I also found the new production kt66s somewhat recessed in the midrange, both in the ZMA and my lampizator DAC (which has a tube buffer). It was like female vocalists were a couple steps back from the band. Perhaps interestingly, I tried a pair of lightly used NOS GEC KT66s in the DAC and everything was noticeably better. Not the absolute best midrange but very good and it did so many other things remarkably well. Too expensive to consider in the ZMA though.

I’m also really happy with the 7027as but sometimes get an itch to change things. I plan to try the new production Gold Lion KT77s in the next couple months. Will post with thoughts if and when.

Yikes, sporadic noisy right channel this week in my system. Started switching positions with KT77 power tubes in the ZMA thinking they were the culprit. Wrong!

This morning really high static sound coming from the right channel, ugh. Quickly powered down the whole system. After checking my tubes, I noticed a discoloration on the top getter in my right channel Sylvania OA3 voltage regulator tube. Went from steel gray to brown copper with some dark discoloration of the glass outside the getter.

I think I was moments away from a flash bang total tube failure. Thankfully I have several back up NOS pairs. Anyway, just a note for ZMA owners to keep an eye out on your voltage regulator tubes. I'm guessing these had 6,000 - 7,000 hours on them. Whew!

HK

Well the quad of Gold Lion KT77 tubes only lasted 7 months, 😭. Two tubes started getting noisy then flashed up and died this morning.

I've put my quad of TAD 7027A tubes back in this morning. The cost of GL KT77's has doubled with the Russian shipping embargo, so I'll wait until prices become more reasonable before I spring for another set.

HK

Purple/blue voltage regulator tubes?  Steve has a beautiful photo of a VR90 style regulator tube that glows blue on the ZMA page.  Anybody know what specific tube it is?  

I know it is (at least must be) and argon tube since argon glows that color.  Neon glows orange which is what we see in the normal OA3's we use.

I've bought several older argon tubes.  None glow much at all and none sound as good as the standard OA3s.

I'd enjoy trying the tube pictured if anyone knows what it is.  

https://www.decwareproducts.com/zma
Scroll down about 8 pages.

thanks,
Jerry

Lon,
What manufacture tube are you using?  Do you have a source?  thanks, Jerry

Thanks Lon.

Just scored another quad, w/ less than 50 hours, of Gold Lion KT77's for a screaming deal. Should have them back in the ZMA shortly. Looking forward to getting that sound back.

HK

Jon
I want to politely challenge (because I don't really know) your statement that you can't use the VR90 in the ZMA.  On the ZMA page Steve has a photo of one and the following words:

"This beautiful tube is a variant of the OA3 regulator tube. It is a VR90 which drops the voltage to the input stage by around 15 volts.  This can be just enough to tickle your exotic N.O.S. 6922 or 7DJ8 inputs tubes into a new level of nirvana.  There are actually three of these tubes you can work with that will give you three different sounds."

So I think Steve is saying that raising the voltage from 75 to 90 is ok.  It doesn't change any of the gain settings.  But I would like to know for sure.

I have to admit that I interpreted this to mean that the VR90 was interchangeable with the OA3, i.e., they are both 90 v regulator tubes.  I ordered a couple and tried them.  Didn't like the sound as much.  I blamed it on poor quality used VR90s that I was able to find.  I just bought a few more old VR90s and I'll try them soon.  

But I haven't found anything that can sound as good as the true NOS sylvannia OA3s that the amp is supplied with.

Jerry

VR (Voltage Regulator) tubes drop voltage.

From Wikipedia.com:

Octal-based tubes, 5–40 mA current:
* 0A3 – 75 volts
* 0B3 – 90 volts
* 0C3 – 105 volts (best regulation of these four)
* 0D3 – 150 volts
Miniature tubes, 5–30 mA current:
* 0A2 – 150 volts
* 0B2 – 108 volts (best regulation of these three)
* 0C2 – 72 volts

So a 400v amp with a 0A3 is 325v to the tubes it's connected to. ZMA 0A3 powers the input tubes. I don't know if the 0A3 on the ZMA or Torii MKV power the inverter tubes or not.

Another update.  Got another pair of WE 396 and have them in both driver and input locations.  superb.

350b are no longer made AFAIK. The ones I've seen for sale have been $600+ per tube. TubeDepot.com is selling Wester Electric 350b for $1,150 each, almost $4,400 for a quad!

I have not tried them and don't have any plans too.

Update on tubes.  I have made a lot of upgrades to my system since I did most of my tube testing.  my entire digital front end has been upgraded, my amp has seen a few upgrades including some new wiring inside and eliminating the fuse (power strainer) in the input.  Not sure I had my PS Audio PP10 at the time I tested tubes.  Here is the list:

TS 7581A--the tubes I've been listening to for months, love them.
TS 7027A--oops, bad tube now fills one channel with static not tested.
Mullard el34   Bland
Golden lion KT66  Good but missing dynamic midrange and highs
TS KT66--the tubes supplied with the amp, the ones i had when i started buying tubes.  i remember them as good.  with the upgrades they are amaing.  the music keeps jumping out at me.  vocals and saxophone are right in the room with me.  Highs are strong.  bass perfect. I guess it makes sense since the amp was built around these tubes.  I wish they made a little more light.  the 7581A tubes look awesome in low light while listening.  Amp light is balanced between the input tubes, power tubes, and regulators.

Ooops, just realized I forgot to test the russian tubes again (whatever the 6l6 equivalent is which I have a set of.

Tubes on my list to try:

GE 6l6GC
807, preferably mullard but a nice set
sylvania 5933

Jerry

Ok.  This thread has become Carlsbad's tube log but that's ok. I hope my comments will help someone some day.  

Jan 2023 update.

I tried the russian 6P3S and they have become my favorite tube.  Excellent clarity with no harshness.  Great bass.  tremendous image.  

I went back to the original KT66 which came with the amp and they are a close second and might be preferred by some.  It is no surprise that the tube that Steve designed the amp around is excellent.  I tried Gold Lion KT66s for quite a while, thinking they were an obvious upgrade and it wan't until I put the originals back in that I realized they are not.

I tried the 6P3S-a, an upgraded tube for longevity and found it slightly lower in fidelity, probably a tradeoff so I recommend not bothering. The tube isn't bad, but isn't quite as good.

I tried the 807s and sylvania 5933s.  Found both to be interesting. looked great, but not as good a sound.  I listened to both for several days.  So they weren't horrible.

I figured out the 350B wouldn't work.

I'm currently using russian SG2S in the rectifier and I think they are slightly superior to the sylvania NOS OA3s but not a lot. I think any tube in the power supply is important and I'm going to watch for other options here.

In the input and driver positions I have WE 396 which is an old favorite of mine.  The russian red tipped 6P23P is very close.  

Finally, as I've been tube rolling I've been upgrading my digital front end (I listen almost exclusively digital).  It would have made tube rolling much easier and less expensive if I'd done that first.  A few tips:  never stream wirelessly.  Get a good streamer. other options drop more bits.  Use silver plated conductors for all digital cables.  Buy the best DAC you can afford.  FPGA is a good thing.

Jerry

Man I love it when new tubes hit the magic zone. ~50 hours later that little switch came on.😊

HK

I ran my ZMA (I no longer have it) with most tubes biased toward the low side.  Some like to bias right at the top of the range but never found it to provide sonic benefits.  two significant benefits:

1.  No redplating.  Tube are happy and not on the edge at a lower bias current so you have a much lower probablility of redplating.
2.  Your power transformers will run cooler.  The power transformers on the ZMA run warm.  I instrumented mine and they never got close to operating limits but I did enjoy keeping them a bit cooler.  I tend to leave my amp on all day so the warm transformers and warm tubes tend to warm up the entire amp.

Finally, I never found the KT88s to be one of my favorite tubes with the ZMA.

Jerry

Hi Hockessinkid. S of T here (formerly stone_of_tone). Its been a while - glad to be back.

2 weeks in with a new quad of Tung-Sol 7581A's. I now realize how much I missed this quad. Past 2.5 years with Tung-Sol 7027A's/which are great. However, the 7581A's are my favorite.

Welcome back Stone, great to see you back posting😊. I'm glad you're enjoying the 7581A power tubes. There are a lot of great choices to change the tonal output of Decware amplifiers.

I encourage you to check out the Swiss Digital Fuse Box (SDFB) thread. This fuse replacement device really uncovers the true potential of the ZMA and many other components. Groovy Sauce brought this device to our collective attention. I think you would be floored by transformation.

Hope you are doing well after relocating a few? years ago. Have a great week and most importantly enjoy the music.

HK

Well, you've been missed and many have hoped you were doing well (and seems our hopes were verified).

S of T.  I bought a ZMA, rolled infinite tubes in it, and have moved to SET amps.  But I read this entire thread, really appreciated your posts, and wondered where you had gone.  We lose a lot of audiophiles and it is great to see you posting again.

Jerry

Hello everyone!

I'm on the waiting list and very happy for that. And because of that I started collecting tubes.
I need some advice on the KT88 tubes for the Zma Full anniversary edition 25.
I bought 6N5P, 6N1P-EV, 6N23P, 6N23P-EB, OA3 Marshall, OA3 Sylvania.
6P3S-E, 6P3S and Mullard KT88.
Considering that the bias window for the new ZMA is adjusted for KT88-Family I want to continue to purchase:
Shuguang WEKT 88 PLUS,
Shuguang KT88Z,
Psvane MarkII KT 88-TII,
Psvane ACME KT 88 and others.
Has anyone tried these tubes on the Full anniversary model?
Being a noob, I don't know how to choose the best version available for the same tube brand, such as:
Mullard KT88 QUAD-30mA,
Mullard KT 88 QUAD 45 mA,
Mullard KT88 QUAD 56mA.
What is the difference between them in terms of durability and sound considering that it is practically the same tube?