Re: Marx generator (fwd)

["High Voltage list" <hvlist@xxxxxxxxxx>]

Original poster: <sroys@xxxxxxxxxxxxxxxxx>



---------- Forwarded message ----------
Date: Tue, 22 Nov 2005 09:07:51 +1300
From: Malcolm Watts <m.j.watts@xxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Marx generator (fwd)

Hi Herwig,

On 21 Nov 2005, at 11:55, High Voltage list wrote:

> Original poster: <sroys@xxxxxxxxxxxxxxxxx>
> 
> 
> 
> ---------- Forwarded message ----------
> Date: Fri, 18 Nov 2005 13:11:52 +0100
> From: Herwig Roscher <herwig.roscher@xxxxxx>
> To: hvlist@xxxxxxxxxx
> Subject: Marx generator
> 
> 
> List,
> 
> I have just finished building my first Marx generator and I am about
> tuning it.
> 
> Capacitors			3.33 nF
> Resistors			2 MOhm
> Stages 			25
> Loading voltage	20 kV
> Spark gaps		0.28"
> Erected C			133 pF
> Bang voltage		500 kV
> Bang size			16 Joule
> Discharge length	13.4"
> 
> However I would like to ask the more experienced builders for some
> help:
> 
> Q1:
> The distance, a voltage of 1 kV can jump, usually is said to be 
> 0.013". For Marx generators I found values of about 0.04" as well.
> 
> Other Marx builders claim:
> 
> 0.052"		Rapp
> 0.045"		Steve Ward
> 0.052"		Kronjaeger
> 0.050"		Mike Gilchrist
> 
> My system jumps only 0.027"/kV. Why? Is this a question of the form of
> the electrodes?

I built two some time ago. The caps were about 7nF each, dry-fired 
rolled poly. In theory, mine should have been 250 - 300kV when 
erected. The uncertainty is in the gap firing voltage/s. I got about 
7" sparks. I was using chokes instead of resistors for charging. 
Total energy was about 14J.
 
> Q2:
> Other Marx builders get:
> 
> 1.75"/Joule		Rapp
> 1.92"/Joule		Steve Ward
> 1.83"/Joule		Mike Gilchrist
> 
> I only get 0.9"/Joule. Again: Why?
> 
> Q3:
> During and after completion of the bank loading there is no sizzling
> noise. Therefor I assume, that there is little or no corona at 20 kV.
> Is it possible, that at ignition of the bank there is too much corona
> at 500 kV?
> 
> What are the secrets of Marx tuning? Any help would be appreciated
> very much.

Gap settings are rather critical. Ideally the it should erect from 
bottom to top. I didn't bother with triggered gaps. 

Malcolm