Re: Re[2]: LF: Valve LF amps and tank coil size / voltage rating?

[Andy Talbot <andy.g4jnt@gmail.com>]

Yes, but that's all an engineering problem. I'm sure the wire probably exists.   I've never played with a valve since dabbling in old TVs of the 1970's era, and never high power stuff.

However, I have built a highly reliable 700 Watt PA, running direct from rectified mains (340V DC).http://www.g4jnt.com/137tx.pdf    OK, I blew FETs designing it in the first place  - but even in the early noughties when I was doing it, those FEts only cost a couple of quid each.  And once proven, I could replace with bigger FETs that nowadays even those cost peanuts.

That direct-from-mains supply could be expanded and at the time I was visualising a 2kW version, but had to see sense considering the smallness of my garden and the possibilities for fires and things.  I already lost a plastic shed housing the loading coil from running the 700W thing.  http://www.g4jnt.com/Melted_ATU_Cabin.JPG

Andy  G4JNT

On 14 November 2015 at 20:00, Chris Wilson <chris@chriswilson.tv> wrote:

Hello Andy,

Saturday, November 14, 2015


OK, but what about wire breakdown voltages? In all the big air cored
LF tanks I have seen the windings are well spaced on ceramic, or
Paxolin type grooved formers, how do I know a close wound toroidal
coil won't break down?


I have built a few HV supplies using decent industrial quality iron
cored transformers, the biggest is 5kV at 1.5 Amps, which can also be
fed from a 40 Amp Variac, to drop the primary down. I use that in my
workshop for running a glue drying machine.

I was also gifted some NOS ceramic triodes, some US, some Russian, and
would consider having a bash at a valved LF amp, just "because" :) I
have to say my limited experience of ceramic triodes has shown no
unreliability, in fact a zero failure rate so long as they are
gettered before use, if they have lain dormant for years.

I do have a reasonable collection of failed FET's though :) In
fairness user error was the demise of most of them.


Thanks Andy.


> I'll say it againV = 4.44.F.N.A.B  (all SI units)


> THAT is how you size ferrite cores.  It tells you more or less
> everything you need to know to make ferrite transformers.  Keep B to
> less than 0.1 at these frequencies


> But.. why would you want to use valves?
> Expensive, unreliable, high voltages...


> 'jnt








--
Best regards,
 Chris  2E0ILY                          mailto:chris@chriswilson.tv