6080 Output Transformerless Power Amp ?

[neon indicator]

yes. Absolutely save money, heat, valve life longer and less interference...

It likely there is no advantage to DC on the signal valves (tubes is American) either, and if there is it has to be regulated. Not just a capacitor and bridge. See Schematic above.

Personally I'd only run direct filament/cathode valves on DC. Perhaps just maybe the preamp for a true raw condenser mic (not electret or integrated modern one) or ribbon mic I might test to see if it makes any difference.

[Stevie342000]

Right got it.

The regulated power supply is for the input/pre/driver stages of the amplifier and its heater is biased to 175V dc from main 550V HT supply.

Which I will stick with and drop the DC for all other heaters.

I know DC shortens life of the tubes/valves on heaters, does it not poison the cathode and stop emission of electrons?

I thought that the volts in on the dc heaters was low anyhow, I mean if you put in 6.3V AC you get more than a drop of 0.2V (that was for the driver section heaters).

And there will be enough of a drain on the 25V 5A heater supply for the output tubes/valves as it is, not to mention heat.

But 25 volts is within permitted tolerance for heaters, slightly under should give them a bit longer life but not much.

[Stevie342000]

I know tubes is American I was being sloppy with my English terminology.

[Stevie342000]

When you say "direct filament/cathode valves" you mean like 2A3 or 300B or 845, which strictly speaking do not have a cathode as they are directly heated as opposed to a 6080 which is an indirectly heated thermionic device.

[neon indicator]

UK Voltage tolerance of 230 V +10%/−6% (216.2 V to 253 V), widened to 230 V ±10% (207 V to 253 V) in 2008. (Formerly Nominally 240V 6%).

So the 25VAC can be 22.2V to 27.5V in theory, plus tolerance of transformer...

But it's rarely that high.

The heaters have a tolerance (varies with valve type).

Why 6.3? 2 x 6.3 = 12.6V, handy rechargeable Lead Acid battery when people had no mains.

Except batteries vary from about 10.5V (nearly flat) to 13.6V (fully charged) and even 14.2V (calcium Lead acid zero maintenance fully charged on charger).

But 34V x 10 % = 37V (bridge + capacitors) compared to worst case 27.5...

I know DC shortens life of the tubes/valves on heaters, does it not poison the cathode and stop emission of electrons?

If the voltage is correct DC wouldn't shorten life of heaters.
Cathode poisoning is complex issue. It's usually due to contamination in valve at manufacture. One theory is that if heater is run too cool this is more likely to happen. But I don't known that's it's proven.

One opinion
http://en.wikipedia.org/wiki/Hot_cathode#Failure_modes

How Valves work
http://www.john-a-harper.com/tubes201/

[Stevie342000]

Ok right.

What I may have meant is that cathode poisoning is a result of heater voltage being outside of specified voltage tolerance for the tube/valve.

Especially so if the heater voltage is DC.

As for tolerance of mains voltage it was never spot on 240 Volts it is the same tolerance as it is now.

The EEC regulation made allowances for the variations in voltage due to load and demand so that no country had to change its generating equipment to come in line with the EEC regulation on voltage supply.

I asked the question of a transformer manufacturer some years ago when I first became aware that it was going to change. He reliably informed me of the changes and its affects.

In other words it changed on paper but not at all in reality. Besides which it is off topic and not what I was asking about.

[Stevie342000]

So we have now established that I need an AC or DC supply of 24 or 25 Volts (dependent upon what I can get transformer wise) at 5A.

I asked the question about the gauge of the wire, is 18AWG enough to carry that amount of current?

[Stevie342000]

However I am intrigued by the maths and do not remember which law/equation it is that is being used to calculate this.

If I am understanding it correctly from the example I used:

In that there are 8 tubes/valves with a heater voltage of 6.3V needing a current of 2.5A per tube/valve.

They are in two series chains of 4 which are being operated in parallel.

1. If you had one set of 8 tubes your current demand would be 20 Amps at 6.3V.
2. If you had a series chain of 4 tubes their current demand would be 10A at 25.2V
3. However two series chains of 4 tubes in parallel uses half the current.
4. Which poses another question for me, I can see that if you ran the 8 tubes/valves in series that you would end up needing 50.4V but what would the current demand be?

Those are all nominal voltages of course.

[Sean Williams]

Cor Stevie, you are making hard work of this.....

Where various items in a series chain all have the same voltage and current rating, the series current will be the same - ergo.....

4 valves 6.3v 2.5A heater - 2.5A will flow, at around 24v.

8 valves same as above - 2.5A will flow at aroind 50v

16 valves same again 2.5A at around 100v

32 valves, same again 2.5A at about 200v...... the same goes on and on and on....

Parallel circuits......

6.3v 2,5A valve

1 valve 6.3v 2.5A
4 valves 6.3v 10A
8 valves 6.3v 20A
16 valves 6.3v 40A
32 valves 6.3v 80A

Does this make any sense?

Sean

[Stevie342000]

Yes maths is hard work to those that were taught badly.

What may seem simple to you does not compute in those that come up against a brick wall when what is obvious to the other is simply stated to those that do not understand.

Besides which what happens if you have two parallel strings of 4 tubes/valves in series.

The current demand halves right!!!

Yes all obvious got that a long time ago.

Just like two equal value resistors that are in parallel then.

Yep might be making hard work of it but how are we to learn if we do not question, challenge and answer. Learning does not stop the minute you walk out of the school, college or university gate.

[Stevie342000]

Sean Like the bit at the bottom of your post about CO2 but think you made a slight mistake, take out people then there is no CO2 or man-made climate change at all then.

A much better solution for the planet. I have a degree in Environmental Science.

[neon indicator]

For heaters or resistors that must run at a constant power:

Series: Voltages add, current stays the same.

Parallel: currents add, voltage stays the same.

Power (heating) in Watts = Volts x Amps (hence VA, though VA can mean volts and current not in phase, so heating in Watts may be less than AC "VA" rating)

Resistance in Ohms of Heater (constant at a particular temperature ) = Volts / Amps

The total power of all the Heaters is always number of heaters x (current x volts of one heater).

Thus if you make a series chain you must add the volts and the current MUST be the same as one heater as they all share the same current, no matter what voltage you put. (if you put 1/2 the voltage the current would be half and the heaters too cold as they would be 1/4 power).

If you put EQUAL numbers of chained heaters (series) in parallel, then each chain has same resistance and same current and same voltage. Thus the currents in parallel add, but the voltage is the same as one chain. The power is always sum of all heater powers if each heater has correct voltage.

"heaters" are just nearly Resistors.

When cold they are slightly lower resistance than hot. But if they have correct voltage, then each 6080 heater for mathematics is exactly a 6.3V / 2.5A resistor = 2.52 Ohms

If you put less voltage it will cool and resistance will be a little lower and if you put more voltage the resistance rises a little. So effect of the + & - 10% variation on the actual heating power is slightly less than a perfect resistor would be.

Heaters are just slightly less than perfect high power resistors.

[Stevie342000]

Thanks that is what I wished to know, as long winded and complicated as it may have been. I got the answer I wanted and it was a WHY question.

I got what happened when you did series/parallel heaters but did not know why?

We/I got what I needed i.e. 25.2 volts at 5 amps but I did not get the why I needed that. As I was not understanding what happened with the parallel/series arrangement in electrical terms. Thus it was a WHY question and because answer which I get completely.

[Stevie342000]

So and finally Wire Gauge question (heads up) is 18 AWG thick enough to take 5 Amps current or is it quicker for me to go look it up?

[glowinganode]

18AWG sounds a bit light.
I'd use 16AWG, or 1.5 mm.sq if you prefer.
Rob.

[Sean Williams]

Sorry Steve - thought you hadnt grasped the series/parallel chain idea - didnt realise you were after a spot of Ohms Law explanation....

The post prior to my first one shows that you have series and parallel mixed up.

Oh, and we still have animals, and CO2 as a result of biodegradeables, but thats a subject for a completely different forum!

Cheers
Sean

[neon indicator]

The 18 SWG only needs to take 2.5A. Wire each chain and then bring back each of the two chains to the common heater terminals. Then 18WG is fine.

[Herald1360]

Current wise, 18SWG is 1.2sq mm which is good for at least 6A. Resistance is about 15milliohm per metre so volt drop will be negligible provided TX is on same chassis as valves.

18SWG will be fine, however you arrange it!

[Stevie342000]

I thought it was related to Ohms Law.

What are the other Laws from electrical/physics point of view that I should know which would help me with my maths?

The point being that if it helps me then it helps others who are new to the subject of DIY, electronics, valve/tube technology.

I know who they were i.e. Faraday, Maxwell but it is a long time since I did what is essentially basic physics.

But if the maths was weak my understanding of physics was not as strong as it should.

Having had a bad maths eduation (and make that English as in grammar as well) but always a passion for electronics which was never really fulfilled. My working life so far may have been very different if I had had a better education in literacy and numeracy.

Or do I need to go back and do some reading? I have an old 'O' Level physics book which I had from school or college.

[Stevie342000]

Sean

Nothing wrong with animals never said that there was but you got natural CO2 cycles mixed up with Human CO2 cycles which it could be argued are not natural although we are part of the natural system.

You see me thinks the planet would be a lot better off with out humans but you are right it is a topic for another forum.

But to argue the point and try to keep this in subject area physics, biology and chemistry are part of our attempts understanding the natural world. In an effort to make sense of it all, life the universe and everything.

Although this is diversion from topic and from subject area of the forum it was a note, comment on your tag, which frankly amused and lead me off in another direction. Always had a wandering mind, never lack ability to challenge but was never challenged which perhaps is why I struggled with numeracy and literacy.

That and teaching methods, oh and the fact that really although I get great fun out of inter-action with people I really do not like people.