[Amps] Fw: "Tubes 201" - How Vacuum Tubes Really Work

Wed Jul 26 07:19:33 EDT 2006

I can say for sure, as an eye-witness, that testing the overload "crow-bar" in Telefunken 100 kW transmitters (RS 1896)
using a 0,2 mm silver wire takes a lot of courage...

Otherwise, the botton line of this discussion appears to be that the "crow-bar" circuit using thyristors or ignitrons
is hard to beat for preserving the tube "innards", as it short-circuits the plate voltage in an early stage of an overcurrent
event. The majority of the fault energy is then dissipated in devices that are far more robust than any power grid tube.

It also appears that most modern power grid tubes are very robust, as a "glitch resistor" usually will absorb sufficient energy to prevent destruction of the grids and cathode. 

Preferences of individual design teams seem to govern if the "glitch resistor" or "crow-bar" route is taken. 
Collins used the "crow-bar" on the 204J-1, but not on the 208U and HF-8022, Philips and Telefunken used ignitron
"crow-bars" in their 30 and 100 kW systems. 

I'm not exactly sure whether the Marconi H1140 and H1141 used ignitron "crow-bars"

Finally, the "flash-overs" in high-power tubes is something we probably have to live with.
I have yet to see a 4CX10000D "out of the box" that will not trip the overcurrent relays a few times
during initial operation.

73/

Karl-Arne
SM0AOM

----- Original Message ----- 
From: "Peter Voelpel" <df3kv at t-online.de>
To: <amps at contesting.com>
Sent: Tuesday, July 25, 2006 11:33 PM
Subject: Re: [Amps] Fw: "Tubes 201" - How Vacuum Tubes Really Work

Hi Will and the group,

OK, I will scan it as it is and load it up tomorrow.

You will have a hard time to find the book, it is called bei Siemens
"Sende- und Genaratorröhren Hochspannungsgleichrichter und Stromtore"
My edition is from 1966.

Here we are with the translation of the most important parts and my comments
following |:   

6. Safety measures

For the use of transmitting tubes certain safety measures are necessary,
which use is mandatory for warranty claims.
They consist of automatically working safety- and trip devices which safe
the tubes from destruction in case of failures.

For the safety of the tube against arcing, beside over current trip of the
HT supply, a means of fast cut off of the anode voltage is necessary, which
provides a fast disconnect from the electrode voltages.
By means of a simple test wire it has to be tested if the quick trip circuit
fulfils the requirements of the fast disconnect of voltages.
For this purpose a small copper wire, of the diameter given in the table,
must be used to short the anode voltage right at the anode electrode.
If the copper wire is not melted the circuit can be used. Also if the short
is present while the anode voltage is switched back it must not melt.

| for me it works very well with my YL 1056 amp (two tubes), the overcurrent
sensor in turn fires the thyristors across the anode voltage without melting
a 0,1mm test wire. 
The 3-phase power supply is 4KV 4A CCS

A few examples of the table:

tube    copper wire diameter

RS 1001    0,16mm
RS 1032    0,13mm   
RS 1052    0,13mm
RS 2041    0,25mm

| The RS2041 is a tetrode with 220KW of dissipation running 18KV 60A
maximum!

Beside that measure there has to be a safety resistor of 5 to 25 Ohms, to be
installed into the B+ line from the HT supply, which absorbs in case of
arcing the energy of the capacitor bank and by this means, the requirement
of the quick disconnect for the test wire condition fulfils.
The anode voltage may be switched in again after 100mS earliest.

The grid circuit also requires safety measures to prevent consistent arcing
in the tube, when a separate bias supply is used, after an arc was developed

| I understand it as when the grid is not strapped to ground

This measure works with an additional resistor of about 50kOhm which must be
switched in with help of the anode over current relay.
Additional safety is reached when this resistor can also be switched in by
an over current relay in the grid circuit.

Against thermal overload of the anode, when made for forced air cooling,
tube fuses were developed which in conjunction with a pull switch cut off
anode and heater supply voltage.

| I am using such a fuse on my YL1050, it is screwed into the anode cooler
and holds through some litz wire the pull switch closed, when the
temperature rises above the critical temperature, the wire is released from
the switch in the tube cooler and the pull switch opens and interrupts the
voltage to the mains relay coils of the transformers.

73
Peter

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Will Matney

Peter,

That's ok. I wouldn't want to ask you to translate it as that would be too
big of a job. I wish they had an English version, I'd buy it if I could find
it for the info.

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