Are all GZ34's born equal?

[joebog1]

I will add to my earlier post!.
IF you can find NOS Ruskie rectifiers, well and good, but all thats available here is modern Svetlana or Sovtek branded junk.
Yes, I know that you can buy them branded Mullard, and then in fine print made in russia.
THESE are the ones to look out for!!. They do rectify in a fuzzy way, and will leave the hum, noise, pops, etc that I mentioned.
GZ34/5AR4 are a little bottle with a big heart, the russian ones are a big bottle with little heart.

Joe

[Murphyv310]

Hi.
In your experience Joe you've had issues but that seems to be in opposition to mine and others for some unknown reason.
Some of the very worst rectifiers were made here in the UK by Mazda, take the U801 for example, worse than those from China and that's saying something............

[Andy M0FYA]

What can be the physics behind a rectifier with the behaviour "They do rectify in a fuzzy way, and will leave the hum, noise, pops"? There's not much to a rectifier other than a heated cathode and an adjacent anode! What does 'fuzzy' mean? And surely any hum should be filtered by the subsequent smoothing components?

Unreliability causing the valve to stop working is another matter.

Andy

[catch29]

Well Guys ( if I'm allowed to say that!). I'm glad it's thrown up so much debate. On my other working pair of MA-12's is a Mullard and a Bugera (Behringer), I can't tell the difference, they're both fine. I might try some vintage old/new russkies if I can't find some Bugera's. I shall dream of a Mullard. 

[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.

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.

Hi Michael.
Indeed I've "less" of a problem with selenium rectifiers and fitting silicon, but the HT rises more with silicon as the forward voltage drop is less with silicon. A common problem after fitting a BY100 and a 25 ohm limiter resistor in a TV would show up a couple of weeks later was the need for new smoothers as they often were hit with 20 odd volts more on switch on, they had aged after many years and the extra volts was enough to ensure a failure not long after.

[joebog1]

Andy,
         Most of my experience with 5AR4's is in modern guitar amplifiers. The complaint is noise and random LOUD popcorn noise.
Hang a CRO off the filter capacitor and watch. Every so often the is a loud pop. Overall hum is "higher than I expect ". The pop is a very short spike on the CRO trace.
I replace the rectifier with GE made in USA made sometime in the 50's. ( I still have a few of them ) Switch back on from the same power point on my bench with various 
other bits of kit plugged in and running. ExactIy the same setup as before, but about 2 minutes later. thought at first it could have been my soldering iron cycling, but its not. 
The hum has dropped to just audible. There are NO pops, there is no more noise in general. I wait several hours and all is well.
 I replace the GE rectifier with Sovtek. Its back!! hum, noise, pops and farts. I have been doing this for 50 years!!.
Im not easily caught out .( mostly :-)  ) I cannot say why they are inferior, unless the vacuum is not as good as the 70 year old GE's.
Its about the only feasable explanation in my head. I do know I will not build any amplifiers with Sovtek EL34/6CA7, KT88 or 6V6's.
I always end up with a crappy amp that always gets warranty claims. In the case of 6V6's I replace the bases and fit 7C5 NOS made by Sylvania.
I dont see the amp again. ( Maybe the customer is so peed off he goes somewhere else ?? ).

In general just the visual inspection shows random QC problems, Mis alighned mica's, Getters at crazy angles totally different in each example.
Sometimes the whole valve is skewiff inside the bottle. I have had dry joints in the pins in the base as well.
The ONLY advantage with the russian stuff is cost. a 5AR4 in sovtek costs about $25 Au. about 12 quid to you.
I paid about double that for the GE NOS ones I have, and I bought them probably 30 years ago.

You asked me to explain, and thats about what I get.

Regards
Joe

[Andy M0FYA]

Joe,
Thanks for your reply, all very mysterious! I bought half a dozen Russian ones a few years ago for stock as they were so much cheaper, but I have to confess I have never used them in anything! However on visual inspection they look very soundly made to me, without the mechanical issues you describe.

Andy

[Mike Watterson]

You'd need a rubbish smoothing cap for any difference in hum or "pops"
1) Selenium/metal sometimes have high leakage, which may destroy the smoothing cap before something burns out. Hum on a valve rectifier is ONLY possible with dried out, or needing reformed, smoothing cap.
2) Pops on rectifier also suggest (a) Overvoltage / noise spikes on mains and (b) Very high ESR smoothing caps.
3) I've never seen Russian valves or Chinese that visually look poorly made.

With correct HT and decent quality smoothing caps the make of valve rectifier is irrelevant. I've seen low emission caused by wear induced by excess HT current caused by leaky caps.

[joebog1]

I agree with what you say Mike, that doesnt alter the fact that I have found them very noisy.
Perhaps it is a problem of microphony  ?. which again suggests poor construction.

If you wish to use them, go for it. I shy away from them at all costs and have merely added my two bobs worth to the origional question.

Joe

[Mike Watterson]

I agree with what you say Mike, that doesnt alter the fact that I have found them very noisy.
Perhaps it is a problem of microphony  ?. which again suggests poor construction.

Impossible to hear unless the electrolytic capacitors have either high ESR or very high leakage or almost no capacitance, i.e. dried out or needing reformed.

The waveform with ANY rectifier has massive 50 Hz (half wave) or 100 Hz hum (full wave) with all mains noise (which can be considerable) superimposed if there is only a resistive load. You can simulate effect of high ESR by having a resistor in series only with capacitor. Sounds awful.