Hello List,

I am looking for a source for a Zener Diode. I am building an HF
Amplifier using a GS-35b and the schematic I'm using to build the amp
calls for a 36v 50w zoner diode for bias. Here in New Zealand there
does not seem to be anyone with anythings close to what I need.

Also, would it be possible to string a few lower volt watt zeners
together to come up with a close value to what is needed?

Thanks for the help

Skip..

Skip wrote:

Hello List,

I am looking for a source for a Zener Diode. I am building an HF
Amplifier using a GS-35b and the schematic I'm using to build the amp
calls for a 36v 50w zoner diode for bias. Here in New Zealand there
does not seem to be anyone with anythings close to what I need.

Also, would it be possible to string a few lower volt watt zeners
together to come up with a close value to what is needed?

Thanks for the help

Skip..

5 each 7.5 volt 10 watt zeners in series might work. Or you might
build a power transistor circuit that current amplifies a small 35
volt zener. It all depends on the details of the circuit. That is
one hell of a bias zener.

--
John Popelish

Skip wrote:

Hello List,

I am looking for a source for a Zener Diode. I am building an HF
Amplifier using a GS-35b and the schematic I'm using to build the amp
calls for a 36v 50w zoner diode for bias. Here in New Zealand there
does not seem to be anyone with anythings close to what I need.

Also, would it be possible to string a few lower volt watt zeners
together to come up with a close value to what is needed?

Thanks for the help

Skip..

5 each 7.5 volt 10 watt zeners in series might work. Or you might
build a power transistor circuit that current amplifies a small 35
volt zener. It all depends on the details of the circuit. That is
one hell of a bias zener.

--
John Popelish

Skip wrote:
Hello List,

I am looking for a source for a Zener Diode. I am building an HF
Amplifier using a GS-35b and the schematic I'm using to build the amp
calls for a 36v 50w zoner diode for bias. Here in New Zealand there
does not seem to be anyone with anythings close to what I need.

Also, would it be possible to string a few lower volt watt zeners
together to come up with a close value to what is needed?

A simple shunt regulator using a TL431 and a pass transistor will give
adjustable voltage and better regulation than a large zener diode, and
is actually cheaper.

There's a lot of information on my website, at:
http://www.ifwtech.co.uk/g3sek/boards [some commercial content]


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'

Skip wrote:
Hello List,

I am looking for a source for a Zener Diode. I am building an HF
Amplifier using a GS-35b and the schematic I'm using to build the amp
calls for a 36v 50w zoner diode for bias. Here in New Zealand there
does not seem to be anyone with anythings close to what I need.

Also, would it be possible to string a few lower volt watt zeners
together to come up with a close value to what is needed?

A simple shunt regulator using a TL431 and a pass transistor will give
adjustable voltage and better regulation than a large zener diode, and
is actually cheaper.

There's a lot of information on my website, at:
http://www.ifwtech.co.uk/g3sek/boards [some commercial content]


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'

or an LM317HVT with PASS transistor


"Ian White, G3SEK" wrote in message
...
Skip wrote:
Hello List,

I am looking for a source for a Zener Diode. I am building an HF
Amplifier using a GS-35b and the schematic I'm using to build the amp
calls for a 36v 50w zoner diode for bias. Here in New Zealand there
does not seem to be anyone with anythings close to what I need.

Also, would it be possible to string a few lower volt watt zeners
together to come up with a close value to what is needed?

A simple shunt regulator using a TL431 and a pass transistor will give
adjustable voltage and better regulation than a large zener diode, and
is actually cheaper.

There's a lot of information on my website, at:
http://www.ifwtech.co.uk/g3sek/boards [some commercial content]


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'

or an LM317HVT with PASS transistor


"Ian White, G3SEK" wrote in message
...
Skip wrote:
Hello List,

I am looking for a source for a Zener Diode. I am building an HF
Amplifier using a GS-35b and the schematic I'm using to build the amp
calls for a 36v 50w zoner diode for bias. Here in New Zealand there
does not seem to be anyone with anythings close to what I need.

Also, would it be possible to string a few lower volt watt zeners
together to come up with a close value to what is needed?

A simple shunt regulator using a TL431 and a pass transistor will give
adjustable voltage and better regulation than a large zener diode, and
is actually cheaper.

There's a lot of information on my website, at:
http://www.ifwtech.co.uk/g3sek/boards [some commercial content]


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'

Bill Turner wrote:
On Sun, 7 Dec 2003 07:24:04 -0500, "John Walton"
wrote:

or an LM317HVT with PASS transistor

The original question was about a zener diode, ie a shunt regulator. I
wasn't aware that a 317 plus a transistor could be configured to emulate
a zener... can it?

The TL431 certainly can.


_________________________________________________ ________

If you're going to use such things, you must protect them against
inadvertent arcs. One good arc and they will be history.


Normally an arc from the B+ supply of a grounded-grid triode is no
threat to the cathode bias device. Arcs inside the tube will ground out
to the grid, and external arcs to the chassis; and then the current
flows back to B-minus. The cathode and the bias device are not part of
that current path, so the bias device is not at risk.

The exception is if an internal arc is severe enough to burn right
though the grid (I've seen that in a mesh-grid tube) or if the current
is high enough to drive the local grid potential positive. Then some of
the arc current - perhaps tens of amps, peak - will flow down through
the cathode. In such extreme cases, no bias device is likely to
survive... at least, not without some additional protection.

That's why, whatever bias device you use, an 80-cent varistor connected
from cathode to chassis is a very good investment.


A big, fat
zener on the other hand, is relatively immune to such abuse.

"Relatively" in this context is hard to judge. In most cases, the bias
device survives because it wasn't actually under threat - see above. If
a device does fail, it's only guesswork to say how a different bias
device would have fared in the same amplifier.

A more reliable picture emerges from a larger number of amplifiers.
There are more than 350 Triode Boards out in the field, with tubes
ranging from the 2C39 to the 3CXP5000, and they all use basically the
same TL431/TIP147 circuit protected by a varistor. Between them, these
boards have seen a lot of arcs, and there's no indication that the bias
circuit is notably fragile. Certainly there are occasional failures -
but in those cases it seems likely that a big, fat zener wouldn't have
survived either.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

Bill Turner wrote:
On Sun, 7 Dec 2003 07:24:04 -0500, "John Walton"
wrote:

or an LM317HVT with PASS transistor

The original question was about a zener diode, ie a shunt regulator. I
wasn't aware that a 317 plus a transistor could be configured to emulate
a zener... can it?

The TL431 certainly can.


_________________________________________________ ________

If you're going to use such things, you must protect them against
inadvertent arcs. One good arc and they will be history.


Normally an arc from the B+ supply of a grounded-grid triode is no
threat to the cathode bias device. Arcs inside the tube will ground out
to the grid, and external arcs to the chassis; and then the current
flows back to B-minus. The cathode and the bias device are not part of
that current path, so the bias device is not at risk.

The exception is if an internal arc is severe enough to burn right
though the grid (I've seen that in a mesh-grid tube) or if the current
is high enough to drive the local grid potential positive. Then some of
the arc current - perhaps tens of amps, peak - will flow down through
the cathode. In such extreme cases, no bias device is likely to
survive... at least, not without some additional protection.

That's why, whatever bias device you use, an 80-cent varistor connected
from cathode to chassis is a very good investment.


A big, fat
zener on the other hand, is relatively immune to such abuse.

"Relatively" in this context is hard to judge. In most cases, the bias
device survives because it wasn't actually under threat - see above. If
a device does fail, it's only guesswork to say how a different bias
device would have fared in the same amplifier.

A more reliable picture emerges from a larger number of amplifiers.
There are more than 350 Triode Boards out in the field, with tubes
ranging from the 2C39 to the 3CXP5000, and they all use basically the
same TL431/TIP147 circuit protected by a varistor. Between them, these
boards have seen a lot of arcs, and there's no indication that the bias
circuit is notably fragile. Certainly there are occasional failures -
but in those cases it seems likely that a big, fat zener wouldn't have
survived either.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

Skip -

If you are build an amplifier .. I would use Ian's boards -
great protection, easy to assemble and takes your guess work out of older
designs

Greg
w9gb


"Ian White, G3SEK" wrote in message
...
Skip wrote:
Hello List,

I am looking for a source for a Zener Diode. I am building an HF
Amplifier using a GS-35b and the schematic I'm using to build the amp
calls for a 36v 50w zoner diode for bias. Here in New Zealand there
does not seem to be anyone with anythings close to what I need.

Also, would it be possible to string a few lower volt watt zeners
together to come up with a close value to what is needed?

A simple shunt regulator using a TL431 and a pass transistor will give
adjustable voltage and better regulation than a large zener diode, and
is actually cheaper.

There's a lot of information on my website, at:
http://www.ifwtech.co.uk/g3sek/boards [some commercial content]


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'