2A3 single plate RCA/Cunningham tube prices

[kmaier]

Well, I'm past amazement on prices now... a pair of these just sold on ebay for $988... and they aren't even unused... they have time on them.

Pr Matched RCA Cunningham 2A3 Tubes Single Plate Tested | eBay

Almost makes me want to sell one of my pairs... well, not really.

Regards, KM

[HollowState]

I've seen this happen many times before with various tubes. Either some filthy rich quack doctor or ambulance chasing lawyer with nothing else better to spend their money on. Or they're going overseas to Japan, Korea or China where their rareness is coveted by some tin eared business shyster. Cynical...who me?

[Miles Prower]

As one tube becomes popular, i.e. expensive, we'll use something else. Because we can.

-- Fred Nachbaur

I quite agree with Fred about this. I definitely use something else because I can. That's how I came to design with the TV horizontal deflection finals: no audiophool pedigree to drive up prices, and no suggested audio use at all in the spec sheets. A good many of these types offer excellent sonic performance, and can put out some serious power even. It's just that they don't work so swell as Class A audio finals, but as Class AB1 PP finals, they sound just great.

One type I based a design on came about from seeing an article in a Brazilian (Portuguese?) ham magazine from the late 1950s that mentioned the use of one of these HD amp tubes. Drew up my own loadlines, and got a pretty good H3 estimate staying in spec. This improved with some spec busting that proved true in actual operation: the hotter bias definitely improved the sonic performance. Like a more powerful 6V6 in operation. Talking 'em up sent prices from $0.98 to $1.30 last time I priced 'em. (Not a prob since I bought a 50-pack awhile back at a remarkable discount so I have more than enough to last.)

Same deal with small signal types: a certain VHF dual triode that likewise has no audio use mentioned in the spec sheet, not even as an after-thought, proved to be a great sonic performer when used to implement a cascoded LTP voltage amp/phase splitter. There are definitely audio "sleepers" out there that don't go for silly high prices.

[astouffer]

Single plate 2A3s have always been rare and much more expensive. Now if they sound any better who knows. One thing is for sure, tube prices are not going to ever go down.

[kmaier]

Originally Posted by astouffer

Single plate 2A3s have always been rare and much more expensive. Now if they sound any better who knows. One thing is for sure, tube prices are not going to ever go down.

Well I have to agree that the single-plate NOS tubes (which are the original design as opposed to the later dual-plate version) are quite rare... and that drives the prices higher... so I guess whatever the bidder is willing to part with.

As for how they sound, I think it depends on how you employ them. The single-plate version requires a more complex support circuit due to it's cathode/filament structure. Having a clean and quiet DC supply on the filament is an absolute must, otherwise the signal-to-noise ratio will render them useless. The dual-plate version is much easier to use and can realize acceptable s/n levels with an AC filament supply.

The real tell-tale between the single- and dual-plate versions is the purity of the tube itself... the former "is a single" triode, while the latter "is a pair" of triodes paralleled inside one glass envelope. Regardless of manufacturing quality and control, they still can't be a perfect match, period. The other issue to be concerned with is plate dissipation. The later dual-plate versions can handle quite a bit more power on the plate as they are generally more robust (especially the older Sylvania with the coil springs for filament tensioners). With the original single-plate you better stick to 15 watts or less, or you run the risk of "red plating" the tube.

Bottom line, the single-plate 2A3 will have a sonic edge if the implementation is done right, but they are more fragile, will handle less power and are more prone to mechanical excitation than the later dual-plate versions.

Regards, KM