Testing Different Tubes in 2 Stroke

[Paul]

I’ve recorded some samples with different tubes. I’m posting 6 different clips recorded with:

-2012 Gibson USA SG Special on bridge pickup
-Two stroke through single 8″ Weber CVA8, 5.5 out of 12 on tone, 8.5 out of 12 on volume, the more trebly boost switch engaged, no negative feedback, and through a 2 stage resistive attenuator (ala Gerald Weber) at -12db
-I used a digital looper to loop the riff over and over, to eliminate differences in the clips due to differences in playing, and changed tubes with the loop running
-recorded with an M-power USB interface and Shure PG57 mic, near the edge of the speaker cone and about 3″ back from the grill.

Can you tell any differences? I’ll post later what the tube differences are. I hear virtually no differences whatsoever in any of them – am I missing something?

The clips sound pretty good to me, but nowhere near as good as the amp itself; I’m brand new at recording. Sorry if you don’t like ACDC, it’s so hard not to play ACDC with that guitar through this amp…and I needed a simple riff.

[Robin]

Thanks for doing the research and posting the clips.

You might notice more differences without the attenuator, although 12dbs is not an extreme amount of attenuation, it might still make a difference.
One of the beauties of the Two Stroke design is how harmonically rich it is. Putting anything in the path to the speaker could have an influence.
I’ve noticed significant differences between tubes from different manufactures, different choices in power tubes (of course), different rectifier tubes and NOS vs. new manufacture tubes.

[Paul]

I don’t find the attenuator changes the amp tone much – the speaker is not driven so hard though and that makes a little difference. There is not as much distortion for the same knob settings with the attenutator on.

The CVA8 is only a 10watt speaker so it really get’s going with one of the bigger output tubes in the amp.

I’ll keep posting clips as I record them. It’s hard to use the amp cranked without the attenuator – it’s so loud even with the 1 8″ speaker.

the attenuator is a great addition – super easy to build. I’ll never use the Triode mode switch I put into the amp again, there’s no point. It makes the amp hum more and doesn’t lower the volume all that much.

the attenuator eliminates what tiny bit of hum the amp has.

If you’re interested:

test1=JJ 6v6, NOS 12ax7 only labeled with “Great Britain”
test2=NOS RCA 6k6, Same 12ax7 as above
test3=NOS RCA 6k6, EHX 12ax7
test4=NOS RCA 6k6, JJ Long Plate 12ax7
test5=NOS RCA 6k6, Chinese no name OEM 12ax7
test6=NOS RCA 6k6, JJ regular short plate 12ax7

[Andy]

There is not as much difference as I would have expected. Before seeing the code, I listened and found the Chinese tube to be the least appealing, I liked the clarity of the EHX and the richness of the JJ’s. Honestly, I would be fine with any of them if the non-attenuated sound was the same.

[Robin]

From time to time, the question of how to get more headroom with a Two Stroke comes up.
As the Two Stroke design is very much in the vane of a “black face” style amp, it’s never going to be as clean as some other designs. But the new Tung-Sol 7581A may offer a significant delay in the onset of breakup and provide a cleaner tone at higher volumes.
JJ now offers a 7591 power tube that is similar to the 7581A as well. I will be testing these tubes and will report back.

Note: reports are that the Tung-Sol 7581 is not the same construction as the 7581A and is inferior to the 7581A. The 7581A is etched into the glass envelop on the new tube just as it was with the old original Tung-Sol version.

[Linn]

Hi everyone..i am new to this forum and by profession i am a DSP engineer and deals with Audion processing. As per my knowledge and before seeing the code, I listened and found the Chinese tube to be the least appealing, I liked the clarity of the EHX and the richness of the JJ’s. Honestly, I would be fine with any of them if the non-attenuated sound was the same.

pcb prototyping

[Ricky]

Hi..i am a new user here. As per my knowledge 12dbs is not an extreme amount of attenuation, it might still make a difference. Two Stroke design is harmonically rich. Putting anything in the path to the speaker could have an influence.

[Author]

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