6502.org

So, really impractical idea for a rube-goldberg cpu here...

Vfds are basically just an array of tiny vacuum tube "transistors", and have been used in ham radios already as amplifiers... don't believe me?

Since triodes seem to work like a pnp bjt when a + voltage is applied to the grid, and a npn bjt when a - voltage is applied, this would make the equivalent of ttl possible with triodes.

If you don't mind making a 10 khz cpu that uses a 90 volt power supply and melts itself after a couple hours, is it possible?

Yes, I think you can make a CPU from any kind of switching element. One which had visuals built in would be amusing.

I just found a youtube video demonstrating his radio. Apparently it required at least 120 volts to drive a pc speaker at high volume. Probably would explode like a firework after 10 minutes of that though XD

Since the VFD picture was on the homepage of H.P Friedrichs:

"Instruments of Amplification", ISBN 0-9671905-1-7, from H.P. Friedrichs
sure was nice reading material.

Especially that part about homebuilt foil-based cuprous oxide transistors.

Pictures are at the end of this gallery:
http://hpfriedrichs.com/mybooks/ioa/bks ... llery2.htm

If I remember correctly, transistors didn't survive much more than 5V,
and only one of 10 homebuilt transistors worked as intended.

If you have success in building a 7400 that way, please post a picture.

Very nice! He starts out with missing some information though. A grid need not be between the filament and plate. It may be on the opposite side of the plate from the filament and work the same. Not that it matters for his project.

It still surprises me that there don't seem to be many people experimenting with flame triodes.

Seems like something like this would fit the bill: KORG INC and Noritake Co., Limited Release Innovative Vacuum Tube: the Nutube

It even seems to be a DIP! No idea about availability though.
I've heard the term "FETs with pilot lights", isn't that the closer analogy?

That always seemed to me like calling horse-drawn carriages "motorless motorcars".

Who replaces 12AX7s regularly? I see a huge market for socket retrofits, with oxygen-free pins.

Tube technology has some fierce advocates among musicians (eg: for guitar amplifiers) and among audiophiles (for home stereo). In the realm of guitar amps, some of the appeal of tube technology relates to aspects which can arguably be considered imperfections -- kind of like the discussion we had recently about a certain 6502 bug/feature! What it's called doesn't matter as long as you get to choose what you like.

-- Jeff

Oh I understand. I have a ton of tube gear (probably literally).

What I don't understand (beyond the obvious copper-free nonsense) is why they are always changing tubes. They're just not that frail. In my opinion, something in constant use for the past forty years is lucky to actually need one new 12AX7 by now. But then I don't normally modify things to work out of tolerance. Maybe others do.

I always expected miniaturised tubes to make a comeback. For some reason I never expected it to come about this way.

While not frail, all tubes leak to some extent and eventually get gassy. The seal between the pins and the glass envelope leaks very slightly due to the cycle of expansion and contraction that occurs with changes in tube temperature. Adding to the fun, hydrogen atoms can actually penetrate the envelope. I've had my share of NOS tubes that were gassy, even though they had done nothing but sit on a shelf or in a box somewhere for the last 30-or-so years. I had two brand new Sylvania 8417 beam power tetrodes that I had to scrap because they had gotten gassy from years of sitting in my junk.

They probably had active getters. A lot of power tubes do, and they will get gassy if you never operate them in such a way to activate the getter.

Otherwise, it's not much of an issue, else there wouldn't be /any/ working 01As.

Guilty as charged. My bass amp is a 1966 Ampeg B15 Portaflex that has tubes throughout the signal path (silicon diode rectification, though, for the B+). I've yet to hear a solid state bass amp with the warmth and smoothness of the B15.
Jeff is likely referring to what happens when the output stage in a tube amp is driven into clipping. The transition from linearity to nonlinearity is smooth and in a guitar amp that isn't driven too hard, produces a even harmonic distortion that evokes the sound of the amps used by the early jazz and blues electric guitar masters, such as Charlie Christian and T-Bone Walker. Most of those amps were capable of 10 to 15 watts maximum before clipping, and as guys like Christian worked to be heard above the horn section in the band, they would play the amp at maximum volume, often driving it into clipping. That sound is considered to be classic and is difficult to produce with solid state gear.

As far as I can recall, the 8417 did not have an active getter. I believe these two simply went bad due to age. I've seen that happen a lot with old tubes, and not just power tubes.

In that case, it must just be bad seals. Otherwise, it would affect all tubes equally.

I've got hundreds of tubes, which I have tested most of in recent years. Very, very few have ever been gassy, less than 1%. But most of mine are receiving tubes, especially television, mostly excluding sweep tubes. That may indicate something, I don't know.

My experience is that the 9 pin miniatures are less prone to leaking around the pins than octal base tubes, especially output tubes and rectifiers. That said, there are some 6SL7s in my bass amp that are OEM (they have "Ampex" on the envelopes) that are still okay. However, these are low signal tubes that barely get warm during extended operation.

When I got the amp it was DOA, due to dried-out electrolytics and a failed B+ rectification diode. I installed new caps and a pair of diodes (1N4007), and after bringing the amp up to full power (I started it off on the Variac), noticed that the two 6L6GC's, both RCAs, appeared to be a bit gassy, but with no color in the plates. A check of the quiescent plate current confirmed my suspicions. I replaced them with two NOS GEs I had and ran into the same problem, though not as bad. I ended up installing some Electro-Harmonix (Russian re-issues) I had laying around and everything was fine.