Shunt Reg Using a 13E1 as Shunt Element

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Paul Barker
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#61

Post by Paul Barker »

Sadly the published tetrode curves for the bigger which you like only show graphs at 600v anode voltage. though they do have one set of characteristic curves where you could pick your anode voltage (pg 4) the grid lines are only shown for currents in excess of 100mA.

they seem to use 100v on the screen.

We could probably derive by experimentation an operating point we could use by starting very negative grid voltage and adjusting towards positive until the valve conducts and stopping at 60mA.

At the end of the day that is all we are doing anyway, adjusting the wiper to 60mA measured through the 75C1. So we could take almost any pentode capable of the dissipation (17 watts) from the cheap and humble 807 to the 6550.
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#62

Post by Cressy Snr »

Well from a practical perspective, a pentode with some characteristics that we can reasonably "get at" would obviously be a better bet than trying to
"underrun" a whacking great industrial valve.

It was just that I liked the look of these things. Totally irrational really, but an education in "reality"

The more practical power pentodes I have are PL519, PL509, 5881, EL84, 6P25 (EL33) 807 and Ant has a couple of spare KT88s I think.
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#63

Post by Paul Barker »

the 519 and 509 are probably highest transconductance from that list. So in theory they are the best.

I was thinking that the 13e1 was a waste of heater power for this application.

The lowest power valve which fits the bill would be best. Of the list I gave that would be the 807.

I'll check the pl509.

There is one proviso that all the supposedly correct valves which we have looked at such as 12e1 13e1 pl509 pl519, they all have a reputation for parasitic oscillation.

Nick reported problems with the 12e1, and I had bizar results from it, which I could attribute to very old resistors I was using but it may have been parasitic oscillation.

The other angle of attack is to use DHT's like 300b 6b4g gm70 etc.

I did a brief scan earlier 300b would control 60mA up to 450v 6b4g 40mA up to 435 v. I didn't get round to looking at gm70 or 813.
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#64

Post by Paul Barker »

the pl509 is quite capable of the power level. the characteristic curves are drawn for anode currents upwards of 500mA so not much use to us.

If we used 150v on G2 we should be able to rein the current down to 60mA within the 75 volts we have available. I would start off at -75v grid potential to cathode (which means your grid has to be grounded, see what current it pulls and work up a voltage devider from there. At -40v on G1 it would pull 250mA, at -20v it would pull 700mA. So with luck somewhere between -40 and -60 we would arrive at 60mA.

Whether it will prove sufficiently stable in this service remains to be seen.

It is uncharted territory for me. I have never used these sweep tube valves.
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#65

Post by Cressy Snr »

Hi Paul you're going to kill me for this!

But.....I have just found in my boxes a pair of Tungsram OT100 transmitter triodes that I had completely forgotten about.

They are electrically the same as the RCA 8005 which I have attached below.

Image

I know it is right in the bottom corner
but let's say between 100 and 150V was allowed to drop across it
then a positive grid voltage of +20V might just give the 60mA we are looking for. :oops:
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#66

Post by Cressy Snr »

I also have a pair of 813s

and looking at the triode curves for it, by extrapolation it looks as if 120V dropped across it will give 60mA with maybe +15 - 20V on the grid?

Image

I have the UX4 sockets for the OT100
and the special septar ones for the 813.

Mind you the 813 has a 50W filament
and the OT100 a 30W filament


I'm going to hide out of your way now :shock:
Last edited by Cressy Snr on Sat Dec 31, 2011 7:01 pm, edited 1 time in total.
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pre65
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#67

Post by pre65 »

Something like an 807 would be a lot easier to heat. :)
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#68

Post by Cressy Snr »

pre65 wrote:Something like an 807 would be a lot easier to heat. :)
Not arf!

With a triode-strapped 807 dropping 100V across itself, a couple or three volts positive bias would give 60mA too.

He's gonna murder me :cry:

Image
Last edited by Cressy Snr on Sat Dec 31, 2011 7:19 pm, edited 1 time in total.
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#69

Post by Paul Barker »

i'll get my coat :arrow:
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#70

Post by Cressy Snr »

Paul Barker wrote:i'll get my coat :arrow:
The moral?

never work with children, animals or

Steve Cresswell

Not if you want to stay sane that is :oops:
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#71

Post by Paul Barker »

If going triode I would use the 6080 wot we already designed.

If going pentode I would go with 807.
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