Used vs modern tubes?

[justinis]

I need a 12AX7 for the driver section of my power amplifier. The tube will provide a little bit of gain before the phase splitter. I posses 4 used, USA-made, Daystrom 12AX7s. I have read that old, USA-made tubes generally have better performance than modern ones like Sovtek or EH, but I've also read that tube testers don't test all the performance characteristics of a tube. I don't want to shell out the cash for NOS tubes.

In your opinion, would it be better to have one of my old tubes tested and use it, or to buy a modern one?

Thanks!

 

[primosounds]

Well, if you could get your 4 tubes tested that would be the best thing..What the tube tester won't tell you is if they are noisy or microphonic.

 

[peterh]

There is more tubes then EH and sovtek ...
New tubes will generally be more predictable, old 'NOS' you never know what you get.
Many dealers also warranties new tubes, replacing any tube that are faulty or fails early.

 

[thorpej]

Honestly, I have had very good experiences with EH 12AX7s as well as JJ ECC83s. Buy them from a reputable dealer like Antique Electronic Supply or Tubedepot or Eurotubes and you will have someone who will make it right if a tube fails early.

 

[GuyNoir]

If the Daystroms don't work out, it is my fervent hope that you will exclaim, "You're out of a job, DAYSTROM!"

 

[gadget73]

I use a lot of used old production tubes. Small signal ones are usually fine, if not they are usually such a small amount of $$ that I'm still ahead once you figure all the other good used ones I've gotten for small money over the years.

 

[triode17]

The tube will provide a little bit of gain before the phase splitter.

"A liitle bit of gain", is this a home made design? The 12AX7 gives a lot of gain. For a little gain, try a 12AU7.

 

[justinis]

Thanks, everyone. Sounds like there's no wrong answer. Maybe the best idea is to buy a modern tube, get my Daystroms tested, and see which one sounds better to me!

 

[FlaCharlie]

Thanks, everyone. Sounds like there's no wrong answer. Maybe the best idea is to buy a modern tube, get my Daystroms tested, and see which one sounds better to me!

That'll work.

Perhaps you're already aware of this but Daystrom didn't actually manufacture tubes. Those were made for Daystrom under contract and they had their name printed on them, which was common practice. Wasn't Daystrom the parent company of Heathkit? I know they were connected somehow. Anyway, if you post a pic of them we can probably tell you who the manufacturer was.

While it would be best to test them first, I'd just try them in the amp and see how it sounds. Unless they are noisy, microphonic or you notice an imbalance from channel to channel, they're probably just fine.

There are many many threads about "what's the best current production 12AX7?" Read a few then buy one and compare.

What amp is this? As mentioned, the 12AX7 is a high gain tube.

 

[justinis]

I have heard Daystrom was the parent co of Heathkit before. I've also heard they didn't mfg their own tubes. I'll post a photo later.

I shouldn't have said "little bit of gain" -- I don't actually know how much gain the 12AX7 stage offers. Here's the amp: http://electricblog.justinis.com/2016/08/the-st-40-scratch-built-tube-stereo.html

 

[kvflyer]

Daystrom owned Heathkit. In the early days, Heath used Mullard tubes and often labeled them Daystrom, saying something like Manufactured for ... by ... etc. Some in later years were made in Japan. And in the 60s, Japan made some very good tubes; Toshiba, Matsushita etc. If you can get the tubes tested, good. If not, no problem. 12AX7 tubes often are not worked hard and end up being as good as new. Save your money, try what you have first.

 

[justinis]

Great advice; thanks!

 

[mnmmt]

I'd wager that those are excellent sounding tubes provided they aren't electronically bad or used up (which you'll know by listening if unable to test). Mullard are excellent tubes (look for the "Made in Gt. Britain" painted on them; Mullard usually have four mold lines on the top of the tube, making an x pattern across the top). If they are later Japanese ones, they should be very good also. Try them out and see how they sound.

 

[E-Stat]

"A liitle bit of gain", is this a home made design? The 12AX7 gives a lot of gain. For a little gain, try a 12AU7.

Or a 5751 for the middle.

 

[triode17]

I shouldn't have said "little bit of gain" -- I don't actually know how much gain the 12AX7 stage offers.

Max. gain levels for various tubes: 12AX7 = 100; 5751=70; 12AT7=60; 12AY7=40; 6DJ8=33; 12AU7 = 17. I can't look at the sch. here at work because it gets blocked by our firewall. Does the amp. use a Split Load inverter or a Long -Tailed Pair? Or something else?

 

[justinis]

Max. gain levels for various tubes: 12AX7 = 100; 5751=70; 12AT7=60; 12AY7=40; 6DJ8=33; 12AU7 = 17. I can't look at the sch. here at work because it gets blocked by our firewall. Does the amp. use a Split Load inverter or a Long -Tailed Pair? Or something else?

Long-tailed pair. I'm using Shannon Parks' DIYtube driver board: http://www.tubezone.net/pdf/diy-st70-manual.pdf

 

[triode17]

Long-tailed pair. I'm using Shannon Parks' DIYtube driver board: http://www.tubezone.net/pdf/diy-st70-manual.pdf

The Long -Tailed pair has some gain. I built a 12BH7 LTP for my 7355 , P-P Pentode amp, (which was an impedance improvement over the 12AX7) and I believe the gain is 6 or 15.5dB. So, I added a 12AU7 to augment it. Most amps. use about 20 dB (Gain=10) of driver gain, so you would only need 10/6 or additional gain of just 1.6, hard to do even with an AU7. You end up with a little extra gain, but that's generally OK.