One for the valvies 2/2....
 

On Sat, 6 Nov 2004 17:44:25 -0000, "Mike Gilmour"
wrote:

With the normal drive voltage of 25kV there were no detectable x-rays.
at 30kV the anode glowed cherry red, and they poured out. 30kV was
just part of a stress test - not a normal operating condition.

d
Pearce Consulting
http://www.pearce.uk.com

I'm fascinated :-) Of what duration were the tests? Did you get much
corona discharge/ozone smell? Any flashovers during tests?

Thanks,
Mike


The test was run for about ten seconds. If you left it on for more
than twenty, there would be a sucking sound and the valve would gently
collapse in on itself. As for ozone - yup, plenty of that. We didn't
really know how poisonous it was then. Flashovers happened, but they
were generally more to do with bad transformers than valves.

We had a specific flashover tester that would induce flashover at any
selected point during the scan. A couple of big metal spheres were
connected to ground and EHT. The ground one had a small extra
electrode like a spark plug set into it, and when we wanted a
flashover, a quick burst of high voltage on this electrode would
provide enough ionisation to seed a big flash from EHT.

d
Pearce Consulting
http://www.pearce.uk.com

One for the valvies 2/2....
 

"Don Pearce" wrote in message
...
On Sat, 6 Nov 2004 17:44:25 -0000, "Mike Gilmour"
wrote:

With the normal drive voltage of 25kV there were no detectable x-rays.
at 30kV the anode glowed cherry red, and they poured out. 30kV was
just part of a stress test - not a normal operating condition.

d
Pearce Consulting
http://www.pearce.uk.com

I'm fascinated :-) Of what duration were the tests? Did you get much
corona discharge/ozone smell? Any flashovers during tests?

Thanks,
Mike


The test was run for about ten seconds. If you left it on for more
than twenty, there would be a sucking sound and the valve would gently
collapse in on itself. As for ozone - yup, plenty of that. We didn't
really know how poisonous it was then. Flashovers happened, but they
were generally more to do with bad transformers than valves.

We had a specific flashover tester that would induce flashover at any
selected point during the scan. A couple of big metal spheres were
connected to ground and EHT. The ground one had a small extra
electrode like a spark plug set into it, and when we wanted a
flashover, a quick burst of high voltage on this electrode would
provide enough ionisation to seed a big flash from EHT.

d
Pearce Consulting
http://www.pearce.uk.com

Adds some excitement to routine testing - except for the poisonous ozone
that is ;-)
I'm not surprised the transformers went, LOP's were always a seat of
problems under normal conditions (called IHVT on schematics now I believe -
why change what everyone knows?) Some sets run at around 30kV now I
believe. It's been a while since I've worked on TV's ( Did repair TV's on
ships from time to time & I worked for Redifusion whilst on leave repairing
TV sets because I got bored with too much time off living it up!).
Many shipborne radars had particularly vicious EHT's as I once discovered
on changing a CRT after the normal discharge procedure - I usually avoid the
EHT point on the CRT due to it 'recharging' - but it got me once when
lifting out a particularly long tube, luckily the neck was clear :-)
I built a Wimshurst machine once just for fun.... using an LP :-) worked
very well :-))
Thanks for all the info, very interesting.

Mike

One for the valvies 2/2....
 

Don Pearce wrote:

On Sat, 06 Nov 2004 07:32:15 +0000, Pooh Bear
wrote:



Keith G wrote:

"Pooh Bear" wrote in message
...


Keith G wrote:

OK, exactly why don't trannies (on valve amps) like it being run without
a
load?

Because with no load on the secondary, the primary of the transformer just
behaves like a huge choke.


It's not like they are going to burst open, is it??

The current swing can cause huge 'back emfs' that can damage both output
valves
and the transformer itself.


Also does quick 'hot-swapping' speakers while an amp's hurt it any? (Oi
dun
a lot o' thaat in tha parrst.... ;-)

If there's any significant signal, the damage can occur.

OK, thanks for that.

YW.

I keep a busted KT88 in my little " rogue's gallery " of broken bits btw, that
experienced being hot-swapped when the bass guitarist shouldn't have been
playing.

The anode is actually *molten* and the glass envelope cracked from the heat !
The output transformer survived in this case luckily. 4 x KT88s was a pricey
enough mistake to make even 25 or so yrs ago.

Graham

A molten anode? Chances are there was a pretty hefty burst of x-rays
as that one went phut. Lead knickers for you!

More a case of lead knickers for his *roadie* actually. He was the culprit !


Graham

One for the valvies 2/2....
 

Mike Gilmour wrote:


Adds some excitement to routine testing - except for the poisonous ozone
that is ;-)

I thought sea air was good for you !


Graham ;-)

One for the valvies 2/2....
 

Don Pearce wrote:

With the normal drive voltage of 25kV there were no detectable x-rays.
at 30kV the anode glowed cherry red, and they poured out. 30kV was
just part of a stress test - not a normal operating condition.

Didn't production sets of that era have an overvoltage cut-off ?


Graham

One for the valvies 2/2....
 

On Sun, 07 Nov 2004 09:02:05 +0000, Pooh Bear
wrote:

Don Pearce wrote:

With the normal drive voltage of 25kV there were no detectable x-rays.
at 30kV the anode glowed cherry red, and they poured out. 30kV was
just part of a stress test - not a normal operating condition.

Didn't production sets of that era have an overvoltage cut-off ?


Graham

Yeah - the LOP valve blew up.

d
Pearce Consulting
http://www.pearce.uk.com

One for the valvies 2/2....
 

On Sun, 07 Nov 2004 08:53:43 +0000, Pooh Bear
wrote:

Don Pearce wrote:

A molten anode? Chances are there was a pretty hefty burst of x-rays
as that one went phut. Lead knickers for you!

More a case of lead knickers for his *roadie* actually. He was the culprit !

Since you need in excess of 25kV to produce X-rays, lead knickers will
be the *least* of your worries if you're working on an amp with those
sort of rail voltages! :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering

One for the valvies 2/2....
 

"Pooh Bear" wrote in message
...
Don Pearce wrote:

On Sat, 06 Nov 2004 07:32:15 +0000, Pooh Bear
wrote:



Keith G wrote:

"Pooh Bear" wrote in message
...


Keith G wrote:

OK, exactly why don't trannies (on valve amps) like it being run
without
a
load?

Because with no load on the secondary, the primary of the
transformer just
behaves like a huge choke.


It's not like they are going to burst open, is it??

The current swing can cause huge 'back emfs' that can damage both
output
valves
and the transformer itself.


Also does quick 'hot-swapping' speakers while an amp's hurt it any?
(Oi
dun
a lot o' thaat in tha parrst.... ;-)

If there's any significant signal, the damage can occur.

OK, thanks for that.

YW.

I keep a busted KT88 in my little " rogue's gallery " of broken bits
btw, that
experienced being hot-swapped when the bass guitarist shouldn't have
been
playing.

The anode is actually *molten* and the glass envelope cracked from the
heat !
The output transformer survived in this case luckily. 4 x KT88s was a
pricey
enough mistake to make even 25 or so yrs ago.

Graham

A molten anode? Chances are there was a pretty hefty burst of x-rays
as that one went phut. Lead knickers for you!

More a case of lead knickers for his *roadie* actually. He was the culprit
!


Graham


Join us in a tale of daring. Experience 30kV!!! Smell the Ozone!!! Handle
toxic Lead!!! and see live anodes melt before your very eyes!! 'Valvies
On The Edge' coming to a cinema near you :-)

One for the valvies 2/2....
 

Mike Gilmour wrote:
"Pooh Bear" wrote in message
...

Don Pearce wrote:


On Sat, 06 Nov 2004 07:32:15 +0000, Pooh Bear
wrote:



Keith G wrote:


"Pooh Bear" wrote in message
...


Keith G wrote:


OK, exactly why don't trannies (on valve amps) like it being run
without
a
load?

Because with no load on the secondary, the primary of the
transformer just
behaves like a huge choke.



It's not like they are going to burst open, is it??

The current swing can cause huge 'back emfs' that can damage both
output
valves
and the transformer itself.



Also does quick 'hot-swapping' speakers while an amp's hurt it any?
(Oi
dun
a lot o' thaat in tha parrst.... ;-)

If there's any significant signal, the damage can occur.

OK, thanks for that.

YW.

I keep a busted KT88 in my little " rogue's gallery " of broken bits
btw, that
experienced being hot-swapped when the bass guitarist shouldn't have
been
playing.

The anode is actually *molten* and the glass envelope cracked from the
heat !
The output transformer survived in this case luckily. 4 x KT88s was a
pricey
enough mistake to make even 25 or so yrs ago.

Graham

A molten anode? Chances are there was a pretty hefty burst of x-rays
as that one went phut. Lead knickers for you!

More a case of lead knickers for his *roadie* actually. He was the culprit
!


Graham



Join us in a tale of daring. Experience 30kV!!! Smell the Ozone!!! Handle
toxic Lead!!! and see live anodes melt before your very eyes!! 'Valvies
On The Edge' coming to a cinema near you :-)


Thats a altogether different bunch of nutters :

http://homepage.ntlworld.com/electri...uktjune04.html

--
Nick

One for the valvies 2/2....
 

"Nick Gorham" wrote in message
...
Mike Gilmour wrote:
"Pooh Bear" wrote in message
...

Don Pearce wrote:


On Sat, 06 Nov 2004 07:32:15 +0000, Pooh Bear
wrote:



Keith G wrote:


"Pooh Bear" wrote in message
...


Keith G wrote:


OK, exactly why don't trannies (on valve amps) like it being run
without
a
load?

Because with no load on the secondary, the primary of the transformer
just
behaves like a huge choke.



It's not like they are going to burst open, is it??

The current swing can cause huge 'back emfs' that can damage both
output
valves
and the transformer itself.



Also does quick 'hot-swapping' speakers while an amp's hurt it any?
(Oi
dun
a lot o' thaat in tha parrst.... ;-)

If there's any significant signal, the damage can occur.

OK, thanks for that.

YW.

I keep a busted KT88 in my little " rogue's gallery " of broken bits
btw, that
experienced being hot-swapped when the bass guitarist shouldn't have
been
playing.

The anode is actually *molten* and the glass envelope cracked from the
heat !
The output transformer survived in this case luckily. 4 x KT88s was a
pricey
enough mistake to make even 25 or so yrs ago.

Graham

A molten anode? Chances are there was a pretty hefty burst of x-rays
as that one went phut. Lead knickers for you!

More a case of lead knickers for his *roadie* actually. He was the
culprit !


Graham



Join us in a tale of daring. Experience 30kV!!! Smell the Ozone!!!
Handle toxic Lead!!! and see live anodes melt before your very eyes!!
'Valvies On The Edge' coming to a cinema near you :-)
Thats a altogether different bunch of nutters :

http://homepage.ntlworld.com/electri...uktjune04.html

--
Nick

Excellent!! Hair standing on end and melted mosfets...next stop the
National Grid :-)