tek 7904A...


Goran <goran.krusell@...>
 

Hello,

the model 7904A is a redesigned and improved version of the 7904. Does anyone know why this was done? Cost, reliability or production margins?
Is there any description available except for the service manual?

Regards
Göran


 

Some reasons for the redesign:

1) Better performance (higher bandwidth) because of improved ICs.
2) Simplified circuitry made it easier and more cost effective to build.
3) Greater profit margins.

Dennis

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of Goran
Sent: Monday, December 21, 2009 11:17 AM
To: TekScopes@...
Subject: [TekScopes] tek 7904A...

Hello,

the model 7904A is a redesigned and improved version of the 7904. Does
anyone know why this was done? Cost, reliability or production margins?
Is there any description available except for the service manual?

Regards
Göran


Greg Werstiuk
 

Tek was in the habit improving their equipment.  The catalog pages for the 7904 and 7904A described the specification differences.  I don’t have them at my fingertips but the “A” has greater bandwidth and faster risetimes.

 

As I recall, the 7904 had a fan which is eliminated in the “A” which reduced noise and eliminated a point of failure.  (Completely different power supplies between the two.)

 

-

Greg

 

 


From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Goran
Sent: Monday, December 21, 2009 11:17 AM
To: TekScopes@...
Subject: [TekScopes] tek 7904A...

 

 

Hello,

the model 7904A is a redesigned and improved version of the 7904. Does anyone know why this was done? Cost, reliability or production margins?
Is there any description available except for the service manual?

Regards
Göran


victor.silva
 

I'm no expert on the 7904, but I believe it's the other way around. The later model 7904A is the one with the fan.

I assume it was added to improve instrument cooling.

--Victor

--- In TekScopes@..., "Greg Werstiuk" <greg_werstiuk@...> wrote:

Tek was in the habit improving their equipment. The catalog pages for the
7904 and 7904A described the specification differences. I don't have them
at my fingertips but the "A" has greater bandwidth and faster risetimes.



As I recall, the 7904 had a fan which is eliminated in the "A" which reduced
noise and eliminated a point of failure. (Completely different power
supplies between the two.)



-

Greg





_____

From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of Goran
Sent: Monday, December 21, 2009 11:17 AM
To: TekScopes@...
Subject: [TekScopes] tek 7904A...





Hello,

the model 7904A is a redesigned and improved version of the 7904. Does
anyone know why this was done? Cost, reliability or production margins?
Is there any description available except for the service manual?

Regards
Göran


d.seiter@...
 

My 7904 (non-A) has no fan.  The non-A's appear to have a picky power supply; my non-A is in tick mode(which has been resisting repair... and my -A is behaving nicely  :-))

Dave

----- Original Message -----
From: "Greg Werstiuk"
To: TekScopes@...
Sent: Monday, December 21, 2009 11:56:01 PM GMT -07:00 US/Canada Mountain
Subject: RE: [TekScopes] tek 7904A...

 

Tek was in the habit improving their equipment.  The catalog pages for the 7904 and 7904A described the specification differences.  I don’t have them at my fingertips but the “A” has greater bandwidth and faster risetimes.

 

As I recall, the 7904 had a fan which is eliminated in the “A” which reduced noise and eliminated a point of failure.  (Completely different power supplies between the two.)

 

-

Greg

 

 


From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Goran
Sent: Monday, December 21, 2009 11:17 AM
To: TekScopes@...
Subject: [TekScopes] tek 7904A...

 

 

Hello,

the model 7904A is a redesigned and improved version of the 7904. Does anyone know why this was done? Cost, reliability or production margins?
Is there any description available except for the service manual?

Regards
Göran


Greg Werstiuk
 

Brain fade.  Was thinking the 7904 had a separate power supply fan.  You are correct the 7904A adds an air stirrer on the right hand side (when faced from the front).

 

-

Greg

 


From: TekScopes@... [mailto:TekScopes@...] On Behalf Of victor.silva
Sent: Monday, December 21, 2009 11:37 PM
To: TekScopes@...
Subject: [TekScopes] Re: tek 7904A...

 

 

I'm no expert on the 7904, but I believe it's the other way around. The later model 7904A is the one with the fan.

I assume it was added to improve instrument cooling.

--Victor

--- In TekScopes@yahoogroups.com, "Greg Werstiuk" ...> wrote:
>
> Tek was in the habit improving their equipment. The catalog pages for the
> 7904 and 7904A described the specification differences. I don't have them
> at my fingertips but the "A" has greater bandwidth and faster risetimes.
>
>
>
> As I recall, the 7904 had a fan which is eliminated in the "A" which reduced
> noise and eliminated a point of failure. (Completely different power
> supplies between the two.)
>
>
>
> -
>
> Greg
>
>
>
>
>
> _____
>
> From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com] On Behalf
> Of Goran
> Sent: Monday, December 21, 2009 11:17 AM
> To: TekScopes@yahoogroups.com
> Subject: [TekScopes] tek 7904A...
>
>
>
>
>
> Hello,
>
> the model 7904A is a redesigned and improved version of the 7904. Does
> anyone know why this was done? Cost, reliability or production margins?
> Is there any description available except for the service manual?
>
> Regards
> Göran
>


David C. Partridge <david.partridge@...>
 

The later 7904As had a REALLY NOISY PC type fan at the rear. Almost as
raucous as the 2430A (which is deafening).

The early 7904As with the same fan type as the 7834 etc. were nice and
quiet.

If ever there were a candidate for replacement with a modern quiet fan ...

Dave

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of Greg Werstiuk
Sent: 22 December 2009 07:45
To: TekScopes@...
Subject: RE: [TekScopes] Re: tek 7904A...


You are correct the 7904A adds an air stirrer on the right hand side (when
faced from the front).


Jim
 

On Tuesday 22 December 2009 2:43:05 am d.seiter@... wrote:
My 7904 (non-A) has no fan. The non-A's appear to have a picky power
supply; my non-A is in tick mode(which has been resisting repair... and my
-A is behaving nicely :-))
Does anyone have any advice on the "picky power supply" issue? My power supply
seems to be within spec. The plug-ins I'm using work fine on a 7514 and a
7704A. But on the 7904, if I try to use a full complement of four plug-ins
things usually get flaky (readout becomes garbled on some plug-ins, the 7D14
counter stops working, etc.). It works with three plug-ins, but does "tic" a
couple of times at start up.

I've been considering recapping the regulated supplies to see if that helps.

thanks,
Jim W4JBM


dnmeeks
 

You are headed in this direction, but I would suspect filter caps that have dropped in value. At light load, they would still work okay, but at heavier loads the ripple may get so large that regulators either drop out of regulation or otherwise pass the ripple along. I have had this same symptom with TM5xxx mainframes.

Having said that, I know nothing about the guts of a ‘7904 – whether the mainframe has rectifier / filter banks or not.

 

Good luck –

Dan

 

From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Jim
Sent: Tuesday, December 22, 2009 5:09 AM
To: TekScopes@...
Subject: [TekScopes] Re: tek 7904A...

 

 

On Tuesday 22 December 2009 2:43:05 am d.seiter@... wrote:
> My 7904 (non-A) has no fan. The non-A's appear to have a picky power
> supply; my non-A is in tick mode(which has been resisting repair... and my
> -A is behaving nicely :-))

Does anyone have any advice on the "picky power supply" issue? My power supply
seems to be within spec. The plug-ins I'm using work fine on a 7514 and a
7704A. But on the 7904, if I try to use a full complement of four plug-ins
things usually get flaky (readout becomes garbled on some plug-ins, the 7D14
counter stops working, etc.). It works with three plug-ins, but does "tic" a
couple of times at start up.

I've been considering recapping the regulated supplies to see if that helps.

thanks,
Jim W4JBM


ditter2
 

--- In TekScopes@..., "Goran" <goran.krusell@...> wrote:

Hello,

the model 7904A is a redesigned and improved version of the 7904. Does anyone know why this was done? Cost, reliability or production margins?
Is there any description available except for the service manual?

Regards
Göran
I don't have the specs in front of me to compare, but with some effort I could find an old catalog with the non"A" model to see what changed.

There is one thing I do know. At the time the 7904 went to the "A" model, Tek had a policy that the model suffix would not increment unless there was a significant specification or feature change for the customer. Improved reliability, manufacturing cost savings, fixing the annoying power supply start up, etc, would not merit the "A" model for the 7904.

Consider the 7A13 upgrade to the electronic DMM for displaying the comparison voltage. The old "odometer" version was prone to mechanical alignment problems that caused it to bind up and ultimately strip its plastic gears. I don't think I have ever seen an old one that was actually well used that did not suffer this problem. The DMM totally eliminated this reliability problem, and changed a significant portion of the circuitry and mechanical parts list. Yet the model remained a 7A13.

This was not always the case. The 310A is essentially the same circuitry as the 310, with no change in performances or features. It returned to ceramic strips. The original 310 tried out this new technology of "etched circuit boards" but before plated through holes were invented. Using rivets for feed throughs proved intermittent, resulting in a reliability nightmare. Sometime in either the late 1960's or early 1970s Tek adopted the policy to denote major internal changes with no performance enhancement using large serial number breaks rather than model number increments.

- Steve


Craig Sawyers <c.sawyers@...>
 

There is one thing I do know. At the time the 7904 went to
the "A" model, Tek had a policy that the model suffix would
not increment unless there was a significant specification or
feature change for the customer. Improved reliability,
manufacturing cost savings, fixing the annoying power supply
start up, etc, would not merit the "A" model for the 7904.
There are major internal changes between the non-A and the -A versions. Tek
moved across to using Hypcon hybrids from the earlier generation hermetic
canned types. In addition they moved the HT from being inside the box to
the more regular 4-bay location on the main chassis. And the mode select
buttons were no longer illuminated.

Essentially there is much in common, electrically and visually (including
Hypcon hybrids) with the 7104. Although the nominal bandwidth of the -A is
the same as the earlier 7904 scope, in practice it comfortably exceeds it by
a big margin. There is a view that Tek knew this, but did not mention it in
the specifications since (MCP based CRT notwithstanding) it was sufficiently
close to the 7104 in bandwith terms to be competitive.

Craig


 

--- In TekScopes@..., "Goran" <goran.krusell@...> wrote:

Hello,

the model 7904A is a redesigned and improved version of the 7904. Does anyone know why this was done? Cost, reliability or production margins?
Is there any description available except for the service manual?

Regards
Göran
-----------------------
Here's what the 7904A MSR dated May 83 said:

//I. Product Description and Specifications

The 7904A will replace the 7904. All spec's will remain the same. The 7904A will have the following improvements.

1. Split casting used in 7800's, 7104 for easier servicing.

2. Power supplies and other parts will be common to existing 7800's, 7104 mainframes.

3. Improvement in reliability and performance made in the 7800's, 7104 will be incorporated in the 7904A.

4. Front and rear panel controls will be the same as the 7104.//

/Håkan


ditter2
 

--- In TekScopes@..., "Craig Sawyers" <c.sawyers@...> wrote:

There are major internal changes between the non-A and the -A versions. Tek
moved across to using Hypcon hybrids from the earlier generation hermetic
canned types. In addition they moved the HT from being inside the box to
the more regular 4-bay location on the main chassis. And the mode select
buttons were no longer illuminated.

Essentially there is much in common, electrically and visually (including
Hypcon hybrids) with the 7104. Although the nominal bandwidth of the -A is
the same as the earlier 7904 scope, in practice it comfortably exceeds it by
a big margin. There is a view that Tek knew this, but did not mention it in
the specifications since (MCP based CRT notwithstanding) it was sufficiently
close to the 7104 in bandwith terms to be competitive.

Craig
I was not aware of the similarities with the 7104. I know a similar thing happened when the 7704 changed to the 'A' model. The CRT was the same one used in the 7904, and I think the vertical amp hybrid is also the same (might be wrong on that), although the channel switch is not the same. The net result is that the 7704A has considerably more real BW and faster rise time than the original non 'A' model. Of course a big change in the A model was the ability to separate the base unit from the display. By adding a crude digitizer module in between, Tek had its first DSO. Not very user friendly, but none of the early DSOs were, including the 2430/2440

- Steve


Greg Werstiuk
 

Interesting.  My 7904A has no fan at the rear.  The rear panel is solid except for a massive finned heatsink in the lower left corner.  The only fan is the one I described.

 

-

Greg

 


From: TekScopes@... [mailto:TekScopes@...] On Behalf Of David C. Partridge
Sent: Tuesday, December 22, 2009 12:24 AM
To: TekScopes@...
Subject: RE: [TekScopes] Re: tek 7904A...

 

 

The later 7904As had a REALLY NOISY PC type fan at the rear. Almost as
raucous as the 2430A (which is deafening).

The early 7904As with the same fan type as the 7834 etc. were nice and
quiet.

If ever there were a candidate for replacement with a modern quiet fan ...

Dave

-----Original Message-----
From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com] On Behalf
Of Greg Werstiuk
Sent: 22 December 2009 07:45
To: TekScopes@yahoogroups.com
Subject: RE: [TekScopes] Re: tek 7904A...

You are correct the 7904A adds an air stirrer on the right hand side (when
faced from the front).