[whirlwind]

Mullard GZ32 is a great bang for the buck for a warmer sounding rectifier also much cheaper than most of the top tier rectifiers...the skinny GZ37 ain't bad either for the price.

 

[MasonStorm]

Just picked up this one in Germany. Any opinions?

I have a pair of these. Great for jazz music!

 

[les24preludes]

I just did a rectifier shootout of all my tubes in a 300b SE amp with NP Acoustics amorphous OPT. Haven't tried with headphones yet. Top of the list were:
2 x AZ1 mesh, 53KU, Sylvania VT-244, GE 5U4, Cossor GZ33. In the original review the RCA 5U4 was preferred to the Sylvania, but I'd put them the other way round. The NOS Mullard 5U4 was rather flat, like the RCA version. I didn't really like any of the 5R4GY types I have - good tone but overly warm which was a step down after the clarity of the preferred tubes above. The GZ34 Sovtek was pretty good but a step down, though I preferred it overall to the 5R4 types. The Russian 5C3S was quite good though a trifle veiled. Good tone and smooth. 5V4G and 5V3A were not liked at all.

 

[gibosi]

I just did a rectifier shootout of all my tubes in a 300b SE amp with NP Acoustics amorphous OPT. Haven't tried with headphones yet. Top of the list were:
2 x AZ1 mesh, 53KU, Sylvania VT-244, GE 5U4, Cossor GZ33. In the original review the RCA 5U4 was preferred to the Sylvania, but I'd put them the other way round. The NOS Mullard 5U4 was rather flat, like the RCA version. I didn't really like any of the 5R4GY types I have - good tone but overly warm which was a step down after the clarity of the preferred tubes above. The GZ34 Sovtek was pretty good but a step down, though I preferred it overall to the 5R4 types. The Russian 5C3S was quite good though a trifle veiled. Good tone and smooth. 5V4G and 5V3A were not liked at all.

Nice job! And I hope you will be able to add pictures soon.

A question... Do you know the manufacturer of your AZ1s? The AZ1 was manufactured by a number of different companies and in my experience, tubes manufactured by different companies in different factories sound different.

And a couple comments... I don't believe Cossor ever manufactured the GZ33, and I would guess that they sourced that tube from Mullard and put their name on it.

Also, the Mullard 5U4G was manufactured both in Blackburn and in Tottenham, which was the old British Tungsram factory. And these two tubes sound different.

But of course, without pictures it's hard to know....

 

[les24preludes]

I have several different mesh AZ1s, various brands, plus mesh AZ11s. It's a favourite.

The Cossor is marked 53KU and GZ33. It's very clean and clear. I prefer my other 53KU which is wrapped in brown tape because of a loose base. Need to fix it. Can't read the make.

The Mullard is a straight glass in original box, as shown. Not fussed about keeping it - should be worth a bit for the name. The VT-244 was special, dismissed as a "cheap tube" originally but not so cheap any more.

 

[gibosi]

I have several different mesh AZ1s, various brands, plus mesh AZ11s. It's a favourite.

The Cossor is marked 53KU and GZ33. It's very clean and clear. I prefer my other 53KU which is wrapped in brown tape because of a loose base. Need to fix it. Can't read the make.

The Mullard is a straight glass in original box, as shown. Not fussed about keeping it - should be worth a bit for the name. The VT-244 was special, dismissed as a "cheap tube" originally but not so cheap any more.

It's great that you can run 4-volt rectifiers as well as 5-volt. I have an OTL that can run 3, 4 and 5 volt rectifiers, but unfortunately, the AZ1 and AZ11 cannot provide enough current. But I can roll AZ4, AZ12 and AZ50. And as it is an OTL, my favorite rectifier depends on the synergy with the driver and output tube. I like Telefunken, Valvo, Lowe Radio, WIRAG and others.

Based on the construction, your Cossor 53KU / GZ33 is actually a Mullard GZ33. The Cossor 53KU is "fatter."

And given that the Mullard 5U4 is clearly marked "foreign made", it is likely that it is American-made or even Japanese-made.

Again, thanks for sharing.

 

[les24preludes]

It's great that you can run 4-volt rectifiers as well as 5-volt. I have an OTL that can run 3, 4 and 5 volt rectifiers, but unfortunately, the AZ1 and AZ11 cannot provide enough current. But I can roll AZ4, AZ12 and AZ50. And as it is an OTL, my favorite rectifier depends on the synergy with the driver and output tube. I like Telefunken, Valvo, Lowe Radio, WIRAG and others.
Again, thanks for sharing.

I build all my own amplification, so I just used 2 sockets for the AZ1. AZ1 and AZ11 mesh are affordable, while AZ4 and AZ12 mesh aren't.

I never use adapters - I just swap sockets. I also swapped in a UX4 socket to try some 5Z3 - that's a nice tube.

 

[UntilThen]

Based on the construction, your Cossor 53KU / GZ33 is actually a Mullard GZ33. The Cossor 53KU is "fatter."

And given that the Mullard 5U4 is clearly marked "foreign made", it is likely that it is American-made or even Japanese-made.

I have the fatter Cossor 53ku. As we have spoken, I also have a Mullard 5U4G made in USA. I'm intrigued by rectifiers now for my SET amp.

 

[les24preludes]

I have the fatter Cossor 53ku. As we have spoken, I also have a Mullard 5U4G made in USA. I'm intrigued by rectifiers now for my SET amp.

Rectifiers do seem to sound different. It's not specially the voltage drop either. My HT with different ones turned out to be as follows:
GZ33 - 370
5V4G - 362
GZ34 - 355
53KU - 352
5U4 - 350
5V3A - 349
5Z3 - 340

My favourites included GZ33 and 5Z3 - top and bottom - as well as 5U4 which was right in the middle.

I was surprised at the results. I previously liked the 5R4 but couldn't take the warm sound and soft treble and bass. The Soviet GZ34 was better than I expected. The 2 x AZ1 mesh which I regarded as unbeatable was arguably equalled by the more dynamic VT-244 version of the 5U4, the GE 5U4, the GZ33 Cossor and the 53KU. My favoured combination now is a 5U4 type for the output stage of the amp and a single AZ1 or AZ11 mesh for the input stage. Best of both. I just use 2 stages in my 300b SE.

 

[UntilThen]

Rectifiers do seem to sound different. It's not specially the voltage drop either. My HT with different ones turned out to be as follows:
GZ33 - 370
5V4G - 362
GZ34 - 355
53KU - 352
5U4 - 350
5V3A - 349
5Z3 - 340

My favourites included GZ33 and 5Z3 - top and bottom - as well as 5U4 which was right in the middle.

I was surprised at the results. I previously liked the 5R4 but couldn't take the warm sound and soft treble and bass. The Soviet GZ34 was better than I expected. The 2 x AZ1 mesh which I regarded as unbeatable was arguably equalled by the more dynamic VT-244 version of the 5U4, the GE 5U4, the GZ33 Cossor and the 53KU. My favoured combination now is a 5U4 type for the output stage of the amp and a single AZ1 or AZ11 mesh for the input stage. Best of both. I just use 2 stages in my 300b SE.

What's HT and what are those numbers? Glad you mention GE 5U4 because I have one too and @bcowen is giving me a hard time . I have 2 tube amps at the moment that use tube rectifications. A 300b and a KT88 / EL34 Set amps.

My GE 5U4G (brand new about 3 weeks ago.) Clock up some hours now.


I've 3 GZ34.

A Miniwatts tv1 56h. See this site http://www.tube-classics.de/TC/Tubes/Valvo GZ34/GZ34.htm, a Mullard BVA GZ34 DD getter code LIJ 1961 Bruxelles Mazda and a Sittard GZ34.

 

[les24preludes]

Hi - HT (high tension) or also called B+ is the DC voltage that operates the tube circuit. So when I tested the rectifiers I planned for a HT of around 350v. That's into my 300b SE amp.

My GE 5U4 is a straight bottle with side getter.

 

[UntilThen]

Hi - HT (high tension) or also called B+ is the DC voltage that operates the tube circuit. So when I tested the rectifiers I planned for a HT of around 350v. That's into my 300b SE amp.

My GE 5U4 is a straight bottle with side getter.

Got you. My KT88 amp has a 450v on the plate, giving an anode -> cathode voltage of about 400V. On my 300b amp, the builder told me the B+ is 500v. Ideal rectifier is the GZ34 for both amps and they are from different builders.

Have you compare the GE 5U4 straight bottle with the 5U4G coke bottle?

 

[les24preludes]

The GE 5U4 straight bottle and the 5U4/VT-244 coke bottle are both good. Different makes and different anode structures. There are a few different types of construction - long plates versus medium plates, smooth versus ribbed etc. It's up to what your ears tell you!

 

[UntilThen]

I hear the GZ34 as linear and tight. Cossor 53ku fat bottle is the warmest to my ears. I like it though. Next is the GZ32. U52 has a very good sweet tone and clean. Only a touch of warmth. Other than that what I hear must be influence by the driver and power tubes. I am still trying to make out 5u4g because the tube amp is less than a month old.

 

[RobertSM]

I hear the GZ34 as linear and tight. Cossor 53ku fat bottle is the warmest to my ears. I like it though. Next is the GZ32. U52 has a very good sweet tone and clean. Only a touch of warmth. Other than that what I hear must be influence by the driver and power tubes. I am still trying to make out 5u4g because the tube amp is less than a month old.

We hear very similarly. I agree with your assessment of the above mentioned rectifiers.