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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 12th Oct 2019, 4:43 pm   #1
Ian - G4JQT
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Default GZ34 - recommended brands?

I'm looking to buy a couple of GZ34/5AR4 rectifier valves. They vary in price considerably on ebay. I'm sure the cheapest are cheap for a reason, but some seem to be branded with a UK supplier's name.

Anyway, suggestions for brands to go for please. I don't need anything fancy, it's just for my Wadar amp, but would prefer ones that might last a while. (GZ37 specified for the Wadar but see this thread.)

Or if anyone has a couple NOS for sale...?

Thank you.

Ian
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Old 12th Oct 2019, 5:02 pm   #2
g4aaw pete
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Default Re: GZ34 - recommended brands?

Hello Ian

I think any will work. Unfortunately, we're into the 'ridiculous theory territory'.
For instance, the view that certain manufacturer's valves perform better when they're made at a certain factory. A good way to elevate the selling price.
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Old 12th Oct 2019, 5:11 pm   #3
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Default Re: GZ34 - recommended brands?

What about: https://brimaruk.com/valves/rectifiers/brimar-gz34/

Or http://pmcomponentsnos.co.uk/Golden-Dragon-5AR4-GZ34

To be honest, it's just a rectifier valve - don't get uptight about particular brands/bottle-shapes/getter-positioning etc being 'better' than others; honestly, I'm sure that if decent/cheap/reliable semiconductor rectifiers had been available when your amp was designed the designer would have used them!
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Old 12th Oct 2019, 6:21 pm   #4
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Default Re: GZ34 - recommended brands?

Quote:
Originally Posted by Ian - G4JQT View Post
... They vary in price considerably on ebay. I'm sure the cheapest are cheap for a reason ...
There are persistent stories of some eBay sellers having access to factory reject valves. They sell them cheaply without mentioning their reject status. Personally I treat any valves with a 'too good to be true' price as, well, unlikely to be 'true'.

Turning to actual first-hand experience, I picked up one of the Golden Dragon GZ34s in a box of random valves at a boot sale once. I took to using it as my test valve when a piece of suspect equipment came my way, on the basis that it was cheap enough that I could afford to have it destroyed by a downstream short if one should ever develop. It lasted for ages and withstood plenty of abuse.

Cheers,

GJ
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Old 16th Oct 2019, 10:21 am   #5
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Default Re: GZ34 - recommended brands?

I bought a couple of these https://www.cricklewoodelectronics.com/GZ34.html about 3 years ago for a friend's Quads. They've been ok, and get used quite a lot.
The price is pretty reasonable, too. Tony. (No connection with company.)
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Old 16th Oct 2019, 10:34 am   #6
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Default Re: GZ34 - recommended brands?

It's only a rectifier..John.
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Old 16th Oct 2019, 12:28 pm   #7
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Default Re: GZ34 - recommended brands?

Does make a difference though, my Radford STA15 had about 30v less HT using a National branded Russian part versus a NOS 'Brimar' (probably made by Mullard). Luckily it was before the internet sent all the prices through the roof!
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Old 16th Oct 2019, 1:06 pm   #8
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Default Re: GZ34 - recommended brands?

Yes. The forward voltage drop in rectifiers is one of the more dramatic differences between them. If we check the Philips data for their GZ34 here http://www.r-type.org/pdfs/gz34.pdf then we find that the results measured in 1952 (5th page of the PDF) indicate a 30V drop at 300mA but by 1958 (the next page) that's become just 18V. And that's supposed to be the 'same' valve from a single manufacturer ! I've come across Quad II amps that have had Russian directly heated rectifiers substituted for the original GZ32. These are not so different from a 5R4 which drops 75V at 300mA !

Cheers,

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Old 16th Oct 2019, 4:37 pm   #9
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Default Re: GZ34 - recommended brands?

I suspect that some of the Russian NOS thermionic indirect FWRs that get hawked around as equivalent for various well-known Western types including the GZ34 are actually nearer to the 5Z4GT in characteristics- the GZ34 was a late-comer to the field and probably benefited from a lot of development in cathode materials and electrode mechanical precision and consistency. It was a notable high achiever as regards heater power vs. cathode current capability, also low forward voltage drop and as GJ says, it got better over just a few years. Perhaps Mullard/Philips could see HV silicon rectifiers inexorably breathing down its neck and tweaked it to reduce obvious shortcomings, such as forward voltage drop.

How arduous is the application in mind?- I'd be fairly content about using one of the low-cost Russian types from the auction site at, say, 300-0-300V and 100mA DC output current but if it was for medium-power amp use at something like 450-0-450V and 150mA output, I'd be a bit more fussy about sourcing.
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Old 16th Oct 2019, 10:44 pm   #10
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Default Re: GZ34 - recommended brands?

If the voltage drops are so low with a good GZ34, and if low drop is seen as good, then it looks like you could take the plunge to use silicon, and blow a raspberry at the hawkers of overpriced fairy-dust.

David
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Old 16th Oct 2019, 11:25 pm   #11
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Default Re: GZ34 - recommended brands?

The warm-up on GZ34s is slow enough that most small (B9A) valves would be faster. So if the regulation on the mains transformer isn't great then using a thermionic rectifier could make the difference between over-volting the reservoir and HT rail smoothing capacitors or not. What voltage drop there is also helps with limiting the size of the charging current pulse on each half-cycle. This can be a noise issue in audio gear as well as limiting the strain on the transformer. Of course in the event of a swap to solid state there's nothing to stop a resistor being put in series with the silicon diode.

And if we want to go the whole hog then we could replace all the valves with nice big FETs .

Cheers,

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Old 16th Oct 2019, 11:54 pm   #12
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Default Re: GZ34 - recommended brands?

As noted on another thread I would go for Ruby brand myself, all their rectifiers I have tested and used have been good. I'm not sure where these are sourced, but whoever made them did a very nice job.

I tried some Russian equivalents of the 5u4 once that have an internal construction where springs support the filaments. They looked well constructed and had a similar voltage drop to a 5u4 at the same current, but they flash over at a lower reverse voltage, and it made them unusable in my Argus TV, but for other applications they would probably be fine.

If you want a very low voltage drop valve rectifier go for an 83 mercury vapor rectifier. They used these in American valve testers, so the fluctuations in HT voltages were minimal with different loads , so as to make the calibration as uniform as possible and the HT supply rail very stiff. However RF hash can be a problem, but possibly not a lot more than a silicon rectifier. There is also the 83V high vacuum version.
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Old 17th Oct 2019, 1:17 am   #13
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Default Re: GZ34 - recommended brands?

In 1961 Mullard introduced an improved version of the PY32 TV HT rectifier diode. The new valve was the PY33 and it had an improved cathode oxide coating which offered a reduced forward voltage drop.

From the valve museum: http://www.r-type.org/exhib/aaa0167.htm

The question is, did later production Mullard GZ34 rectifier valves also benefit from the improved cathode oxide coating?

DFWB.
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Old 17th Oct 2019, 6:20 am   #14
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Default Re: GZ34 - recommended brands?

One of the great advancements I think with indirectly heated rectifier valves was the 6X5.
Relatively low forward drop around 20v for a 70mA plate current, could run the heater off the same 6.3v supply as other valves in the radio, didn't need the 5V winding on the power transformer. All in all a leap forward in efficiency for valve radios. These came out either in the late 1930's or early '40's, quite revolutionary.
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Old 17th Oct 2019, 7:34 am   #15
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Default Re: GZ34 - recommended brands?

Having used GZ34 valves in guitar amps since the early 70s, my experience is that cheap replacements are susceptible to catastrophic failure and/or do not last as long as a Mullard. You cannot beat a genuine new old stock Mullard GZ34. Yes they are rare and exorbitantly priced. My choice these days is the drop (plug) in solid state replacements.
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Old 17th Oct 2019, 7:53 am   #16
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Default Re: GZ34 - recommended brands?

Quote:
Originally Posted by g4aaw pete View Post
I think any will work. Unfortunately, we're into the 'ridiculous theory territory'.
For instance, the view that certain manufacturer's valves perform better when they're made at a certain factory. A good way to elevate the selling price.
Valves definitely do vary in build quality and reliability. But there's an irony and it's my opinion that for hi-fi and general purpose use, different brands will not sound so different. It's in guitar amps where, when driven into distortion, that the sound 'quality' tells. I first proved this to myself twenty years ago when I replaced the stock Chinese ECC83 valves in a Mesa Boogie preamp for good, tested Mullards. Driven hard into distortion - the normal mode for this type of unit - with the Chinese valves fitted the sound was thin, brittle, harsh and discordant. With Mullards fitted it was rich, creamy, harmonic and pleasant to hear within the idiom. Conversely, valves are not (should not) be driven into distortion in hi-fi amps, they'll be working within their limits and hence will sound very similar. That's my opinion.
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Old 17th Oct 2019, 8:47 am   #17
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Default Re: GZ34 - recommended brands?

Quote:
Originally Posted by Argus25 View Post
As noted on another thread I would go for Ruby brand myself, all their rectifiers I have tested and used have been good. I'm not sure where these are sourced, but whoever made them did a very nice job ...
An internet search for Ruby and Shuguang returns a lot of sites, largely independent of one another, claiming that Ruby is one of the brands that the Chinese Shuguang factory supports. This looks very plausible. The Golden Dragon valves are also made by Shuguang and my experience was that their GZ34 was strong too.

Cheers,

GJ
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Old 20th Oct 2019, 6:49 pm   #18
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Default Re: GZ34 - recommended brands?

Update:

Well I got a pair of GZ34 valves branded "JJ" from karltone.co.uk

With the original GZ37 volts either side of the Wadar PSU choke was 260 and 270V. With the GZ34 it's now 285/295 with a noticeable increase in volume.

I know in an amp the rectifier valve has no significant effect on sound quality if working properly and I could have used silicon diodes, but I wanted the keep the cct original using valves. And there's no noticeable arching in the rectifier if the amp is switched off then on again with the GZ34.

Note for anyone joint this thread late; this Gerry Wells amp used a GZ37 rectifier which theoretically at least was not really up to the current surge of the PSU electrolytic capacitors. Maybe Gerry decided it practice it didn't really matter...
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Old 20th Oct 2019, 7:09 pm   #19
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Default Re: GZ34 - recommended brands?

Quote:
Note for anyone joint this thread late; this Gerry Wells amp used a GZ37 rectifier which theoretically at least was not really up to the current surge of the PSU electrolytic capacitors. Maybe Gerry decided it practice it didn't really matter...
Undoubtedly Gerry knew his theory but he also had a strong practical approach to wireless and audio.
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