Are all GZ34's born equal?

[catch29]

I need a couple of GZ34's (or 5AR4, CV1377} for 2 MA12's I'm renovating. I've seen some advertised "for guitar", is there a difference?, surely all would be made to the same design spec'?. Would I really hear the difference between a Mullard (too expensive) and a cheaper Russian/China make?. Is reliability an issue. Now to put the cat amongst the pigeons = what about a solid state replacement!! - Heresy! I hear the cry!, Will I be drummed out of the forum!.

[ppppenguin]

Difference in sound is for the golden eared only. Or perhaps platinum eared given next weekend's events.

Some GZ34 may be of inferior quality giving poor reliability, especially if run hard. I'm not familiar with the MA12 but if it's a sensbly designed hifi amp the GZ34 shouldn't be run very hard. Assuming this is it: https://andydoz.blogspot.com/2020/12/hea...ifier.html then the GZ34 should be living a pretty easy life.

Solid state is great, especially if built into an octal base so it can be readily unplugged. Definitely need limiting resistors, though not sure what value. Watch out for high voltage on the reservoir and smoothing caps because it will be present and higher than normal until the valves have warmed up.

[joebog1]

Keep well away from any russian or chinese ones. They are real crap!!. The hum, they crackle, they fart, if you want a noise generator you can use them.
Reliability??? maybe 6 months if only driven to church by grandmah on sundays. Just my experience.

Joe

[Andy M0FYA]

I'm surprised at the criticism of Russian examples, specifically if they are older stock made for military use during the 60's and 70's. I wouldn't lump them with Chinese examples made much later by manufacturers with no pedigree.

Andy

[Diabolical Artificer]

At £20 - £28 a pop I'd be tempted if possible to use silicon diodes. As Joe says some aren't much cop, bit of a minefield trying to find a good one but both Langrex & Billington have them, whether Chinese or Soviet who knows but they're the only ones making valves nowadays. It's either that or a NOS Mullard for £100 up! That said a 5R4WGB CV4026 might be cheaper and easier to find as NOS. A lot of folk don't like them as they look "wrong"

Andy.

[ppppenguin]

EZ81 would work, but heater voltage is wrong. Probably not enough spare current available on the 6.3V winding to heat it and a little autotransformer from the 5V winding is too much faff when you could just go solid state.

[Murphyv310]

Hi.
I've used many Russian rectifiers that are every bit as good as Mullard, Philips and American versions and often better rated. The Chinese ones are a different kettle of fish.
The GZ34 has a lower forward voltage drop than the GZ32 and for a given load will run cooler than the 32, hence the smaller envelope.
If contemplating silicon monitor the peak HT prior to the load increasing as the valves warm, then add 20% to that voltage and see if smoothing caps and other caps on the HT line are suitably rated, if not you'll have to replace them or stick with the valve rectifier which I would if humanly possible.

[Andy M0FYA]

I just can't agree with the idea of replacing valve rectifiers with silicon diodes.
Sure, they are better, that's technical progress. If that is what you want, replace the whole valve radio, amplifier or whatever by a later solid-state unit, it will offer much higher performance.
But this forum is about the preservation and restoration of vintage equipment!

Andy

[Murphyv310]

Totally Agree Andy.
The equipment was designed for a valve rectifier and really should always have one.
There are big disadvantages with silicon, obviously the surge then adding limiting resistors to tame the running HT which defeats the purpose of silicon as the resistors have to dissipate waste through heat, the big issue for me is the peak voltages that shorten the life of smoothers and of course breakdown on paxolin tag strips and even valve bases
A good indirectly heated rectifier removes all of the aforementioned issues.

[Mike Watterson]

Totally Agree Andy.
The equipment was designed for a valve rectifier and really should always have one.
There are big disadvantages with silicon, obviously the surge then adding limiting resistors to tame the running HT which defeats the purpose of silicon as the resistors have to dissipate waste through heat, the big issue for me is the peak voltages that shorten the life of smoothers and of course breakdown on paxolin tag strips and even valve bases
A good indirectly heated rectifier removes all of the aforementioned issues.

I'm happy to replace metal rectifiers with Silicon because the peak HT before the valves heat up is the same. I've seen ECH42 etc flash-over from too high HT before rail loaded on sets meant to take a valve rectifier, resistors in series don't fix that. Also good luck getting any reliable NOS selenium replacement! I've always been able to find a valve rectifier.