It will work great!

Thank you for your replies. I appreciate it.

More to the story. I realized the Mullard GZ-34 I have is from my original Dynaco ST-70 and is probably no longer any good.

I replaced the Dynaco with a Vacuum Tube Audio ST-70. Rather than going all in on an NOS Mullard GZ-34 I purchased a NOS Mullard GZ-33 rectifier tube. I felt it did very nicely. It's this tube that I'm considering swapping into my SE84UFO.

So I had it exactly reversed in my initial post. NOT a GZ-34, but a GZ-33, will this safely replace the stock rectifier tube in the SE84UFO?

Thanks.

Lon, I appreciate the reply.

The threads seem to mention the GZ-32 mostly for the SE84UFO. Bob Latino of VTA posted on the Dynaco Tube Audio Forum that the GZ-33 "is not an exact replacement for the GZ-34 as it draws a little more current". Does this make the other tubes run hotter?

Bob also notes that the rectifier tube does not affect sound quality for his push-pull model ST-120 unless played loudly or with inefficient speakers, which is not me.

It's either roll the GZ-33, or try the input tube first, and roll a Mullard Philco 6DJ8. I'm leaning towards the input tube first.

Dan have a look at the GZ34 that you pulled from your ST70.  If the bottle goes straight into the base and the base is wider than the bottle then it’s a FAT Base.  The bottle must go straight into the base.  Next look at the plates. If there are no notches in the plates then you likely have a rare production GZ34 that was the first itineration after The Metal Base.  They did not make these for a long time and it was replaced by the FAT Base with 4 notches in the plates, which is not as refined.

The GZ34 Fat Base/no notch was also branded with the names of amplifiers it went into.  Mine was an EICO Branded GZ34.

This was the rectifier that for my tastes and set up bested all the others, until I got the itch and tried a Miniwatt GZ34 1958 Metal Base.  What a mistake that was -:)!  Of the GZ34’s that I have tried those are the only two that I liked.  The other variations aren’t even close.

The rectifier makes a huge difference in the sound of the amp if the amp is transparent, and the UFO25 most certainly is.  I also found that my SE84UFO2 was very transparent, and I believe that yours is as well.

So if you have a GZ34 Fat Base no notches on the plates... by all means try it.  Then as Lon suggested try rolling the input tube.  I think you’ll have a lot of fun.

Glad your enjoying the music, that’s what it’s all about.

The organic nature that became evident after trying the GZ34’s that I mentioned in my earlier posts is one of the first things that I noticed as well as the other attributes that you mention.

The Metal base took that to an entirely different level in my UFO25.  In addition there was this decay and and detail that came across as it would in live music.  Not saying it’s the same as live, rather theres enough enough of the live that it gives a sense of the real, it’s quite disarming actually.

My conclusion after trying the specific GZ34’s that I mention in my earlier post isn’t that it makes the component better.  Rather it allows the full potential of a component to come through.  It also allows the associated tubes to be at their best.

So in some amps it may make no difference because the amp is limited.  In other amps there will be a difference because the full potential of the amp is limited by the tubes.

These tubes will tell you just how capable your amp and system really is.  ENJOY!

Dan, Piezo is correct.  I did not try this particular version so I cannot comment.  However, take the time and look up Dub step Girls Massive Rectifier reviews.  In this review the GZ34 that you have is reviewed and compared to the  Metal Base version.  Based on my experience with the Metal base, I would say that this review is very accurate.

I did have the Fat Base, Smooth Plate version which is the one that came immediately after the Metal Base.  When I tried it, part way to my listening chair I stopped dead in my tracks, turned around and tried to process what I was hearing.

I started to wonder “how much better could a Metal Base GZ34 be?  Is the review on target?”  There was only one way to find out.  This was a somewhat painful process as at one time I felt that I would never spend the kind of money that the Metal Base were getting and here I was looking for one (I now have two, amp and preamp).  As I looked for a reasonably priced Metal Base I came across ads that would claim that certain “GZ34 were equal to the Metal Base or very close to.”  So I picked up a couple of later release, used GZ34 smooth plate versions as well (skinnier black base).

Bottom line... The Metal Base is in a completely different league!  Even the successor fat base, smooth plate was not it’s equal.  But the immediate successor (Fat Base, Smooth plate) was extremely good in it’s own right and had I not tried the Metal Base I would still have it.  I did not find it unrefined as the review commented on the notched plate version.  I suspect that the notched plate 60’s version has a lot of what the Fat Base, Smooth Plate does with less refinement and bass impact.

Based on your comments I feel that a lot of the early Fat Base, Smooth Plate GZ34 character is still “in” the notched plate version.  I still have the two used GZ34’s that were supposed to be as good as the metal base so I decided to put one in my UFO25 before commenting.  NOT EVEN CLOSE to my Metal base or the successor Fat Base, Smooth Plate and likely not close to your notched plate GZ34.

I believe that you quite liked the notched plate GZ34 that you pulled from your ST70.  If that is the case I’m going to to do something that I rarely do... recommend that you try the Metal Base GZ34.

I came across the following, bidding started at $152.00 and there are 25 bids with 5 days to go:

https://www.ebay.ca/itm/1-vintage-1955-Amperex-metal-base-GZ34-5AR4-tube-tested-...

If you were to get it at a good price you can easily re sell it if you didn’t like it.

Dan,
I have not had experience with the RCA5U4G.  I did have an Australian made 5U4G, the AWV Radiaotron version and liked it.  I did have the CV593 and the Philips 5R4GYS.  Preferred the CV593 to the Philips 5R4GYS.

None of these came close to the Mullard Fat Base, Smooth Plate and not even remotely close to the Metal Base Mullard/Phillips.  There in lies the problem... how close to is close to???  These are words that attempt to describe something that is very multi faceted.  It’s like trying to describe a painting or a fall scene, you would need a thousand words and still not be able to capture the feeling that one gets.

Last night before responding I wanted to check my memory so I subbed the Metal Base with an Amprex Smooth Plate GZ34 in my UFO25.  It was very nice but something was obviously missing.  I re installed the Philips Miniwatt Metal Base GZ34.  The best words that I can use to give an idea of the difference is that I started to get goose bumps with the Metal Base in place.  I could wax on about the sonic differences but that would not describe the “feeling” that I got.  I didn’t have to think about it, it just happened.  

That’s what music and song does to me, that’s what I pay for, unfortunately more than I would like at times.  It’s not just the tube or tubes, it’s also the Decware components that I have.  If one appreciates music and is willing to pay hundreds of dollars for a watt, why stop short at the tubes, especially if the tubes allow the component to be at it’s best?

Not trying to persuade or push you into spending your hard earned cash on the GZ34 Metal Base.  Just trying to help you understand why I did.  Be careful here... once you experience this, if it suits you, there will be no going back!

"Not trying to persuade or push you into spending your hard earned cash on the GZ34 Metal Base.  Just trying to help you understand why I did.  Be careful here... once you experience this, if it suits you, there will be no going back! "

JOMAN, just wanted to thank you. I'm grateful that you pointed me in this direction. The metal base suits me.

Ah, the beauty and the sorrow. Some months ago I decided to investigate the GZ34, and after a couple of baby steps bought some Mullard fat base smooth plates and they really took my UFOs to the next level. I'll admit to being #MetalBaseCurious but realistically since I need a pair they are out of reach and the FBSPs are the end of the line for me.

Fast forward 5 months almost to the day and what is the first tube to fail in my UFO? Not a relatively inexpensive input tube or power tube, But a Mullard fat base smooth plate GZ34. Not exactly the most expensive tube I've ever bought, but close. Ah well, at least I have a spare, and yet another reminder that nothing, including ourselves, lasts forever. The tube was a year and change older than I am, I'm hoping I've still got a few more good years.

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I hear you. I thought the same way, and then against my better judgement I bought some "audiophile" fuses at a hundred bucks a pop, and really liked the results. So I figured I shouldn't be afraid to spend over a hundred dollars on a rectifier that will make bigger difference (it did) and should last a decade or more (it didn't). This last year has been really hard on my Scottish Heritage .