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Recently installed a GZ34 into my 6L6 project amp, and after my usual fashion of obsessing about startup voltages, I measured the ascent of the B+ voltage to see if it came close to my new 600vdc first filter cap.
I was pleasently suprised to find the GZ34 rectifier in this amp ramps up voltage to more or less the stable operating B+ of 473vdc. The prior rectifier tube was a 5U4GB, and that allowed the B+ to go all the way up to 540vdc or so, exceeding the original 450vdc filter cap by a good margin. I attributed this large 90vdc overage to modern higher wall voltages (the amp is from the 1940's).
It seems I got more protection out of the new Rectifier tube in having a slow startup. Just to be safer though, I also installed two series CL-80 3 amp Thermistors on a primary AC transformer lead, to limit current inrush, as I am using a large first filter capacitance (94uf) to reduce hum. I want the new JJ GZ34 Rectifier to last a while and it's rated to 60uf for first filter capacitance. The thermistors in steady state only trim off perhaps 10vdc from B+ so that is fine by me.
Question: What is different about the GZ34 vs the 5U4GB that slows the B+ voltage rise so much ? Thanks !
I was pleasently suprised to find the GZ34 rectifier in this amp ramps up voltage to more or less the stable operating B+ of 473vdc. The prior rectifier tube was a 5U4GB, and that allowed the B+ to go all the way up to 540vdc or so, exceeding the original 450vdc filter cap by a good margin. I attributed this large 90vdc overage to modern higher wall voltages (the amp is from the 1940's).
It seems I got more protection out of the new Rectifier tube in having a slow startup. Just to be safer though, I also installed two series CL-80 3 amp Thermistors on a primary AC transformer lead, to limit current inrush, as I am using a large first filter capacitance (94uf) to reduce hum. I want the new JJ GZ34 Rectifier to last a while and it's rated to 60uf for first filter capacitance. The thermistors in steady state only trim off perhaps 10vdc from B+ so that is fine by me.
Question: What is different about the GZ34 vs the 5U4GB that slows the B+ voltage rise so much ? Thanks !
I understand about obsessing over pedantic matters like input surge voltage and capacitor ratings. And I've taken measures in builds to ensure against the problem. Major manufacturers commonly ignore this, some of our more experienced techs notice this without wincing and the filter cap failure in amps that stress this matter is actually very low. But I'm with you and have taken above industry measures to circumvent it. Maybe it's a non issue because capacitors are typically very good with surge voltages.?. But I also know that I've had marginal luck with newer design caps going outside their rating and older design caps seem to be up for anything until they're not. I guess what I'm saying is that I know the materials are at least a little different than they use to be. So the old standard of relying on repeated surges not being an issue didn't sit well with me building new amps. I see to it that all my filter circuits are rated over the unloaded voltage. (<period) Since we really don't know what modern capacitor architecture will do in these conditions compared to the golden age stuff it gives me solace. The reality is that it's probably a non issue. But after the era of the gray Illinois caps (late 80's to late 90's) failing in everything I just don't take chances.
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