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    GZ37 in st70?

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    Corona

    Posts : 32
    Join date : 2010-03-11

    GZ37 in st70?

    Post by Corona on Mon May 31, 2010 11:48 pm

    I've seen a lot of ebay listings like this one and I've been wondering if a 5v4g would actually work the same as a 5ar4 in an st-70. Anyone know if this is just typical misleading ebay bs or if it's actually legit?
    http://cgi.ebay.com/RCA-CRC-5V4G-5V4-5V4GA-5AR4-Amp-Vacuum-Tube-MATCHED1958-/110540237488?cmd=ViewItem&pt=Vintage_Electronics_R2&hash=item19bcb62ab0


    Last edited by Corona on Thu Jun 03, 2010 12:38 am; edited 1 time in total

    RichJB603

    Posts : 14
    Join date : 2010-05-10

    Re: GZ37 in st70?

    Post by RichJB603 on Tue Jun 01, 2010 12:11 am

    Sounds like it's possible, I believe you can also use a 5u4g if you have upgraded power supply caps and such. However @ that price I think you would be better off buying a mullard, who have a pretty good reputation. I know the JAN stuff is usually pretty good (I have those in my preamp) but mullard seems to be the standard for high quality rectification tubes.

    Corona

    Posts : 32
    Join date : 2010-03-11

    Re: GZ37 in st70?

    Post by Corona on Tue Jun 01, 2010 1:13 am

    RichJB603 wrote:Sounds like it's possible, I believe you can also use a 5u4g if you have upgraded power supply caps and such. However @ that price I think you would be better off buying a mullard, who have a pretty good reputation. I know the JAN stuff is usually pretty good (I have those in my preamp) but mullard seems to be the standard for high quality rectification tubes.
    They can actually be found cheaper. It's about $50 for a nice NOS 5v4g vs $150 for a NOS mullard. Also they have a really unique look.
    The problem with 5u4g's is that they're directly heated and apply full voltage faster and that stresses your components and output tubes. I wonder if it's the same with 5v4g's.

    GP49

    Posts : 735
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: GZ37 in st70?

    Post by GP49 on Tue Jun 01, 2010 10:56 am

    The 5V4 types (5V4, 5V4G, 5V4GA) have indirectly-heated cathodes but in my experience they don't have as much a delay to application of DC as do the 5AR4/GZ34. However the 5V4 types are rated at a lower maximum current, and they have more internal voltage drop than the 5AR4, so the amp will run at a lower B+ voltage and will not produce as much output power. They CAN be used as an emergency substitute in the Stereo 70.

    The 5V4 has less internal voltage drop than the 5U4, but a slightly lower maximum current. They can be substituted for the 5U4 tube in most cases except where power supply capacititive storage is marginal, or a continuous full power output is required, such as industrial applications.

    Tube specifications are available at many sites on the Web. Probably the most-often used is the Duncan Amps site. If there is a particular parameter that their data pages don't cover, there are also links on each page to other sources of data.

    http://tdsl.duncanamps.com/tubesearch.php

    Bill Beech's site is also a good one for tube data:

    http://www.nj7p.org/Tube.php

    Luddite

    Posts : 235
    Join date : 2009-02-04
    Age : 66
    Location : Texas

    Re: GZ37 in st70?

    Post by Luddite on Tue Jun 01, 2010 11:00 am

    I checked my tube substitution guide and while it suggests substituting a 5AR4 for a 5V4GA, there is no suggested substitute for a 5AR4. Referring to my RCA tube manual shows the likely reason. The 5AR4 is rated for a maximum (per) plate current of 825 ma, while the 5V4GA is rated for a maximum (per) plate current of 525 ma. A 300 ma difference.

    Best Regards,
    Charlie

    Corona

    Posts : 32
    Join date : 2010-03-11

    Re: GZ37 in st70?

    Post by Corona on Tue Jun 01, 2010 5:13 pm

    Ok so basically it would work, but it's not recommended cause the 5v4g has a lower current rating and output voltage. Guess I'll be sticking to the 5ar4. Thanks for the help.

    Corona

    Posts : 32
    Join date : 2010-03-11

    Re: GZ37 in st70?

    Post by Corona on Thu Jun 03, 2010 12:35 am

    Ok new question. How would the st70 handle a gz37? They supposedly have a higher current rating, are considerably cheaper than a NOS mullard 5a4r and should last much longer than a 5ar4.
    The cons=2.8A filament current vs 1.9A for 5ar4 and it has something like a 12 volt B+ voltage drop compared to a 5ar4.
    I was reading about them here
    http://www.audioasylum.com/forums/bottlehead/messages/5998.html

    I'm using a new kit built st70 with the upgraded power transformer and kt88 output tubes. Think it can handle another amp of filament current?

    Currently I've got a heavily used GE 5ar4 of questionable quality in the amp and it's either damaged or dying. After about 300 hours of use it momentarily flashed blue from arcing and it still works, but the bias dropped by about 40-60 millivolts per tube. The original ruby 5ar4 randomly arced and started blowing fuses after like 15 minutes of use. I figure it's time to get a nice NOS rectifier that should last the life of the amp.

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