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Re: HV Power Supply - 7704A - Neon Bulbs

n4buq
 

Mark,

On the subject of the HV supply, I seem to recall an email (which I can't find) where you mentioned a suitable replacement for C4201 (8.2uF, 200V). I presume anything around 15uF to 25uF and, maybe, a slight increase in the voltage rating would be okay but thought I'd ask before ordering.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Barry" <n4buq@knology.net>
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, October 4, 2021 9:07:58 PM
Subject: Re: [TekScopes] HV Power Supply - 7704A - Neon Bulbs
Hi Mark,

I was just about to post that the older manual shows a 5AB-T for those. I plan
to replace all four in that board (along with the caps). I have a box of A9A
leaded bulbs but, unfortunately, those are the wrong striking voltage for this
application. So close...

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@gmail.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, October 4, 2021 9:02:51 PM
Subject: Re: [TekScopes] HV Power Supply - 7704A - Neon Bulbs
Barry,

A 5AB is a direct replacement for a NE23. Mouser has these in stock. Get several
to have spares on hand. Broken leads at the base of neons is common.

Mark



Re: 2445B vertical non-linearity other issues.

Roger Evans
 

Given the cost of a replacement U400 and the oddities you observe on the readout, it is well worth checking the waveforms at <51> and <52> in the service manual schematic <6>, this is with the readout turned off. They should be closely balanced about ground and the transistor array U475 is a likely culprit for any problems here.

Best of luck,

Roger


Re: Pease PDF for reading a datasheet

Roy Thistle
 

On Mon, Oct 4, 2021 at 06:26 PM, Gary Robert Bosworth wrote:


PDF copy of Pease's "reading
datasheets"?
'How to get the right information from a datasheet' ? ... by Pease... and yes, it's appendix F in the,
National Semiconductor(1995 Edition)National Operational Amplifiers Databook
Also page 199 in his book,
Pease(1991)Troubleshooting Analog Circuits(Butterworth-Heinemann, Newnes)

other than that, there are his comments on how to do it (or how he did it), here and there, in many of his EDN articles.

A lots changed since his, all too soon, passing: many 'analog' data sheets are about 'analog systems' and can run into dozens (if not a hundred, or more) pages. But a lot of what Pease has to say is IMO relevant to many of the data sheets analog chips and discrete semiconductors used in the Tek equipment discussed in the threads posted on TekScopes.

--
Roy Thistle


Re: Pease PDF for reading a datasheet

Ozan
 

On Mon, Oct 4, 2021 at 06:26 PM, Gary Robert Bosworth wrote:

Anyone know where I can get a clean PDF copy of Pease's "reading
datasheets"?
Gary Bosworth
Are you looking for Appendix F on page 904 of National Semiconductor Linear Databook?
http://bitsavers.trailing-edge.com/components/national/_dataBooks/1988_National_Linear_Databook_Vol_3.pdf

Ozan


Re: HV Power Supply - 7704A - Neon Bulbs

Mark Vincent
 

Barry,

The A9A is NE-2E. Hold on to those. They are ,7mA.

Mark


Re: HV Power Supply - 7704A - Neon Bulbs

n4buq
 

Hi Mark,

I was just about to post that the older manual shows a 5AB-T for those. I plan to replace all four in that board (along with the caps). I have a box of A9A leaded bulbs but, unfortunately, those are the wrong striking voltage for this application. So close...

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@gmail.com>
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, October 4, 2021 9:02:51 PM
Subject: Re: [TekScopes] HV Power Supply - 7704A - Neon Bulbs
Barry,

A 5AB is a direct replacement for a NE23. Mouser has these in stock. Get several
to have spares on hand. Broken leads at the base of neons is common.

Mark



Re: HV Power Supply - 7704A - Neon Bulbs

Mark Vincent
 

Barry,

A 5AB is a direct replacement for a NE23. Mouser has these in stock. Get several to have spares on hand. Broken leads at the base of neons is common.

Mark


HV Power Supply - 7704A - Neon Bulbs

n4buq
 

The lead on one of the NE23 neons in my 7704A broke very easily when I moved it just a bit (apparently brittle from heat and age). Is a 5AB a suitable replacement? If not, what are some good choices?

Thanks,
Barry - N4BUQ


Pease PDF for reading a datasheet

Gary Robert Bosworth
 

Anyone know where I can get a clean PDF copy of Pease's "reading
datasheets"?
Gary Bosworth


Re: 7000 series parts hulks

n4buq
 

Hi Oz,

I'd be interested in the 7D14. Up until the pandemic, I was travelling very regularly to DFW. Too bad as I could have saved the shipping.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Oz-in-DFW" <lists@ozindfw.net>
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, October 4, 2021 6:15:02 PM
Subject: [TekScopes] 7000 series parts hulks
I have a 7603, 7613, and 7633 parts hulk. All are for sale for $20 plus
whatever shipping actually costs if you can't pickup in the DFW Area. I may
need to buy a box and bubble wrap.

The plug in bays are damaged beyond hope. Teh tubes and PS's look intact based
om my casual inspection. If there is interest I'll post detailed photos for
download off my site to keep the load off the group.

I also have 7000 plugins, also pars. at least a 7A11, 7A18, and 7D14, a test
plugin of some sort and what is basically a frame with few guts. Detailed
photos later in the week. $5-$15 depending on shape.
--
Oz (in DFW) N1OZ



Re: 2445B vertical non-linearity other issues.

Harvey White
 

Part of the reply is to help you, if needed, and the other part is to help people who may want a take on the problem itself when they search the topic.   If I get it wrong, then the corrections are useful.

if it's the hybrid, the rebake program is problematical, from what I remember.  I don't have a 2465 of any variety, but I do have a 2430A as a second/third/etc scope.  Most of what  I do works well enough with workable 7904's and the occasional 7103/4. My portable scopes (468, 2430A, and a digital japanese scope) top out at about 150 Mhz.

Good luck.  As I understand it, be careful when replacing the hybrid.

Harvey

On 10/4/2021 8:11 PM, Robin Szemeti wrote:
Yep, I am familiar with class A/B amp biasing .. I have built "a few" audio amplifiers.

There is only one resistor, R401 I Bias, that seems relevant. From other threads it looks like the fault with this device usually lies on the thick film itself. It seems in the past, there was a re-bake programme for these devices which recovered 70% of them ... but I'll check R401 and see what gives ...





Re: 2445B vertical non-linearity other issues.

Robin Szemeti
 

Yep, I am familiar with class A/B amp biasing .. I have built "a few" audio amplifiers.

There is only one resistor, R401 I Bias, that seems relevant. From other threads it looks like the fault with this device usually lies on the thick film itself. It seems in the past, there was a re-bake programme for these devices which recovered 70% of them ... but I'll check R401 and see what gives ...


Re: Help needed bringing a 555 back to life

Mark Vincent
 

Selinica,

I sent you an email about what I did in mine last month. I have one of these I fully restored as a birthday gift to myself a few years ago. I had to restuff the cans because I had ones that were shorted, the resistors would burn open when the relay energized. I like mine with the new 1% resistors and new condensers. The horiz. position control is dissipating more power than it is rated. Mine has increased value resistors on each side and I still have enough range. Mine is an early S/N with P11 crt. The plug-ins were also restored and aligned. I did modification of the timebases to allow some plug-ins to be used that need that mod. to work (triggering). I also have the A versions I restored for the time bases.

Mark


7000 series parts hulks

Oz-in-DFW
 

I have a 7603, 7613, and 7633 parts hulk. All are for sale for $20 plus whatever shipping actually costs if you can't pickup in the DFW Area. I may need to buy a box and bubble wrap.

The plug in bays are damaged beyond hope. Teh tubes and PS's look intact based om my casual inspection. If there is interest I'll post detailed photos for download off my site to keep the load off the group.

I also have 7000 plugins, also pars. at least a 7A11, 7A18, and 7D14, a test plugin of some sort and what is basically a frame with few guts. Detailed photos later in the week. $5-$15 depending on shape.
--
Oz (in DFW) N1OZ


Re: 2445B vertical non-linearity other issues.

Harvey White
 

In a totem pole pair (NPN on the top, PNP on the bottom), if no current flows through the transistors when at zero voltage in, then there's going to be a dead spot until the input voltage rises enough to turn on the NPN, or lowers enough to turn on the PNP.

This is generally fixed by allowing a certain fixed current to go through both NPN and PNP so that the NPN turns on while the PNP is still on.  It increases the power consumption, but minimizes what's called "crossover distortion".

The suggestion to check the emitter currents is precisely this for the output stage.  The physical design of the output stage can vary (the example I used is generally used in audio amplifiers, NPN transistor as an emitter follower for + voltages, PNP transistor ditto, but for negative voltages).

For the typical Tektronix scope, you have an emitter coupled differential pair (likely towards the beginning of the amplifier, and then a DC coupled amplifier from then on.  The turn on/turn off points of the transistors is critical to the crossover distortion issue.  That's the quiescent emitter currents of the amplifiers.

Harvey

On 10/4/2021 4:51 PM, Robin Szemeti wrote:
I'll try the emitter resistors, but there are so many cases of U400 failure that I suspect it is going to be that. Which sucks. A lot.





Re: 2445B vertical non-linearity other issues.

Robin Szemeti
 

I'll try the emitter resistors, but there are so many cases of U400 failure that I suspect it is going to be that. Which sucks. A lot.


Re: 2445B vertical non-linearity other issues.

Roger Evans
 

Vertical nonlinearity on Ch1 and Ch2 but not on Ch3 and Ch4 is typical of a fault in U400. The other symptoms are new to me but I am sure someone here will offer some insight. It would be worth checking the resistors that set the emitter currents for U400, I need a large screen in order to look up part numbers!

Regards

Roger


Re: Help needed bringing a 555 back to life

Selinica Harbinger
 

Got it. Resistors and caps are on order, there are some of the black beauty and bumblebee caps in the unit, I ordered replacements for all of them in the power supply. There will be some delays since a couple other caps tested bad and the replacement is on backorder.
I'll update when I have the resistors and caps swapped and new tests done and what the results are.
It's going to be a few weeks, but the unit will get a nice set of new resistors and caps. I've got a copy of the component list and I'll just start marking parts off. I'll definitely swap out all bumblebee and black beauty caps for modern film or other caps. Electrolytics probably not. The carbon comp resistors are going to slowly go onto the replace list, knowing the issues they can have. The ones that have drifted badly are getting replacement asap (when the order arrives, someday) and the remainder get assumed suspicious.
The main factor with the electrolytics is just how hard suitable replacements are to find, much less the mount issue. I may put it on the someday list depending on how they reform (if needed). Maybe.


RAMS opening

Dave Brown
 

RAMS asked me to post this message.

RAMS store will be reopening on Thursday, October 21st, 2021. The days and hours will be as they were before, first and third Thursday each month, 2-4pm for the public.

We've gotten a lot of inquires at the museum about RAMS. We are not associated, just good neighbors.

Dave


2445B vertical non-linearity other issues.

Robin Szemeti
 

I have a 2445B that has gone a bit odd recently.

Ch2 and to a lesser extent CH1 have developed vertical non-linearity. Put a sine wave through it and it is obvious, a sort ot cross-over distortion around the centre of the tube .. Moving the trace around with the vertical position control it appears the distortion stays stationary and the trace moves through it. I also noticed the text had moved vertically off the bottom of the display ... and if I move CH1 or CH2 beams into the upper part of the display, the text starts to jitter and shake .. this does not happen with CH3 or 4

This non linearity does not affect CH3 or 4 so I think the vertical amp U600 is fine, and swapping with a good spare I have did not improve it. I'm beginning to suspect the channel switcher IC, U400 ... do the symtoms sound typical?

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