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Michael Black[_2_]

On Thu, 24 Jul 2014, wrote:

On Thu, 24 Jul 2014 13:13:42 -0400, wrote:

On Thu, 24 Jul 2014 02:01:36 -0500, Tim Wescott
wrote:

On Thu, 24 Jul 2014 00:31:38 -0400, Michael Black wrote:

On Wed, 23 Jul 2014, Tim Wescott wrote:

On Thu, 24 Jul 2014 08:16:30 +1000, Barry OGrady wrote:

On Mon, 02 Dec 2013 12:58:56 -0600, Tim Wescott
wrote:

It's winter, and the amplifier in my PC speakers just died.

I think it'd be kinda cool to have a toob speaker amp, but I'm too
lazy (and time-challenged) to build one up from scratch.

Are there, by any chance, kits out there? I'm not looking for
nickel- cored transformers with solid silver windings, genuine paper
caps rolled on the thighs of virgins, toobs dipped in LN2, and all
that crap: I'm just looking for something that'll give the audio
quality of a mid-range amplified speaker set, in a cabinet that shows
off the fact that it all uses ancient technology to get the job done.

Suggestions welcome.

Is toob a brand name? What sort of amps does toob make?

Someone should start a retro amplifier company and call it "Toob".
Really. Someone who loves vacuum tube amps, but doesn't suffer much
from audiophoolery.

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.

Vacuum-mode field effect transistor?

Indirectly heated source field effect transistors.

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

Hmm. I thought glass was silicon.

Or more precisely glass Fetrons.

Fetrons were pin compatible JFETs with direct replacement for e.g.
6AK5 12AX7 etc.

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
1968. It gave him a good foundation, but he could add things (like an FM
detector and I seem to recall mechanical filter) and do things like an
audio amplifier IC as the output or an IC IF amplifier, instead of
directly trying to emulate what was there originally.

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
+12v.

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