Toob Amplified PC Speakers

Someone came out with a book a year or two ago, where he came up with some different name for "tube", almost as if a new hip name would make tubes trendy again.

Michael

Vacuum-mode field effect transistor?

I had a prof that referred to them as "GlassFETs".

Blech. Not for any rational reason, but -- blech.

For whatever reason my emotional sweet spot is for a solid state power supply but all toobs and transformers in the signal chain.

No, it's not rational, it's just what works for me.

That's been done: non-thermal electron emitters, vacuum gap, plate. That should be the ultimate high-voltage, superfast fet. The emitters (microtips, strange diodes) don't seem to last.

Since you asked, I checked, and it was "Thermatrons".

This is a book published within the past five years and written by someone named Grayson Evans.

Michael

Indirectly heated source field effect transistors.

Hmm. I thought glass was silicon.

Or more precisely glass Fetrons.

Fetrons were pin compatible JFETs with direct replacement for e.g.

A home for wayward electrons...

BTW, I am sitting with a hot laptop in my... well lap and the last thing I would think is "cool" is a valve power amp. I do like the fake toob idea with LEDs. Lol.

I remember the soft blue glow of the mercury vapor rectifiers (bright blue if you drew too much current :) ).

I've though in the past about putting a HV a transformer in the base with a MV rectifier mounted on top (all enclosed in a grounded wire mesh for safety reasons). Turn it on and the glow would make a nice night light and cute antique conversation piece.

Don't know where you can get the parts any more though.

But there were limitations. I remember a long letter in QST about those limits. There were only a few Fetrons created. And the 6AK5 Fetron wasn't good with AGC, it was intended more for use as a limiter if I remember properly.

There were various schemes back then for solid stating tube equipment.

One wsa to use the chassis and mechanical parts, and rebuild mostly from scratch. Hank Cross did that with a BC348 in a Ham Radio article about

Others did attempt to replace a tube with a solid state device or two, though generally there was sculpting, figure out some arrangement to replace that tube there, and then even if the next stage used the same tube, it might require a different arrangement or at least biasing.

It often was simpler when FETs became available, at the very least they had high impedance so they might be a sort of direct replacement.

Some tried to keep the unit intact, o the replacement was plug in, others lived with some added circuitry and modification of existing resistors. The former camp may have tried to keep the supply voltage as is, the latter camp was more likely to start with lower voltage.

Then others tried to create universal replacements, like the Fetrons, though I'm not sure how successful that was. Those tended to be in separate articles, "how to build tube replacements", without a lot said about when they were used in equipment. The other categories of replacement were always about specific equipment.

Then there was a whole different camp, just update the tubes. Fred Brown had an article in CQ in 1970 about updating an HRO, he put in miniature tubes, which if nothing else meant less filament current (and heat). But he also ran the B+ at a relatively low voltage, explaining the benefits.

IT was also the time of hybrid tubes, so you could run some tubes off

Nobody seems to talk about tube replacement anymore, except for that elusive oscillator tube in the Zenith Transoceanics. It was mostly an interim thing, stretching out the life of existing equipment when everyone wanted to go solid state. Now, people want to keep their old equipment intact, and for many, there are enough tubes to keep going. They want the old equipment precisely because they are tubes, so solid stating them, even if they could keep the existing circuitry intact, isn't appealing.

Michael

I've used mains transformers for audio out before, and done ok with them. They're far from ideal but with cautious use of nfb they've been ok. For a little few watts a channel project they're a fair candidate.

If you want to drive piezo tweeters made from bleepy things, just connect them to the primary side after removing dc & excessive V_out.

NT

A recipe for lousy sound.

NT

I really cant agree. Scrap mains transformers all round make it a cheap project. Even if you buy new, a pair of 3w PA transformers wont cost you 100.

NT