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No semiconductors used project, my new old (pre WW2 technology) computer audio amp, 3W per channel triode connected 807's. Just for fun. The 807's were available in 1938.

G'day Ken,
Have you put 600v on the plate caps?
I used 807s in the modulator for my first home brew 100 W HF AM TX rig in 1958.
They operated in Class B so not exactly hifi but fine for a TX.
John

Very nice - and it keeps you warm on colder days.
I remember my dad made a PA amplifier for our local primary school back in the mid 1950's and that used an 807 valve.  Not to be confused with valves that had grid on the top when doing the wet finger hum checks.
By the mid 60's I was building my own valve gear and remember getting "plated" on several occassions.
These days I would hate to think what an octal socket would be worth let alone a good quality output transformer.
An old timer movie projectionist once told me that they filled the Civic Theatre here in Auckland with 2 1/2 Watts and got excited when a new tube was shipped from the US boosting output to 3 1/2 Watts.  I should add that the speaker used was an exponential horn that started down under the stage and ended up with an opening big enough to fall in to.
Great to see the chassis work and your finished product.

Cheers,
David

Quote from: John Drew on Jun 27, 2023, 03:01 AMG'day Ken,
Have you put 600v on the plate caps?
I used 807s in the modulator for my first home brew 100 W HF AM TX rig in 1958.
They operated in Class B so not exactly hifi but fine for a TX.
John

Hi John
With 600V on the anode and 300V on the screen one can obtain almost 60W from 807's, the distortion was not too bad so I guess the transmitter sounded OK. Do you still have it?

I have 380V on the plates (with a 5Y3GT rectifier) a 680 ohms cathode resistor gives a bias of 31V with a cathode current of 45mA, the anode/screen dissipation is about 15W so the tubes should last a long time. The 807's were used because I like the look of them.

Quote from: david on Jun 27, 2023, 03:18 AMVery nice - and it keeps you warm on colder days.
I remember my dad made a PA amplifier for our local primary school back in the mid 1950's and that used an 807 valve.  Not to be confused with valves that had grid on the top when doing the wet finger hum checks.
By the mid 60's I was building my own valve gear and remember getting "plated" on several occassions.
These days I would hate to think what an octal socket would be worth let alone a good quality output transformer.
An old timer movie projectionist once told me that they filled the Civic Theatre here in Auckland with 2 1/2 Watts and got excited when a new tube was shipped from the US boosting output to 3 1/2 Watts.  I should add that the speaker used was an exponential horn that started down under the stage and ended up with an opening big enough to fall in to.
Great to see the chassis work and your finished product.

Cheers,
David

Hi David
Interesting story, horn speakers can be very efficient. These days one can buy Hi-Fi speakers with an efficiency of 100dB SPL @ 1 meter @ 1 watt (if you spend enough money), one can also purchase speaker with an efficiency of 84dB SPL @ 1 meter @ 1 watt, it seems as power goes up speaker efficiency goes down.

Quote from: https://support.klipsch.com/hc/en-us/articles/360025619391-Speaker-Sensitivity

Horn loaded speakers—such as Klipsch products—can have a sensitivity approaching 110 dB at 2.83 volts (1 watt at 8 ohms) at 1 meter. This is a hundred times the output of a loudspeaker rated at 90 dB sensitivity, which would be excellent for a traditional radiating cone type.

I made my first (mono) valve amplifier from a kit in 1965/66, I still remember it. It was based on a 6V6 which was also a large envelope valve. This ushered in a period of experimentation and quite a few high voltage shocks which I managed to survive...

Quote from: John Lawton on Jun 27, 2023, 06:06 AMI made my first (mono) valve amplifier from a kit in 1965/66, I still remember it. It was based on a 6V6 which was also a large envelope valve. This ushered in a period of experimentation and quite a few high voltage shocks which I managed to survive...

Hi John
I guess the 6V6 amplifier sounded quite good.
The 6V6GT is still a current production valve, the 6V6 was introduced in 1936, the 6V6GT is the same device in a smaller glass envelope. The 6V6 family is now 87 years old. How many PIC's will be in production for 87 years? Many of the new 6V6 tubes seem to be like 6V6's on steroids that can be pushed well beyond the original rating with no ill effects.

https://www.tubedepot.com/products/jj-6v6s-power-vacuum-tube

https://www.jj-electronic.com/images/stories/product/power_tubes/pdf/6v6s.pdf


For those not into tubes these can dissipate 14 watts (from the anode) with no heatsink, mind you they waste 3.15W to run the heater.

Like it. Been there, done it and felt the tingle of H.T. many times.

I still have several new 807 and 6V6 and my favourite period for restoring old radios is the Octal one, even though they were becoming obsolete when I was born (1951).

A wonderful creation Ken. It is in fact a work of art.

My dad showed me how to build with valves when I was a boy, even though germanium transistors had been around for a while and silicon transistors were getting more popular, and I was building circuits with them (BC107, BC108 and BC109 transistors from B-Pak, and if I had a bit of money, the 2N2926 with its top hat casing). :-) But I always had a fascination with valves, and still have. :-)

A lot of dad's valves were second hand ones from old radios and old televisions, so I could not use the P type valves (PL84, PL36) etc, because their heaters were different voltages and had to be wired in series, with a big drop down resistor (A mains dropper) so they could operate from the mains voltage supply in televisions. But he also had the E types from radios and amplifiers. i.e. ECL84, ECC83 etc, and they were the first ones I used, with their 6.3 volt heaters. Wonderful memories.

Charlie sent me some E type valves a few years ago, and once I get my workshop up and running I intend to build a regen radio with valves, just like I did when I was young to bring back the memories of the joy of working with dad in our back garden shed. Many thanks Charlie.

When I was serving my apprenticeship as a TV engineer, there were still many valve televisions around, and the colour TVs were mostly hybrid types, because the rectifiers and transistors of the time they were built could not handle the high voltages and the high currents required for EHT, Line and Frame. Also, because the colour televisions were so expensive to buy, and their quality was so good, they lasted a long time and were part of the furniture of a room. So... I have had many, many high voltage wallops in my time, when I got a bit too close to the EHT, and even more mains wallops off capacitors and anodes of the valves in the older TVs. I remember being walloped so hard, it actually knocked me back from my chair and I ended up at the other end of the room, but that is what 26000 to 28000 volts will do to you when you least expect it. LOL

This forum is so full of men after my own heart. :-)

Ken, I don't think I have 5 pin sockets for the 807 any more but definitely not the AM rig. Too much stuff in the shed.
I still have octal, loctal and 7 pin miniature sockets though.

No fancy trannies in the modulator, I used a mains transformer with a 375V a side centre tapped winding to the two plates, centre tap to 500V. The mains winding to the transmitting final a 6146. Output was about 60W. Not sure where the 100W  memory came from

I think I had a proper audio trannie supplying the grids from a 6AQ5. The 807s were running in zero bias and the screens tied to the plates with the tubes running as triodes. 65 years ago!
Some of the hams here might remember the Geloso VFO which drove the 6146.
Wonderful memories, back when everyone built their gear.

I'd better stop before I bore you all.
Cheers from the SE Ken,
John

"Real" electronics is never boring John, but modern digital and microcontroller electronics is getting more and more boring with time.

It has come to the same stage as PCs came to in the 1990s, where they cannot make their mind up what is good or not so good, and there is a huge mis-match of microcontroller boards out their that most users do not have a clue, or care, what actual microcontroller it contains, and then it is almost certain to be yet another flavour of Arm that will go out of favour in a few years and on the the next one that makes rip-off merchants more money for using other people's skills and software etc...

Also. With the languages now, we are actually back in the realms of the 1980s! With interpreted languages and cumbersome object languages that should have no place anymore. Then the linux boards that are used to flash an LED, or display "Hello World" on an LCD! When a single microcontroler is more that capable of doing the job, but that would require "real" skill and control, and not just knocked up in a weekend using other peoples libraries that they do not understand, and sold to the "buzz word" idiots out there. So faster and faster, and more expensive and power-hungry microcontroller need to be developed to cater for the extremely inefficient languages. Just like the late 1980s and 1990s! Whereas, if they hade created the software with more efficiency, as they did in the early 1980s, there would be no need for stupid speed microprocessors/microcontrollers or stupid sized RAM and NVM etc... 

OK..... Rant over. :-)

Once I have my workshop completed (I know I keep saying that, but funds are tight and health not so good, so I cannot just jump into it), I will get back into "real" electronics with, maybe, a splash of microcontroller to control it.

I've been pleasantly surprised recently by a couple of industrial customers asking for purely analogue electronics. In one case it has been a number of signal processing boards with frequency response shaping and out-of-band filtering for the 100mHz - 1kHz frequency range.

In another case a low voltage source and current measurement circuit with a peak hold circuit for a fuel cell testing machine. In both cases no digital processors were used so there would be no 'update' issues over the life of the equipment and/or if I fell under a bus...

It occurred to me I probably could have designed something similar at the start of my career, but it was quite nice to revisit those skills today and I'm sure I did a more thorough job in the light of gained experience.

Quote from: John Lawton on Jun 27, 2023, 03:18 PMI've been pleasantly surprised recently by a couple of industrial customers asking for purely analogue electronics. In one case it has been a number of signal processing boards with frequency response shaping and out-of-band filtering for the 100mHz - 1kHz frequency range.

In another case a low voltage source and current measurement circuit with a peak hold circuit for a fuel cell testing machine. In both cases no digital processors were used so there would be no 'update' issues over the life of the equipment and/or if I fell under a bus...

It occurred to me I probably could have designed something similar at the start of my career, but it was quite nice to revisit those skills today and I'm sure I did a more thorough job in the light of gained experience.

John your story made me smile, your analogue devices may still be working long after memory failure has rendered a microcontroller solution useless. I suspect many users of this forum are quite at home in the analogue world.
Ken K

Our rebuilt Colossus computer uses 807's when a hefty pulse s needed to drive several circuits: resets etc. We have loads of 807's in storage at the museum. I thought about a guitar amp but never got round to it. There is something wonderful about the warm, musty smell of 2500 valves quietly beavering away.

Les, did you ever get that oscilloscope working; I sent you a small CRT?

Happy memories.

Charlie

Hi All,
I still have the ability to do valve simulations via an old version of Protel's CircuitMaker 2000.  It came with a modest collection of valves and one finished circuit example as attached.
I don't think it supports multi-tapped output transformers so I can't do an ultra-linear output stage.  They also ignore transformer leakage inductance and inter-winding capacitance.
I think I'd draw the line at 2500 valves in a logic circuit.

Cheers,
David

Hi David
Impressive!
LTspice also works fine with tubes, the device models can be placed on the schematic this saves placing them in the library and they are much easier to edit. Enclosed is a working file. The 6V6.txt should be changed to 6V6.asc to run in LTspice.
One day I should post a PIC powered auto bias, clipping light and power display project to one of the tube audio forums, must be about number 300 on my list of things to do. Try and beat an Arduino project for once.

Find vacuum tube spice models here  https://www.diyaudio.com/community/threads/vacuum-tube-spice-models.243950/
transformer model data also on same site. Caution some tube models don't include grid current and some are just bad.

Ken - I will have to simulate your circuit with my package.  I'm curious about the plate to grid feedback so will give it a go.

My vacuum tube swan song was a hybrid PA amp using push-pull, parallel EL34s (4 tubes) driven by a transistor front end running a -90V rail.  I was young and stupid in those days but I'm much older now.  Sadly I never got to put the amp through its paces.  I heard later from a workmate that it was producing close to 300W but I'm not sure they really knew how to measure it.
It's an interesting thread Ken - nothing to do with PICs but most interesting.

Cheers,
David

Quote from: david on Jun 29, 2023, 03:08 AMKen - I will have to simulate your circuit with my package.  I'm curious about the plate to grid feedback so will give it a go.

My vacuum tube swan song was a hybrid PA amp using push-pull, parallel EL34s (4 tubes) driven by a transistor front end running a -90V rail.  I was young and stupid in those days but I'm much older now.  Sadly I never got to put the amp through its paces.  I heard later from a workmate that it was producing close to 300W but I'm not sure they really knew how to measure it.
It's an interesting thread Ken - nothing to do with PICs but most interesting.

Cheers,
David

Your EL34 amp sounds like a beast. It is possible to get 100W out of a pair of EL34's the big trap is the screens will get red hot and be destroyed by a continuous sinewave at full power, one must use burst testing at high power levels, many a good EL34 has been destroyed by testing.
It is worthwhile  down loading LTspice the file I posted it should run fine. LTspice is very popular and free.
Re Schade feed back (plate to plate) some love it some hate it. It can give triode like performance from a pentode. Open circuit output on a straight pentode amp with no feedback can destroy the output transformer with high voltage as pentode is essentially a current drive, schade feedback can reduce the output impedance such that the open circuit voltage is quite controlled and the output Z quite low. The driver tube has a much steeper loadline when the feedback is applied, this needs to be taken into consideration. Running FFT and looking at the harmonics in spice is worthwhile.
Keep Well
Ken K

This is an excellent thread, with true electronics experts that I take my hat off to. :-) I just wish I knew half of what you people know about electronics.

And I say again. "A work of art" Ken.

Hammerite paint brings back so many good memories of my younger days, but we always used the blue hammerite.

Quote from: top204 on Jun 29, 2023, 11:23 AMThis is an excellent thread, with true electronics experts that I take my hat off to. :-) I just wish I knew half of what you people know about electronics.

And I say again. "A work of art" Ken.

Hammerite paint brings back so many good memories of my younger days, but we always used the blue hammerite.

Thank you for your kind comments regarding the 807A amplifier. I agree with you regarding the many experts that we have on this forum.
Ken K