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Old 2nd July 2005, 08:33 PM   #1
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Question GZ37 Substitution?

I'm planning to build the Angela SE 6SL7->EL34 (triode strapped) amp. Their designs call for GZ37 rectifiers, but as this is to be a low-cost project, I don't want to chase NOS tubes down at high $$.

I'm thinking a 5AR4/GZ34 might be a decent replacement here-- draws 1A less current, but is rated for 160mA Irect compared to the GZ37's 250. So perhaps a 5U4G, rated for 225mA Irect would be preferable, and I have some of those around.

Thanks in advance for any advice.
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Old 2nd July 2005, 10:48 PM   #2
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Hackensack , I have two GZ37's that I purchased from Ned at triode tubes in early 1990s when I was updating my Dynaco MK2s.
I did not use them because the top covers would not fit.
If your interested email me. Thanks
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Old 2nd July 2005, 10:52 PM   #3
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Check the data sheets out. The 5AR4/GZ34 is rated for a 250 mA. draw. The GZ37 is rated at 275 mA. into a cap. I/P filter and 350 mA. into a choke I/P filter. Also, the GZ37 data sheet says 4 muF. max. for a cap. I/P filter.

The forward drop in a GZ37 is greater than that in a GZ34. So, the B+ rail voltage will be somewhat higher. Current production 5AR4s have improved significantly of late and that's what I'd use.
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Old 4th July 2005, 05:18 PM   #4
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Thanks for the replies!
I will most likely follow Eli's advice, however, I would also consider Freddy's offer, but the diyaudio mail function is turned off for him.
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Old 4th July 2005, 07:18 PM   #5
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by Eli Duttman
Also, the GZ37 data sheet says 4 muF. max. for a cap. I/P filter.
Which data sheet would that have been? My Mullard data sheet simply gives data using 4uF as a reservoir, but given that the data sheet was from 1958 (and probably an update of an earlier one), perhaps that's not indicative? The peak current ratings suggest that it ought to be equivalent to a GZ34 - it just uses more heater current.

Of course, you could always use a pair of 6CL3/6CK3 or 12CL3/12CK3, which are substantially beefier than GZ34, and in your neck of the woods, probably cheaper.
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Old 4th July 2005, 11:30 PM   #6
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The 5R4 can deliver plenty of current too. 4 muF. is max. for that type too. Arc over at start up is NOT good.

There are reports about the GZ37 sounding mediocre when used as a substitute for the GZ34. My hunch is that the tube is stressed, even if it does not arc over with a substantial filter cap.

The data sheet I've seen was published by Chelmer Valve.
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Old 4th July 2005, 11:42 PM   #7
SHiFTY is offline SHiFTY  New Zealand
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If you want an even better sub get a mullard GZ33, that is the holy mother of god rectifier that is indestructible by conventional means.

But even a GZ34 should have a life of several decades used with 40 or 60uF input cap...
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Old 25th April 2014, 09:37 PM   #8
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Hi I have a Dynaco VTA ST-120 . It is a Bob Latino modified st-70 that Bob himself says you can run the GZ 37 as a drop in rep also it can run kt-88 kt 90 kt 120 tubes .It is 60 wpc . I run the kt 88 at .55volts but the kt 120 in this amp I run at .6volts nice
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