Theory, Practice and Sexlife of the "Reflected Plate Amplifier" Hybrid, low Voltage Tube circuit

[leadbreath]

Seriously doubt anyone will voluntarily apply a megger to their nutsack, but in this day and age you never know!!??

 

[leadbreath]

 

[Tubetec]

I have a buddy , havent run into him in a few years now as he had to curtail his drinking career due to ill health .
He told me a story about his days in the UK military ,
They were playing some kind of game of king of the castle where the objective was to capture a hut on a hill ,
It wound up with him and an officer getting into it hand to hand style , officer came out second best .
I guess they could have thrown the book at him for his infraction but instead a few of the officers grabbed him ,applied croc clips/wires to his tackle and hooked him up to an old style field telephone.
He said he was willing to tell them anything they wanted to hear to stop the pain ,

He blundered on a few more few more years in munitions disposal , his guess was they hoped he'd eventually blow himself up . The final straw was when he started pinching diesel from what he was given to soak down the old weeping munitions , powders and flares , the pit went off with a gigantic boom , he was told to report to a nuclear submarine base in the north of Scotland or hand in his resignation , he took option B ,went back to the humdrum civilian life .

Nic Tesla was able to safely demonstrate hundreds or thousands of volts upon his body , the trick was he never allowed the current a path across his chest .

 

[abbey road d enfer]

Nic Tesla was able to safely demonstrate hundreds or thousands of volts passing through his body , the trick was he never allowed the current a path across his chest .

Not through, upon. That is a huge difference.

 

[Tubetec]

Right you are sir ,

 

[Somkereki]

A 120V DC-t semmiképpen sem tartanám "elégséges" módon biztonságosnak - tényleg nem értem, honnan veszik ezt az adatot?

Nálunk az LVD biztonságos részét hagyományosan 48 VDC-nél határozták meg, ezért a fantomtápot és a telefonokat ilyen módon látják el.

/Jakob E.
Akit mostanában elég erősen lecsapott a +118V

Én is így gondolom, 50 év tapasztalata alapján. De ezt tanították a technikumban és az egyetemen is. A 12 voltos feszültségről üzemelő A osztályú erősítő (Motorola 15J04) mérésénél viszont a BNC csatlakozó 900 MHz-es frekvencián megégette az ujjam!

 

[Somkereki]

Nem keresztül, rá. Ez óriási különbség.

Csak nagyfrekvenciás árammal mutatta meg, ami nem nagyon hatol be az emberi szervezetbe

 

[Somkereki]

The police in my town in South Africa used to apply 1000V on wind up meggers to the nutsack of the unfortunate uncooperative individuals who they had in custody all the time and they were fine...not sure about the reproductive abilities afterwards...

When I was young, in the 70s, I was hit by a TV set "booster voltare" 800 Volts. I still remember it today!

 

[abbey road d enfer]

abbey road d enfer said:

Nem keresztül, rá. Ez óriási különbség.

I certainly didn't say that, nor write it!
You may want to check your translator, posting here is (almost) strictly english.

 

[abbey road d enfer]

Just took some time to read the Aphex patent, where they state that the tube's load is a current mirror.
I beg to differ.
Actually, the topology is very similar to the NPN+PNP variant of the two-transistor preamp. In order to provide good performance, NFB is required.
I guess if P-type tubes had been available, this circuit would have been used long ago in full vacuum style.

 

[Tubetec]

Then again unless your fluent in Hungarian , the second translation back to English might have clouded the meaning even further ,
lost in translation .

 

[thor.zmt]

Just took some time to read the Aphex patent, where they state that the tube's load is a current mirror.

It is a current mirror with gain. A current mirror does not need a second transistor per se, that is only needed to get accuracy.

Actually, the topology is very similar to the NPN+PNP variant of the two-transistor preamp.

Yes.

In order to provide good performance, NFB is required.

For the Aphex circuit, yes. In absolute terms, no. It is completely possible to make this a non-NFB circuit.

I guess if P-type tubes had been available, this circuit would have been used long ago in full vacuum style.

Yes, it is in effect equivalent to 2-Stage RC coupled amplifier, without the RC coupling.

If you use a P-FET with a largeish unbypassed source resistor in the 2nd stage and then a resistive load to the negative rail and sufficiently high voltage on the positive rail (say +48V/-12V) you have two stages no (looped) feedback.

Or, you could use resistive Miller feedback on the second stage and a CCS load for the second stage. Then you have the tube stage open loop and the Solid state par local loop, with low output impedance and low input impedance, forming a virtual cascode for the tube input. We could even do it differential.

Lot's of interesting things to be done on this principle.

Thor

 

[abbey road d enfer]

It is a current mirror with gain.

And distortion, thanks to the non-linearity of hFE.

A current mirror does not need a second transistor per se, that is only needed to get accuracy.

That's right!

If you use a P-FET with a largeish unbypassed source resistor in the 2nd stage....

...Or, you could use resistive Miller feedback on the second stage
That would not be NFB-free.
Global or local, NFB is NFB.

 

[Somkereki]

I certainly didn't say that, nor write it!
You may want to check your translator, posting here is (almost) strictly english.

You're right ! I admit I was lazy, so I used Google translate. However, my knowledge of written English is relatively good, even spelling is not a problem. For 40 years, I have only read technical literature in English. As a junior engineer, I worked at the Hungarian HT Cooperative for many years, and I got used to it there. (This was the Silicon Valley of "Europe" beyond the Iron Curtain. ) I had a Tektronix oscilloscopes on my desk, just like anywhere else in the world. Now that I'm retired, I have them (TDS224 + MM module) for sound frequency spectrum analysis, a Neutrik A2-D (a very good instrument! )" readout output in distortion mode, where the fundamental harmonic is filtered out, only the "distortion harmonics" fill the screen. Of course, there is also the old analog Tektronix 465, which still works perfectly today, and a LeCroy WaweAce 204. (Color display, USB port, but the "old" Tektronix TDS224 is much better in FFT mode, so I prefer to print it with an old HP Laserjet printer. So thanks for the warning! from now on, I won't be "lazy" and read the original English text!

 

[Mr. Moscode]

I fixed my neighbors old b&w tv which had a pix tube with a metal cone upon which sat the 15kv anode voltage and I got zapped until I realized the anode was bare metal and was the outside of the CRT. I was about 12 at the time. This was a very early tv set. never saw one like that again.

Color tv brought bigger screens and crts with all glass construction and 30+KV anode voltage. Even after bleeding them down I still got nailed sometimes due to charge migration. The anode was an inside coating and the outside a sprayed on metallic coating which created a large cap that functioned as a HV filter cap.

Anyone beat 35kv dc?

That aside there are some older vacuum tubes made for early car radios that ran on 12 volts as the plate supply. You may want to try and find those for the LV projects. Personally I like 300+ vdc for tube gear. tubes were made for that and sound better, IMHO.

 

[ruffrecords]

I fixed my neighbors old b&w tv which had a pix tube with a metal cone upon which sat the 15kv anode voltage and I got zapped until I realized the anode was bare metal and was the outside of the CRT. I was about 12 at the time. This was a very early tv set. never saw one like that again.

I did exactly the same at exactly the same age. Shot me right across the room. I kept away from TVs from that day on but I quickly got used to 250V HT shocks. Just a tickle.

Color tv brought bigger screens and crts with all glass construction and 30+KV anode voltage. Even after bleeding them down I still got nailed sometimes due to charge migration. The anode was an inside coating and the outside a sprayed on metallic coating which created a large cap that functioned as a HV filter cap.

Anyone beat 35kv dc?

Not me.

That aside there are some older vacuum tubes made for early car radios that ran on 12 volts as the plate supply. You may want to try and find those for the LV projects. Personally I like 300+ vdc for tube gear. tubes were made for that and sound better, IMHO.

I remember there were ones that had a vibrator, a kind of mechanical SMPS, to generate a regular HT voltage. Got a belt or two of those.

Cheers

Ian

 

[rock soderstrom]

Anyone beat 35kv dc?

I am not sure what HV voltage a moped ignition coil generates. When I was young and stupid, we actually used to light cigarettes on the ignition spark of our mopeds from time to time. You take the spark plug connector in your hand and generate a spark gap to the spark plug with the engine running. This works, but has minor safety problems. Once I got a nasty electric shock directly on my mouth when lighting the cigarette. I haven't done that since. Learning by pain.

 

[PermO]

I'd like to add my very rudimentary saturation amplifier to this discussion.

https://groupdiy.com/threads/low-voltage-vacuum-tube-saturation-amplifier.77783/
The whole circuit runs on the heater voltage 12.6V

Circuit design is beyond my scope in general, I just fiddled around with a distortion circuit I found online to the point that I got something from it that I could use on a mixbus, hence... the bussfukker.

Any suggestions on this circuit are welcome as I would not mind exploring some more options.
The hardest part was to get it to behave somewhat exeptable as it started out pretty nasty.

It can run from a wallwart and be build safely by anyone who can hold a soldering iron.

 

[thor.zmt]

That would not be NFB-free.
Global or local, NFB is NFB.

Is a triode feedback free? Or is it a akin to a penthode with shuntfeedback? Is it local feedback?

I find after much experience that the feedback debate is bogus. Feedback is a tool. So is feedforward. Tools need to be used with care. Measure trice, cut once.

The issue is not the tool, but the use. Used correctly in the correct context negative feedback is useful tool. Used as "fix it all" to correct bad inherent design it's a disaster.

Thor

 

[thor.zmt]

I fixed my neighbors old b&w tv which had a pix tube with a metal cone upon which sat the 15kv anode voltage and I got zapped until I realized the anode was bare metal and was the outside of the CRT. I was about 12 at the time. This was a very early tv set. never saw one like that again.

Color tv brought bigger screens and crts with all glass construction and 30+KV anode voltage. Even after bleeding them down I still got nailed sometimes due to charge migration. The anode was an inside coating and the outside a sprayed on metallic coating which created a large cap that functioned as a HV filter cap.

Happened to me. I used to own a RuSSian "Raduga" Colour TV, it was hybrid, the entire front-end was solid state, but everything driving the picture tube was tube. It allowed us to wind the HT way up, getting very bright and sharp pictures. Every few weeks the picture tube would have a brief flashover, which in an all solid state TV tended to be terminal.

Using PAL & SECAM colour (rather than "Never The Same Colour" - NTSC as used in the USA) the results were great for SD (nothing like my 55" 4k Flatscreen now, mind you), in the 1980's.

But I occasionally had to work on it. And even Glass turned out to have significant dielectric absorption. So even after discharging everything, I ended up getting a mighty shock that threw me half way across the room.

Famous last words of the TV Repair Man: "It's ok to turn on now!"

Thor