How to approach vacuum tube circuits exploration?

[VSV_electron]

Hello,

I'd like to start learning vacuum tubes at the fundamental level but in a practical sense. I want to gain an understanding how the tubes work, how to properly provide all the necessary voltages to grids etc.
Honestly, I don't know where to start.
I'm mostly interested in vacuum tubes RF applications and maybe somewhat in audio amps but not much in the latter.

When I read the audio tube amp forums the guys there seem to be very knowledgeable and are discussing fine circuit details that I'm not sure even how to interpret. Too advanced for me. Not many are interested in RF tube electronics so I doubt I can find any active forum for that.

I have a few questions that you might answer to steer me in the right direction of tube learning path:

- Is it practical to assemble a universal Tube Lab Power Supply for "tube breadboarding"? Such an LPS would have to provide several variable voltage outputs for various tube types according to their individual requirements. Does anyone know of such an LPS schematics?
If there is no standard solution how would you regulate voltages from a standardized FSU anode series transformer (TA) such as this one:
TA175-127/220-50, having the following specs (in the 220V mode):
* Power: 86VA, 0.45A primary
* Secondaries (two windings of each): 2x315V (0.065A each), 2x125V (0.14A each), 2x35V (0.14A each)
The voltage sets look like a good compromise for various basic tube types, aren't they?

- What types of high voltage non-polar capacitors are suitable for tube circuit applications? Will, for instance, basic Asian polypropylene film capacitors such as these ones...
https://aliexpress.com/item/1005002535062542.html
... work in RF circuits up to say, 150 MHz ?
If NOT, what types of high voltage capacitors are most suitable for that application? Please advise.

- Are there any good practical tube books in the style of "Make Electronics" that would guide the tube learner in a step by step manner? It looks like not, just because such books are more recent trend and in the 1960's when tubes were still popular there were either quite a few academic tube books with piles of formulas on the one hand or otherwise short "assemble this that way" brochures on the other with no insights into how the circuits work.

- One specific question. Why is there often a choke used in the tube power supplies like L1 in the attached schematics? Semi- PS circuits get away without it.


All in all, I'd like to approach the tubes study in an organized and consistent manner but what would give me the best guidance for that task? I doubt there is a single 'Know it all' resource for tube circuits but I need to start somewhere.

[Circlotron]

Two reasons for the choke or lack thereof. Permanent magnets were not that great in the early days of radio, so up until about 1950 it was usual for a loudspeaker to have a big electromagnet on the back instead of a permanent magnet. This electromagnet often doubled as a filter choke like in your diagram.

Second reason- radios in those days almost universally had a single ended class A audio power output stage and these by nature are sensitive to power supply ripple, so a choke helped a lot to smooth things out. Solid state stuff  almost always has a class B push pull output stage that is nowhere near as sensitive to power supply rippple.

Maybe thirdly, large high voltage  electrolytic capacitors were not easily and cheaply available like they are now, with the advent of offline SMPSs.

Also, vacuum tube rectifiers are sensitive to how much current you pull at the peaks of the AC waveform, so you can’t just put in a huge capacitor and be done with it. A choke helps smoothing without needing gigantic capacitors. In fact, a choke input filter is best of all in these situations as far as peak rectifier current is concerned.

[Circlotron]

These particular magazines are a good read.

https://www.worldradiohistory.com/Radio_World_Master_Page.htm

[CatalinaWOW]

Starting with your last question, the series choke serves the same purpose as parallel capacitance in more recent low voltage supplies.  Tube supplies were most frequently half wave rectified, and thus needed a way to store energy to cover the other half of the AC power cycle.  In the earliest radios this inductance had an iron core and provided the magnetic field for the speaker.  Most of these supplies also have parallel capacitance.

Most tube circuits did not depend on regulation and supplies ran "open loop".  Resistive voltage dividers, or a simple series resistor which will give the appropriate voltage drop at operating current were how the various operating voltages were derived.

Your transformer should work fine as the basis for a supply.  Before you start building think through the implications of working with higher voltage.  Understand the one hand rule.  Check voltage ratings on components and instruments.  Figure out what a bleed down resistor is.

While building your supply with tubes is a good learning stage, appropriate tubes are now expensive and you should look into using silicon rectifiers.

For understanding, look into operating curves and curve tracers.  Building your own curve tracer is a big job, and commercial ones that handle tubes are expensive collectors items, but understanding what they do and what the curves look like will take you a long way towards understanding tube operation.

[Kim Christensen]

Read some of the old ARRL handbooks.

[ledtester]

I'd have a look at the following playlists from the Usagi Electric Youtube channel:

Vacuum Tube Logic
https://youtu.be/watch?v=rY-a6UUhvhY&list=PLnw98JPyObn057XAfTSPdvBrr86y62SnP

UE-1 Vacuum Tube Computer
https://youtu.be/watch?v=y149hLe1zYo&list=PLnw98JPyObn0v-98gRV9PfzAQONTKxql3

Audio Projects
https://youtu.be/watch?v=HL5BIE5TD3s&list=PLnw98JPyObn14amHyyK6VsqmQl9vEGuAH

One nice thing about the digital logic videos is that only low voltage is used (perhaps as low as 12V). I think the audio projects also use low voltage - like 24V.

[schmitt trigger]

I learned the basics with these books:

https://archive.org/details/BasicElectronicsVolumes151955

Simple and straightforward explanations. Highly recommended for a novice.

[T3sl4co1l]

Practical in what sense? Almost certainly not, but, you may have a different need, or opinion, of "practical" than I.

MOSFETs are excellent for power supplies of all voltages, it just takes a bit more design work -- and the margins for failure are narrower, shorter -- it blows up in 100µs instead of 10s.

Capacitors, literally anything will do for coupling and bypass.  Impedances are high, any available cap has ESR of ohms or less.  When high Q is required, resonant, tuning, etc., polypropylene for bigger values and C0G ceramic for smaller is the way to go.  Or whatever NTC/PTC as needed for compensating coils.

All the old handbooks are excellent -- RCA Receiving Tube Manuals, GE, etc.  Pete Millet's website http://www.tubebooks.org/ is basically a who's-who of good ones, and also see some of the books collected on Frank's https://frank.pocnet.net/

RDH4 is still excellent; while we have better ways of doing almost everything in it, now, it still teaches a number of design techniques, in a refreshingly simple manner, that is so often missed today.

Tim

[David Hess]

To get some ideas beyond RF, including about power supplies, check out the service manuals for the Tektronix 545 and 547 oscilloscopes.  They include a theory section describing each circuit function in detail.

[Xena E]

First pass, treat the triode as a big hot, (often HV), field efect transistor!

Tim's suggestion (post 7) of Pete Millets site is a good call.

A thorough treatment of the subject is 'The Radiotron Designers Handbook' (handbook is a misnomer, it's big). A more elementary approach is found in the Rider series of books.

The inclusion of a choke in early circuitry is for reasons stated previously, but also a limitation on maximum value was placed on the reservoir capacitor by the ratings of early rectifier valves/tubes, so the circuit was often a small reservoir > choke > larger smoothing capacitor.

Regards X.

(Post Tube era thermionic junkie)

[Andy Chee]

I'd like to start learning vacuum tubes at the fundamental level but in a practical sense. I want to gain an understanding how the tubes work, how to properly provide all the necessary voltages to grids etc.
Honestly, I don't know where to start.

You might want to also start by looking around at what valves you can easily get a hold of.  The type of tube you're able to obtain may dictate the types of circuits you're able to build.

Hamfest/radio rallies would normally be the place to go.  And I would avoid guitar amp & audiophile tube suppliers, due to the enormous markups they typically demand!

You might also want to download the service manuals for, say, the Kenwood TS-520 or Yaesu FT-101.  Both radios were hybrid designs that used transistors for much of the low level signals and a tube power amplifier for the output.  The tube PA section of the schematic will be the most relevant of interest.

[Xena E]

There are quite a few subminature types as historically used in ordinace for proximity fuse duty that are interesting and can be found for not much dollar.

Also, if just for experimentation look at the types that were designed for use in series heater design TV sets, they often have odd voltage heaters so are usually unwanted by the audiophiles and guitar amp builders.

Edit:

Just noted your home flag:
You may be able to obtain some "Rod pentodes" locally ... interesting Russian take on the minaturised 'tube'.

[vk6zgo]

First pass, treat the triode as a big hot, (often HV), field efect transistor!

Tim's suggestion (post 7) of Pete Millets site is a good call.

A thorough treatment of the subject is 'The Radiotron Designers Handbook' (handbook is a misnomer, it's big). A more elementary approach is found in the Rider series of books.

The inclusion of a choke in early circuitry is for reasons stated previously, but also a limitation on maximum value was placed on the reservoir capacitor by the ratings of early rectifier valves/tubes, so the circuit was often a small reservoir > choke > larger smoothing capacitor.

Regards X.

(Post Tube era thermionic junkie)

At one stage I worked at a TV site where the Transmitters were full of valves--not only in the high power stages, but in low level stages as well.
We used to get young "bright eyed, bushy tailed" guys coming through the system who boasted that "they knew nothing about valves/tubes".
They were perplexed when confronted by valve circuitry, so we had to help them out.
I found the best approach was to get them to think about a valve as "A FET with a fire in it"!

[vk6zgo]

First pass, treat the triode as a big hot, (often HV), field efect transistor!

Tim's suggestion (post 7) of Pete Millets site is a good call.

A thorough treatment of the subject is 'The Radiotron Designers Handbook' (handbook is a misnomer, it's big). A more elementary approach is found in the Rider series of books.

The inclusion of a choke in early circuitry is for reasons stated previously, but also a limitation on maximum value was placed on the reservoir capacitor by the ratings of early rectifier valves/tubes, so the circuit was often a small reservoir > choke > larger smoothing capacitor.


Regards X.

(Post Tube era thermionic junkie)

A little known fact amongst non-Australians is that the Radiotron Designer's Handbook was written by Fritz Langford Smith for Amalgamated Wireless Australasia Pty Ltd.
Their valve/tube offshoot, AWV, had bought the right to the "Radiotron" name from RCA.

RCA liked the book & arranged to produce an edition in the USA, minus the AWA labelling.

There were a lot of monthly magazines back in the 1940s & 1950s in the USA, UK, & Australia which went fairly deeply into tube theory & practice in ongoing articles.
There were probably similar mags in most countries.

[vk6zgo]

Starting with your last question, the series choke serves the same purpose as parallel capacitance in more recent low voltage supplies.  Tube supplies were most frequently half wave rectified, and thus needed a way to store energy to cover the other half of the AC power cycle.  In the earliest radios this inductance had an iron core and provided the magnetic field for the speaker.  Most of these supplies also have parallel capacitance.

In Australia, half wave rectification was rare, with the most common power supply using a power transformer with a centre-tapped secondary & a full wave rectifier tube like a 5Y3GT, 6X5GT, or a 6X4.
They still used LC filters on the HT line.

Even countries which used transformerless designs with half wave rectifiers for domestic receivers used transformers & full wave rectification in test, professional & broadcast equipment.

Most tube circuits did not depend on regulation and supplies ran "open loop".  Resistive voltage dividers, or a simple series resistor which will give the appropriate voltage drop at operating current were how the various operating voltages were derived.

Your transformer should work fine as the basis for a supply.  Before you start building think through the implications of working with higher voltage.  Understand the one hand rule.  Check voltage ratings on components and instruments.  Figure out what a bleed down resistor is.

While building your supply with tubes is a good learning stage, appropriate tubes are now expensive and you should look into using silicon rectifiers.


For understanding, look into operating curves and curve tracers.  Building your own curve tracer is a big job, and commercial ones that handle tubes are expensive collectors items, but understanding what they do and what the curves look like will take you a long way towards understanding tube operation.

[Wallace Gasiewicz]

The power supply you illustrated is a common full wave tube supply.  It was very common to use large chokes that looked like transformers.   Here is a link to something that might help.   

http://www.emissionlabs.com/Articles/APP-NOTES/AN-01-Designing-with-5U4G-and-274B-POWER-SUPPLIES/Designing-with-5U4G-and-274B-POWER-SUPPLIES.html

[Wallace Gasiewicz]

There were Lab Power supplies that were designed for tube experiment.   We had a B&K that had outputs for different filament volts. a high volt plate adjustable source and a negative adjustable source for grid bias.   We did sell it. But this was in USA.     
Your location might suggest that there may be old USSR power supplies for tube experimentation available. \

[TimFox]

In the US, Heath(kit) and Eico made similar plate, bias, and heater lab supplies.
The HV plate supply typically used two 6L6 pass tubes, and the bias supply was merely a pot across the negative reference voltage from a gas VR tube.

[VSV_electron]

...
Just noted your home flag:
You may be able to obtain some "Rod pentodes" locally ... interesting Russian take on the minaturised 'tube'.

That's the thing! We have hundreds of unopened boxes (and I'm talking of bulk boxes!) of all kinds of FSU tubes floating around.

[VSV_electron]

There were Lab Power supplies that were designed for tube experiment.   We had a B&K that had outputs for different filament volts. a high volt plate adjustable source and a negative adjustable source for grid bias.   We did sell it. But this was in USA.     
Your location might suggest that there may be old USSR power supplies for tube experimentation available. \

While FSU tubes are still a plenty in the FSU countries the test and PS standard equipment is normally worn out or when offered by some kind of local "estate diggers" is rather pricey.
However the Anode series transformers (there were pure Anode series transformers and combined Anode-Cathode heater transformers) designed specifically for tube equipment are still being found at reasonable prices locally even in NOS state.
That's why I asked if someone could share with me a schematic for turning such a transformer into a regulated PS for tube experiments. I understand that my question was too optimistic. I doubt such a schematic is common and well known because this is quite a specialized task.
Anyway - thank you and all the others who shared with me your/their thoughts!

[Wallace Gasiewicz]

If you can get the transformers cheaply enough, perhaps you could get a copy of the schematic of a Heathkit or B&K power supply and make one.   
The B&K I was talking about was all Solid State.   
It would be easy to build a single volt supply, a little harder to build a variable PS. See if you can find some schematics.     

It might be fun and profitable to build a tube audio amp if you have have the audio output transformer available also.  I built the one in the back of an RCA Tube manual, It was not hard and I was only 10 Years Old.

[mag_therm]

I had this experimental tube power supply question a few years ago. I decided to build a push pull pwm Dc-Dc converter rated 50 ~ 220 V at 1 Amp.
It has Volt regulator and Current regulator and inhibit/soft start switch.
Main use is to power a ham radio linear amplifier using SiC Mosfets, it has an output socket on front panel for tube experiments and also to power a Hg UV lamp for exposing pcb.

To allow using surface mount components with tube circuits, try to select more "modern" (tv etc) tubes using lower anode voltages like 200 V.
500 to 630 V MLCC capacitors are available. I recently obtained some old "sweep" power pentodes to try on 200V.
Refer also to my recent post over on the Ham Radio where I am using a VHF triode as SDR lightning suppressor, using anode voltage of only 13.8V.

[Xena E]

...I asked if someone could share with me a schematic for turning such a transformer into a regulated PS for tube experiments. I understand that my question was too optimistic. I doubt such a schematic is common and well known because this is quite a specialized task.

These may give you some ideas.

http://www.r-type.org/articles/art-010g.htm

http://www.r-type.org/addtext/add158.htm

If you have lots of FSU tubes available there will no doubt be types equivalent to any schematics you find on the Internet for western designs of equipment.

Regards
Xena.

[VSV_electron]

These may give you some ideas.

http://www.r-type.org/articles/art-010g.htm

http://www.r-type.org/addtext/add158.htm

If you have lots of FSU tubes available there will no doubt be types equivalent to any schematics you find on the Internet for western designs of equipment.

Regards
Xena.

Thanks much! I checked your links and found they are the parts of a very helpful practical primer on the Audio amps:
http://www.r-type.org/articles/art-010.htm
What's important, that short course is very clear and consistent with explanation of fine details.

[Andy Chee]

I had this experimental tube power supply question a few years ago. I decided to build a push pull pwm Dc-Dc converter rated 50 ~ 220 V at 1 Amp.

Incidentally, I implemented a similar switchmode HV power supply for my tube experiments, though far more cruder and basic.

Essentially I used this kit:

https://oatleyelectronics.com/files/K111B%20NOTES.pdf

....which I would think if one has a few junked AT/ATX computer power supplies, one could extract the transformer and PWM control IC (and maybe MOSFETs if they're still good), and run it backwards in a new perfboard/protoboard circuit.