Date   

Re: 7603 HV oscillator doesn’t start up

 

Hi Christian,

Rollyn is absolutely right about the 2N3055. The original hometaxial process was switched to an epitaxial process. Unfortunately the side effects of this change were not considered important enough to include in the data sheets.
The most significant changes were the increase in Ft - the transition frequency - from 0.8MHz to 2.5MHz and greater risk from secondary breakdown.
I found this out the hard way when a 2N3055 (they were all hometaxial) used in one channel of the Dynaco Stereo 120 Amplifier I built from a kit in 1968 failed. It failed in the mid-1970s and by then the 2N3055s were epitaxial. A few months after I replaced it I noticed the high frequency hiss (noise from the input transistors in the Dynaco PAT-4 preamp) was gone in that channel. At first I thought this was an improvement. When I investigated further the hiss was still there at the output of the power amplifier on both channels. I didn't hear it because the tweeter was blown out. I got the tweeter repaired and a few weeks later the tweeter blew out again.
The gain of the hometaxial 2N3055s began rolling off around 10KHz which was fine for audio amplifiers. Because the Ft of the epitaxial 2N3055 was 3X greater the small inductor Dynaco used at the output of their Stereo 120 to prevent oscillations was no longer sufficient. That was what blew out my tweeters. I only found this out years later.

There is still one more thing and this may be something you need to be aware of: The Wikipedia article on the 2N3055 at
https://en.wikipedia.org/wiki/2N3055
warns against erroneous readings you may get with a multi-meter when checking the gain of the epitaxial versions of the 2N3055. It says: "[Beta] may be 100 to 200 when testing using a multimeter."

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of ROLYNN PRECHTL K7DFW
Sent: Saturday, July 04, 2020 7:49 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7603 HV oscillator doesn’t start up

It isn't that they were selected, the 2N3055 devices at the time were all homotaxial and had low beta compared to more modern versions.

Even with this in play some HV circuits were cranky and wouldn't do well with very low and very high betas.

Look for a 150-0140-xx with a beta in the range of approx 20-50.

We fought this in the B Phase of the 611 and I'm familiar with the problem.

Rolynn
Tek Bvtn and Sunset 1966-1971





--
Dennis Tillman W7pF
TekScopes Moderator


WTD SC-501

Joseph Orgnero
 

Looking for a Tek SC-501 scope part of the TM-500 system
Thank you
Jose Orgnero


Tek TS-4353/U Distortion Analyzer and 500 series plug-ins

Dick Wilson at DiLette Sales
 

Tom: Just for reference, you might show that I do have a copy of the Tektronix TS-4353/U Distortion Analyzer manual.
I sold a dozen or so of these sets many years ago while owner of DiLette Sales/DiLette.com
I ran that company on my free time from my job as a Boeing 747 Captain for American Airlines (40+ years).
I am now retired in Florida, and no longer active in the technical electronics market.
However, I am somewhat knowledgeable about the TM-504A, which does not seem to be widely understood.
The TM-504A mainframe is quite different from the standard TM-504.
The TS-4353/U was produced for the military to house the AA501/SG505/WQ and SG-505WR plug-ins.
The 100+ page civilian version TS-4353/U manual explains it's functions quite well.
The backplane of the TM-504A was wired specifically to allow crosstalk between these three plug-ins.
I had one customer that modified a standard TM-504, but he continued to have problems to the extent that he later ended up buying a TM-504A case which eliminated his problems. So, my guess is that it was a complicated conversion.
In any event, I have a ton of old Tek hardware and manuals. At 78, I'm not inclined to spend my future scanning docs, but might be willing to help with specific requests.
Capt. R. A. "Dick" Wilson, retired.


Re: S-52 only works with lowered +15 V power supply

Albert Otten
 

Hi Max,

For comparison I added a photo of the waveform at timing pin E to your album.
Because of both the "+15V" effect and the temperature effect also Q32 might be suspect. As far as I can see Q32 serves only for protection and normally should never conduct. In my unit the base of Q32 is around -4 V with some spikes op to -3.5 V while the emitter is -3 V. When the "+15V" increases the base voltage will also become less negative. When Q32 conducts for some reason timing then pin E is pulled down, causing zeroing the pulse output.

Albert


Re: 7603 HV oscillator doesn’t start up

ROLYNN PRECHTL K7DFW
 

It's been fifty years so I don't remember what current setting we used on the 575 to check the Hfe of the 0140's. This had to do with the HV osc in the 611 during B Phase in Plant 2 and Building 50.

My experience with the 7603 is limited to one cranky unit (out of a half dozen here) that I repaired.

I still have my stash of graded 0140's from 1970 and I found that low Beta examples in the 7603 cause a HV failure to start and high Beta examples caused it to take on a life of it's own and do silly things.

RP


Re: S-52 only works with lowered +15 V power supply

Albert Otten
 

Hi Max,
The waveform at the point "E" is very critical.
Blowing some compressed air in the zone around R26 / 27 / 30/37 the pulse width at pin "E"
(positive pulse at right of waveform 10) changes noticeably, influencing the width of TD pulse.
I'm reaaaaally puzzled.
At the more negative level Pin E resets the output to true zero in periods 3-6 and 9, by switching the pair Q86/Q88 such that Q86 conducts and Q88 is off. Pin E is the only Timer board output which can force zero output. We saw already that zeroing also occurs at high "+15V". Now zeroing also seems to occur before the official end of the output pulse in period 8 because of temperature effects, likely also via the observed changes at Pin E.
How locally concentrated is your pressed air? The Control board (with the comparator pairs) is probably not much affected, so the cause of your problem might well be in the Timing board. I'd still like to see the base voltages of Q86/Q88 to confirm things.

Albert


Re: 7603 HV oscillator doesn’t start up

 

I peaked into this HV circuit and its push-pull oscillator. It seems quite simple, primitive,
It appears that before the negative HV appears there is plenty of current to the bases of the two transistors 2N3055 to motivate them to start oscillating.
If HV does not appear, it looks like Q1214 would be saturated, and the two transistors 2N3055 would be conducting plenty and getting hot.
If this is the case, something could be shorting the secondary of the transformer in its load of rectifiers/filters.

It seems strange that the beta of the 2N3055 is so critical. Why would a high value hurt the operation?
And if it is too low, lowering R1214 would inject more base current. A design issue?

Ernesto


Re: S-52 only works with lowered +15 V power supply

Dan G
 

On Sat, Jul 4, 2020 at 07:10 PM, unclebanjoman wrote:

Just discovered that R27 on the schematic is 510 ohm: on the board there a 2.0
kohm is mounted instead.
My timing board has the code number 670-1320-02 so I don't have the latest
schematic.
The timing board A1 rolled to revision -01 at s/n B080000,
then to revision -02 at s/n B091450.

R12 changed from 4.3K to 3K at s/n B091450.
R26 changed from 15K to 13K at s/n B080000.
R27 changed from 510 Ohm to 2K at s/n B080000.

On the trigger board, the snap-off diode CR66 changed
to Tek p/n 152-0252-01 (GHZ Devices, Inc. p/n GC-2534-15)
at s/n B080000. C65/R64 probably had to change at the same
time to compensate for different diode characteristics.


dan


Re: 7603 HV oscillator doesn’t start up

C G
 

Thanks Rollyn for the trick. Will check that. As for your beta range, I suppose it is meant at its specific operation current within the 7603?

Christian

Le 4 juil. 2020 à 16:49, ROLYNN PRECHTL K7DFW <k7dfw@...> a écrit :

It isn't that they were selected, the 2N3055 devices at the time were all homotaxial and had low beta compared to more modern versions.

Even with this in play some HV circuits were cranky and wouldn't do well with very low and very high betas.

Look for a 150-0140-xx with a beta in the range of approx 20-50.

We fought this in the B Phase of the 611 and I'm familiar with the problem.

Rolynn
Tek Bvtn and Sunset 1966-1971



Re: S-52 only works with lowered +15 V power supply

unclebanjoman
 

Just discovered that R27 on the schematic is 510 ohm: on the board there a 2.0 kohm is mounted instead.
My timing board has the code number 670-1320-02 so I don't have the latest schematic. I bought mine from Dave's Artekmedia and it references the 670-1320-00 version of the pcb with only two schematic changes/additions (R60 and CR10).
Moreover: the voltages -2.5V and -3V, they vary if the + 15V varies, changing the operating point of BJTs. The -5.1 V is rock- steady.
The waveform at the point "E" is very critical.
Blowing some compressed air in the zone around R26 / 27 / 30/37 the pulse width at pin "E" (positive pulse at right of waveform 10) changes noticeably, influencing the width of TD pulse.
I'm reaaaaally puzzled.

Max


Re: S-52 only works with lowered +15 V power supply

Jim Ford
 

Probably to decrease parasitic inductance on the power and ground pins.  Wirebonds make great inductors, and as the edge speeds increased, ground and power bounce became a problem.  V = L*di/dt.  I assume the power and ground pins went to the center of the package.  Corner pins are the worst possible choice for inductance.Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Harvey White <madyn@...> Date: 7/4/20 12:47 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] S-52 only works with lowered +15 V power supply 74L series of chips should be checked for pin compatibility with anything else.  Not sure why they did that, but that's been a design problem for any number of years when substituting.Also, not all 7400 series chips have power and ground at 14/7 or 16/8.  Surprise....HarveyOn 7/4/2020 2:21 PM, unclebanjoman wrote:> While checking the circuit I just discover that SN74L93 and SN74LS93 are NOT pin-to-pin compatible!> I was using the "classical" 7493 datasheet from Texas Instruments datasheet and wondering how it worked ...> I never imagined that the 74L93 had a different pinout! I found the correct pin-out in a very old National databook.>> Max>> >>


Re: S-52 only works with lowered +15 V power supply

Harvey White
 

74L series of chips should be checked for pin compatibility with anything else.  Not sure why they did that, but that's been a design problem for any number of years when substituting.

Also, not all 7400 series chips have power and ground at 14/7 or 16/8.  Surprise....

Harvey

On 7/4/2020 2:21 PM, unclebanjoman wrote:
While checking the circuit I just discover that SN74L93 and SN74LS93 are NOT pin-to-pin compatible!
I was using the "classical" 7493 datasheet from Texas Instruments datasheet and wondering how it worked ...
I never imagined that the 74L93 had a different pinout! I found the correct pin-out in a very old National databook.

Max



Re: S-52 only works with lowered +15 V power supply

Carl Hallberg
 

That is true for other 74 series.  Should always check pinout.  Example, 74L,LS,W: 95, 85, 78, 72, 74 and maybe others.
Carl Hallberg (W9CJH)

On Saturday, July 4, 2020, 1:21:11 PM CDT, unclebanjoman <mmazza@...> wrote:





While checking the circuit I just discover that SN74L93 and SN74LS93 are NOT pin-to-pin compatible!
I was using the "classical" 7493 datasheet from Texas Instruments datasheet and wondering how it worked ...
I never imagined that the 74L93 had a different pinout! I found the correct pin-out in a very old National databook.

Max


Re: S-52 only works with lowered +15 V power supply

unclebanjoman
 

While checking the circuit I just discover that SN74L93 and SN74LS93 are NOT pin-to-pin compatible!
I was using the "classical" 7493 datasheet from Texas Instruments datasheet and wondering how it worked ...
I never imagined that the 74L93 had a different pinout! I found the correct pin-out in a very old National databook.

Max


Re: S-52 only works with lowered +15 V power supply

unclebanjoman
 

Work still in progress.
Yesterday I put a normal metal film resistor in parallel with the other two (R65/R68). Measured total resistance now is 1,33 ohm. OK.
Behavior is almost unchanged. With +15 V on the positive supply the main pulse appears only with R90 fully CW.
A strange thing I noticed: with the unit just powered up the pulse width initially is approx 500 ns or so.
While the unit warms up, the pulse width gradually decreases until it disappears completely after 1 or two minutes.
To make it reappear I have to decrease the supply to 14.5 V.
Suspecting some thermal drift, I tried to blow (with my breath) over the zone around R109 ( the resistor in series with the 5.1 V zener): the pulse reappears except to shrink in duration and then disappear again within 30 sec.
Oh yeah, in that pcb zone there are the resistors R106,R107 and R108 which generates the -3 V and - 2.5 V reference voltages. Measured, they are 3.1 and -2.6 respectively.

I don't think Tek made such a critical temperature circuit. I suppose that the optimal operating conditions are reached after a few minutes of warm-up and that the engineers have taken into account the heating produced by the 85 ohm resistor for the zener polarization.
Resistor values in the circuit area around Q86, Q88, Q80 are all in the range.

I will patiently check all the waveforms by comparing them with those shown on the diagram and I will check the voltage values on the basis of Q86 and Q88 also.

Varying the voltage between 13 and 15.5 V I noticed another phenomenon: the DURATION of the main pulse first decreases, then abruptly increases and then decreases again until it disappears completely at 15.1 / 15.2 V. Seems to be a timing problem, just like Albert said.
To better describe this phenomenon, a video would be needed. If I can do it, I'll upload it on the TekScopes forum.

Max


Re: 7603 HV oscillator doesn’t start up

ROLYNN PRECHTL K7DFW
 

It isn't that they were selected, the 2N3055 devices at the time were all homotaxial and had low beta compared to more modern versions.

Even with this in play some HV circuits were cranky and wouldn't do well with very low and very high betas.

Look for a 150-0140-xx with a beta in the range of approx 20-50.

We fought this in the B Phase of the 611 and I'm familiar with the problem.

Rolynn
Tek Bvtn and Sunset 1966-1971


Re: Wikipedia is not an appropriate topic for TekScopes. WAS repair tools: Autotransformers/variacs

Roy Thistle
 

On Fri, Jul 3, 2020 at 04:59 PM, nonIonizing EMF wrote:


Thinking I can make a Tekwiki wiki on Wikipedia
I'm against it.
We've got the curated (and excellent) Tekwiki.
Marketing campaigns don't belong on any of the wikis.


Re: Tektronix 2230

Saroj Pradhan
 

Hi Bert
OK it means in my case t906.
Do you have the schematic for 2230 so that we can confirm the transformer.
Thanks.

On Sat, Jul 4, 2020, 9:12 AM Bert Haskins <bhaskins@...> wrote:


On 7/3/2020 9:50 PM, Saroj Pradhan wrote:
Hi Bert
Thanks for your concern and suggestion.

But it operates normally with external power supply (in my case I used
38v
dc across tp950 and tp940).

Saroj
No, I mean the HV supply, the one that runs off the input AC and
supplies the +40V.

Shorted turns make it draw too much current.




On Sat, Jul 4, 2020, 1:28 AM Bert Haskins <bhaskins@...>
wrote:

On 7/2/2020 8:51 PM, Saroj Pradhan wrote:
Hi Leo
No worry. It happens.
Sure I will check the component.
I confirmed that the scope is still working with external supply.
But before going further I want share with you my experience during the
testing of scope with limiter bulb.
1. That day you suggested to put on the scope without limiter bulb. And
you know the outcome.
2.It seems that even with shorted q9070
I could hear the same high pitch(with limiter bulb lighting)
3 changed q9070 and put on the scope(with limiter bulb). This time I
had
flashing light and there was power led at front panel also flashing.
And I
could hear the pitch at the same frequency as of bulb or led flashing.

Put off the scope. Again put on the scope with same result. Third time
when I put on the scope q9070 damaged again. Any logic behind this?
Thanks.
Saroj
First, let me say that I have several 223x family scopes and had very
few problems with them.

I did have a 2215A that uses a similar power supply that gave me fits
until I finally figured out that the high voltage transformer had
shorted windings.

I proved this to myself by doing a ringing test after removing the
transformer.

Good luck,

Bert









Re: Tektronix 2230

Bert Haskins
 

On 7/3/2020 9:50 PM, Saroj Pradhan wrote:
Hi Bert
Thanks for your concern and suggestion.

But it operates normally with external power supply (in my case I used 38v
dc across tp950 and tp940).

Saroj
No, I mean the HV supply, the one that runs off the input AC and supplies the +40V.

Shorted turns make it draw too much current.




On Sat, Jul 4, 2020, 1:28 AM Bert Haskins <bhaskins@...> wrote:

On 7/2/2020 8:51 PM, Saroj Pradhan wrote:
Hi Leo
No worry. It happens.
Sure I will check the component.
I confirmed that the scope is still working with external supply.
But before going further I want share with you my experience during the
testing of scope with limiter bulb.
1. That day you suggested to put on the scope without limiter bulb. And
you know the outcome.
2.It seems that even with shorted q9070
I could hear the same high pitch(with limiter bulb lighting)
3 changed q9070 and put on the scope(with limiter bulb). This time I had
flashing light and there was power led at front panel also flashing. And I
could hear the pitch at the same frequency as of bulb or led flashing.

Put off the scope. Again put on the scope with same result. Third time
when I put on the scope q9070 damaged again. Any logic behind this?
Thanks.
Saroj
First, let me say that I have several 223x family scopes and had very
few problems with them.

I did have a 2215A that uses a similar power supply that gave me fits
until I finally figured out that the high voltage transformer had
shorted windings.

I proved this to myself by doing a ringing test after removing the
transformer.

Good luck,

Bert







Re: Tektronix 2230

Saroj Pradhan
 

Hi Bert
Thanks for your concern and suggestion.

But it operates normally with external power supply (in my case I used 38v
dc across tp950 and tp940).

Saroj

On Sat, Jul 4, 2020, 1:28 AM Bert Haskins <bhaskins@...> wrote:


On 7/2/2020 8:51 PM, Saroj Pradhan wrote:
Hi Leo
No worry. It happens.
Sure I will check the component.
I confirmed that the scope is still working with external supply.
But before going further I want share with you my experience during the
testing of scope with limiter bulb.
1. That day you suggested to put on the scope without limiter bulb. And
you know the outcome.
2.It seems that even with shorted q9070
I could hear the same high pitch(with limiter bulb lighting)
3 changed q9070 and put on the scope(with limiter bulb). This time I had
flashing light and there was power led at front panel also flashing. And I
could hear the pitch at the same frequency as of bulb or led flashing.


Put off the scope. Again put on the scope with same result. Third time
when I put on the scope q9070 damaged again. Any logic behind this?
Thanks.
Saroj
First, let me say that I have several 223x family scopes and had very
few problems with them.

I did have a 2215A that uses a similar power supply that gave me fits
until I finally figured out that the high voltage transformer had
shorted windings.

I proved this to myself by doing a ringing test after removing the
transformer.

Good luck,

Bert