Hi!
Over the years I kept buying tubes which I found interesting based on their tube data but which are completely unknown in the audio world. One of these is the 6AW8A.
The 6AW8A has a triode and a pentode section. The triode section caught my attention due to the technical parameters which seemed interesting for audio use.
The 6AW8A is a 9 pin miniature tube. The pinout is shown on the left. It has a 6,3V heater which needs 0,6A. It is suitable for series connected heating in a 600mA heater string as well as parallel heating. There is also a version called 8AW8A which has a 8,4V/450mA heater. The 6AW8A has a high mu triode section and a sharp cut off pentode. The characteristics of the triode section are quite interesting. It has a high amplification factor of 70, similar to that of a
6SL7 but at a much lower plate resistance of only 17500 Ohms. That's what made me buy a bunch of 6AW8A and put them into the box 'interesting tubes to be checked for use in audio later'. Well the check later turned out to be more than 20 years now while the 6AW8A had been lingering in tube drawers. I don't know if I well ever get to actually use the 6AW8A in a project but at last I pulled it out for a closer look and a tube of the month post. For the complete technical specs see the
General Electric data sheet. As always let's have a look at the plate curves, starting with the triode section:
And here the curves taken with a tracer:
The pentode section:
The pentode triode wired:
A very interesting tube indeed and definitely deserves more attention.
Here we have a General Electric 6AW8A.
Tung-Sol:
Here the three grids of the pentode are nicely visible:
Sylvania 6AW8A:
A very interesting tube. Both sections should be well useable for audio. Maybe a phono stage?
Best regards
Thomas
Entry-level SET amp? Triode for gain stage and pentode-wired-as-triode to drive a DHT (10y, 2A3, …)
ReplyDeleteHi Mr. Mayer, what is the scale do you use on the tracer? Triode curves for the pentode are usefull. Where do you connect screen for triode measurements? Thanks!! Love your work.
ReplyDeleteSorry forgot to note the scale when I took that trace. Screen is connected to plate
DeleteI just bought a couple of these, also with the hopes of using them in some sort of audio circuit. I've never worked with vacuum tubes, so there is some experimenting in my future.
ReplyDeleteThese tubes are often used in Shindo amps including two that I own: Montille CV391 and Apetite integrated.
ReplyDeleteCheap Tubes with a Long Warm-up heater Time
DeleteHaha! I bought a few sleeves of these hoping for geetar use. Tried the pentode sections at push-pull at ~250VDC 22k a-a load until I cooked the OPT with open-circuit flybacck whoopsies. Sounded real nice and clean, cleaner than I had hoped for, as I was going for a 3W PP distorted guitar amp.
ReplyDeleteRan the pentode as a gain stage/PI driver in another build. Pin-compatible with 6BH8 and 6AU8A. I swapped to the short-plate 6AU8 for microphonics reasons.
Some hifi company used 6AU8 as pentode+concertina, and Telectro also used them as a PP power amp, at unknown Zout but 250VB+/225Vg2. Likely a 10k-20k a-a OPT.
Neat tubes, and a gorgeous exposed cathode. And big 3.75W true-pentode plates make it a winner if your build can show them off.