Tube Rolling w/Crack

Dr. Toobz · 742999

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Offline tintin

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Reply #2175 on: September 29, 2020, 12:02:53 AM
Have been enjoying rolling 6SN7 tubes with an adaptor, I personally enjoy them a lot more than 12AU7! I have had a slight problem with one 6SN7 in particular and was wondering if anyone could explain what was going on.

my volume pot is aligned with 0 as 7 oclock. The tube produces loud, constant crackle in the right channel from 9 oclock to 4 oclock, but this crackle is barely audible from 7-9 oclock, and dead silent from 4-5 oclock (max volume). Once warmed up a bit, the crackling range is from 10oclock to 4 oclock.

I've never had a tube do this; the other 7 or so 6SN7s I've rolled into this adaptor have all been dead silent, with only one having a faint buzzing noise at the very max volume. I'm currently working around the situation by putting crack volume at max and -50dB on my DAC. I have tried reseating the tube and cleaning the pins. Any insight is appreciated!



Offline Paul Birkeland

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Reply #2176 on: September 29, 2020, 05:23:00 AM
Use a different tube.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline tintin

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Reply #2177 on: September 29, 2020, 05:41:33 AM
Have swapped it out, but just wanted to learn some more or hear some opinions about what could possibly cause this? I have had my fair share of noisy tubes but never one that runs silent at different points on the pot!



Offline cddc

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Reply #2178 on: October 03, 2020, 11:06:36 PM
Use a different tube.

Hi PB, I have a question regarding the power output of 6080/6AS7 tubes. From datasheet 6080 tube has a max plate dissipation of 13W (vs only 3.5W out of 2A3 tube). So it seems 6080 has much higher power output than 2A3 does. But why 2A3 or 300B tubes are normally considered to be more powerful tubes than the 6080/6AS7 class?

I also read somewhere (couldn't remember where now) Crack outputs 0.3W into 300 ohms headphones. The number 0.3W is quite low compared to the max output of 13W from 6080 tubes, why so? Does that mean 6080 is not used up to its full potential, and a lot more juice can be squeezed out of it?

Thanks.



Deke609

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Reply #2179 on: October 04, 2020, 04:59:11 AM
That 13W figure in the datasheets refers to maximum "plate dissipation" -- i.e., the waste energy burned off as heat at the plate.  Max power of the signal output of the tube will be a fraction of that figure. For example, the RCA datasheet for the 2A3 shows max. plate dissipation of 15W but max output power of 3.5W.  I don;t know what the max output of the 6080 tube is, but it's a safe bet that it's nowhere near 13W.

cheers, Derek



Offline Paul Birkeland

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Reply #2180 on: October 04, 2020, 05:19:49 AM
I also read somewhere (couldn't remember where now) Crack outputs 0.3W into 300 ohms headphones. The number 0.3W is quite low compared to the max output of 13W from 6080 tubes, why so? Does that mean 6080 is not used up to its full potential, and a lot more juice can be squeezed out of it?
How much power does an OTL headphone amplifier need?  If we are to make 600mW, but we double the wasted heat and the size of the power transformer in the process, is that a worthwhile trade?

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline cddc

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Reply #2181 on: October 04, 2020, 07:18:38 AM
That 13W figure in the datasheets refers to maximum "plate dissipation" -- i.e., the waste energy burned off as heat at the plate.  Max power of the signal output of the tube will be a fraction of that figure. For example, the RCA datasheet for the 2A3 shows max. plate dissipation of 15W but max output power of 3.5W.  I don;t know what the max output of the 6080 tube is, but it's a safe bet that it's nowhere near 13W.

cheers, Derek


Thanks, you are correct, I missed the max power dissipation figure from the 2A3 datasheet. I read it again and indeed 2A3 has 15W max plate dissipation and 3.5W max power output. But for 6080/6AS7 tubes datasheets only show 13W max plate dissipation, nowhere can I find their max power output figure.

But as you said max power output is a fraction of max plate dissipation, so I think the max power output of 6080/6AS7 should come close to 3-ish Watt, which means 6080/6AS7 could possibly output as much power as the 2A3's ?



Offline cddc

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Reply #2182 on: October 04, 2020, 07:28:22 AM
How much power does an OTL headphone amplifier need?  If we are to make 600mW, but we double the wasted heat and the size of the power transformer in the process, is that a worthwhile trade?

Thanks, PB! You are correct 0.3W should be enough to drive 300 ohms headphones in an OTL design. I'm just interested in the potentials from 6080/6AS7 tubes, considering the huge power demand from planars, but of course not in an OTL design as their low impedances are not appropriate for OTL's.



Offline Paul Birkeland

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Reply #2183 on: October 04, 2020, 08:39:24 AM
For planar headphones to do OTL, you would want to look more at a speaker type amplifier with multiple output tubes and some feedback to straighten things out.  We of course would suggest the SEX amp... 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline cddc

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Reply #2184 on: October 04, 2020, 08:59:22 AM
Thanks PB, my knowledge on electronics is very limited, impossible to design an amp  :-[

I always think it would be a great idea for BH to add a headphone jack to the 300B/2A3 speaker amps (with some modification to the circuit of course). Amps like WA5 or WA33 that can power both speakers and headphones are quite popular. There should be a niche market there  :)



Deke609

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Reply #2185 on: October 04, 2020, 09:23:18 AM
For planar headphones ... We of course would suggest the SEX amp...

But if you're going all out, I would recommend the combination of BeePre and Kaiju, or BP and Stereomour.  I haven't heard the S.E.X., but in my experience BeePre+Kaiju > BeePre+Stereomour > Stereomour.

I always think it would be a great idea for BH to add a headphone jack to the 300B/2A3 speaker amps (with some modification to the circuit of course). Amps like WA5 or WA33 that can power both speakers and headphones are quite popular. There should be a niche market there  :)

You can just use a speaker taps to headphone adapter cable -- I still use one with my Stereomours.  But from a business perspective, you might have point -- I've often thought something similar. Folks who are willing to pay $2K to $6K for planar headphones are probably willing to pay at least that much for amps to drive them. But how many of those folks are interested in soldering the amps together themselves?  Dunno, but I suspect not many. But I agree that there is a niche, spendy market there waiting to be tapped.

cheers, Derek



Online Paul Joppa

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Reply #2186 on: October 04, 2020, 10:13:21 AM
The 6080 was not designed for audio and is not very linear. In Crack, it operates at a small fraction of its power capability, and with negative feedback (as a cathode follower). Both substantially reduce distortion.

As a power amp, running (for example) 130v at 100mA without feedback into a 600-ohm load, it will deliver about 1.5 watts - at about 15% distortion! At 5% distortion, it is only capable of 0.15 watts.

That's why there is no audio power output specification.

Paul Joppa


Offline cddc

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Reply #2187 on: October 05, 2020, 08:35:37 AM
Thanks, PJ and Derek. With distortion that high there is definitely not much potential for 6080/6AS7 to deliver high power, even though they have 13W max plate dissipation (what a waste  :-\). Otherwise, they would have been used widely in place of 2A3 or 300B  ;D
« Last Edit: October 05, 2020, 08:37:25 AM by cddc »



Online Paul Joppa

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Reply #2188 on: October 05, 2020, 10:22:10 AM
There was a brief period in the early 50s where push-pull designs were popular with the 6AS7 / 6080. Push-pull cancels the even order harmonics, which improves the situation even without feedback. I think it was overtaken by the greater power available from pentodes and beam tetrodes.

Paul Joppa


Offline Raymond P.

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Reply #2189 on: October 05, 2020, 11:27:02 AM
For planar headphones to do OTL, you would want to look more at a speaker type amplifier with multiple output tubes and some feedback to straighten things out.  We of course would suggest the SEX amp...
Off topic, but I just got a pair of 25ohm planars, and I can attest to to the SEX amp driving them well, as well as my SS amp. I also briefly tried them on the Mainline, which also seem to drive the planars well.

Raymond P.