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    Rectifier/Diode question

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    Wired

    Posts: 1
    Join date: 2010-02-18

    Rectifier/Diode question

    Post by Wired on Thu Feb 18, 2010 10:09 pm

    I was wondering what good inexpensive rectifiers people are using with their ST70's or ST120's?

    I'd love a Mullard 5AR4 but they're too expensive. How are the JJ's or other NEW types of 5AR4's? Any I should stay away from?

    I've been thinking of trying other NOS rectifiers like 5U4's or 5R4's..etc... that will handle the voltage. Some won't handle the first capacitor value though. Is there any way around this besides lowering the value of the capacitor or inserting a choke?

    I read somewhere that people like to use a pair of HF4007? diodes in series with the recifier to reduce/eliminate occasional arcing on startup (of JJ 5AR4's). Anyone ever had any experience with this and can tell how to wire it up?

    I know the difference between direct/indirectly heated Rectifiers.. I don't worry about the difference.. I just wire in a standby switch. Smile

    Thanks,

    Wired (in Triode)

    Bob Latino
    Admin

    Posts: 1956
    Join date: 2008-11-26
    Location: Massachusetts

    Re: Rectifier/Diode question

    Post by Bob Latino on Fri Feb 19, 2010 5:14 am

    Wired wrote:I was wondering what good inexpensive rectifiers people are using with their ST70's or ST120's?

    I'd love a Mullard 5AR4 but they're too expensive. How are the JJ's or other NEW types of 5AR4's? Any I should stay away from?

    I've been thinking of trying other NOS rectifiers like 5U4's or 5R4's..etc... that will handle the voltage. Some won't handle the first capacitor value though. Is there any way around this besides lowering the value of the capacitor or inserting a choke?

    I read somewhere that people like to use a pair of HF4007? diodes in series with the recifier to reduce/eliminate occasional arcing on startup (of JJ 5AR4's). Anyone ever had any experience with this and can tell how to wire it up?

    I know the difference between direct/indirectly heated Rectifiers.. I don't worry about the difference.. I just wire in a standby switch. Smile

    Thanks,

    Wired (in Triode)

    Hi Wired,

    Of the presently available GZ34 rectifier tubes (JJ, Sovtek, Ruby), I have found the Ruby to be the most reliable and longest lasting.

    You can use a 5U4 rectifier in place of the a GZ34 rectifier in an ST-70. A 5U4 has a greater voltage drop than a GZ34 and you will restrict overall power of the amp very slightly by using a 5U4. The nice thing about 5U4's are that you can pick up used USA made 5U4's at a fairly reasonable price here in the USA. The 5U4 was used as a rectifier in many tube color TV's of the 1960's and they are still fairly plentiful.

    You don't really need a "standby switch" with any tube amp that has a GZ34 rectifier tube. The fact that a GZ34 is indirectly heated and won't apply high voltage for at least 15 seconds gives you an automatic delay every time you turn the amp on. The 5U4 mentioned above is directly heated but still gives a short delay until the filament is fully lit.

    Bob

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