Ebay for relatively low money. Some are new but most are used but still working. Most good sellers will test the tubes before selling the tube. These older 5U4 or 5V3's are built better with higher quality metal alloys and better quality control. Check out the two Ebay links below for 5U4 and 5V3 rectifier tubes being sold on Ebay.

    5U4 tubes on Ebay

    5V3 tubes on Ebay

    Bob

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    Hops


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    Location : South Detroit, Michigan

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    Post by Hops Fri Jun 17, 2022 7:04 pm

    Will the 5U4 or 5V3 work with an older st-120 ( low gain board ) that was designed for a 5AR4 ? Or would I need to rewire or substitute components? My ST-120 is a wonderful amp, I truly appreciate that I had the opportunity to buy the wonderful kit and build it. It sounds great, but it eats 5AR4s. I am currently using a Weber SS ( WS-1 with thermistor ? ), but I like the looks of a tube rectifier. The Weber actually sounds great, but the idea of Tube Rectifier appeals to me. Just would prefer not to rewire or change components on a working Amp.
    Bob Latino
    Bob Latino
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    Post by Bob Latino Fri Jun 17, 2022 7:23 pm

    Hops wrote:Will the 5U4  or 5V3 work with an older st-120 ( low gain board ) that was designed for a 5AR4 ?  Or would I need to rewire or substitute components?   My ST-120 is a wonderful amp,   I truly appreciate that I had the opportunity to buy the wonderful kit and build it.   It sounds great, but it eats 5AR4s.   I am  currently using a Weber SS ( WS-1 with thermistor ? ),  but I like the looks of a tube rectifier.   The Weber actually sounds great,  but the idea of Tube Rectifier appeals to me.   Just would prefer not to rewire or change components on a working Amp.

    Yes - The 5U4 or 5V3 rectifiers will also work just fine in a VTA ST-120 amp.

    Bob

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    Tubes4ever
    Tubes4ever


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    Post by Tubes4ever Mon Jun 27, 2022 9:50 am

    Bob Latino wrote:
    Hops wrote:Will the 5U4  or 5V3 work with an older st-120 ( low gain board ) that was designed for a 5AR4 ?  Or would I need to rewire or substitute components?   My ST-120 is a wonderful amp,   I truly appreciate that I had the opportunity to buy the wonderful kit and build it.   It sounds great, but it eats 5AR4s.   I am  currently using a Weber SS ( WS-1 with thermistor ? ),  but I like the looks of a tube rectifier.   The Weber actually sounds great,  but the idea of Tube Rectifier appeals to me.   Just would prefer not to rewire or change components on a working Amp.

    Yes - The 5U4 or 5V3 rectifiers will also work just fine in a VTA ST-120 amp.

    Bob


    Just make sure to use 5u4GB not 5u4G. 50mA difference in current rating.

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