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    GZ37 in st70: Results

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    Corona

    Posts : 32
    Join date : 2010-03-11

    GZ37 in st70: Results

    Post by Corona on Wed Jun 09, 2010 12:51 am

    I had a thread here asking about alternative rectifiers for the st-70 and never got any conclusive answers on the gz37. Anyway I researched it some online and decided to go for it. I got a nos mullard gz37 for about 2/3 the cost of a 5ar4. I put in in the amp and I can honestly say it's working great. Everything biased normally and the power transformer doesn't seem to get noticeably hotter than before. I've had it on for about 10 hours now without a problem.

    Basically it's cheaper than a mullard 5ar4 and it has a higher current rating/should have a longer life. Also it looks sick compared to the bland 5ar4's Twisted Evil

    JunkyJan

    Posts : 103
    Join date : 2008-12-09
    Location : BC, Canada

    That's good news!

    Post by JunkyJan on Wed Jun 09, 2010 4:16 pm

    Thanks for the info - and I agree, it looks totally "sick" (as in modern slang, not diseased)!

    Speaking of rectifiers: I have a massive big guitar store down the road from me (and I mean, BIG - there must be a helluva lot of guitar players in Western Canada, perhaps because of these long winters I guess) and they have a lot more tube amps + spare tubes in that store than I have ever seen in any audiophile store... On the whim of the moment I bought a GZ34 (Mesa / Boogie Engineering - I think they mostly market to the Guitar players) and I am running that now in my VTA/ST-70. No discernible difference in sound quality but at least mechanically speaking, it is a really well-made tube - the Ruby I had in there seemed to have been made on a Friday afternoon as the whistle blew.

    -- JunkyJan

    GTOJim
    Guest

    GZ37 with Stock Power Transformer.

    Post by GTOJim on Mon Jun 28, 2010 1:11 pm

    I don't have electrical knowledge but for what it is worth I'll pass on my experience using a GZ37 in a freshly rebuilt stock ST-70.

    The dealer an Dynaco expert said the GZ37 was perfectly safe to use in a stock ST-70 so I made the purchase.
    The second or third time I used the GZ37 it smoked the power transformer. A cloud of smoke came poring out of my ST-70. Later I was told using the GZ37 exceeded the rating of the stock power transformer.

    I did use the GZ37 after sending my ST-70 for repair. The replacement transformer was much larger, I was told it could safely handle the extra draw of the GZ37.

    From my experience I would use caution when using a stock power transformer with a GZ37.

    Maybe it was a fluke it took out my power transformer, I don't really know this stuff. My opinion is from what I was later told from others more knowledgeable than I.







    Bob Latino
    Admin

    Posts : 2413
    Join date : 2008-11-26
    Location : Massachusetts

    Re: GZ37 in st70: Results

    Post by Bob Latino on Mon Jun 28, 2010 2:09 pm

    GTOJim wrote: I don't have electrical knowledge but for what it is worth I'll pass on my experience using a GZ37 in a freshly rebuilt stock ST-70.

    The dealer an Dynaco expert said the GZ37 was perfectly safe to use in a stock ST-70 so I made the purchase.
    The second or third time I used the GZ37 it smoked the power transformer. A cloud of smoke came poring out of my ST-70. Later I was told using the GZ37 exceeded the rating of the stock power transformer.

    I did use the GZ37 after sending my ST-70 for repair. The replacement transformer was much larger, I was told it could safely handle the extra draw of the GZ37.

    From my experience I would use caution when using a stock power transformer with a GZ37.

    Maybe it was a fluke it took out my power transformer, I don't really know this stuff. My opinion is from what I was later told from others more knowledgeable than I.

    Hi,

    Corona's ST-70 is one of my kits and the power transformer on his amp has a much higher power transfer capability than the stock PA-060 power transformer as found in the original ST-70. The 5 volt rectifier line on his amp is rated at 4 amps and a GZ37 draws 3 amps while a GZ34 draws just 1.9 amps. It was not a fluke that the GZ37 took your stock PA-060 power transformer. The original power tranny was marginal and designed to minimum standards so that the amp could be sold at a price point. The original OUTPUT transformers on the ST-70's were very good but the POWER transformers were not.

    Bob

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