Loadlines

[david C]

thanks Guys
this could be interesting,

so by running the heaters on a separate circuit I'm floating them,
yipee I've learnt something,

[Darren]

David, you can still float them using the mains trans. I just used a battery to separate and hopefully give a clearer picture.

[david C]

thanks Darren,
I understand, so my AC heaters off the mains tx are floating,

[Darren]

I've not seen your circuit, are you using a DHT or a IDHT valve?

But yes it prob will be.
My 833 heaters are not floating because there is no cathode resistor and it's a DHT.

[david C]

if you took my Loftin White for example,
it has 2 ECC83s and 2 2A3s,
the ECC83 6.3vAC from the mains tx and the 2A3s are 2.5 AC from their own txs,

[Dave the bass]

Ok, its been suggested that we have a go at describing load lines. The link suggested

If we did have a go at this, what would people want?

Maybe a set of lines, then a description, then any questions, then more descriptions. What peeps views on this?

Or should we go further back and start with the basics, current, voltage, resistance, capacitance, inductance?

Sorry for the late response, my step son got back from Reading Festival with a fractured thumb collected in the 'moshpit' and was on the PC all last night telling his mates how he did it I dunno, yoof of today...I never damage myself!

Valve school...

Yeah, I think basic lessons are the best place to start and if you've got time and inclination set simple tasks (like solve the following <insert problem>) then we could post answers and see if whats being explained has sunk in .... good idea?

I'm prolly the same as others, bought the Rozenbliztenbuger and MJ books but without that 2 way communication it's just not going in. TBH I've picked up more from chatting with you blokes here on this and the WD BB than I have from the books. Building stuff has helped a bit but I'm still floundering on even the basics.

DTB

[Darren]

if you took my Loftin White for example,
it has 2 ECC83s and 2 2A3s,
the ECC83 6.3vAC from the mains tx and the 2A3s are 2.5 AC from their own txs,

The ECC83 is an IDHT so yes it would float unless you grounded the neg of it's heater.

The 2a3 is a DHT but it still floats as the cathode resistor raises it's heater neg above ground by the same amount as the bias voltage set by said resistor. You could put the cathode resistor on the + of the heaters and ground the neg to earth. Then it would not be floating.

Floating is one way to isolate hum circuits, or at least that's the theory. Doesn't always work, but then that's hum for you.

[david C]

thanks Darren

[Nick]

You could put the cathode resistor on the + of the heaters and ground the neg to earth. Then it would not be floating.

Hang on, you would have also shorted the cathode resistor out, and possibly removed any bias from the valve. So that would be a bad thing (IMHO).

[Darren]

Ah yes, quite right, the easiest path would then be straight to ground and not via the cathode resistor.

Good point Nick, that's what comes of suggesting something one has not tried in real life. Otherwise I'd have known...!!

Thanks, saved me finding out the hard way, which would be quite normal for me..

[colin.hepburn]

Thanks for that view steve, I think you are right, but to take up a point, maybe it might show a problem.

On the question of what is current, voltage and resistance.

The problem is that once you understand those three terms, then the rest should fall into place. Maybe thats a result of my equivilant to dyslexia. I can't remember things, never have done. But I can work them out, I could do maths and physics at school, coz you didn;t need to remember, you could always derive the equations. Couldn't do chemistry, as that needed memory.

Now my point with this reference to my schooling, is that if you know what E, I and R are, and their relationship in Ohm's law, it all can be worked out. Once you add both of Kirchhoff's laws to that, just about any DC circuit can be analysed.

My question is should we start with that, as IMHO, once they are understood, then the rest, especially load lines fall into place, but without them, its all guesswork.

Example question: Why does the slope of the tangent to the grid curve at a chosen operating point equal the plate resistance? Answer, cos its just Ohm's law. But I am not sure how clear that will be untill its understood that resistamce is just the third part of any relationship between current and voltage.

I hope you see my point.

Hi All
I have found this ohms law calc which will probably be a good start in all this stuff
Current, Power, Resistance, or Voltage.

http://www.the12volt.com/ohm/page2.asp

[pre65]

Hi Colin-thanks for that link.

Here is one i use for resistor and capacitor calculations,see under the calculators sub heading.

http://www.electronics2000.co.uk/

[colin.hepburn]

Hi Phillip
Thats a Handy set of Calcs in that link
Cheers

[colin.hepburn]

Hi All
heres some more usefully info for the first time amp builder probably covers most of the basics plate voltage's/cathode currents etc http://members.tripod.com/~gabevee/mytubamp.html

[simon]

Just read John Broskie's latest blog which explains loadlines...

http://www.tubecad.com/2007/10/blog0122.htm