Decware // Reference ZMF OTL

[ckhirnigs113]

The very best I have found were 1940s era rca 5u4g tubes. 70s era were very good as well. Be prepared to pay though, I believe the 1940s were around $350-400 each, and 70s era were around $180 each.

1940s give a more ethereal presentation, 70s a bit more thump and presence.

You can verify the era by the date code that is stamped on the box and also the tube base. They should match.

@AcousticMatt I don’t have the ZMF OTL, but I have been switching between RCA 5U4G’s and 5R4GY’s in my Aegis for a while now. I can second this recommendation for 1940’s RCA rectifiers, specifically 1943-45.

I have two RCA 5U4G/VT-244’s from this era that I really like. One is from 1944 and the other is from 1945, and they are both equally excellent. My favorite rectifier is the double-d getter version of the RCA 5R4GY, but the 5U4G/VT-244’s are right there with them and might be preferred by some depending on the rest of their setup and what kind of sound they’re after. Here’s what to look for:

Another thing you’ll need to know is what the date codes look like on these RCA rectifiers. You’re looking for 3-digit date code. The first letter of the code gives you the production year.

K = 1943
H = 1944
V = 1945

This one has a date code of “H3E”, so it’s from the third production cycle of 1944.

Hope this helps!

 

[goldwerger]

I think I'm going to do the Tung Sol 5687s and an RCA 6BQ7A. I'd need a pair of Tung Sols and just one RCA, correct? Still getting used to these tube types...

Yes - the 5687 would be output tubes, so you'd need 2 of them (and 2 adapters). The 6BQ7a would be an input tube, so one o fthat.

Here are a couple of pictures of my RCA 6BQ7A (black plates, O getter, 1957):

On adapters - anyone have suggestions for the Tung Sols?

So one thing to note is that the cutouts in the black top cover of the amp are as wide as the tubes. So one needs an adapter that's as slim as the tube to fit in. The on I had does, but the link is no longer available and I already looked for that for someone else and can't find it anymore.

Option B is to get any 5687 to 6922 adapter, which will likely be a bit wider than the cut out, and also get socket savers, which will simply act as extenders. You put the socket saves, the adapters on top of them, and the 5687 on top of those. A small little tower, but these are all small components so it works. That's what I first had (and I shared this spare setup with my friend to whom I shipped it).

or a U52 instead?

I now use the GEC U52 rectifier. In short, it is just outstanding, and a true step up from the GZ34 I used previously. It is a very sweet sounding, "musical" tube. It is also getting quite expensive.

 

[AcousticMatt]

@AcousticMatt I don’t have the ZMF OTL, but I have been switching between RCA 5U4G’s and 5R4GY’s in my Aegis for a while now. I can second this recommendation for 1940’s RCA rectifiers, specifically 1943-45.

I have two RCA 5U4G/VT-244’s from this era that I really like. One is from 1944 and the other is from 1945, and they are both equally excellent. My favorite rectifier is the double-d getter version of the RCA 5R4GY, but the 5U4G/VT-244’s are right there with them and might be preferred by some depending on the rest of their setup and what kind of sound they’re after. Here’s what to look for:


Another thing you’ll need to know is what the date codes look like on these RCA rectifiers. You’re looking for 3-digit date code. The first letter of the code gives you the production year.

K = 1943
H = 1944
V = 1945

This one has a date code of “H3E”, so it’s from the third production cycle of 1944.

Hope this helps!

Super helpful, thank you!

Yes - the 5687 would be output tubes, so you'd need 2 of them (and 2 adapters). The 6BQ7a would be an input tube, so one o fthat.

Here are a couple of pictures of my RCA 6BQ7A (black plates, O getter, 1957):






So one thing to note is that the cutouts in the black top cover of the amp are as wide as the tubes. So one needs an adapter that's as slim as the tube to fit in. The on I had does, but the link is no longer available and I already looked for that for someone else and can't find it anymore.

Option B is to get any 5687 to 6922 adapter, which will likely be a bit wider than the cut out, and also get socket savers, which will simply act as extenders. You put the socket saves, the adapters on top of them, and the 5687 on top of those. A small little tower, but these are all small components so it works. That's what I first had (and I shared this spare setup with my friend to whom I shipped it).






I now use the GEC U52 rectifier. In short, it is just outstanding, and a true step up from the GZ34 I used previously. It is a very sweet sounding, "musical" tube. It is also getting quite expensive.

Super helpful too, thank you!

 

[LXMc]

Been about 2 months with the ZMF Reference OTL and I continue to absolutely love this amp with my Auteur Classic and Atrium Closed.

I don't have an extensive tube collection yet but have still gathered a good few to try out based on the helpful suggestions here and in other threads. Up until today my favourite rectifier has been the Brimar 5R4GY, just a silky, smooth but not over-soft sound with a nicely holographic stage. My go-to has been that, combined with Tung-sol 5687's in the power sockets and a Phillips JAN 6992 for the input (a couple inputs I quite like are the Tungsram PCC189 & RCA 6BQ7A). I also tried an RCA 5u4G VT-244 recently which I was a little more mixed on. I like some aspects but something about it didn't quite jive the same as the Brimar for me. Still, I really enjoy how different it can sound with the one tube change.

Today I received a couple U52's, being curious due to the reputation it has. I wasn't really sure what to expect, but man, I am really impressed with it. It's vibrant without any sort of harshness or over-intensity. Larger and still more holographic than the Brimar without sounding diffuse and also tighter and cleaner while still retaining a similar warmth.

One day I'll take a plunge on the Takatsuki but real happy with this right now.

 

[OnlySoMany]

Are these still listed on the zmf site? I checked the other day and didn't see the zmf OTL.

 

[mattiastomas]

Are these still listed on the zmf site? I checked the other day and didn't see the zmf OTL.

Unfortunately they are no longer available. The builder who was making it is no longer with them.

 

[LXMc]

Are these still listed on the zmf site? I checked the other day and didn't see the zmf OTL.

Unfortunately they are no longer available. The builder who was making it is no longer with them.

Yeah, maybe there's a chance they get a new builder, but a shame if not.

Zach's mention of this: https://www.head-fi.org/threads/zmf...uncements-and-megathread.974608/post-18405218

 

[OnlySoMany]

Unfortunately they are no longer available. The builder who was making it is no longer with them.

Probably due to their own issues of a 2 plus year wait list. I can't imagine the tremendous success of the ZMF OTL made that any easier.

 

[zach915m]

We're Working With A New Builder, but getting him up to speed may take a moment. hope to have them back in stock sometime this year, will update.

 

[jonathan c]

We're Working With A New Builder, but getting him up to speed may take a moment. hope to have them back in stock sometime this year, will update.

..... beyond getting a 'new builder' up to speed, is parts availability an issue? -- or is that addressed by the 'new builder'?

 

[goldwerger]

Today I received a couple U52's, being curious due to the reputation it has. I wasn't really sure what to expect, but man, I am really impressed with it. It's vibrant without any sort of harshness or over-intensity. Larger and still more holographic than the Brimar without sounding diffuse and also tighter and cleaner while still retaining a similar warmth.

One day I'll take a plunge on the Takatsuki but real happy with this right now.

Congrats! The GEC U52 is my favorite rectifier for this amp (my preciously shared impressions below). It was a profound upgrade for me. I really love it.

I did try the Tak 274b when I had it on loan with the WA23 and, for this Decware/ZMF amp, it was not as good as the U52 (or 422A) synergy wise. So rest assured you’ve landed on one of the best possible outcomes with your latest tube..

I now use the GEC U52 rectifier. In short, it is just outstanding, and a true step up from the GZ34 I used previously. It is a very sweet sounding, "musical" tube. It is also getting quite expensive.

We're Working With A New Builder, but getting him up to speed may take a moment. hope to have them back in stock sometime this year, will update.

Great news! This wonderful amp deserves to live on

 

[LXMc]

I did try the Tak 274b when I had it on loan with the WA23 and, for this Decware/ZMF amp, it was not as good as the U52 (or 422A) synergy wise. So rest assured you’ve landed on one of the best possible outcomes with your latest tube..

Good to hear, that will help fend off the inevitable curiosity a bit

Honestly after hearing this I almost just want to secure one or two more in case. This was a matched pair of the Osram rectangle getter versions, so not what most, I think, would consider the holy grail version of this tube. But I got these for about half of what the the cup getters versions tend to go for and I wasn't confident, based on impressions I'd seen, that I would be able to tell a difference there.

 

[busseysound]

Been about 2 months with the ZMF Reference OTL and I continue to absolutely love this amp with my Auteur Classic and Atrium Closed.

I don't have an extensive tube collection yet but have still gathered a good few to try out based on the helpful suggestions here and in other threads. Up until today my favourite rectifier has been the Brimar 5R4GY, just a silky, smooth but not over-soft sound with a nicely holographic stage. My go-to has been that, combined with Tung-sol 5687's in the power sockets and a Phillips JAN 6992 for the input (a couple inputs I quite like are the Tungsram PCC189 & RCA 6BQ7A). I also tried an RCA 5u4G VT-244 recently which I was a little more mixed on. I like some aspects but something about it didn't quite jive the same as the Brimar for me. Still, I really enjoy how different it can sound with the one tube change.

Today I received a couple U52's, being curious due to the reputation it has. I wasn't really sure what to expect, but man, I am really impressed with it. It's vibrant without any sort of harshness or over-intensity. Larger and still more holographic than the Brimar without sounding diffuse and also tighter and cleaner while still retaining a similar warmth.

One day I'll take a plunge on the Takatsuki but real happy with this right now.

I had the Takatsuki for about 6 months. Don't get me wrong, it's a fantastic rectifier, but I prefer the GEC U52 (it's in the Taboo). I use the WE 274B in the ZMF OTL as a preamp, but that GEC is the best I've heard in either amp.

 

[goldwerger]

This was a matched pair of the Osram rectangle getter versions, so not what most, I think, would consider the holy grail version of this tube. But I got these for about half of what the the cup getters versions tend to go for and I wasn't confident, based on impressions I'd seen, that I would be able to tell a difference there.

Osram and GEC were part of the same company and likely these tubes were manufactured in the same plant. However, if shaped differently those would likely be distinctly different tube variants, but similar quality of manufacturing. I’m sure you got a great one either way.

I prefer the GEC U52 (it's in the Taboo). I use the WE 274B in the ZMF OTL as a preamp, but that GEC is the best I've heard in either amp.

The two best rectifiers I’ve heard for both are the GEC U52 and the WE422A, which I currently use in the OTL and Taboo, respectively (though the 422A have become too expensive frankly).