• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube DAC (without silicon)

NickKUK

Member
2019-12-28 9:16 pm
I was thinking how this could be done, but in an analogue domain only. Sort of a hard problem for fun..

The sample byte bits are carried in a square wave - a phase correlation against an analogue oscillation at the sample rate. This would allow the values to separate the bits and bytes of each channel.

Valves setup as an T2T ladder replacing the R2R resistor ladder with each valve being biased to a different level - thus the digital input level bit could be made to output from a number of valves to the output.

The idea is to use the oscillating valve at a high frequency to clock the changes through the valves, then a low RC pass filter at the end could remove that. One thought is that each tube input has a 'trigger' or a specific delay once the trigger has been fired. One way of doing this could be with a phase shift but the output of the valves would then have to be shifted back?

The difficult bit I'm trying to work out is how to split a bit pattern 1000101010110101 into the gates of separate valves. timing the correlation of the valve inputs for the T2T ladder.

Thoughts? Could it be done?
 
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Bell labs made telephone-quality ADCs and DACs in 1948 and ones suitable for television in 1951. Actually I'm sure they already made telephone-quality converters a few years earlier, since the Americans used digital voice encryption in WWII.

L. A. Meacham and E. Peterson, "An experimental multichannel pulse code modulation system of toll quality", BSTJ January 1948, pages 1...43
BSTJ 27: 1. January 1948: An Experimental Multichannel Pulse Code Modulation System of Toll Quality. (Meacham, L.A.; Peterson, E.)

W. M. Goodall, "Television by pulse code modulation", BSTJ January 1951, pages 33...49
BSTJ 30: 1. January 1951: Television by Pulse Code Modulation. (Goodall, W.M.) : Free Download, Borrow, and Streaming : Internet Archive
 

NickKUK

Member
2019-12-28 9:16 pm
Bell labs made telephone-quality ADCs and DACs in 1948 and ones suitable for television in 1951. Actually I'm sure they already made telephone-quality converters a few years earlier, since the Americans used digital voice encryption in WWII.

L. A. Meacham and E. Peterson, "An experimental multichannel pulse code modulation system of toll quality", BSTJ January 1948, pages 1...43
BSTJ 27: 1. January 1948: An Experimental Multichannel Pulse Code Modulation System of Toll Quality. (Meacham, L.A.; Peterson, E.)

W. M. Goodall, "Television by pulse code modulation", BSTJ January 1951, pages 33...49
BSTJ 30: 1. January 1951: Television by Pulse Code Modulation. (Goodall, W.M.) : Free Download, Borrow, and Streaming : Internet Archive

Superb. Both x,y based encoding and the decoding - which is interesting in this scenario.

I see they use a charged capactor so a known quanta then use the discharge rate sliced up according to the bitstream. The discharge rate precisely matches the sample time so you then get 2^x values.

Maybe worth trying a spice model for fun.