Sovtek vs JJ 2A3s

[rlyach]

I think I have found a definite advantage to using the JJ 2A3 in the Stereomour with mid sensitivity speakers. The JJ 2A3 appears to have a higher limiting plate voltage. When I use the Sovteks and play them at full volume I can hear the plate arching (popping) at very loud bass. The JJ's do not have this issue. I have found two songs that have strong enough base to cause the problem. Also, the Sovteks have a noticeable distortion at full volume compared to the JJs. If you have high sensitivity speakers, this wont be a problem but with my Orcas (89db) I tend to play the amp at a higher level. The Sovtek's sound great as long as you don't run the amp all out. Also, I find that I like the sound of the Mullard 12AT7 paired with the JJs and the RCA 12AT7 paired with the Sovteks. Now that I have two amps built, I have been doing a lot of comparisons with tubes and amps. This is when I ran across the issue. Incidentally, the two amps preform almost identically.

[Paul Birkeland]

Can you describe the popping a little bit more?

Arcing inside a tube is exceptionally rare outside of rectifiers.  Are you sure the speaker drivers aren't bottoming out?  If there is arcing in the tube, it would be very easy to see with the lights off.

-PB

[rlyach]

It sounds like a spark. A similar sound would be when an AC appliance switches on and off that comes through the radio. I suppose the tube may not be arching but whatever it is it goes away with the JJs.

[rlyach]

I guess I need to do some more experiments to isolate this but I am a little apprehensive. If it is the former bottoming out I don't want to damage it more. Also, it only happens at full volume where there is a VERY heavy bass. Some of the modern mixes really push the bass frequencies. I don't hear it at any other times. To be honest I would never listen to the amp at those volumes anyway. I was just doing some "engineering" testing and not "listening" testing.

[Doc B.]

Your description matches what bottoming the driver sounds like.

[rlyach]

Thanks Doc, That makes sense. The JJs probably have slightly lower gain when compared to the Sovteks, which is why I heard a difference. The spec sheet that shipped with the tubes does shows that the JJs are on the lower side of their specified range. I hope the former was not damaged by bottoming out. I didn't think it would be possible to overdrive the Orcas with 3.5 watts. I guess the instantaneous power is quite a bit higher though.

[Doc B.]

If the speaker sounds OK you didn't do any damage. But I wouldn't keep doing it 

[rlyach]

Guess what... One of the Sovtek's was arcing. When I got home I played the amp loud but not at full volume and turned the light off. The left channel tube was glowing blue at the top and was arching intermittently. The right tube was fine. I replaced the Sovtek with another I had from my first kit that I was not currently using and it worked fine. No more glow and no more arching. Now the amp will play loudly without popping. I am glad I was not bottoming out my drivers.

[vrgard]

Hey Randy,

I would be interested to read more about what you like about the Mullard with the JJs versus the RCA with the Sovteks.  Thanks in advance for any further impressions you care to share (as well as for all your past posts about the Stereomour and the Orcas - of course, you're a bad influence since I now own a Stereomour and have Orcas on order!).

Thanks,
(another) Randy

[Paul Joppa]

Guess what... One of the Sovtek's was arcing. ...

Thanks for following up, Randy! That's a good thing to know, and not something we've observed before.

[rlyach]

I would be interested to read more about what you like about the Mullard with the JJs versus the RCA with the Sovteks. 

Randy,

When I played the mullard with the Sovteks the sound was very dark to me and the sound stage seemed muddy. As soon as I put the RCA back in it was like the music came alive. Now with the JJs it is a different story. The mullard smoothed out the sound and really enhanced the bass. Drums sounded more defined. With the RCA (and the JJ gold pin 12AT7) the sound was too bright. To shimmery. It almost sounded like there was some sibilance. The RCA was better than the JJ gold pin however. I gave the JJ gold pin away. I won't be needing it again. I also bought a couple more Mullards for the future.  I hope you enjoy your Stereomour and the Orcas when they arrive. They are worth the wait (so was the Stereomour!).

[vrgard]

Thanks Randy.  Now you've got me itching to do some tube rolling.  But I gotta get my Orcas first.  And then I gotta get them at least somewhat broken in.  And I gotta get some variations on the driver tube (already have a few flavors of 2A3s).  But I'm looking forward to playing when I get there.  Thanks again for sharing your impressions.

-Randy