[Boatanchors] PS for tube stuff: Follow up

[shoppa_boatanchors at trailing-edge.com]

"Eugene Hertz" <ehertz at tcaf.org> wrote:

> Follow up question about power supplies for experimenting with tube gear...
>
> I was looking through some tubes I had for possibly building a cw transmitter.
>  I had the following tubes that I had collected
>
> one 813
> two 211 (VT4C)
> one 250th (it just looks so cool!) 
>
> I then looked up some of the plate voltages/current of these and boy!
> Looks like I need a 2KV supply for the 211's for example (anyone 
> have a simple push pull cw circuit that uses 211's?)
>
> So I went to epay and did see some HV supplies, 2KV, 6KV 10KV etc.  
> So do you fine fellows use bench supplies that high to experiment 
> with transmitter/amp circuits or is it just simpler to build an HV supply?

Watch the current ability too - many 2KV, 6KV etc. supplies are for
lab use in powering photomultipliers etc. and have current capabilities
of just a few mA.

You pretty much just build a HV supply.  Sometimes for tinkering it's
easy to "borrow" an existing HV supply.

> ONE LAST QUESTION!
> Seems some tubes want DC filament voltages and some use AC? 
> I would have thought that AC would induce a 60hz hum onto the 
> signal, no? Can one use DC on a filament rated for AC? Pros? Cons? 

Many 1.5V and 3V filament tubes (e.g. 1H5, 3Q5, 1R5, 3V4) were indeed
designed for operation off of DC batteries.  In reciever use putting
an AC filament voltage on them would indeed induce a lot of hum.
In transmitter use it's not gonna make any difference.

Putting DC on a filament is occasionally done but for rather
specialized low-hum purposes.

> Ok, I lied, one last last question.  What is "getter"?!

The metallic coating on the inside glass of a tube to "soak up"
any residual air/gas from manufacturing.  If a lot of air gets
in (cracked tube, bad seal) the getter turns a powdery white.

Tim.