Aoshida A6 amplifier: This is NOT a review

[fpitas]

https://frank.pocnet.net/sheets/127/5/5725.pdf

Sharp cutoff pentode for RF service. Probably nobody knows what to do with them these days, so now it's an audio tube lol.

 

[mhardy6647]

There are, or at least were in the relatively recent past, immense stockpiles of surplus JAN tubes. I.e., they could well be legit. The label looks a little messier than I'd expect on a legitimate JAN tube, too -- but there were tubes being made - somewhere - for US military purposes (?!) into the '80s, at least, and I really don't know what the quality of the last of them might've been like.

I reckon they're running in a plate-starved "space charge" configuration -- but, who knows?! They're probably doing something, but not necessarily anything good with respect to the input signal(s).
EDIT: PS, persuant to @fpitas's post, they could be connected as triodes. I don't intend this as a value judg(e)ment, just a statement.

 

[fpitas]

There are, or at least were in the relatively recent past, immense stockpiles of surplus JAN tubes. I.e., they could well be legit. The label looks a little messier than I'd expect on a legitimate JAN tube, too -- but there were tubes being made - somewhere - for US military purposes (?!) into the '80s, at least, and I really don't know what the quality of the last of them might've been like.

I reckon they're running in a plate-starved "space charge" configuration -- but, who knows?! They're probably doing something, but not necessarily anything good with respect to the input signal(s).
EDIT: PS, persuant to @fpitas's post, they could be connected as triodes. I don't intend this as a value judg(e)ment, just a statement.

A single-ended pentode with any amount of signal will certainly give a tube sound. Triode connection will make that a lot better, I suppose.

 

[Blumlein 88]

Yes, another post I found indicated they are running them in triode at low voltage. The filaments are also running on 5 volts presumably for longer life. Apparently the audio signal goes thru them, but don't perform any amplification. So there just as a tube sound purpose.

In the past I've had NOS tubes JAN that were that messy on the script. If I recall, early GE's were white, RCA's were usually black or red and green was later GE or Sylvania. I first used JAN's in my old Conrad-Johnson PV5 preamp. So it has been awhile.

 

[TonyJZX]

i dont think infineon have any way to insert a tube into their pwm stage...

i mean i'm not opposed to stuff like this... i know its stupid but i would probably purchase a tube stage preamp to control the digital amps i have

 

[tomtoo]

Its interesting for that price. Wish Amir would measure it.

At least i could say it has usa tubes certified for airborne army use. Imagine this!

 

[mhardy6647]

There's a very (!) difficult to substantiate report that RCA demonstrated long ago that running indirect-heated cathode tubes at lower than spec'd heater voltage drastically decreases the tubes' lifespan.

I've only managed to trace this back to a post at DIY audio -- I'd love to find the original resource. I wouldn't at all be surprised that it were in an RCA technical document... but I haven't managed to find it, or attributable documentation of the study, yet.

That said, here's the DIY Audio reference and the data presented therein.
Take it for what it's worth.

Filament voltage ?

What are the effects of using a vacuum tube (9 pin dual triode) operating at reduced filament voltage, say 5.7 volts rather than 6.3? Sonic degradation? Reduced dynamics? Reduced tube life? Just curious... -S

www.diyaudio.com

and, in particular: https://www.diyaudio.com/community/...good-the-bad-and-the-ugly.211731/post-3012333
We'll note that the post author is listed as banned. -- so... who knows?

Note that the y-axis is logarithmic -- i.e., the drop-off in tube ban (per this graph of fundamentally unknown provenance) is really steeply correlated to reduced filament voltage!

 

[Talisman]

.Meanwhile I got to test the headphone output.
When headphones are plugged in, the power output to the passive speakers is muted.
In terms of volume, I managed to make my Hifiman Sundara play at uncomfortable levels that I wouldn't want to keep them at. It is difficult to make a qualitative comparison because I normally use them with hidisz ap80pro with balanced output and with 10-band equalization calibrated on the sundara, so inevitably the sound is different from what I am used to. But power doesn't seem to be a problem, and that's a good point in itself..

 

[fpitas]

There's a very (!) difficult to substantiate report that RCA demonstrated long ago that running indirect-heated cathode tubes at lower than spec'd heater voltage drastically decreases the tubes' lifespan.

I've only managed to trace this back to a post at DIY audio -- I'd love to find the original resource. I wouldn't at all be surprised that it were in an RCA technical document... but I haven't managed to find it, or attributable documentation of the study, yet.

That said, here's the DIY Audio reference and the data presented therein.
Take it for what it's worth.

Filament voltage ?

What are the effects of using a vacuum tube (9 pin dual triode) operating at reduced filament voltage, say 5.7 volts rather than 6.3? Sonic degradation? Reduced dynamics? Reduced tube life? Just curious... -S

www.diyaudio.com

and, in particular: https://www.diyaudio.com/community/...good-the-bad-and-the-ugly.211731/post-3012333
We'll note that the post author is listed as banned. -- so... who knows?

Note that the y-axis is logarithmic -- i.e., the drop-off in tube ban (per this graph of fundamentally unknown provenance) is really steeply correlated to reduced filament voltage!

But the emission is much lower at 5V, so you get that nice grungy tube sound.