300b/GM70 Amp
 

Hi,

Given its been a bit quiet on here, I thought I would post some of DIY
output.

Here is a link to some pictures of the GM70 amp that I have been working
on for the past eight months.

http://www.lurcher.org/nick/images/gm70/

Circuit is a C3g Pentode voltage amplifier with VR tube screen
regulator, then 300b driver to 1:1 amorphous interstage to GM70 grid.
Output TX 7k amorphous. Driver and 300b supply, series regulator using
6080, ecl82 and 0d3 (Steve Bench inspired). TJ-Meshplate 300b, running
330v @ 55ma. Copper plate GM70 running 1020v @ 110ma.

All transformers by Automatic Electric Europe.

Rough specs, -3dB points (5w into 8ohm) 18Hz, 52kHz. 3% distortion
reached at 42w into 8 ohm.

It was designed to drive a set of large panel electrostatics, but I have
been using the breadboard version driving a pair of Yamaha NS1000's. My
normal 94dB/W speakers are slightly overpowered for them :-).

I can't take too much pride in them, as their owner did the construction
and I did the design and internal build. But I am still very pleased how
they have come out.

--
Nick

300b/GM70 Amp
 

"Nick Gorham"

Here is a link to some pictures of the GM70 amp that I have been working
on for the past eight months.

http://www.lurcher.org/nick/images/gm70/

Circuit is a C3g Pentode voltage amplifier with VR tube screen regulator,
then 300b driver to 1:1 amorphous interstage to GM70 grid. Output TX 7k
amorphous. Driver and 300b supply, series regulator using 6080, ecl82 and
0d3 (Steve Bench inspired). TJ-Meshplate 300b, running 330v @ 55ma. Copper
plate GM70 running 1020v @ 110ma.



** The GM70's heater is rated for 20 volts at 3 amps - means it
dissipates 60 watts, mainly by radiating it to the surrounding plate
structure. The plate dissipates 112 watts on its own - adds up to around
170 watts.

So the tube glows red all the time - right ?





....... Phil

300b/GM70 Amp
 

Phil Allison wrote:
"Nick Gorham"

Here is a link to some pictures of the GM70 amp that I have been working
on for the past eight months.

http://www.lurcher.org/nick/images/gm70/

Circuit is a C3g Pentode voltage amplifier with VR tube screen regulator,
then 300b driver to 1:1 amorphous interstage to GM70 grid. Output TX 7k
amorphous. Driver and 300b supply, series regulator using 6080, ecl82 and
0d3 (Steve Bench inspired). TJ-Meshplate 300b, running 330v @ 55ma. Copper
plate GM70 running 1020v @ 110ma.




** The GM70's heater is rated for 20 volts at 3 amps - means it
dissipates 60 watts, mainly by radiating it to the surrounding plate
structure. The plate dissipates 112 watts on its own - adds up to around
170 watts.

So the tube glows red all the time - right ?





...... Phil





Almost, there is a lot of light from the fillament, but at that op
point, the anode is just below the temperature at which it starts to
glow. The graphite plate version is a dull red at that point (only
visable when the fill is turned off).

if the diss was taken to (say) 130w then it starts to glow visably. As a
experiment we tried to see just what a GM70 would take, we got to 1500v
and 140ma, at 210w it is was glowing red in the center of the plate and
we left it like this for ten minutes until we decided not to push our
luck :-).

That particular GM70 is still going strong, the old USR certainly knew
how to make robust triodes.

There is a lot of ventilation in the base for that very reason, the
convection from below the valve carries a lot of the (non radiated) heat
away from the amp, the TX's near get warm, but not worryingly so.

--
Nick

300b/GM70 Amp
 

On Wed, 08 Aug 2007 07:58:46 +0100, Nick Gorham
wrote:

Phil Allison wrote:
"Nick Gorham"

Here is a link to some pictures of the GM70 amp that I have been working
on for the past eight months.

http://www.lurcher.org/nick/images/gm70/

Circuit is a C3g Pentode voltage amplifier with VR tube screen regulator,
then 300b driver to 1:1 amorphous interstage to GM70 grid. Output TX 7k
amorphous. Driver and 300b supply, series regulator using 6080, ecl82 and
0d3 (Steve Bench inspired). TJ-Meshplate 300b, running 330v @ 55ma. Copper
plate GM70 running 1020v @ 110ma.




** The GM70's heater is rated for 20 volts at 3 amps - means it
dissipates 60 watts, mainly by radiating it to the surrounding plate
structure. The plate dissipates 112 watts on its own - adds up to around
170 watts.

So the tube glows red all the time - right ?





...... Phil





Almost, there is a lot of light from the fillament, but at that op
point, the anode is just below the temperature at which it starts to
glow. The graphite plate version is a dull red at that point (only
visable when the fill is turned off).

if the diss was taken to (say) 130w then it starts to glow visably. As a
experiment we tried to see just what a GM70 would take, we got to 1500v
and 140ma, at 210w it is was glowing red in the center of the plate and
we left it like this for ten minutes until we decided not to push our
luck :-).

That particular GM70 is still going strong, the old USR certainly knew
how to make robust triodes.

There is a lot of ventilation in the base for that very reason, the
convection from below the valve carries a lot of the (non radiated) heat
away from the amp, the TX's near get warm, but not worryingly so.

In my earliest work days I designed colour TVs. We had an X-Ray
detector permanently covering the bench, because if the line output
valve got a few too many volts, and a bit too much current, its anode
would start to glow red, and X-Rays would come flooding out.

I really wouldn't be sitting close to this thing for ten minutes if I
were you.

d

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

300b/GM70 Amp
 

Don Pearce wrote:
On Wed, 08 Aug 2007 07:58:46 +0100, Nick Gorham
wrote:


Phil Allison wrote:

"Nick Gorham"


Here is a link to some pictures of the GM70 amp that I have been working
on for the past eight months.

http://www.lurcher.org/nick/images/gm70/

Circuit is a C3g Pentode voltage amplifier with VR tube screen regulator,
then 300b driver to 1:1 amorphous interstage to GM70 grid. Output TX 7k
amorphous. Driver and 300b supply, series regulator using 6080, ecl82 and
0d3 (Steve Bench inspired). TJ-Meshplate 300b, running 330v @ 55ma. Copper
plate GM70 running 1020v @ 110ma.




** The GM70's heater is rated for 20 volts at 3 amps - means it
dissipates 60 watts, mainly by radiating it to the surrounding plate
structure. The plate dissipates 112 watts on its own - adds up to around
170 watts.

So the tube glows red all the time - right ?





...... Phil





Almost, there is a lot of light from the fillament, but at that op
point, the anode is just below the temperature at which it starts to
glow. The graphite plate version is a dull red at that point (only
visable when the fill is turned off).

if the diss was taken to (say) 130w then it starts to glow visably. As a
experiment we tried to see just what a GM70 would take, we got to 1500v
and 140ma, at 210w it is was glowing red in the center of the plate and
we left it like this for ten minutes until we decided not to push our
luck :-).

That particular GM70 is still going strong, the old USR certainly knew
how to make robust triodes.

There is a lot of ventilation in the base for that very reason, the
convection from below the valve carries a lot of the (non radiated) heat
away from the amp, the TX's near get warm, but not worryingly so.


In my earliest work days I designed colour TVs. We had an X-Ray
detector permanently covering the bench, because if the line output
valve got a few too many volts, and a bit too much current, its anode
would start to glow red, and X-Rays would come flooding out.

I really wouldn't be sitting close to this thing for ten minutes if I
were you.

d


Why?

The x-ray generation is caused by the impact speed of the electrons on
the anode, this is only running at 1kv, I think you need at least 5kev
to start worrying about x-rays.

The red-ness is neither here or there.

--
Nick

300b/GM70 Amp
 

On Wed, 08 Aug 2007 09:29:32 +0100, Nick Gorham
wrote:

Don Pearce wrote:
On Wed, 08 Aug 2007 07:58:46 +0100, Nick Gorham
wrote:


Phil Allison wrote:

"Nick Gorham"


Here is a link to some pictures of the GM70 amp that I have been working
on for the past eight months.

http://www.lurcher.org/nick/images/gm70/

Circuit is a C3g Pentode voltage amplifier with VR tube screen regulator,
then 300b driver to 1:1 amorphous interstage to GM70 grid. Output TX 7k
amorphous. Driver and 300b supply, series regulator using 6080, ecl82 and
0d3 (Steve Bench inspired). TJ-Meshplate 300b, running 330v @ 55ma. Copper
plate GM70 running 1020v @ 110ma.




** The GM70's heater is rated for 20 volts at 3 amps - means it
dissipates 60 watts, mainly by radiating it to the surrounding plate
structure. The plate dissipates 112 watts on its own - adds up to around
170 watts.

So the tube glows red all the time - right ?





...... Phil





Almost, there is a lot of light from the fillament, but at that op
point, the anode is just below the temperature at which it starts to
glow. The graphite plate version is a dull red at that point (only
visable when the fill is turned off).

if the diss was taken to (say) 130w then it starts to glow visably. As a
experiment we tried to see just what a GM70 would take, we got to 1500v
and 140ma, at 210w it is was glowing red in the center of the plate and
we left it like this for ten minutes until we decided not to push our
luck :-).

That particular GM70 is still going strong, the old USR certainly knew
how to make robust triodes.

There is a lot of ventilation in the base for that very reason, the
convection from below the valve carries a lot of the (non radiated) heat
away from the amp, the TX's near get warm, but not worryingly so.


In my earliest work days I designed colour TVs. We had an X-Ray
detector permanently covering the bench, because if the line output
valve got a few too many volts, and a bit too much current, its anode
would start to glow red, and X-Rays would come flooding out.

I really wouldn't be sitting close to this thing for ten minutes if I
were you.

d


Why?

The x-ray generation is caused by the impact speed of the electrons on
the anode, this is only running at 1kv, I think you need at least 5kev
to start worrying about x-rays.

The red-ness is neither here or there.

I can't remember the anode voltage we were running back then, but I'm
pretty sure it was closer to 1kV than 5.

d

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

300b/GM70 Amp
 

On 2007-08-08, Don Pearce wrote:
On Wed, 08 Aug 2007 07:58:46 +0100, Nick Gorham
wrote:
That particular GM70 is still going strong, the old USR certainly knew
how to make robust triodes.

There is a lot of ventilation in the base for that very reason, the
convection from below the valve carries a lot of the (non radiated) heat
away from the amp, the TX's near get warm, but not worryingly so.

In my earliest work days I designed colour TVs. We had an X-Ray
detector permanently covering the bench, because if the line output
valve got a few too many volts, and a bit too much current, its anode
would start to glow red, and X-Rays would come flooding out.

In days long gone, articles in Scientific American (from my school library
stock) told you how to do interesting but potentially dangerous things.

One showed how to take an old triode, cover the outside of the envelope
with thin aluminium foil, common all of the pins (possibly leaving
the filament still powered? - it's a long time ago) and apply a few kV
across it.

Apparently, suitably energetic electrons striking the silicon in the
envelope glass produced X-rays and there were examples including X-rayed
fish (non-filleted, of course).

I really wouldn't be sitting close to this thing for ten minutes if I
were you.

For which reason Scientific American is now rather boring. I sometimes
wish we could still see articles on making 2-metre-long zinc powder and
sulfur (sic) powered rockets that could reach 1,000 metres, etc.

--
John Phillips

300b/GM70 Amp
 

In my earliest work days I designed colour TVs. We had an X-Ray
detector permanently covering the bench, because if the line output
valve got a few too many volts, and a bit too much current, its anode
would start to glow red, and X-Rays would come flooding out.

Wasn't that the shunt stabiliser that did that?.

Hence the metal can in some sets?..

--
Tony Sayer

300b/GM70 Amp
 

On Wed, 8 Aug 2007 10:37:35 +0100, tony sayer
wrote:

In my earliest work days I designed colour TVs. We had an X-Ray
detector permanently covering the bench, because if the line output
valve got a few too many volts, and a bit too much current, its anode
would start to glow red, and X-Rays would come flooding out.

Wasn't that the shunt stabiliser that did that?.

Hence the metal can in some sets?..

No, definitely the line output valve. After a few minutes the problem
was self-curing though - a slight popping noise, and there was a neat
melted hole at the top of the glass envelope.

d

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

300b/GM70 Amp
 

On 08 Aug 2007 09:30:25 GMT, John Phillips
wrote:

On 2007-08-08, Don Pearce wrote:
On Wed, 08 Aug 2007 07:58:46 +0100, Nick Gorham
wrote:
That particular GM70 is still going strong, the old USR certainly knew
how to make robust triodes.

There is a lot of ventilation in the base for that very reason, the
convection from below the valve carries a lot of the (non radiated) heat
away from the amp, the TX's near get warm, but not worryingly so.

In my earliest work days I designed colour TVs. We had an X-Ray
detector permanently covering the bench, because if the line output
valve got a few too many volts, and a bit too much current, its anode
would start to glow red, and X-Rays would come flooding out.

In days long gone, articles in Scientific American (from my school library
stock) told you how to do interesting but potentially dangerous things.

One showed how to take an old triode, cover the outside of the envelope
with thin aluminium foil, common all of the pins (possibly leaving
the filament still powered? - it's a long time ago) and apply a few kV
across it.

Apparently, suitably energetic electrons striking the silicon in the
envelope glass produced X-rays and there were examples including X-rayed
fish (non-filleted, of course).

I really wouldn't be sitting close to this thing for ten minutes if I
were you.

For which reason Scientific American is now rather boring. I sometimes
wish we could still see articles on making 2-metre-long zinc powder and
sulfur (sic) powered rockets that could reach 1,000 metres, etc.

And don't forget the instructions for making Tesla coils. Happy days.

d

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