1S1 sampling bridge GaAs diodes: What alternatives?


leonard scheepsma
 

Dear all, my 1S1 gave up. It looks at least one of my sampling diodes has died. Searching through the related messages I noticed most comments are pretty old, so I hope some new ideas might have been launched on getting alternatives for the original GaAs diodes, just assuming these are completely unobtainable.
Looked at the Agilent/KeySight site, they mention some ultra fast GHz diodes there but these go through a distributor and I suspect ut won't be easy to get 4 of these at reasonable cost (not knowing they would work either)
Any tips, suggestions?

Thanks so much, Leonard


Tom Lee
 

I have not actually fixed one this way, but I would expect an HSMS-28xx Schottky to be a perfect replacement here. These are readily available.

Tom

Sent from my iThing, so please forgive the terseness and typos.

On Dec 9, 2020, at 14:26, "leonard scheepsma" <tubes.leonard@hetnet.nl> wrote:

Dear all, my 1S1 gave up. It looks at least one of my sampling diodes has died. Searching through the related messages I noticed most comments are pretty old, so I hope some new ideas might have been launched on getting alternatives for the original GaAs diodes, just assuming these are completely unobtainable.
Looked at the Agilent/KeySight site, they mention some ultra fast GHz diodes there but these go through a distributor and I suspect ut won't be easy to get 4 of these at reasonable cost (not knowing they would work either)
Any tips, suggestions?

Thanks so much, Leonard





Jim Ford
 

Although discontinued by Avago/Broadcom, I'm sure. That's the way it goes these days. They discontinued me and a whole lot of others as well, as some of you are probably tired of hearing me say!

The HSMS-28XX and other former HP Semiconductor devices just don't have the volume they once had, and the suits at Avago/Broadcom don't like that, nor do their investors.

Jim Ford

------ Original Message ------
From: "Tom Lee" <tomlee@ee.stanford.edu>
To: "TekScopes@groups.io" <TekScopes@groups.io>
Sent: 12/9/2020 2:31:43 PM
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What alternatives?

I have not actually fixed one this way, but I would expect an HSMS-28xx Schottky to be a perfect replacement here. These are readily available.

Tom

Sent from my iThing, so please forgive the terseness and typos.

On Dec 9, 2020, at 14:26, "leonard scheepsma" <tubes.leonard@hetnet.nl> wrote:

Dear all, my 1S1 gave up. It looks at least one of my sampling diodes has died. Searching through the related messages I noticed most comments are pretty old, so I hope some new ideas might have been launched on getting alternatives for the original GaAs diodes, just assuming these are completely unobtainable.
Looked at the Agilent/KeySight site, they mention some ultra fast GHz diodes there but these go through a distributor and I suspect ut won't be easy to get 4 of these at reasonable cost (not knowing they would work either)
Any tips, suggestions?

Thanks so much, Leonard








Dave Wise
 

I replaced my 1S1's four sampling diodes with four HSMS-8202 dual diodes, with each part wired to use the two diodes in series to increase the breakdown voltage and reduce the capacitance.
They are marked Obsolete at the major distributors, but Quest Components appears to have a few, as do MiniKits in Australia. There are about a dozen auctions at eBay.

Today I would use the Macom MA4E2054B1-287T which they list as a direct cross-ref. They are in stock at DigiKey and Mouser.
Or the Infineon BAT15, BAT17, or BAT62.

HTH,
Dave Wise

These are SOT-23. I made a little T-shaped "chip carrier" out of bare PCB material that fits in the original clips.
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Jim Ford via groups.io <james.ford=cox.net@groups.io>
Sent: Wednesday, December 09, 2020 2:43 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What alternatives?

Although discontinued by Avago/Broadcom, I'm sure. That's the way it
goes these days. They discontinued me and a whole lot of others as
well, as some of you are probably tired of hearing me say!

The HSMS-28XX and other former HP Semiconductor devices just don't have
the volume they once had, and the suits at Avago/Broadcom don't like
that, nor do their investors.

Jim Ford

------ Original Message ------
From: "Tom Lee" <tomlee@ee.stanford.edu>
To: "TekScopes@groups.io" <TekScopes@groups.io>
Sent: 12/9/2020 2:31:43 PM
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What
alternatives?

I have not actually fixed one this way, but I would expect an HSMS-28xx Schottky to be a perfect replacement here. These are readily available.

Tom

Sent from my iThing, so please forgive the terseness and typos.

On Dec 9, 2020, at 14:26, "leonard scheepsma" <tubes.leonard@hetnet.nl> wrote:

Dear all, my 1S1 gave up. It looks at least one of my sampling diodes has died. Searching through the related messages I noticed most comments are pretty old, so I hope some new ideas might have been launched on getting alternatives for the original GaAs diodes, just assuming these are completely unobtainable.
Looked at the Agilent/KeySight site, they mention some ultra fast GHz diodes there but these go through a distributor and I suspect ut won't be easy to get 4 of these at reasonable cost (not knowing they would work either)
Any tips, suggestions?

Thanks so much, Leonard








Tom Lee
 

Hi Dave,

I’ve used that very combination for 10GHz sampling bridges and it works very well. The rest of the 1S1 would be the performance limiter.

Less-capable diodes would work as well in this case, and would probably be more robust. As you and Jim Ford have noted, the HSMS diodes are now officially obsolete, so the usual distributors no longer stock them. But I see that Dan’s Small Parts and Kits has HSMS-2825 (dual diodes) at 10 for a buck. Hard to beat that. Buy a bunch more stuff to get your shipping dollar’s worth. And as with all of Dan’s deliveries, you’ll also get a large amount of tobacco smoke as a free bonus. Open your package outdoors if you’re sensitive. I’m only partly joking.

— Cheers,
Tom

Sent from my iThing, so please forgive typos and brevity.

On Dec 9, 2020, at 3:31 PM, Dave Wise <david_wise@phoenix.com> wrote:

I replaced my 1S1's four sampling diodes with four HSMS-8202 dual diodes, with each part wired to use the two diodes in series to increase the breakdown voltage and reduce the capacitance.
They are marked Obsolete at the major distributors, but Quest Components appears to have a few, as do MiniKits in Australia. There are about a dozen auctions at eBay.

Today I would use the Macom MA4E2054B1-287T which they list as a direct cross-ref. They are in stock at DigiKey and Mouser.
Or the Infineon BAT15, BAT17, or BAT62.

HTH,
Dave Wise

These are SOT-23. I made a little T-shaped "chip carrier" out of bare PCB material that fits in the original clips.
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Jim Ford via groups.io <james.ford=cox.net@groups.io>
Sent: Wednesday, December 09, 2020 2:43 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What alternatives?

Although discontinued by Avago/Broadcom, I'm sure. That's the way it
goes these days. They discontinued me and a whole lot of others as
well, as some of you are probably tired of hearing me say!

The HSMS-28XX and other former HP Semiconductor devices just don't have
the volume they once had, and the suits at Avago/Broadcom don't like
that, nor do their investors.

Jim Ford

------ Original Message ------
From: "Tom Lee" <tomlee@ee.stanford.edu>
To: "TekScopes@groups.io" <TekScopes@groups.io>
Sent: 12/9/2020 2:31:43 PM
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What
alternatives?

I have not actually fixed one this way, but I would expect an HSMS-28xx Schottky to be a perfect replacement here. These are readily available.

Tom

Sent from my iThing, so please forgive the terseness and typos.

On Dec 9, 2020, at 14:26, "leonard scheepsma" <tubes.leonard@hetnet.nl> wrote:

Dear all, my 1S1 gave up. It looks at least one of my sampling diodes has died. Searching through the related messages I noticed most comments are pretty old, so I hope some new ideas might have been launched on getting alternatives for the original GaAs diodes, just assuming these are completely unobtainable.
Looked at the Agilent/KeySight site, they mention some ultra fast GHz diodes there but these go through a distributor and I suspect ut won't be easy to get 4 of these at reasonable cost (not knowing they would work either)
Any tips, suggestions?

Thanks so much, Leonard


















Brian
 

Hi DaveI have also used HSMS8202 to repair S3A probes and have even made a replacement sampling sampling gate for an S6 sampling head . I can recommend them for the purpose , they have a higher reverse breakdown voltage than the 2825 I think .
regardsBrian

On Wednesday, 9 December 2020, 23:59:22 GMT, Tom Lee <tomlee@ee.stanford.edu> wrote:

Hi Dave,

I’ve used that very combination for 10GHz sampling bridges and it works very well. The rest of the 1S1 would be the performance limiter.

Less-capable diodes would work as well in this case, and would probably be more robust. As you and Jim Ford have noted, the HSMS diodes are now officially obsolete, so the usual distributors no longer stock them. But I see that Dan’s Small Parts and Kits has HSMS-2825 (dual diodes) at 10 for a buck. Hard to beat that. Buy a bunch more stuff to get your shipping dollar’s worth. And as with all of Dan’s deliveries, you’ll also get a large amount of tobacco smoke as a free bonus. Open your package outdoors if you’re sensitive. I’m only partly joking.

— Cheers,
Tom

Sent from my iThing, so please forgive typos and brevity.

On Dec 9, 2020, at 3:31 PM, Dave Wise <david_wise@phoenix.com> wrote:

I replaced my 1S1's four sampling diodes with four HSMS-8202 dual diodes, with each part wired to use the two diodes in series to increase the breakdown voltage and reduce the capacitance.
They are marked Obsolete at the major distributors, but Quest Components appears to have a few, as do MiniKits in Australia. There are about a dozen auctions at eBay.

Today I would use the Macom MA4E2054B1-287T which they list as a direct cross-ref.  They are in stock at DigiKey and Mouser.
Or the Infineon BAT15, BAT17, or BAT62.

HTH,
Dave Wise

These are SOT-23.  I made a little T-shaped "chip carrier" out of bare PCB material that fits in the original clips.
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Jim Ford via groups.io <james.ford=cox.net@groups.io>
Sent: Wednesday, December 09, 2020 2:43 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What alternatives?

Although discontinued by Avago/Broadcom, I'm sure.  That's the way it
goes these days.  They discontinued me and a whole lot of others as
well, as some of you are probably tired of hearing me say!

The HSMS-28XX and other former HP Semiconductor devices just don't have
the volume they once had, and the suits at Avago/Broadcom don't like
that, nor do their investors.

Jim Ford

------ Original Message ------
From: "Tom Lee" <tomlee@ee.stanford.edu>
To: "TekScopes@groups.io" <TekScopes@groups.io>
Sent: 12/9/2020 2:31:43 PM
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What
alternatives?

I have not actually fixed one this way, but I would expect an HSMS-28xx Schottky to be a perfect replacement here. These are readily available.

Tom

Sent from my iThing, so please forgive the terseness and typos.

On Dec 9, 2020, at 14:26, "leonard scheepsma" <tubes.leonard@hetnet.nl> wrote:

Dear all, my 1S1 gave up. It looks at least one of my sampling diodes has died. Searching through the related messages I noticed most comments are pretty old, so I hope some new ideas might have been launched on getting alternatives for the original GaAs diodes, just assuming these are completely unobtainable.
Looked at the Agilent/KeySight site, they mention some ultra fast GHz diodes there but these go through a distributor and I suspect ut won't be easy to get 4 of these at reasonable cost (not knowing they would work either)
Any tips, suggestions?

Thanks so much, Leonard


















Tom Lee
 

Nope. The 8202 is a VERY delicate beast (typical trade off between robustness and speed here). It is easily damaged by ESD during handling. It’s a 4V breakdown device, as compared to a 2825’s much greater 15V breakdown.

Sent from my iThing, so please forgive typos and brevity.

On Dec 9, 2020, at 4:05 PM, Brian via groups.io <brianas1948=yahoo.co.uk@groups.io> wrote:

 Hi DaveI have also used HSMS8202 to repair S3A probes and have even made a replacement sampling sampling gate for an S6 sampling head . I can recommend them for the purpose , they have a higher reverse breakdown voltage than the 2825 I think .
regardsBrian

On Wednesday, 9 December 2020, 23:59:22 GMT, Tom Lee <tomlee@ee.stanford.edu> wrote:

Hi Dave,

I’ve used that very combination for 10GHz sampling bridges and it works very well. The rest of the 1S1 would be the performance limiter.

Less-capable diodes would work as well in this case, and would probably be more robust. As you and Jim Ford have noted, the HSMS diodes are now officially obsolete, so the usual distributors no longer stock them. But I see that Dan’s Small Parts and Kits has HSMS-2825 (dual diodes) at 10 for a buck. Hard to beat that. Buy a bunch more stuff to get your shipping dollar’s worth. And as with all of Dan’s deliveries, you’ll also get a large amount of tobacco smoke as a free bonus. Open your package outdoors if you’re sensitive. I’m only partly joking.

— Cheers,
Tom

Sent from my iThing, so please forgive typos and brevity.

On Dec 9, 2020, at 3:31 PM, Dave Wise <david_wise@phoenix.com> wrote:

I replaced my 1S1's four sampling diodes with four HSMS-8202 dual diodes, with each part wired to use the two diodes in series to increase the breakdown voltage and reduce the capacitance.
They are marked Obsolete at the major distributors, but Quest Components appears to have a few, as do MiniKits in Australia. There are about a dozen auctions at eBay.

Today I would use the Macom MA4E2054B1-287T which they list as a direct cross-ref. They are in stock at DigiKey and Mouser.
Or the Infineon BAT15, BAT17, or BAT62.

HTH,
Dave Wise

These are SOT-23. I made a little T-shaped "chip carrier" out of bare PCB material that fits in the original clips.
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Jim Ford via groups.io <james.ford=cox.net@groups.io>
Sent: Wednesday, December 09, 2020 2:43 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What alternatives?

Although discontinued by Avago/Broadcom, I'm sure. That's the way it
goes these days. They discontinued me and a whole lot of others as
well, as some of you are probably tired of hearing me say!

The HSMS-28XX and other former HP Semiconductor devices just don't have
the volume they once had, and the suits at Avago/Broadcom don't like
that, nor do their investors.

Jim Ford

------ Original Message ------
From: "Tom Lee" <tomlee@ee.stanford.edu>
To: "TekScopes@groups.io" <TekScopes@groups.io>
Sent: 12/9/2020 2:31:43 PM
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What
alternatives?

I have not actually fixed one this way, but I would expect an HSMS-28xx Schottky to be a perfect replacement here. These are readily available.

Tom

Sent from my iThing, so please forgive the terseness and typos.

On Dec 9, 2020, at 14:26, "leonard scheepsma" <tubes.leonard@hetnet.nl> wrote:

Dear all, my 1S1 gave up. It looks at least one of my sampling diodes has died. Searching through the related messages I noticed most comments are pretty old, so I hope some new ideas might have been launched on getting alternatives for the original GaAs diodes, just assuming these are completely unobtainable.
Looked at the Agilent/KeySight site, they mention some ultra fast GHz diodes there but these go through a distributor and I suspect ut won't be easy to get 4 of these at reasonable cost (not knowing they would work either)
Any tips, suggestions?

Thanks so much, Leonard

























Brian
 

Hi Tom 
sorry about that I must be remembering one of the other devices from that series . I have not had any fail on me yet and it was several years ago that I made both of those repairs , naturally I took ESD precautions while assembling everything .
regards
Brian

On Thursday, 10 December 2020, 00:15:23 GMT, Tom Lee <tomlee@ee.stanford.edu> wrote:

Nope. The 8202 is a VERY delicate beast (typical trade off between robustness and speed here). It is easily damaged by ESD during handling. It’s a 4V breakdown device, as compared to a 2825’s much greater 15V breakdown.

Sent from my iThing, so please forgive typos and brevity.

On Dec 9, 2020, at 4:05 PM, Brian via groups.io <brianas1948=yahoo.co.uk@groups.io> wrote:

 Hi DaveI have also used HSMS8202 to repair S3A probes and have even made a replacement sampling sampling gate for an S6 sampling head . I can recommend them for the purpose , they have a higher reverse breakdown voltage than the 2825 I think .
regardsBrian

    On Wednesday, 9 December 2020, 23:59:22 GMT, Tom Lee <tomlee@ee.stanford.edu> wrote:

Hi Dave,

I’ve used that very combination for 10GHz sampling bridges and it works very well. The rest of the 1S1 would be the performance limiter.

Less-capable diodes would work as well in this case, and would probably be more robust. As you and Jim Ford have noted, the HSMS diodes are now officially obsolete, so the usual distributors no longer stock them. But I see that Dan’s Small Parts and Kits has HSMS-2825 (dual diodes) at 10 for a buck. Hard to beat that. Buy a bunch more stuff to get your shipping dollar’s worth. And as with all of Dan’s deliveries, you’ll also get a large amount of tobacco smoke as a free bonus. Open your package outdoors if you’re sensitive. I’m only partly joking.

— Cheers,
Tom

Sent from my iThing, so please forgive typos and brevity.

On Dec 9, 2020, at 3:31 PM, Dave Wise <david_wise@phoenix.com> wrote:

I replaced my 1S1's four sampling diodes with four HSMS-8202 dual diodes, with each part wired to use the two diodes in series to increase the breakdown voltage and reduce the capacitance.
They are marked Obsolete at the major distributors, but Quest Components appears to have a few, as do MiniKits in Australia. There are about a dozen auctions at eBay.

Today I would use the Macom MA4E2054B1-287T which they list as a direct cross-ref.  They are in stock at DigiKey and Mouser.
Or the Infineon BAT15, BAT17, or BAT62.

HTH,
Dave Wise

These are SOT-23.  I made a little T-shaped "chip carrier" out of bare PCB material that fits in the original clips.
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Jim Ford via groups.io <james.ford=cox.net@groups.io>
Sent: Wednesday, December 09, 2020 2:43 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What alternatives?

Although discontinued by Avago/Broadcom, I'm sure.  That's the way it
goes these days.  They discontinued me and a whole lot of others as
well, as some of you are probably tired of hearing me say!

The HSMS-28XX and other former HP Semiconductor devices just don't have
the volume they once had, and the suits at Avago/Broadcom don't like
that, nor do their investors.

Jim Ford

------ Original Message ------
From: "Tom Lee" <tomlee@ee.stanford.edu>
To: "TekScopes@groups.io" <TekScopes@groups.io>
Sent: 12/9/2020 2:31:43 PM
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What
alternatives?

I have not actually fixed one this way, but I would expect an HSMS-28xx Schottky to be a perfect replacement here. These are readily available.

Tom

Sent from my iThing, so please forgive the terseness and typos.

On Dec 9, 2020, at 14:26, "leonard scheepsma" <tubes.leonard@hetnet.nl> wrote:

Dear all, my 1S1 gave up. It looks at least one of my sampling diodes has died. Searching through the related messages I noticed most comments are pretty old, so I hope some new ideas might have been launched on getting alternatives for the original GaAs diodes, just assuming these are completely unobtainable.
Looked at the Agilent/KeySight site, they mention some ultra fast GHz diodes there but these go through a distributor and I suspect ut won't be easy to get 4 of these at reasonable cost (not knowing they would work either)
Any tips, suggestions?

Thanks so much, Leonard

























Jim Ford
 

Yeah, I did stock up on one of the HP/Agilent/Avago PIN diode models not too long ago, once I got the list of EOL items from Broadcom Ltd. About 1000 parts on the list, and maybe 2 had recommended substitutes, I kid you not! Gee, thanks a lot, Hock Tan! Lots and lots of them used in Raytheon systems (my employer post-Broadcom), and we have at least half a dozen component engineers working full-time on parts obsolescence.
They will have work basically forever.

Jim

------ Original Message ------
From: "Tom Lee" <tomlee@ee.stanford.edu>
To: TekScopes@groups.io
Sent: 12/9/2020 3:58:58 PM
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What alternatives?

Hi Dave,

I’ve used that very combination for 10GHz sampling bridges and it works very well. The rest of the 1S1 would be the performance limiter.

Less-capable diodes would work as well in this case, and would probably be more robust. As you and Jim Ford have noted, the HSMS diodes are now officially obsolete, so the usual distributors no longer stock them. But I see that Dan’s Small Parts and Kits has HSMS-2825 (dual diodes) at 10 for a buck. Hard to beat that. Buy a bunch more stuff to get your shipping dollar’s worth. And as with all of Dan’s deliveries, you’ll also get a large amount of tobacco smoke as a free bonus. Open your package outdoors if you’re sensitive. I’m only partly joking.

— Cheers,
Tom

Sent from my iThing, so please forgive typos and brevity.

On Dec 9, 2020, at 3:31 PM, Dave Wise <david_wise@phoenix.com> wrote:

I replaced my 1S1's four sampling diodes with four HSMS-8202 dual diodes, with each part wired to use the two diodes in series to increase the breakdown voltage and reduce the capacitance.
They are marked Obsolete at the major distributors, but Quest Components appears to have a few, as do MiniKits in Australia. There are about a dozen auctions at eBay.

Today I would use the Macom MA4E2054B1-287T which they list as a direct cross-ref. They are in stock at DigiKey and Mouser.
Or the Infineon BAT15, BAT17, or BAT62.

HTH,
Dave Wise

These are SOT-23. I made a little T-shaped "chip carrier" out of bare PCB material that fits in the original clips.
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Jim Ford via groups.io <james.ford=cox.net@groups.io>
Sent: Wednesday, December 09, 2020 2:43 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What alternatives?

Although discontinued by Avago/Broadcom, I'm sure. That's the way it
goes these days. They discontinued me and a whole lot of others as
well, as some of you are probably tired of hearing me say!

The HSMS-28XX and other former HP Semiconductor devices just don't have
the volume they once had, and the suits at Avago/Broadcom don't like
that, nor do their investors.

Jim Ford

------ Original Message ------
From: "Tom Lee" <tomlee@ee.stanford.edu>
To: "TekScopes@groups.io" <TekScopes@groups.io>
Sent: 12/9/2020 2:31:43 PM
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What
alternatives?

I have not actually fixed one this way, but I would expect an HSMS-28xx Schottky to be a perfect replacement here. These are readily available.

Tom

Sent from my iThing, so please forgive the terseness and typos.

On Dec 9, 2020, at 14:26, "leonard scheepsma" <tubes.leonard@hetnet.nl> wrote:

Dear all, my 1S1 gave up. It looks at least one of my sampling diodes has died. Searching through the related messages I noticed most comments are pretty old, so I hope some new ideas might have been launched on getting alternatives for the original GaAs diodes, just assuming these are completely unobtainable.
Looked at the Agilent/KeySight site, they mention some ultra fast GHz diodes there but these go through a distributor and I suspect ut won't be easy to get 4 of these at reasonable cost (not knowing they would work either)
Any tips, suggestions?

Thanks so much, Leonard





















snapdiode
 

Could a simple 1N5711 be jammed in there for that job?

I would think so, and it's in a package that is easy to handle.


Tom Lee
 

You are obviously a very careful engineer. My students are much less so. About a third of the class zapped their diodes enough to increase leakage significantly. The diodes still behaved as diodes, but no longer met spec. After seeing that the other two-thirds had been careful about ESD and got their circuits working without much trouble, they decided that maybe I wasn't making stuff up about ESD and started to follow instructions. :)

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 12/9/2020 16:18, Brian via groups.io wrote:
Hi Tom
sorry about that I must be remembering one of the other devices from that series . I have not had any fail on me yet and it was several years ago that I made both of those repairs , naturally I took ESD precautions while assembling everything .
regards
Brian
On Thursday, 10 December 2020, 00:15:23 GMT, Tom Lee <tomlee@ee.stanford.edu> wrote:
Nope. The 8202 is a VERY delicate beast (typical trade off between robustness and speed here). It is easily damaged by ESD during handling. It’s a 4V breakdown device, as compared to a 2825’s much greater 15V breakdown.

Sent from my iThing, so please forgive typos and brevity.

On Dec 9, 2020, at 4:05 PM, Brian via groups.io <brianas1948=yahoo.co.uk@groups.io> wrote:

 Hi DaveI have also used HSMS8202 to repair S3A probes and have even made a replacement sampling sampling gate for an S6 sampling head . I can recommend them for the purpose , they have a higher reverse breakdown voltage than the 2825 I think .
regardsBrian

    On Wednesday, 9 December 2020, 23:59:22 GMT, Tom Lee <tomlee@ee.stanford.edu> wrote:

Hi Dave,

I’ve used that very combination for 10GHz sampling bridges and it works very well. The rest of the 1S1 would be the performance limiter.

Less-capable diodes would work as well in this case, and would probably be more robust. As you and Jim Ford have noted, the HSMS diodes are now officially obsolete, so the usual distributors no longer stock them. But I see that Dan’s Small Parts and Kits has HSMS-2825 (dual diodes) at 10 for a buck. Hard to beat that. Buy a bunch more stuff to get your shipping dollar’s worth. And as with all of Dan’s deliveries, you’ll also get a large amount of tobacco smoke as a free bonus. Open your package outdoors if you’re sensitive. I’m only partly joking.

— Cheers,
Tom

Sent from my iThing, so please forgive typos and brevity.

On Dec 9, 2020, at 3:31 PM, Dave Wise <david_wise@phoenix.com> wrote:

I replaced my 1S1's four sampling diodes with four HSMS-8202 dual diodes, with each part wired to use the two diodes in series to increase the breakdown voltage and reduce the capacitance.
They are marked Obsolete at the major distributors, but Quest Components appears to have a few, as do MiniKits in Australia. There are about a dozen auctions at eBay.

Today I would use the Macom MA4E2054B1-287T which they list as a direct cross-ref.  They are in stock at DigiKey and Mouser.
Or the Infineon BAT15, BAT17, or BAT62.

HTH,
Dave Wise

These are SOT-23.  I made a little T-shaped "chip carrier" out of bare PCB material that fits in the original clips.
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Jim Ford via groups.io <james.ford=cox.net@groups.io>
Sent: Wednesday, December 09, 2020 2:43 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What alternatives?

Although discontinued by Avago/Broadcom, I'm sure.  That's the way it
goes these days.  They discontinued me and a whole lot of others as
well, as some of you are probably tired of hearing me say!

The HSMS-28XX and other former HP Semiconductor devices just don't have
the volume they once had, and the suits at Avago/Broadcom don't like
that, nor do their investors.

Jim Ford

------ Original Message ------
From: "Tom Lee" <tomlee@ee.stanford.edu>
To: "TekScopes@groups.io" <TekScopes@groups.io>
Sent: 12/9/2020 2:31:43 PM
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What
alternatives?

I have not actually fixed one this way, but I would expect an HSMS-28xx Schottky to be a perfect replacement here. These are readily available.

Tom

Sent from my iThing, so please forgive the terseness and typos.

On Dec 9, 2020, at 14:26, "leonard scheepsma" <tubes.leonard@hetnet.nl> wrote:

Dear all, my 1S1 gave up. It looks at least one of my sampling diodes has died. Searching through the related messages I noticed most comments are pretty old, so I hope some new ideas might have been launched on getting alternatives for the original GaAs diodes, just assuming these are completely unobtainable.
Looked at the Agilent/KeySight site, they mention some ultra fast GHz diodes there but these go through a distributor and I suspect ut won't be easy to get 4 of these at reasonable cost (not knowing they would work either)
Any tips, suggestions?

Thanks so much, Leonard



























Tom Lee
 

A 1N5711 would certainly function, but its couple-pF capacitance and couple-nH package inductance, augmented by additional lead inductance, are a bit on the high side for a 1GHz sampler. But no harm in trying. It's dead now, so some functionality would certainly be an improvement over its current state. If nothing else, it would be an easy way to verify that a dead bridge is his only problem. Luckily, this part is still readily available from many sources at low cost (including a member of this group, from whom I recently purchased 100 or so to refresh my depleted stock), so that's a plus.

Series-connected pairs of these diodes might get him across the goal line, but I don't know if that can be done without adding significant lead inductance beyond a single part.

Just out of curiosity, is there anyone here who knows the history of Tek and its GaAs diodes? To produce good sampling diodes and SRDs out of GaAs was definitely a black art in the 1960s, so I'm very curious how they pulled that off. I'm sure that there are a lot of good stories about the problems they had and how they overcame them. All I could find were little bits and pieces in Tek Talk and such. If anyone here knows, pr knows someone who knows, please contact me.

Cheers,
Tom

--
Prof. Thomas H. Lee
Allen
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 12/9/2020 21:25, snapdiode via groups.io wrote:
Could a simple 1N5711 be jammed in there for that job?

I would think so, and it's in a package that is easy to handle.




snapdiode
 

I love the 1N5711. I've replaced several of the GaAs diodes in the 1S1 memory circuit with 1N5711s and it works fine.


Tom Lee
 

It is definitely a very good small-signal Schottky, which accounts for its enduring popularity. It's my go-to through-hole diode below ~1GHz, and I'm not suprised it works well in the memory subcircuit. What I do not know is how well it would work in the sampling bridge, whose requirements are more stringent. The 1N5711 seems marginal -- not obviously unsuitable, but not obviously a win, either. I would love to have someone try it and report back.

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 12/10/2020 21:50, snapdiode via groups.io wrote:
I love the 1N5711. I've replaced several of the GaAs diodes in the 1S1 memory circuit with 1N5711s and it works fine.




Dave Wise
 

Which circuit numbers?

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of snapdiode via groups.io <snapdiode=yahoo.com@groups.io>
Sent: Thursday, December 10, 2020 9:50 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 1S1 sampling bridge GaAs diodes: What alternatives?

I love the 1N5711. I've replaced several of the GaAs diodes in the 1S1 memory circuit with 1N5711s and it works fine.


snapdiode
 

Sadly all my 1S1s are basically bookends these days. I'd love to give it try too but it's not in my plans right now.


Kurt Rosenfeld
 

Do we know the original selection criteria Tek used for the diodes used in the sampling bridge?


snapdiode
 

No idea, but they need to withstand 2 volts reverse bias. Then they need to conduct with 2 volt forward bias from the pulse network. In about 350 ps.

Naively applying I=CdV/dT, you get a large number for dV/dT, around 11.5E9. So if you swing 2pF 4 volts in 350ps, you need about 20mA from the pulse network.

The 1N5711 is specified at 2pF junction capacitance, but that is at 0 volts. With 2 volts reverse bias, I am guessing from the graph it's more like 1pF. In any case, it's lower.

"But Snapdiode", I hear you say, "the 1N5711 is only rated for 15mA current!" But that's continuous, the 1S1 blasts this current pulse for probably much less than 350pS and at a quite low PRR.

Now Tek says the diode quad was "matched". In the days of hand-made diodes I assume this was to select for diodes with similar capacitance.

I'm going to theorize that modern manufacturing processes for the 1N5711 make them all very nearly identical.

But still, that 15mA number bugs me. Does anyone have 25 cents to spare to give this a try?


toby@...
 

On 2020-12-11 1:21 p.m., snapdiode via groups.io wrote:
No idea, but they need to withstand 2 volts reverse bias. Then they need to conduct with 2 volt forward bias from the pulse network. In about 350 ps.

Naively applying I=CdV/dT, you get a large number for dV/dT, around 11.5E9. So if you swing 2pF 4 volts in 350ps, you need about 20mA from the pulse network.

The 1N5711 is specified at 2pF junction capacitance, but that is at 0 volts. With 2 volts reverse bias, I am guessing from the graph it's more like 1pF. In any case, it's lower.

"But Snapdiode", I hear you say, "the 1N5711 is only rated for 15mA current!" But that's continuous, the 1S1 blasts this current pulse for probably much less than 350pS and at a quite low PRR.

Now Tek says the diode quad was "matched". In the days of hand-made diodes I assume this was to select for diodes with similar capacitance.

I'm going to theorize that modern manufacturing processes for the 1N5711 make them all very nearly identical.

But still, that 15mA number bugs me. Does anyone have 25 cents to spare to give this a try?
The cheap ones are 15mA.

https://www.mouser.ca/datasheet/2/389/1n5711-1848799.pdf

Digikey sells a 33mA _average_ current version for much more.
https://www.digikey.ca/en/products/detail/microsemi-corporation/1n5711-1/4899004

--Toby







snapdiode