Date   

Re: Ovenized 2901 Time Mark Generator

Kuba Ober <ober.14@...>
 

I'm frequently tempted to buy a newer 10MHz ovenized crystal and substitute
it for the one in the 2901. It would be an easy way to improve the accuracy
of the instrument by 1 to 2 orders of magnitude for less that $50. The
existing crystal is in a tube socket so it is trivial to remove it and
replace it. There is plenty of room for a substitute part.

But OTOH, building a GPS Frequency Standard sounded more interesting and
since it would have 4 orders of magnitude better accuracy and require no
calibration I decided to give that a try instead.
AFAIK: A GPS standard by itself is jittery. It has nice long-term stability,
but short-term it is as bad as its internal oscillator. Nothing that fits in
your palm will have a good, stable oscillator, unless it's some clever hybrid
design with active gradient compensation (multipoint heaters and
thermocouples). Normally, thermal stability implies size. You'll want an
ovenized crystal slaved to the GPS to compensate for long-term drift. Feel
free to look at a recent discussion about this on the hp_agilent_equipment
forum.

Cheers, Kuba


Re: 7623A, 7633 Bistabile Storage Mode?

Kuba Ober <ober.14@...>
 

I have a question about the bistabile storage mode on 7623A, 7633 scopes.
I have repaired four of them and when I try the bistabile mode, the stored
image has only a small contrast, since the backround is almost so bright
as the stored image.

Is this normal or the crt's are worn out?
Pretty much normal, as I see the same thing even on an almost unused 7934 (got
it as NOS early this year).

Cheers, Kuba


Re: 531A TRIGGER

Stan and Patricia Griffiths <w7ni@...>
 

Looking at the 531A Modification Summary, I think the only dates I see are
the date that the Mod Summary was last updated and not the date the mod was
first installed so I don't think the Mod Summary alone will help much to
date an instrument by serial number. This may not be the case for all
Modification Summaries.



Stan



_____

From: TekScopes@yahoogroups.com [mailto:TekScopes@yahoogroups.com] On Behalf
Of David Wise
Sent: Wednesday, November 01, 2006 9:43 AM
To: TekScopes@yahoogroups.com
Subject: RE: [TekScopes] RE:531A TRIGGER



There's no direct translation from serial number to date.

The product improvements documented in the "Mod Summary"
have the serial number effectivity range listed. They
are also dated, which would give an approximate date
for a given serial number. Stan probably has the 531A
Mod Summary; what he lacks is the time to peruse it.
Give me your serial number; if I remember, next time
I visit, I'll do it. Note: I was confused and thought
you had a 531. Please translate my comments about
Preset Stability in this light; that is, your 531
manual may not mention it, but it's easy to do.

Dave Wise

-----Original Message-----
From: TekScopes@yahoogrou <mailto:TekScopes%40yahoogroups.com> ps.com
[mailto:TekScopes@yahoogrou <mailto:TekScopes%40yahoogroups.com> ps.com]On
Behalf Of michael Smith
Sent: Tuesday, October 31, 2006 5:10 PM
To: TekScopes@yahoogrou <mailto:TekScopes%40yahoogroups.com> ps.com
Subject: [TekScopes] RE:531A TRIGGER


Stan & David, thanks. This scope followed me home recently with a bad
diode in 100 volt supply. sweep speeds are spot on and clean
as is case
and front panel.so yes its a keeper;-) is there any way to date these
scopes from serial number?


Re: 7623A, 7633 Bistabile Storage Mode?

Craig Sawyers <c.sawyers@...>
 

Is this normal or the crt's are worn out?
Entirely normal. I have no idea why Tek incorporated bistable on their fast
variable persistence scopes - you get around 3:1 contrast; all that
encourages is turning the brightness up in an attempt to dredge up some
contrast resulting in a burned storage phosphor.

A specialised bistable CRT is capable of excellent contrast though - but the
7623, 7633, 7834 and 7944 multimode storage scopes are not.

Craig


Re: 7623A, 7633 Bistabile Storage Mode?

stefan_trethan
 

On Fri, 03 Nov 2006 21:20:51 +0100, Holm Tiffe <holm@freibergnet.de> wrote:

Hi all,
I have a question about the bistabile storage mode on 7623A, 7633 scopes.
I have repaired four of them and when I try the bistabile mode, the stored
image has only a small contrast, since the backround is almost so bright
as the stored image.
Is this normal or the crt's are worn out?
On my own 7633 I can store a 100Mh sine wave in fast persistence without
much trouble, altough the readout gets slightly defocused if I set the
brightness to high, but it is usable.
Kind Regards,
Holm

Same here, i don't use bistable.
As far as i know it's normal.

ST


7623A, 7633 Bistabile Storage Mode?

Holm Tiffe <holm@...>
 

Hi all,

I have a question about the bistabile storage mode on 7623A, 7633 scopes.
I have repaired four of them and when I try the bistabile mode, the stored
image has only a small contrast, since the backround is almost so bright
as the stored image.

Is this normal or the crt's are worn out?

On my own 7633 I can store a 100Mh sine wave in fast persistence without
much trouble, altough the readout gets slightly defocused if I set the
brightness to high, but it is usable.


Kind Regards,

Holm
--
FreibergNet.de IT Systems Holm Tiffe Administration, Development
09627 Bobritzsch Hauptstrasse 19, phone +49 3731 4193411, www.freibergnet.de
Bereich Server & Technik: Am St.Niclas Schacht 13, 09599 Freiberg
phone +49 3731 419010, mobile +49 172 8790 741, fax +49 3731 4196026


Re: Ovenized 2901 Time Mark Generator

jfor@...
 

Hi J,

My estimates came off the top of my head while at my desk at work. I
mentioned them to give people an idea of the order of magnitude
differences between the various frequency standards rather than precise
values for each type of standard. I thought I was at least in the ball
park but it sounds like I was off by quite a bit. I will have to have my
memory recalibrated.
They may be reasonable, if you just turn the unit on when needed. Mine
stay on all the time and the crystals settle downto a pretty low aging
rate.

I don't recall the 2901's crystal being accurate to 1x10-7. I could be
wrong. I will have to take a look at the manual. I think the crystal is
the weakest part of the design. The ON/OFF oven control causes a
pronounced frequency drift up and down. In addition the crystal suffers
from the usual long term stability that all crystals have - they drift
slowly over time (months) towards their final frequency. Evey time you
power up the crystal this long term drift starts all over again. Its
better to leave the 2901 on all the time which is what I used to do.
Mine has been on for years.

I'm frequently tempted to buy a newer 10MHz ovenized crystal and
substitute it for the one in the 2901. It would be an easy way to
improve the accuracy of the instrument by 1 to 2 orders of magnitude for
less that $50. The existing crystal is in a tube socket so it is trivial
to remove it and replace it. There is plenty of room for a substitute
part.
WHY? Which of your scopes require (or even can be) calibrated to better
than 1 part in 10,000 ??? The 2901 is 2 or more orders better than that.

But OTOH, building a GPS Frequency Standard sounded more interesting and
since it would have 4 orders of magnitude better accuracy and require no
calibration I decided to give that a try instead. My understanding of
the GPS receiver is that it is locked to the cesium beam standards on
the GPS satellites and that it benefits from the combined readings of
multiple satellites. An additional plus is that a GPS based frequency
standard can fit in the palm of your hand and run from batteries. It has
one weakness - like all GPS receivers it must have line of sight access
to the sky. It won't work indoors. You can run an outdoor antenna to it
if you are not too far from a window.
You have to have a view of 3 or more birds for many GPS systems to work.
My LORAN uses a loop in the attic and works 24/7. I prefer it to the GPS.
Note that there are 'disciplined' oscillators that tweek their crystals
automatically. I DON'T like those because some have phase discontinuities
when they adjust things. I use the LORAN and a Tracor frequency comparator
and only adjust the crystal units when the error gets out of 1 x 10 -10.
This lets sleeping crystals alone. :=))

I don't have any access to LORAN equipment so I can't speak about it. I
was fortunate to find two Efratom FRK based Rb systems on eBay. Their
accuracy is about the same as your FTS units.
Agreed. BTW, you may not want to keep a Rb running all the time. The Rb
lamps in them have a very finite life and are expensive. IMO a good
crystal is plenty good enough for almost all labs.

One overlooked frequency standard in this thread, is the 7D15 scope
plugin. It has an excellent crystal oscillator in it. It is an order of
magnitude better than the 2901. And it is much more versatile being a
universal counter/timer. Of course it requires a 7000 series scope to
work.

Dennis
As I remember, the 7D15 and various similar TM500 PIs have TCXOs, not
ovenized.

Bottom line, IMO, is that a 2901 is for calibrating time bases. It was
NEVER designed to be a house standard of frequency. For the intended
purpose, I prefer it to the TG501. I really don't find the TG501s %
feature all that useful, BTW, but do like the pulse overlay feature of the
2901.

-John


Re: Ovenized 2901 Time Mark Generator

Dennis Tillman <Dennis@...>
 

Hi J,

My estimates came off the top of my head while at my desk at work. I
mentioned them to give people an idea of the order of magnitude differences
between the various frequency standards rather than precise values for each
type of standard. I thought I was at least in the ball park but it sounds
like I was off by quite a bit. I will have to have my memory recalibrated.

I don't recall the 2901's crystal being accurate to 1x10-7. I could be
wrong. I will have to take a look at the manual. I think the crystal is the
weakest part of the design. The ON/OFF oven control causes a pronounced
frequency drift up and down. In addition the crystal suffers from the usual
long term stability that all crystals have - they drift slowly over time
(months) towards their final frequency. Evey time you power up the crystal
this long term drift starts all over again. Its better to leave the 2901 on
all the time which is what I used to do.

I'm frequently tempted to buy a newer 10MHz ovenized crystal and substitute
it for the one in the 2901. It would be an easy way to improve the accuracy
of the instrument by 1 to 2 orders of magnitude for less that $50. The
existing crystal is in a tube socket so it is trivial to remove it and
replace it. There is plenty of room for a substitute part.

But OTOH, building a GPS Frequency Standard sounded more interesting and
since it would have 4 orders of magnitude better accuracy and require no
calibration I decided to give that a try instead. My understanding of the
GPS receiver is that it is locked to the cesium beam standards on the GPS
satellites and that it benefits from the combined readings of multiple
satellites. An additional plus is that a GPS based frequency standard can
fit in the palm of your hand and run from batteries. It has one weakness -
like all GPS receivers it must have line of sight access to the sky. It
won't work indoors. You can run an outdoor antenna to it if you are not too
far from a window.

I don't have any access to LORAN equipment so I can't speak about it. I was
fortunate to find two Efratom FRK based Rb systems on eBay. Their accuracy
is about the same as your FTS units.

One overlooked frequency standard in this thread, is the 7D15 scope plugin.
It has an excellent crystal oscillator in it. It is an order of magnitude
better than the 2901. And it is much more versatile being a universal
counter/timer. Of course it requires a 7000 series scope to work.

Dennis

-----Original Message-----
From: jfor@quik.com [mailto:jfor@quik.com]
Sent: Thursday, November 02, 2006 6:10 PM
To: dennis@silicondesigns.com
Subject: RE: [TekScopes] Ovenized 2901 Time Mark Generator

Hi Dennis,

I did point out the utility of the multiple push button marker thing. No
big deal.

Also, I'd argue with your estimates of accuracy. IMO the 2901 is good to 1
x 10-7, my HP 105 is better than 1 x 10-10 and my FTS Rb is in the 10-11
range, all compared to LORAN. IMO LORAN is easier than GPS. I use an
Austron 2100F.

Take care,
-J


Re: Ovenized 2901 Time Mark Generator

Kuba Ober <ober.14@...>
 

On Friday 03 November 2006 13:08, you wrote:
I think that the TG501 and PG506 could really be just one
single plugin. Maybe
the CG's are that way?

Again, thanks for all the input, now if I could only get my
PG506 -- I missed
the end of one auction where it sold for nothing ($60 or so),
then another
one went for $104.
I have a PG506 and TG501, and they are good and compact units.
Compact? They could have fit both of them into the same enclosure, even the
switch and display could be shared between both. That would both save costs
and make them more compact.

I'm also
lucky enough to have an SG503, which is invaluable for checking bandwidths
up to 250MHz.
Now I've got the same -- the PG506 for $100. My TG501 is a little ailing in
that the <10ns ranges don't seem to work. The SG503 works fine, although the
frequency counter seems to loose sensitivity at higher frequencies. It won't
count when amplitude is "low", although it does when the frequency is set to
a lower value.

I haven't yet had time to fix those up (they are otherwise in-spec calibration
wise, quirks accounted for). The PG506 will need work, as it has known
defects, but I'm enjoying this a lot.

I also have a type 106 and type 184, which were the previous generation
instruments to the PG506 and TG501. The build standard of the old
generation units is much higher - the TM5xx series plug ins were very cost
engineered and very difficult to work on by comparison.
Except for overlaid timing pulses, I don't think that there's anything that I
miss on TG501. SG503 also does its job.

Cheers, Kuba


FG501 repair

Kuba Ober <ober.14@...>
 

Hi,
I've got a FG501 S/N B127250, ex-University of Louisville EE dept. Here's what
I did to get it up and running (interspersed with service manual calibration
steps).

0. The thing looks pretty beat up (ex EE student lab), had to get all the
knobs off, clean them with a toothbrush and windex, and clean the front panel
in the same fashion.

1. Power light out. +20V checks out OK, bulb out, so change R495 to 1.02k,
DS495 to a green LED.

2. Visually inspect: broken connecting wires to R27 (frequency vernier), also
loose mounting nut, resoldered and retightened.

3. Check out power supplies, stupidly enough missed DCPL -20V. Adjusted +20V
and current ref. 13.8V, all supplies (miss one) are fine.

4. No output, so check current sources and diodes with a multimeter,
everything is fine (current sources source/sink current, diodes are not
dead).

5. Remove U80, feed 4V/1kHz/450Ohm cal signal (from scope cal output) to
U80:13 to get diode bridge current switch to flip back and forth.

6. Set frequency to 10^1 x 10 to get a triangle on TP6.

7. TP6 shows 2Vpp triangle @ -6V, same at source of Q120 and emitter of Q125.

8. Noting is coming out of the following transistor, so check biases and DUH
-20V DCPL is dead. U420 (ua741) turns out to have the output pin (6) at 0V.
Had no 741s handy, so replaced U420 and its companion with OP177.

9. U195:3 <4> seems to be low, but methinks it's OK as it's below B130000 and
waveforms really apply to B130000 and up. Output span checks out OK at
+/-7.8V (compared to minimum +/-10V for B130000 & up).

10. Output [amplitude] and offset pots are very noisy, heating them up just a
bit with the heat gun and rotating them a few dozen times back and forth
seems to have gotten them back into shape.

11. Could not get 10^3x10 R20 in range, frequency is 4% high, so change R18 to
9.31k

12. After calibrating 10^3 and 10^5, check of various ranges shows 10^2 range
to be consistently 2% low in frequency.

13. Suspect 10^2 timing capacitor C74 0.1u/100V (bottom of board). Desoldered
it, and replaced with a mechanically larger capacitor from a junker 5B12
timebase plugin. The x1 and x10 frequencies are now within .5%.

Replacement BOM: two resistors (what a luck: they were adjacent!), one
precision cap, one LED, two opamps.

All in all, I think that I'm pretty lucky as at x1 and x10 all the frequencies
check out well within +/-1%. This is a nice, simple instrument and it was a
joy calibrating it.

Cheers, Kuba


Re: Ovenized 2901 Time Mark Generator

Kuba Ober <ober.14@...>
 

The 2901 wasn't a stop-gap at all, as Craig described it. It has some very
interesting features that the TG501 doesn't have. For instance, the 2901
puts out multiple markers at the same time. Press in as many buttons as you
want and it mixes the markers together and they are easy to distinguish
from each other because they are different heights. This is real handy when
checking a timebase.
Thank you all for your greatly informative replies. I guess I will pass on
that one, as calibration instruments currently only interest me to the extent
that they allow me to get the scopes going. This Tek hobby can be a real time
drain if you don't control yourself :) I'm happy though, as all the Tek gear
I have is in daily use in my work.

I think that the TG501 and PG506 could really be just one single plugin. Maybe
the CG's are that way?

Again, thanks for all the input, now if I could only get my PG506 -- I missed
the end of one auction where it sold for nothing ($60 or so), then another
one went for $104.

Thanks, Kuba


Manuals available/needed

benj3867
 

Hi Guys,

I just went through my manuals and found out that I have spare
original 3A6 and 564B manuals in perfect condition, except for the
spines.

On the other hand, I am in need of a 466 SERVICE manual (with the
schematics etc., NOT the operator's manual available on BAMA) for the
old serial numbers pre B090000.

So, if anybody wants to swap manuals I will be glad to do so. An
electronic version of the 466 manual is also fine, though an original
is obviously preferred.

Feel free to email me even if you need my manuals but you do not have
the 466 manual for me. If it turns out nobody wants to swap, I will
be glad to just send the manuals to whoever wants them.

P.S.

Bama has the 464 service manual. I know that except for the
reduced scan feature the 464 and 466 are identical in features. Are
they also identical in construction, circuits, etc.?

Benjamin


Re: Model 647 Graticule Cover

Dave
 

My 647A is beginning to look very good so I can't part with it, however,,, you could check with Larry Christopher's Oscilloscope Store


http://cgi.ebay.com/Tektronix-647-647A-Oscilloscope-CRT-Frame-Filter-Ring_W0QQitemZ7588248372QQihZ017QQcategoryZ25414QQtcZphotoQQcmdZViewItem

Don't know if that's the part you are talking about but you could ask him if it's not. I recently got the plug-in release levers that were missing from my 647A. And the whistle you mention is probably just the normal sound of the calibrator crystal. Try turning the Calibrator off and see if it goes away.

Below is my yet to properly function 647A. Recently got the 516 and Scope-Mobile, and now looking and working fine!

http://wtv-zone.com/DaveCam1/scopes/Tektronix647A/561_647A.jpg

Dave


"j.foster" <j.foster@mmb.usyd.edu.au> wrote: Hi All:

Does anybody have a parts 647 that they are willing to sell this item from? It's the rectangular part that mounts in front of the CRT face, held by four screws. I am in Australia.
BTW my scope produces a high pitched whistle from the HV supply. I have a bit of hearing loss so this would be *really* loud for anybody with "normal" hearing; any on the list care to comment?

Regards: John Foster.


Re: Ovenized 2901 Time Mark Generator

Morris Odell
 

--- In TekScopes@yahoogroups.com, "Dennis Tillman" <Dennis@...> wrote:

My two cents regarding the 2901:

The 2901 is like a fine heirloom watch. Open one up and you are
struck by
the beauty of the gold plated PC boards
<snip>

Agreed. I have a 2901 and I think it's a fine instrument for its
intended purpose which is calibrating timebases. I always thought the
ovenized crystal was overkill for that purpose as most timebases of
the era couldn't be adjusted to anything like the precision of the
oscillator.

What I don't like about it is the Bulova crystal unit with its heater
that runs from the mains. My manual shows 2 heater elements in there,
for 115 and 230 volts, that are selected by the same switch that
configures the power transformer primaries. Living in a 240 volt
country I feel uncomfortable with mains heaters in a dinky little
octal based crystal unit connected to the beautiful electronics on the
other side of the power transformer!

In my case it was academic anyway as the innards of the crystal oven
was a charred mess when I got it. Fortunately the insulation held and
the electronics were intact. I replaced it with a 10 MHz computer
style rock on an octal plug and it works perfectly. Much later I got a
replacement oven from Deane Kidd but it turned out to be a 115 volt
only model so it's unusable down here, probably just as well. If
anyone in the US would like it I'd be happy to send it across for the
cost of postage. If I really wanted precision I'd connect my freq
standard to the ext clock input.

Morris


Re: Ovenized 2901 Time Mark Generator

Craig Sawyers <c.sawyers@...>
 

The 2901 wasn't a stop-gap at all, as Craig described it. It
has some very
interesting features that the TG501 doesn't have.
The 2901 is basically an entirely transistorised version of the 184 (which
uses nuvistors in the multipliers, and transistors elsewhere). The
specification, number of ranges, pulse stacking, trigger outputs are
precisely the same - the only additional feature that the 2901 had is the
external clock input.

The 2901 was not listed in the 1969 catalogue, and was listed with the TG501
as the suggested replacement in 1975. So it could only have been available
for at most 4 years as the only time/mark instrument offered.

So yes - it was indeed a stop-gap, I would suggest. And the printing on the
buttons was second rate (as far as normal Tek standards go) and on all the
samples I have seen is worn off the most frequently used ranges.

A couple of years ago I put up a review of time/mark generators, which I
repeat below for reference.

Type 180A
=========
1us - 5s markers in 1-5-10 sequence. 5, 10 or 50MHz sine waves (ie 200ns,
100ns, 20ns). Pulse stacking possible. Ovenised crystal standard.

53 tubes. $575 in 1960.

Type 181/RM181
==============
1us - 10ms markers in 5 decade steps. 10MHz sine wave (100ns). Ovenised
crystal option or retrofit. No pulse stacking.

20 tubes. $260 in 1960 with oven crystal option.

Type 184
========
Replaced the above units. 100ns - 5s markers in 1-5-10 sequence. 50ns,
20ns, 10ns, 5ns, 2ns sine waves. Pulse stacking possible. Ovenised crystal
standard. Separate high amplitude 25V output 1us - 5s markers. Separate
trigger output, independently selectable 1us - 1s in decades.

6 nuvistors, 61 transistors. $725 in 1969.

Type 2901
=========
Transitional unit between the Type 184 and the TG501. Essentially the same
features and specification as the 184, but smaller. I'm guessing that it
contains no nuvistors, but I don't have the schematic, and not as much
detail as for the other units. $845 in 1975.

TG501
=====
TM5xx mainframe plug-in. 10ns - 5s markers in 1-2-5 sequence. 5ns, 2ns and
1ns sine wave output. No pulse stacking. Digital timing error display.
Trigger slaved to marker down to 100ns. Standard crystal oscillator
timebase, TCXO optional.

Entirely ECL, TTL and discrete transistor. $1,145 in 1977 rising to $2,670
in 1988 with TCXO.

Craig


Model 647 Graticule Cover

j.foster <j.foster@...>
 

Hi All:

Does anybody have a parts 647 that they are willing to sell this item from? It's the rectangular part that mounts in front of the CRT face, held by four screws. I am in Australia.
BTW my scope produces a high pitched whistle from the HV supply. I have a bit of hearing loss so this would be *really* loud for anybody with "normal" hearing; any on the list care to comment?

Regards: John Foster.


Re: 531A TRIGGER - Tek 504

Bill R <bill1904@...>
 

I have a 503, working, in need of a good cleaning. The trace is good, looks like a P-31. Any takers? I would want to clean it and calibrate it before shipping.

Ashton Brown wrote:

If you like the 504, try to zero-in on a clean 503!
While it lacks the true differential inputs and sub-mV gain of the larger 502 (and at half the 502's BW and weight IIRC) -- provides 1 mV/DIV sensitivity and all the display expansion you can get, without a dual timebase.

Great for most audio work (before folks started looking for phase-shift at 10 MHz). 'Twas first Tek of my very own - a demo from Tek.

Ashton

Chuck Harris wrote:


According to Stan's book, it was last sold in 1971, mostly
to schools. It has a 450KHz bandwidth, and cost $735.

I remember using them in a physics lab when I was an undergraduate.
They work pretty nicely as a school scope.

-Chuck

Jerry Massengale wrote:


Hum, Forgot about that. My new old 504 I just recieved doesn't have IC's either. I wonder how old it is. It looks
new, has been setting in a classroom in New York. The trace has a ripple in it and is a bit dim but basically works.
The scale illumination control is on the power switch. I was surprised to find that the illumination is brightest
with the control ccw. I never thought I would be so pleased to get a one channel scope. $19.95 ($25 shipping) on
ebay. Jerry


Yahoo! Groups Links







Re: Ovenized 2901 Time Mark Generator

Dennis Tillman <Dennis@...>
 

My two cents regarding the 2901:

The 2901 is like a fine heirloom watch. Open one up and you are struck by
the beauty of the gold plated PC boards. Not much of Tektronix' famous
"Golden Days" equipment is around anymore. Most has been scrapped for the
gold. The 2901s are all gold inside. Buy one while you can, they are going
cheap on eBay these days because nobody realizes how valuable they are and
what they can do.

I can't speak for the 184 since I never had one but I do own a TG501 and it
is OK too. I also own a couple of Rubidium (Rb) Atomic Standards and I'm in
the process of building a GPS stabilized frequency standard (which it turns
out is fairly simple to do). As far as accuracy goes the Rb Atomic Standard
is 10x-9, the GPS clock is ~10x-10 or better, the 2901 is 10X-5 or better. I
don't know what the TG501 is but I would guess it is 10x-6.

The 2901 wasn't a stop-gap at all, as Craig described it. It has some very
interesting features that the TG501 doesn't have. For instance, the 2901
puts out multiple markers at the same time. Press in as many buttons as you
want and it mixes the markers together and they are easy to distinguish from
each other because they are different heights. This is real handy when
checking a timebase.

Also lacking on the TG501, but present on the 2901, is an external signal
input on the back that allows you to plug in a precision timebase and use
that instead of the internal crystal. With that external signal input I was
able to lock all of the 2901 outputs (including the 500MHz sine wave output)
to my Rb Frequency Standard. I verified that the 2901 was locked by
displaying the 500 MHz Rb standard's output versus the 2901's 500 MHz output
on my 7104 in X-Y mode. I got a nice oval indicating they were locked
perfectly with little or no phase noise. Note: The 7104 is the only 7000
series scope with the horizontal bandwidth wide enough to show this in XY
mode.

As jfor@quik.com said, the crystal is ovenized but not proportional so it is
not as stable as some later oscillators. You can tweak it to 10x-6 if you
have a reference.

daviddigiacomo@gmail.com commented that "it's hard to get the multiplier
stages all working right, and when you tune them, they pull the crystal
oscillator frequency around quite a bit." I didn't notice the oscillator
being pulled around. The multiplier stages require a fine touch. But come
on, we are talking about a 500 MHz oscillator designed back in 1968. It's a
miracle Tek was able to design a transistorized circuit that could do this.

There are some pro's to this finicky behavior that you should consider.
First, because Tek designed it, it is easy to calibrate and the procedure is
straight forward. Everything is well laid out and easy to get to. I found
the calibration to be an enjoyable, interesting learning experience. Second,
because some of the multipliers are a bit sensitive to how they are tuned,
it is possible to find 2901s cheap on eBay. The reason for this is that a
2901 sometimes appears to be non-functional when all they need is a bit of
cleaning and adjusting to be brought back into spec.

If your goal is to have a stable frequency standard on your bench this
minute then buy something else. But if you want to have something you can
play around with and learn from, and be proud to own, then there is no
comparison to the 2901. Its worth its weight in Gold!

Dennis


Re: 531A trigger

michael Smith <mtmps@sbcglobal.net>
 

MY post seem to be going into the ether! Once again thanks Stan for
your always helpful comments, appreciated! The fans date-code is July
27,1966 (Thanks for the tip John)so that will suffice for that issue.
after looking at 6DJ8's on EBAY I am happy that mine are in good
shape :>o I was thinking about getting a 545 or 555 but after seeing
this insanity on one of the more common tubes!! Thanks fellows, mike


Re: 531A TRIGGER - Tek 504

Ashton Brown <ashton@...>
 

If you like the 504, try to zero-in on a clean 503!
While it lacks the true differential inputs and sub-mV gain of the larger 502 (and at half the 502's BW and weight IIRC) -- provides 1 mV/DIV sensitivity and all the display expansion you can get, without a dual timebase.

Great for most audio work (before folks started looking for phase-shift at 10 MHz). 'Twas first Tek of my very own - a demo from Tek.

Ashton

Chuck Harris wrote:

According to Stan's book, it was last sold in 1971, mostly
to schools. It has a 450KHz bandwidth, and cost $735.

I remember using them in a physics lab when I was an undergraduate.
They work pretty nicely as a school scope.

-Chuck

Jerry Massengale wrote:

Hum, Forgot about that. My new old 504 I just recieved doesn't have IC's either. I wonder how old it is. It looks
new, has been setting in a classroom in New York. The trace has a ripple in it and is a bit dim but basically works.
The scale illumination control is on the power switch. I was surprised to find that the illumination is brightest
with the control ccw. I never thought I would be so pleased to get a one channel scope. $19.95 ($25 shipping) on
ebay. Jerry

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