Need substitute for old Siliconix FET to replace Thyratron...

J

John Robertson

Guest
I have a circuit to replace a 2050 Thyratron tube with a FET and an SCR
C106, but I am having trouble sourcing the FET as I am not sure how to
translate the only specs on it that I can find to something more modern.

It was made by Siliconix # U266 or FN2651.

Specs are as follows:
-------
https://www.flippers.com/pdfs/Siliconix_RAE_1968_Catalog_Redacted.pdf

Igss = 6.0 nA
BVgss = 150V
Vp = 15.0V
Ipss = 100mA (min) to 300mA (max)
Gfs (umho) = 20K (min) to 40K (max)
Rds = 100 Ohms
Id(off) = 1.5nA
-------

Igss looks like Maximum gate current
BVgss is breakdown voltage Gate - Source I assume
What is Vp? Minimum turn on voltage?
Ipss is maximum current of what?
Gfs is inductance it would appear...
Rds is maximum On resistance
Id(off) - is that leakage?

Modern FETs don\'t use all the same descriptors though - at least not
that I\'ve found on digikey and I can\'t find any info on the U266(FN2651)
other than the page out of the RAE distributor\'s catalog

Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf

Thanks!

John :-#)#


--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
#7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
 
On Thursday, August 3, 2023 at 5:27:06 PM UTC-7, John Robertson wrote:
I have a circuit to replace a 2050 Thyratron tube with a FET and an SCR
C106, but I am having trouble sourcing the FET as I am not sure how to
translate the only specs on it that I can find to something more modern.

It was made by Siliconix # U266 or FN2651.

Specs are as follows:
-------
https://www.flippers.com/pdfs/Siliconix_RAE_1968_Catalog_Redacted.pdf

Igss = 6.0 nA
BVgss = 150V
Vp = 15.0V
Ipss = 100mA (min) to 300mA (max)
Gfs (umho) = 20K (min) to 40K (max)
Rds = 100 Ohms
Id(off) = 1.5nA
-------

Igss looks like Maximum gate current
Maximum Source Gate leakage current
BVgss is breakdown voltage Gate - Source I assume
Maximum Source Drain voltage.
What is Vp? Minimum turn on voltage?
Ipss is maximum current of what?
Minimum/Maximum Source Drain current.
Gfs is inductance it would appear...
Rds is maximum On resistance
Id(off) - is that leakage?
Source Drain leakage current when off
Click to expand...

Source Drain is likely negative in most case, since they are talking about electrons.
Or look at Drain Source.
 
On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <jrr@flippers.com>
wrote:

I have a circuit to replace a 2050 Thyratron tube with a FET and an SCR
C106, but I am having trouble sourcing the FET as I am not sure how to
translate the only specs on it that I can find to something more modern.

It was made by Siliconix # U266 or FN2651.

Specs are as follows:
-------
https://www.flippers.com/pdfs/Siliconix_RAE_1968_Catalog_Redacted.pdf

Igss = 6.0 nA
BVgss = 150V
Vp = 15.0V
Ipss = 100mA (min) to 300mA (max)
Gfs (umho) = 20K (min) to 40K (max)
Rds = 100 Ohms
Id(off) = 1.5nA
-------

Igss looks like Maximum gate current
BVgss is breakdown voltage Gate - Source I assume
What is Vp? Minimum turn on voltage?
Ipss is maximum current of what?
Gfs is inductance it would appear...
Rds is maximum On resistance
Id(off) - is that leakage?

Modern FETs don\'t use all the same descriptors though - at least not
that I\'ve found on digikey and I can\'t find any info on the U266(FN2651)
other than the page out of the RAE distributor\'s catalog

Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf

Thanks!

John :-#)#
Click to expand...

Although it\'s mounted in a stud package and has that
weird gate voltage rating, it\'s only rated at 20Vds

Big one is 500-900mA Idss .

U244 similar at 25Vds.

Old soviet surplus part KP903 (2P903) (~ ebay or amazon) might fit.

https://ipelectron.ru/upload/iblock/17f/17f60436ccfccebfbb284f2c7eaa89f3.pdf

I picked up two last year when they were offered by multiple
vendors @ US$5, if that\'s any use to you.

RL
 
On 04/08/2023 1:26 am, John Robertson wrote:
I have a circuit to replace a 2050 Thyratron tube with a FET and an SCR
C106, but I am having trouble sourcing the FET as I am not sure how to
translate the only specs on it that I can find to something more modern.

It was made by Siliconix # U266 or FN2651.

Specs are as follows:
-------
https://www.flippers.com/pdfs/Siliconix_RAE_1968_Catalog_Redacted.pdf

Igss = 6.0 nA
BVgss = 150V
Vp = 15.0V
Ipss = 100mA (min) to 300mA (max)
Gfs (umho) = 20K (min) to 40K (max)
Rds = 100 Ohms
Id(off) = 1.5nA
-------

Igss looks like Maximum gate current
BVgss is breakdown voltage Gate - Source I assume
What is Vp? Minimum turn on voltage?
Ipss is maximum current of what?
Gfs is inductance it would appear...
Rds is maximum On resistance
Id(off) - is that leakage?

Modern FETs don\'t use all the same descriptors though - at least not
that I\'ve found on digikey and I can\'t find any info on the U266(FN2651)
other than the page out of the RAE distributor\'s catalog

Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf

Thanks!

John :-#)#
Click to expand...

Vp is the pinchoff voltage; how negative the gate voltage has to be for
drain-source to be non-conducting - which could be Id(off) or some other
specified \"off\" current.

Gfs is forward transconductance; how drain-source current changes per
change in gate voltage.

Idss is the saturation drain-source current at zero gate volts.

High voltage JFETs are now very hard to get but you should be easily
able to use a modern depletion mosfet like LND150/250

piglet
 
On 04/08/2023 7:20 pm, piglet wrote:
On 04/08/2023 1:26 am, John Robertson wrote:
I have a circuit to replace a 2050 Thyratron tube with a FET and an
SCR C106, but I am having trouble sourcing the FET as I am not sure
how to translate the only specs on it that I can find to something
more modern.

It was made by Siliconix # U266 or FN2651.

Specs are as follows:
-------
https://www.flippers.com/pdfs/Siliconix_RAE_1968_Catalog_Redacted.pdf

Igss = 6.0 nA
BVgss = 150V
Vp = 15.0V
Ipss = 100mA (min) to 300mA (max)
Gfs (umho) = 20K (min) to 40K (max)
Rds = 100 Ohms
Id(off) = 1.5nA
-------

Igss looks like Maximum gate current
BVgss is breakdown voltage Gate - Source I assume
What is Vp? Minimum turn on voltage?
Ipss is maximum current of what?
Gfs is inductance it would appear...
Rds is maximum On resistance
Id(off) - is that leakage?

Modern FETs don\'t use all the same descriptors though - at least not
that I\'ve found on digikey and I can\'t find any info on the
U266(FN2651) other than the page out of the RAE distributor\'s catalog

Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf

Thanks!

John :-#)#



Vp is the pinchoff voltage; how negative the gate voltage has to be for
drain-source to be non-conducting - which could be Id(off) or some other
specified \"off\" current.

Gfs is forward transconductance; how drain-source current changes per
change in gate voltage.

Idss is the saturation drain-source current at zero gate volts.

High voltage JFETs are now very hard to get but you should be easily
able to use a modern depletion mosfet like LND150/250

piglet
Click to expand...

That schematic you linked depicting the FET+SCR replacement for a
thyratron tube shows the fet drain supply coming from rectified heater
filament 6.3V supply. That is neat as it prevents triggering without the
heater supply and C31 has charged up.

I think they are assuming that 6.3V has either one side or its
center-tap (if present) near cathode 0V ground which means the drain
voltage is going to be well below 20V. Which makes the JFET requirements
look very undemanding, I can\'t see why they specified the U266 - I
reckon you can probably use just about any garden variety n-channel JFET
(2N5458, J113, 2N3819 etc etc)

I haven\'t figured out how shield grid 2 influences the triggering, do
you have a schematic showing how the 2D21 is used in the jukebox?

piglet
 
On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <jrr@flippers.com>
wrote:


Modern FETs don\'t use all the same descriptors though - at least not
that I\'ve found on digikey and I can\'t find any info on the U266(FN2651)
other than the page out of the RAE distributor\'s catalog

Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf
Click to expand...

From the solid state schematic, it looks like you could protect the
substitute fet\'s gate with a suitable diode/zener combination.

RL
 
piglet <erichpwagner@hotmail.com> wrote:

I haven\'t figured out how shield grid 2 influences the triggering, do
you have a schematic showing how the 2D21 is used in the jukebox?

piglet
Click to expand...

I used these in the 1950\'s. Grid #2 is set to zero.

See https://frank.pocnet.net/sheets/049/2/2D21.pdf



--
MRM
 
On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <jrr@flippers.com>
wrote:


Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf
Click to expand...

There may be something seriously wrong with your solidc state sub
pinout.

2D21 pins 7 and 5 are normally connected together, internally.

2D21 pin 3 is a heater terminal, with no cathose or anode contact.
Your solid state drawing seems to anticipate an anode function.

2D21 pins 2 and 7 will normally never see useful low voltage juice for
rectification. I suspect that the sub wants a heater supply on these
terminals. 2D21 isolated heater is on pins 3 and 4.

Recheck it. maybe you\'re numbering from the top view rather than the
bottom.

RL
 
On Sat, 05 Aug 2023 16:29:52 -0400, legg <legg@nospam.magma.ca> wrote:

On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <jrr@flippers.com
wrote:



Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf


There may be something seriously wrong with your solidc state sub
pinout.

2D21 pins 7 and 5 are normally connected together, internally.

2D21 pin 3 is a heater terminal, with no cathose or anode contact.
Your solid state drawing seems to anticipate an anode function.

2D21 pins 2 and 7 will normally never see useful low voltage juice for
rectification. I suspect that the sub wants a heater supply on these
terminals. 2D21 isolated heater is on pins 3 and 4.

Recheck it. maybe you\'re numbering from the top view rather than the
bottom.

RL
Click to expand...

2D21 doesn\'t have a pin #8 - It\'s a 7 pin tube.

RL
 
On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <jrr@flippers.com>
wrote:


Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf
Click to expand...

Pin numbers are for 2050

http://www.r-type.org/pdfs/2050a.pdf

RL
 
On Saturday, August 5, 2023 at 7:02:38 PM UTC-4, legg wrote:
On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <j...@flippers.com
wrote:
Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf
Pin numbers are for 2050

http://www.r-type.org/pdfs/2050a.pdf
Click to expand...

Right, that\'s in the title of schematic.

RL
Click to expand...
 
On Friday, August 4, 2023 at 8:55:36 AM UTC-4, legg wrote:
On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <j...@flippers.com
wrote:
I have a circuit to replace a 2050 Thyratron tube with a FET and an SCR
C106, but I am having trouble sourcing the FET as I am not sure how to
translate the only specs on it that I can find to something more modern.

It was made by Siliconix # U266 or FN2651.

Specs are as follows:
-------
https://www.flippers.com/pdfs/Siliconix_RAE_1968_Catalog_Redacted.pdf

Igss = 6.0 nA
BVgss = 150V
Vp = 15.0V
Ipss = 100mA (min) to 300mA (max)
Gfs (umho) = 20K (min) to 40K (max)
Rds = 100 Ohms
Id(off) = 1.5nA
-------

Igss looks like Maximum gate current
BVgss is breakdown voltage Gate - Source I assume
What is Vp? Minimum turn on voltage?
Ipss is maximum current of what?
Gfs is inductance it would appear...
Rds is maximum On resistance
Id(off) - is that leakage?

Modern FETs don\'t use all the same descriptors though - at least not
that I\'ve found on digikey and I can\'t find any info on the U266(FN2651)
other than the page out of the RAE distributor\'s catalog

Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf

Thanks!

John :-#)#
Although it\'s mounted in a stud package and has that
weird gate voltage rating, it\'s only rated at 20Vds
Click to expand...

BVgss is breakdown voltage D-S with G-S shorted. Datasheet says 150V. Where are you getting 20V?


Big one is 500-900mA Idss .

U244 similar at 25Vds.

Old soviet surplus part KP903 (2P903) (~ ebay or amazon) might fit.

https://ipelectron.ru/upload/iblock/17f/17f60436ccfccebfbb284f2c7eaa89f3.pdf

I picked up two last year when they were offered by multiple
vendors @ US$5, if that\'s any use to you.

RL
Click to expand...
 
On 2023/08/05 1:29 p.m., legg wrote:
On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <jrr@flippers.com
wrote:



Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf


There may be something seriously wrong with your solidc state sub
pinout.

2D21 pins 7 and 5 are normally connected together, internally.

2D21 pin 3 is a heater terminal, with no cathose or anode contact.
Your solid state drawing seems to anticipate an anode function.

2D21 pins 2 and 7 will normally never see useful low voltage juice for
rectification. I suspect that the sub wants a heater supply on these
terminals. 2D21 isolated heater is on pins 3 and 4.

Recheck it. maybe you\'re numbering from the top view rather than the
bottom.

RL
Click to expand...

Actually the schematic drawing is from an old application note (I assume
Siliconix made it) for replacing a 2050 with an SCR and JFET - as the
original title said.

I\'m figuring (hoping) that the 2D21 is close enough in response to the
2050 that the circuit can be used with just putting the 2050 pins to
where the 2D21 is.

I have updated the schematic by adding the 2D21 pins (in brackets) - I
was fully aware of this, but perhaps this wasn\'t clearly presented - my
apologies!

John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
#7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
 
On 2023/08/05 12:18 p.m., piglet wrote:
On 04/08/2023 7:20 pm, piglet wrote:
On 04/08/2023 1:26 am, John Robertson wrote:
I have a circuit to replace a 2050 Thyratron tube with a FET and an
SCR C106, but I am having trouble sourcing the FET as I am not sure
how to translate the only specs on it that I can find to something
more modern.

It was made by Siliconix # U266 or FN2651.

Specs are as follows:
-------
https://www.flippers.com/pdfs/Siliconix_RAE_1968_Catalog_Redacted.pdf

Igss = 6.0 nA
BVgss = 150V
Vp = 15.0V
Ipss = 100mA (min) to 300mA (max)
Gfs (umho) = 20K (min) to 40K (max)
Rds = 100 Ohms
Id(off) = 1.5nA
-------

Igss looks like Maximum gate current
BVgss is breakdown voltage Gate - Source I assume
What is Vp? Minimum turn on voltage?
Ipss is maximum current of what?
Gfs is inductance it would appear...
Rds is maximum On resistance
Id(off) - is that leakage?

Modern FETs don\'t use all the same descriptors though - at least not
that I\'ve found on digikey and I can\'t find any info on the
U266(FN2651) other than the page out of the RAE distributor\'s catalog

Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and
writing to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf

Thanks!

John :-#)#



Vp is the pinchoff voltage; how negative the gate voltage has to be
for drain-source to be non-conducting - which could be Id(off) or some
other specified \"off\" current.

Gfs is forward transconductance; how drain-source current changes per
change in gate voltage.

Idss is the saturation drain-source current at zero gate volts.

High voltage JFETs are now very hard to get but you should be easily
able to use a modern depletion mosfet like LND150/250

piglet


That schematic you linked depicting the FET+SCR replacement for a
thyratron tube shows the fet drain supply coming from rectified heater
filament 6.3V supply. That is neat as it prevents triggering without the
heater supply and C31 has charged up.

I think they are assuming that 6.3V has either one side or its
center-tap (if present) near cathode 0V ground which means the drain
voltage is going to be well below 20V. Which makes the JFET requirements
look very undemanding, I can\'t see why they specified the U266 - I
reckon you can probably use just about any garden variety n-channel JFET
(2N5458, J113, 2N3819 etc etc)

I haven\'t figured out how shield grid 2 influences the triggering, do
you have a schematic showing how the 2D21 is used in the jukebox?

piglet
Click to expand...

G\'day!

Here is a link to the section of the manual covering that:

https://www.flippers.com/pdfs/Seeburg/V200/Seeburg_V200_Pg_5113-5143_B&W.pdf

The schematics for the 2D21s as used is on page 5128.

I drew a nasty sketch layout out the external and internal connections
for the Read-Out and Write-In 2D21s. The \'scope\' sketch is showing the
Detent Sw. pulse at the junction of R14 and R12 AIR.

https://www.flippers.com/pdfs/Seeburg/V200/TSR1-L6_Write-In&Read-Out.pdf

Thanks for your efforts!

John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
#7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
 
On Saturday, August 5, 2023 at 9:07:07 PM UTC-4, John Robertson wrote:
On 2023/08/05 1:29 p.m., legg wrote:
On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <j...@flippers.com
wrote:



Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf


There may be something seriously wrong with your solidc state sub
pinout.

2D21 pins 7 and 5 are normally connected together, internally.

2D21 pin 3 is a heater terminal, with no cathose or anode contact.
Your solid state drawing seems to anticipate an anode function.

2D21 pins 2 and 7 will normally never see useful low voltage juice for
rectification. I suspect that the sub wants a heater supply on these
terminals. 2D21 isolated heater is on pins 3 and 4.

Recheck it. maybe you\'re numbering from the top view rather than the
bottom.

RL
Actually the schematic drawing is from an old application note (I assume
Siliconix made it) for replacing a 2050 with an SCR and JFET - as the
original title said.

I\'m figuring (hoping) that the 2D21 is close enough in response to the
2050 that the circuit can be used with just putting the 2050 pins to
where the 2D21 is.
Click to expand...

All the 2D21 circuits are configured for EC2=0V shied grid to cathode. That puts you on the 0V parametric on the Average Control Characteristics datasheet curve, which shows an EC1 trigger voltage of -2V for an anode voltage of 125V, which is about what they\'re using.

Relative to cathode and within a few PN junction drops, the EC1 external drive has to be VP + VCR39 to bias Q31 into conduction. If CR39 is a 6.2V, then for Vp=-15, the circuit will trigger at about -15 + 6.3 = -8.7V applied to EC1 by external circuit, mainly because gfs is so huge-ish.

CR38, CR40 are there to clamp positive EC1 drives required to trigger with EC2 biases around -2V or more negative, which is not used AFAICS.

Schematic shows the heater potential pinned at about 30V more positive than the cathode (R25/R26). This means it is not necessary for Q31 to have a 150V BVGSS, and you can probably get away with 60V breakdown, and those are available. Just select one with 20,000 umho or so.

If parts of the circuit still functional, measure those potentials with high-z meter, especially heater-cathode differential, to verify before proceeding. the heater-cathode potential is determining the BVGSS required of the JFET.

I have updated the schematic by adding the 2D21 pins (in brackets) - I
was fully aware of this, but perhaps this wasn\'t clearly presented - my
apologies!
John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
#7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
Click to expand...
 
On Saturday, August 5, 2023 at 9:07:07 PM UTC-4, John Robertson wrote:
On 2023/08/05 1:29 p.m., legg wrote:
On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <j...@flippers.com
wrote:



Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf


There may be something seriously wrong with your solidc state sub
pinout.

2D21 pins 7 and 5 are normally connected together, internally.

2D21 pin 3 is a heater terminal, with no cathose or anode contact.
Your solid state drawing seems to anticipate an anode function.

2D21 pins 2 and 7 will normally never see useful low voltage juice for
rectification. I suspect that the sub wants a heater supply on these
terminals. 2D21 isolated heater is on pins 3 and 4.

Recheck it. maybe you\'re numbering from the top view rather than the
bottom.

RL
Actually the schematic drawing is from an old application note (I assume
Siliconix made it) for replacing a 2050 with an SCR and JFET - as the
original title said.

I\'m figuring (hoping) that the 2D21 is close enough in response to the
2050 that the circuit can be used with just putting the 2050 pins to
where the 2D21 is.

I have updated the schematic by adding the 2D21 pins (in brackets) - I
was fully aware of this, but perhaps this wasn\'t clearly presented - my
apologies!
John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John\'s Jukes Ltd.
#7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
\"Old pinballers never die, they just flip out.\"
Click to expand...

Pretty sure this will work in the V3, V7 slots:

https://www.nteinc.com/specs/400to499/pdf/nte466.pdf

Chopper doped to transition over quite small gate voltage excursions is what\'s needed. Breakdowns are minimums, and still safe in the Seeburg.

CR39 will need to be adjusted or eliminated.

Whatever you do, try to test it non-destructively.
 
On Sat, 5 Aug 2023 17:10:39 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

<snip>
Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf

Thanks!

John :-#)#
Although it\'s mounted in a stud package and has that
weird gate voltage rating, it\'s only rated at 20Vds

BVgss is breakdown voltage D-S with G-S shorted. Datasheet says 150V. Where are you getting 20V?
Click to expand...
Must be a misprint in Towers Intl Fet Selector. - Vdsmax=20V
U244, with the same package listed as sub with Vds<=25V.

Big one is 500-900mA Idss .

U244 similar at 25Vds.

Old soviet surplus part KP903 (2P903) (~ ebay or amazon) might fit.

https://ipelectron.ru/upload/iblock/17f/17f60436ccfccebfbb284f2c7eaa89f3.pdf

I picked up two last year when they were offered by multiple
vendors @ US$5, if that\'s any use to you.

RL
Click to expand...
 
On 06/08/2023 2:18 am, John Robertson wrote:
On 2023/08/05 12:18 p.m., piglet wrote:
On 04/08/2023 7:20 pm, piglet wrote:
On 04/08/2023 1:26 am, John Robertson wrote:
I have a circuit to replace a 2050 Thyratron tube with a FET and an
SCR C106, but I am having trouble sourcing the FET as I am not sure
how to translate the only specs on it that I can find to something
more modern.

It was made by Siliconix # U266 or FN2651.

Specs are as follows:
-------
https://www.flippers.com/pdfs/Siliconix_RAE_1968_Catalog_Redacted.pdf

Igss = 6.0 nA
BVgss = 150V
Vp = 15.0V
Ipss = 100mA (min) to 300mA (max)
Gfs (umho) = 20K (min) to 40K (max)
Rds = 100 Ohms
Id(off) = 1.5nA
-------

Igss looks like Maximum gate current
BVgss is breakdown voltage Gate - Source I assume
What is Vp? Minimum turn on voltage?
Ipss is maximum current of what?
Gfs is inductance it would appear...
Rds is maximum On resistance
Id(off) - is that leakage?

Modern FETs don\'t use all the same descriptors though - at least not
that I\'ve found on digikey and I can\'t find any info on the
U266(FN2651) other than the page out of the RAE distributor\'s catalog

Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and
writing to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf

Thanks!

John :-#)#



Vp is the pinchoff voltage; how negative the gate voltage has to be
for drain-source to be non-conducting - which could be Id(off) or
some other specified \"off\" current.

Gfs is forward transconductance; how drain-source current changes per
change in gate voltage.

Idss is the saturation drain-source current at zero gate volts.

High voltage JFETs are now very hard to get but you should be easily
able to use a modern depletion mosfet like LND150/250

piglet


That schematic you linked depicting the FET+SCR replacement for a
thyratron tube shows the fet drain supply coming from rectified heater
filament 6.3V supply. That is neat as it prevents triggering without
the heater supply and C31 has charged up.

I think they are assuming that 6.3V has either one side or its
center-tap (if present) near cathode 0V ground which means the drain
voltage is going to be well below 20V. Which makes the JFET
requirements look very undemanding, I can\'t see why they specified the
U266 - I reckon you can probably use just about any garden variety
n-channel JFET (2N5458, J113, 2N3819 etc etc)

I haven\'t figured out how shield grid 2 influences the triggering, do
you have a schematic showing how the 2D21 is used in the jukebox?

piglet


G\'day!

Here is a link to the section of the manual covering that:

https://www.flippers.com/pdfs/Seeburg/V200/Seeburg_V200_Pg_5113-5143_B&W.pdf

The schematics for the 2D21s as used is on page 5128.

I drew a nasty sketch layout out the external and internal connections
for the Read-Out and Write-In 2D21s. The \'scope\' sketch is showing the
Detent Sw. pulse at the junction of R14 and R12 AIR.

https://www.flippers.com/pdfs/Seeburg/V200/TSR1-L6_Write-In&Read-Out.pdf

Thanks for your efforts!

John :-#)#
Click to expand...

Ok, good to know that grid 2 is nothing to emulate. I can\'t figure out
from the jukebox schematics how the thyratrons are commutated off after
firing. Are they unlatched by disconnect switches in series or are they
fed from unsmoothed HV rails so get zero voltage at 120Hz rate?

If a low parts count solid state replacement is wanted then I think a
high voltage depletion mosfet makes the job very simple. Otherwise if
using the heater supply to delay operation a few hundred milliseconds
during power up is wanted then any jelly bean jfet could be used. I put
series caps in both heater supply lines in the hope it solves floating
heater supply issues.

My sketches here:

<https://www.dropbox.com/scl/fi/b292ch3sl7pbpv7o0si2h/Thyratron_emulator.pdf?rlkey=2gdmf8ph4wi7r2g5eq2incmb2&raw=1>

piglet
 
On Sun, 6 Aug 2023 08:37:41 -0700 (PDT), Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote:

On Saturday, August 5, 2023 at 9:07:07?PM UTC-4, John Robertson wrote:
On 2023/08/05 1:29 p.m., legg wrote:
On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <j...@flippers.com
wrote:



Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf


There may be something seriously wrong with your solidc state sub
pinout.

2D21 pins 7 and 5 are normally connected together, internally.

2D21 pin 3 is a heater terminal, with no cathose or anode contact.
Your solid state drawing seems to anticipate an anode function.

2D21 pins 2 and 7 will normally never see useful low voltage juice for
rectification. I suspect that the sub wants a heater supply on these
terminals. 2D21 isolated heater is on pins 3 and 4.

Recheck it. maybe you\'re numbering from the top view rather than the
bottom.

RL
Actually the schematic drawing is from an old application note (I assume
Siliconix made it) for replacing a 2050 with an SCR and JFET - as the
original title said.

I\'m figuring (hoping) that the 2D21 is close enough in response to the
2050 that the circuit can be used with just putting the 2050 pins to
where the 2D21 is.

All the 2D21 circuits are configured for EC2=0V shied grid to cathode.
That puts you on the 0V parametric on the Average Control Characteristics
datasheet curve, which shows an EC1 trigger voltage of -2V for an anode
voltage of 125V, which is about what they\'re using.

Relative to cathode and within a few PN junction drops, the EC1 external
drive has to be VP + VCR39 to bias Q31 into conduction. If CR39 is a 6.2V,
then for Vp=-15, the circuit will trigger at about -15 + 6.3 = -8.7V applied
to EC1 by external circuit, mainly because gfs is so huge-ish.

CR38, CR40 are there to clamp positive EC1 drives required to trigger
with EC2 biases around -2V or more negative, which is not used AFAICS.

Schematic shows the heater potential pinned at about 30V more positive
than the cathode (R25/R26). This means it is not necessary for Q31 to
have a 150V BVGSS, and you can probably get away with 60V breakdown,
and those are available. Just select one with 20,000 umho or so.

If parts of the circuit still functional, measure those potentials with
high-z meter, especially heater-cathode differential, to verify before
proceeding. the heater-cathode potential is determining the BVGSS
required of the JFET.
Click to expand...

Using the isolated heater supply for local DC biasing in a circuit
where the heater supply actually serves multiple tubes could be a
right mess, with a resulting direct connection between sections.

RL
 
On 06/08/2023 7:33 pm, legg wrote:
On Sun, 6 Aug 2023 08:37:41 -0700 (PDT), Fred Bloggs
bloggs.fredbloggs.fred@gmail.com> wrote:

On Saturday, August 5, 2023 at 9:07:07?PM UTC-4, John Robertson wrote:
On 2023/08/05 1:29 p.m., legg wrote:
On Thu, 3 Aug 2023 17:26:58 -0700, John Robertson <j...@flippers.com
wrote:



Schematic is here:
https://www.flippers.com/pdfs/2D21_2050_Solid_state_Thyratron.pdf

My goal is to replace the 2D21 Thyratron tube used reading and writing
to core memory for a 1955 jukebox:
https://www.flippers.com/pdfs/2D21_Thyratron_tube.pdf


There may be something seriously wrong with your solidc state sub
pinout.

2D21 pins 7 and 5 are normally connected together, internally.

2D21 pin 3 is a heater terminal, with no cathose or anode contact.
Your solid state drawing seems to anticipate an anode function.

2D21 pins 2 and 7 will normally never see useful low voltage juice for
rectification. I suspect that the sub wants a heater supply on these
terminals. 2D21 isolated heater is on pins 3 and 4.

Recheck it. maybe you\'re numbering from the top view rather than the
bottom.

RL
Actually the schematic drawing is from an old application note (I assume
Siliconix made it) for replacing a 2050 with an SCR and JFET - as the
original title said.

I\'m figuring (hoping) that the 2D21 is close enough in response to the
2050 that the circuit can be used with just putting the 2050 pins to
where the 2D21 is.

All the 2D21 circuits are configured for EC2=0V shied grid to cathode.
That puts you on the 0V parametric on the Average Control Characteristics
datasheet curve, which shows an EC1 trigger voltage of -2V for an anode
voltage of 125V, which is about what they\'re using.

Relative to cathode and within a few PN junction drops, the EC1 external
drive has to be VP + VCR39 to bias Q31 into conduction. If CR39 is a 6.2V,
then for Vp=-15, the circuit will trigger at about -15 + 6.3 = -8.7V applied
to EC1 by external circuit, mainly because gfs is so huge-ish.

CR38, CR40 are there to clamp positive EC1 drives required to trigger
with EC2 biases around -2V or more negative, which is not used AFAICS.

Schematic shows the heater potential pinned at about 30V more positive
than the cathode (R25/R26). This means it is not necessary for Q31 to
have a 150V BVGSS, and you can probably get away with 60V breakdown,
and those are available. Just select one with 20,000 umho or so.

If parts of the circuit still functional, measure those potentials with
high-z meter, especially heater-cathode differential, to verify before
proceeding. the heater-cathode potential is determining the BVGSS
required of the JFET.


Using the isolated heater supply for local DC biasing in a circuit
where the heater supply actually serves multiple tubes could be a
right mess, with a resulting direct connection between sections.

RL
Click to expand...

Completely agree! I think the old schematic the OP posted used the
heater supply to avoid using (at the time) non-existant HV fets. Now we
have 500-600V fets it becomes easy.

piglet
 
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