Topics

PG506 vs. PG506A risetime?


Jeff Keyzer
 

I have a Lecroy DA1855A differential amplifier with DXC100A probes. I am trying to calibrate the probes. The calibration manual calls for a PG506A "or equivalent" for calibration. They are using both the high amplitude and fast rise outputs of the pulser to adjust LF/HF probe compensation and CMRR.

There is also a paragraph that reads "If pulse generators such as the Tektronix PG506 that do not have a high enough slew rate are encountered in measurement situations..." and then they go on to describe a way of compensating the probes without access to a pulser.

I'm a little confused by their note, and since this the DA1855A a discontinued product I'm not expecting much help from Lecroy. I'm wondering if this is their way of saying that they prefer the PG506A over the PG506?

My question for the group - did the risetime/slew rate change between the PG506 and the PG506A? Would Lecroy have reason to prefer one over the other, or am I misreading their note?


Eric
 

They might be talking about the 284 Vs the 506. The 284 is much faster about 70ps

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Jeff Keyzer
Sent: Wednesday, February 17, 2021 1:01 PM
To: TekScopes@groups.io
Subject: [TekScopes] PG506 vs. PG506A risetime?

I have a Lecroy DA1855A differential amplifier with DXC100A probes. I am trying to calibrate the probes. The calibration manual calls for a PG506A "or equivalent" for calibration. They are using both the high amplitude and fast rise outputs of the pulser to adjust LF/HF probe compensation and CMRR.

There is also a paragraph that reads "If pulse generators such as the Tektronix PG506 that do not have a high enough slew rate are encountered in measurement situations..." and then they go on to describe a way of compensating the probes without access to a pulser.

I'm a little confused by their note, and since this the DA1855A a discontinued product I'm not expecting much help from Lecroy. I'm wondering if this is their way of saying that they prefer the PG506A over the PG506?

My question for the group - did the risetime/slew rate change between the PG506 and the PG506A? Would Lecroy have reason to prefer one over the other, or am I misreading their note?


Albert Otten
 

The PG506 and PG506A have the same spec 1 ns for rise time (to zero) of the fast pulse outputs.
The TD pulser 067-0681-01 is mentioned under as Optional Accessories is faster caibration aid but is no part of the TG506(A).

Albert


Jean-Paul
 

We use PG506 but prefer Leo Bodnar 40 pS pulser for risetime and transients adjustment

It is USB powered and £50 from UK and USA Ham equipment outlets
http://www.leobodnar.com/shop/index.php?main_page=product_info&products_id=295

Available in BNC and SMA version

Jon


 

On Wed, Feb 17, 2021 at 07:01 PM, Jeff Keyzer wrote:


I have a Lecroy DA1855A differential amplifier with DXC100A probes.
That's around 100 MHz bandwidth. Leo Bodnar's pulser isn't just overkill in this case but could also result in less-than-desirable waveforms because of the amplifier's phase behavior and large high-harmonics content of the source signal.

Raymond


Jean-Paul
 

Hello again Raymond

We use the 40 pS Leonard Bodnar pulser on many scopes from 100 MHz analog to 1 ghz digital, no problem to accurately reveal the transient response.

The PG506 are not as fast and do not resolve as fine a structure of the response. some fast pulse and transients photos were posted long ago to the photos albums.

Bon Journée


Jon


 

Hi Jeff,
I got this reply from John Addis. He is the absolutely brilliant designer of many Tektronix ICs, circuits, amplifiers, and the DA1855!
Dennis Tillman W7pF

From: John Addis
Sent: Thursday, February 18, 2021 7:19 PM
To: dennis@ridesoft.com
Subject: RE: LeCroy DA1855A Differential Amplifier

Jeff,

The Preamble 1855 was designed in Beaverton. The LeCroy DA1855A was designed and built by Preamble Instruments in Beaverton until LeCroy bought Preamble Instruments and ultimately changed the 1855A front panel and body color from tan to gray. LeCroy never made the non-A version.

My copy of the Preamble 1855 Operator’s Manual (which should be the same as the LeCroy 1855A) lists the equipment required as PG506A. The PG506 and PG506A are essentially the same for the purpose of adjusting the 1855A. I am responsible for the inconsistency.

Later, my copy says “Pulse generators such as the Tektronix PG506 do not have a slew rate as high as might be encountered in some measurement situations...” There is no “If” at the beginning of the sentence. The intention was to allow additional fine adjustment, not to provide a basic means of adjusting CMRR because some device under test might not have an appropriately long enough pulse to adjust the probes over the entire frequency range. Best to use a flat top fast rise pulse such as the PG506/PG506A.

There are few generators providing a higher amplitude and faster rise pulse. I built one at Preamble that had 150V output with a 1.5ns risetime. I still have it. I don’t remember if that was used in calibration at the Preamble factory or not. That was up to the person calibrating the 1855 or 1855A and probes (Steve Lindberg is still around, and I can provide a phone number if requested). That 1.5ns rise time might make calibration even more difficult to do because you could see much more.

Don’t worry about it. It’s a tough calibration to do, and you can’t make it perfect.

Incidentally, the difference between the Preamble 1855 and 1855A is in the logic board. The A model uses a microprocessor and the non-A uses discrete logic. The A model turns the reference oven off with the power switch, the 1855 does not. The LeCroy version has an additional “Remote” digital interface. The amplifiers and probes are all the same to my knowledge

LeCroy may have made some minor changes in the circuit. For example, if they could not obtain a particular transistor, they may have substituted another. I know of no significant changes to the amplifier over the 19 years or so that the 1855/1855A was in production.

Someday I may release the schematic to the public. I hope you like the instrument. If you ever mess with or calibrate an 1855A itself, there are several unmarked holes in the top panel for input attenuator adjustments. I have a template which names those controls that I could make available. I do not recommend messing with those adjustments unless they are screwed up.

John Addis

-----Original Message-----

From: Dennis Tillman W7pF
Sent: Thursday, February 18, 2021 5:02 PM
To: John Addis
Subject: LeCroy DA1855A Differential Amplifier

Is this the LeCroy Differential Amplifier you designed?

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jeff Keyzer
Sent: Wednesday, February 17, 2021 10:01 AM
To: TekScopes@groups.io
Subject: [TekScopes] PG506 vs. PG506A risetime?

I have a Lecroy DA1855A differential amplifier with DXC100A probes. I am trying to calibrate the probes. The calibration manual calls for a PG506A "or equivalent" for calibration. They are using both the high amplitude and fast rise outputs of the pulser to adjust LF/HF probe compensation and CMRR.

There is also a paragraph that reads "If pulse generators such as the Tektronix PG506 that do not have a high enough slew rate are encountered in measurement situations..." and then they go on to describe a way of compensating the probes without access to a pulser.

I'm a little confused by their note, and since this the DA1855A a discontinued product I'm not expecting much help from Lecroy. I'm wondering if this is their way of saying that they prefer the PG506A over the PG506?

My question for the group - did the risetime/slew rate change between the PG506 and the PG506A? Would Lecroy have reason to prefer one over the other, or am I misreading their note?








--
Dennis Tillman W7pF
TekScopes Moderator


Jeff Keyzer
 

Dennis,

Sorry for the late reply, it's been a busy week.

Imagine my surprise to see a response from John Addis. Thank you for forwarding my question to him. I had the privilege of meeting John a couple years ago at the VintageTek museum.

I have access to a PG506 (non-A) so I think I am all set.

It is a remarkable instrument.

Thanks again for passing on John's reply.