[Emil]

Looking to add a bit of "warmth" to my system and RCA  was one recommendation that I was given.

So off to Ebay I went only to find many variations of that tube.

Here's ebay's current crop
https://www.ebay.com/sch/i.html?_nkw=rca+12sn7

What should I be looking for? What to avoid?

Any other recommendations besides RCA?

Thanks in advance

[JackD]

Emil

Though it may cost you a couple of dollars more I would call Andy at Vintage Tube Services and talk to him about what sound you are trying to achieve.  His tubes are thoroughly tested.

http://vintagetubeservices.com/

[FullRangeMan]

Why do you buy the 12V version amp?
It has fewer manufacturers options, it just have stronger emission than the 6V, In this scenario I would be glad with RCA 12SN7GT.

Avoid that Admiral, smoked tubes and rebranded tubes.
RCA is always great sound, best years are 1940/50
Some GE tubes have bad sound but I dont know what are these tubes
Phillips-Holand and subsidiaries Mullard Amperex AdZam Valvo are great sound too.

[Freo-1]

Depends on what your application is.  I have a pair of mono power amps that was using 12SN7 as driver and phase splitter duties.  The amp was modified to use 6BL7 tubes, which resulted in a big improvement in performance. 


The one issue with the 6BL7 is it needs a more robust filament supply.   

[JohnR]

"More robust" is one way of putting it! 1.5A per tube instead of 600 mA (at 6.3V).

[Emil]

Emil

Though it may cost you a couple of dollars more I would call Andy at Vintage Tube Services and talk to him about what sound you are trying to achieve.  His tubes are thoroughly tested.

http://vintagetubeservices.com/

Yes, of course!
Will give Andy a call Tuesday

[Emil]

Why do you buy the 12V version amp?
It has fewer manufacturers options, it just have stronger emission than the 6V, In this scenario I would be glad with RCA 12SN7GT.
.

Thanks. I ordered a pair.
Inexpensive enough to give it a go.

[Tyson]

"More robust" is one way of putting it! 1.5A per tube instead of 600 mA (at 6.3V).

Very true.  From a pure sound-quality standpoint, the 6BL7 is a very special tube, one of the few "sleeper" tubes out there that people haven't discovered yet.  But you are right, it's absolutely not a drop in replacement for a 6sn7. 

[Freo-1]

Very true.  From a pure sound-quality standpoint, the 6BL7 is a very special tube, one of the few "sleeper" tubes out there that people haven't discovered yet.  But you are right, it's absolutely not a drop in replacement for a 6sn7.

Yes, agreed.  Since my amp was a DIY, and the power transformer was spec'ed out with a lot of overkill, was able to modify the amp to implement the 6BL7.  The filament supply was wired in series to drop the voltage to 6.3V. 


Would likely need to add a separate supply for most amps to support a changeover, but it is possible in many cases.


 

[FullRangeMan]

Freo, what 1625 you are using?

[Freo-1]

This one...

[FullRangeMan]

Thanks for the image bro, I meant what 1625 tubes you have been using in this amp and your sound impressions?  any time life info?

[Freo-1]

Thanks for the image bro, I meant what 1625 tubes you have been using in this amp and your sound impressions?  any time life info?

Sure, no worries.


I've tried RCA, Hytron, and and Sylvania tubes, all dated from 1942 to 1944.   All of the brands sound very similar, very little difference between the brands sonic wise.  I've had very good luck with longevity regarding the 1625 tubes.  A set of 10 tubes will usually last 2 to 3 years with moderate to heavy usage (one or two go early) before they need to be changed out due to reduced trans-conductance.  They still sound good at that point, but would rather be safe.  The 1625 is an outstanding sounding tube, one of the best I've come across for push/pull usage.


Luckily, I've got a boatload of NOS WW2 vintage spares on hand.  It is an excellent sounding tube, and the 6BL7 tubes are a outstanding match for the 1625.  A replacement of the 12SN7's for the 6BL7 provided a major upgrade in amp performance.

[FullRangeMan]

Thanks for inform, seems a right purchased amp so.

[Rusty Jefferson]

Looking to add a bit of "warmth" to my system and RCA  was one recommendation that I was given.....

If these are for your MicroZOTL, don't neglect the 12au7 input/driver tubes.  Discuss with Andy as well.  These have a significant impact on performance.

[Emil]

If these are for your MicroZOTL, don't neglect the 12au7 input/driver tubes.  Discuss with Andy as well.  These have a significant impact on performance.

Thanks

I forgot I had some Sylvania 6sn7 and replaced the stock Westinghouse 12sn7 with them. Much better!

I have some RCA 12sn7s coming in a few days

I've already replaced the stock RCA 12au7 with Brimars. Again, Much better

[jsm71]

Emil, it sounds like you have handle on the driver tubes for the MZ2.  I'm also using NOS JAN Sylvania 6SN7GT for my MZ2.  These are good.

For the input tubes, by far I am enjoying Seimens 12AT7 triple mica tubes more than any of the 12AU7s I tried.  The 12AT7s give better gain but of more importance, the Seimens really bring midrange more forward.  The sound is much more alive with better dynamics.  This was a greater/better change than swapping the driver tubes IMO.

[avahifi]

The 12AT7 has more gain than a 12AU7 tube (voltage gain of 40 as compared to 20 for the 12AU7).

In an audio circuit with feedback, changing from a 12AU7 to a 12AT7 will significantly change the feedback, increasing it.  This will lower harmonic distortion, but possibly increase transient intermodulation distortion.  The sonic result will be greater clarity, but possibly excessive high frequency brightness as TIM rears its ugly head.

Unless the tube circuit has no overall loop feedback, changing tube gain does not change overall gain, just the way the feedback loop works.

It is best to know more about how the audio circuits in your unit  actually work before changing tube types.

Just saying,

Frank

[Tyson]

Agreed with Frank - 12au7s and 12at7s are not direct subs for each other, best to stick with the one the circuit was optimized for. 

The good news is that there's a ton of legitimate subs that you can play around with:

12AU7 Substitutes: 12AU7A, ECC82, 5814, 5814A, 5814WA, 6189, 6680, CV4003, E82CC, ECC186, ECC802, ECC802S, M8136, 7025#, ECC83#, B749, 6067, 6670, 7730, B329, 5963, 7316, 7489

Taken from this site:

https://positive-feedback.com/Issue76/tubes.htm

Have fun!

[jsm71]

The Linear Tube Audio MZ2, which the OP and I have is a remake from David Berning's original MicroZOTL product.  LTA licenses David's designs in its products.  LTA's website does state that the 12AT7 input tube is the standard tube and it ships with those.  Using 12AU7S is supported with the understanding that gain does drop some.  Many people have AU7s they can play with so there is likely more swapping with that tube type.

The preamp is designed to allow swapping between 12SN7s and 6SN7s which pretty much sound the same.  Again, a lot of people have 6SN7s laying around and they happen to be my best sounding for the output side.  You just have to change voltage pins to accommodate the type used.