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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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Bob Latino
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peterh
eickmewg
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    Direct- vs. indirect-heated rectifiers in ST120

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    eickmewg


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    Direct- vs. indirect-heated rectifiers in ST120 Empty Direct- vs. indirect-heated rectifiers in ST120

    Post by eickmewg Sat May 14, 2016 6:31 am

    As I understand, a direct-heated rectifier applies high voltage to driver and power tubes faster than an indirect-heated rectifier. But what I read suggests that a direct-heated rectifier takes 3-4 seconds to heat which I think is about equal to the Weber Copper top SS rectifiers which I have used in the past in my ST120. So, my question is can a 5 V 3 A tube rectifier be used in the ST120 without undue stress on the tubes? As a side question, it appears direct-heated rectifiers have 4 pins while an indirect-heated rectifier will have 5 pins. Is this correct?
    peterh
    peterh


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    Post by peterh Sat May 14, 2016 9:09 am

    eickmewg wrote:As I understand, a direct-heated rectifier applies high voltage to driver and power tubes faster than an indirect-heated rectifier.  But what I read suggests that a direct-heated rectifier takes 3-4 seconds to heat which I think is about equal to the Weber Copper top SS rectifiers which I have used in the past in my ST120.  So, my question is can a 5 V 3 A tube rectifier be used in the ST120 without undue stress on the tubes?  As a side question, it appears direct-heated rectifiers have 4 pins while an indirect-heated rectifier will have 5 pins.  Is this correct?

    No rectifier , tube or solidstate, will stress the tubes.

    What might be of concern is that if a rectifiers is active before the powertubes start conducting
    B+ will be higher then in normal use. If the caps rating is close to normal use then
    they might have overvoltage during the time until the powertubes start conducting.

    Tubes4ever
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    Post by Tubes4ever Sun May 15, 2016 3:11 am

    The 5V3A will work just fine in the ST120. It will be much more reliable than a 5AR4. You'll likely have no trouble with it for many years. You'll have slightly lower B+, but unless you are trying to rattle your neighbor's windows, you'll never notice.

    I asked Bob L. awhile back about the exact same issue that peterh mentioned about the capacitors. Bob said that he has not had a single Cap failure from any of his customers and that the Caps can take the voltage.
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    eickmewg


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    Post by eickmewg Sun May 15, 2016 7:19 am

    This is good to know. I always learn something new when I ask a simple question. I was unaware the primary issue was with the cap voltage surge on startup. I was looking at a 5Z3P rectifier but I think that tube won't fit into a standard octal socket. I'll look into the 5V3A. Thanks all for your help.
    Bob Latino
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    Post by Bob Latino Sun May 15, 2016 7:44 am

    You can use a 5V3 as a rectifier in any of the VTA amps .. A 5V3 will have a different bias point so the amp will have to be rebiased when going from a 5AR4 or Weber WZ68 to a 5V3. The fact that a 5V3 is directly heated and has a slightly quicker warm up than a 5AR4 in these amps does not make any real difference in the operation of the amps.

    Bob
    GreggW
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    Post by GreggW Mon May 16, 2016 7:17 pm

    I use a 5V3A in a ST120 and now have several hundred hours on it. Plate voltage is between 445-450 volts depending on line voltage. I've picked up a handful of spares on eBay but haven't used one yet. Bias hasn't been adjusted in months.....
    MarcVBelgium
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    Direct- vs. indirect-heated rectifiers in ST120 Empty direct-vs-indirect-heated-rectifiers-in-Stereo120

    Post by MarcVBelgium Tue May 17, 2016 8:56 am

    Well , I had a 5U3C Winged C NOS, made in CCCP on hand. The accompanying leaflet is unreadable (Russian) but underneath states "20000 25-XI-70. This suggests a batch of 20.000 in 1970.....

    Anyhow, I finally mounted it in my ST-120, it biased perfectly and is now playing as good (or better??) as always.

    The bottle is a bit shorter and thicker than Skizo's favourite Mullard GZ37 (that I also have on hand.)

    Those rectifiers really keep us going...... Must admit that I like tube over Solid State rectifiers, if alone for the looks and the glow of it..
    sKiZo
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    Post by sKiZo Tue May 17, 2016 3:50 pm

    Good to know yet another option verified by a happy user.

    The 5U3C is way more affordable than the big bottle mullards too. I see the winged C going for around $50 ... afraid to see what a NOS GZ37 goes for nowadays. Glad I got spares when I did!

    PS ... as usual, the Cyrillic alphabet can get confusing. The Russian 5U3C is actually a 5U4-G ... Same thing, only different, as they say.
    MarcVBelgium
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    Direct- vs. indirect-heated rectifiers in ST120 Empty https://dynacotubeaudio.forumotion.com/t3036-direct-vs-indirect-heated-rectifiers-in-st120#26473

    Post by MarcVBelgium Tue May 17, 2016 4:10 pm


    Well Skizo, I've just ordered two more Svetlana Winged C NOS 5U3C (5u4-g) for 16 € (19$) each at TAD (Tube Amp Doctor)
    The amp seems to like it........and it will probably outlast a whole box of GZ34's

    My GZ37 was well over 130$....... including VAT and shipment , so I keep it for "special occasions"
    (http://www.watfordvalves.com/search.asp?search=GZ37&Submit=Search)==> 72 £ excl VAT and shipment.
    peterh
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    Post by peterh Tue May 17, 2016 5:05 pm

    Are you folks eating rectifiers ???

    I had the chinese 5ar4 that bob sent, it broke in a power surge, since then i have used a JJ 5ar4
    for 1 1/2 year. This is not a st120 but a vta70. I do however have a "power sequencer" that
    will make sure that no hot-switching occurs. In total 1 5ar4 in 2 1/2 years. ( 2335h powered on)

    If the 5ar4 breaks, i will install 2 1n4007 , at least that's my plan.

    corndog71
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    Post by corndog71 Tue May 17, 2016 5:27 pm

    peterh wrote:Are you folks eating rectifiers ???

    I had the chinese 5ar4 that bob sent, it broke in a power surge, since then i have used a JJ 5ar4
    for 1 1/2 year.  This is not a st120 but a vta70.  I do however have a "power sequencer" that
    will make sure that no hot-switching occurs.   In total 1 5ar4 in 2 1/2 years. ( 2335h powered on)

    If the 5ar4 breaks, i will install 2 1n4007 , at least that's my plan.


    Lucky! I never had a newer rectifier tube last more than a year and on 2 occasions not more than 1 day. affraid Never again! I built my ST120 with UF4007's and never looked back.
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    Post by eickmewg Tue May 17, 2016 5:51 pm

    Based on this thread, I have snagged a supposedly NOS Svetlana Winged =C= 5U4G rectifier off the bay for $14.98 shipped. It was the only tube I found in the US, all the others were coming from Eastern Europe. I will be pleased if it outlasts a box-full of GZ34/5AR4 rectifiers. I also tried some 5Z3PAT tubes from China but they may not be octal-socket tubes. We shall see.
    Tubes4ever
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    Post by Tubes4ever Tue May 17, 2016 11:03 pm

    eickmewg wrote:Based on this thread, I have snagged a supposedly NOS Svetlana Winged =C= 5U4G rectifier off the bay for $14.98 shipped.  It was the only tube I found in the US, all the others were coming from Eastern Europe.  I will be pleased if it outlasts a box-full of GZ34/5AR4 rectifiers.  I also tried some 5Z3PAT tubes from China but they may not be octal-socket tubes.  We shall see.

    The 5Z3PAT is an octal socket tube. I have 2 of them. It acts just like a 5U4.

    Just about any rectifier tube will last longer than a 5AR4.

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