Date   

Re: Advice about buying a 7904

saipan59 (Pete)
 

I had a 7904A recently for a short time.
The fan was one reason I sold it - the noise is obnoxious to me. I don't think there was anything wrong with the fan, but I'm sensitive to that white noise - it bugs me.

Pete


Re: 475 questions

ciclista41@...
 

It might help if I posted the values of the capacitors that were originally in the scope. I'll do this below in the quoted text.

On Thu, May 28, 2020 at 05:59 PM, <ciclista41@yahoo.com> wrote:


‎Hi folks,

Here's my proposed parts order on Digi-Key, except that I haven't decided
between the first or second set of tantalums. The caps below those are to
replace the large C1412, 14, 42, 52, 62, and 72 capacitors. I tried to go up
a bit on the rating of both the capacitance and the voltage, but was hampered
somewhat by a lack of choice when only purchasing one or two of each. I'd had
Nichicon recommended to me, so I stuck with them where I could. Apparently,
Nichicon sold their tantalum capacitor manufacturing to AVX. I don't know
about Kemet, but couldn't find Nichicon near those specs. Also, I haven't yet
received the circular PCB's, so I assumed from the photos of them that they
can accommodate a range of lead spacings. Just thought I'd run it by you all
before I place the order in case I'd be advised to change anything.
To replace the tantalum I broke (C1091), and the other one I removed (C1093). Originals were 2.2μF 20V.
478-1870-ND‎
‎TAP225K025SCS‎
AVX Corporation
CAP TANT 2.2UF 10% 25V RADIAL
Immediate
0.46400
$9.28

or

478-8972-1-ND‎
‎TAP225M035SRW‎
AVX Corporation
CAP TANT 2.2UF 20% 35V RADIAL
Immediate
0.63500
$12.70
To replace C1414 1000μF 75VDC
‎493-17708-ND‎
‎UBY1K102MHL‎
Nichicon
CAP ALUM 1000UF 20% 80V T/H
Immediate
3.34000
$3.34
To replace C1412 350μF 75VDC
‎493-17783-1-ND‎
‎UBY2A361MHL6TN‎
Nichicon
CAP ALUM 360UF 20% 100V T/H
Immediate
3.18000
$3.18
To replace C1442 and C1462 5500μF 30VDC
‎399-19618-ND‎
‎ALC70A562BB040‎
KEMET
SNAP-IN HIGH CV 85C 5600UF 40V
Immediate
5.10000
$10.20
To replace C1452 5000μF 25VDC
‎493-14637-ND‎
‎UBY1V512MHL‎
Nichicon
CAP ALUM 5100UF 20% 35V RADIAL
Immediate
5.44000
$5.44
To replace C1472 3000μF 35VDC
‎493-14660-1-ND‎
‎UBY1V302MHL1TN‎
Nichicon
CAP ALUM 3000UF 20% 35V RADIAL
Immediate
3.02000
$3.02

Thanks for your input!

Bruce


Re: Tek 4041 GPIB Controller

Monty McGraw
 

I just finished creating the binary files for each of the Option ROMs v2.1 and also a 16bit binary that could be used for disassembly and posted them in the ROMs folder on my github repository for the 4041:

https://github.com/mmcgraw74/Tektronix-4041-GPIB-Controller/tree/master/4041%20ROMs


Re: Advice about buying a 7904

Harvey White
 

I can speak of this from the 7904 perspective, since I have two that work, and some backup parts sources,

I had 7904's available, and no 7904As.

the 7A19 are the "appropriate" plugin for a 500 mhz single channel plugin.  However, they're protected by fuses which may be (impossible) hard to find.  The 7A29 has a higher bandwidth and is apparently not protected by fuses (and by something that can be reset), so I prefer them.

My general setup is a 7A26, 7D12 (with sampling plugin), 7D15, and 7B92A.

I've swapped the vertical plugins as needed, 7A22, 7A13, 7A24, 7A29.

I've used the 7B10 and 7B15, but only rarely.

Don't have the 7B8x or 7b7X to speak of, at least, I may have some of them, but don't use them.

I've had (generally) few issues, a hybrid perhaps bad, a PS bad, but nothing that I thought was system wide.

Harvey

On 5/28/2020 6:50 PM, Reginald Beardsley via groups.io wrote:
I have a 485 and a 7104. The fragile CRT of the latter discourages regular use unless needed. Reed refurbished my 485 and obviously it's a really fine instrument.

I'm mulling over getting a 7904 for more routine work because I find the overshoot on DSOs very annoying. My 1.5 GHz LeCroy has a spec of 17% overshoot. I don't consider anything above 2-3% acceptable. I've asked Tek for a step response for a 3 or 4 series 1 GHz DSO using one of Leo's pulsers or similar. After my adventures with Keysight's MSOX3104T and the Rohde & Schwarz RTM3104 I don't want to get a demo unit unless it has an acceptable step response. It will be interesting to see if I get one.

I've never touched a 7904 and have no knowledge of them other than what I've read on TekWiki.

So some questions:

which is the best choice from a long term support basis, 7904 or 7904A?

what plugins? 2x 7A19 and 7B92 + ???

common issues (e.g things like the 576 transformer problem)?

anything else?

Thanks,
Reg



Re: 475 questions

Harvey White
 

As a precaution, some switching supplies don't work well with a voltage below the operating voltage.

For a linear supply, as the voltage to the supply rises, the regulator generally (if it has a decent reference) will turn on full until the input voltage to the regulator reaches a threshold where the output voltage would exceed the setting, then the regulator stops being a short circuit and starts regulating. Depending on the circuit, for example a 5 volt regulator may need anything from 5.25 volts to 8 volts to start regulating.

On the other hand, a switching regulator is not so well behaved.

Remember that a switching regulator has a transistor that, instead of being a variable resistor, is a switch.  It's either on or off.  The switching regulator works by pulsing the transistor on with a limited duty cycle.  That complete (on) dead short lasts for enough time to build up the output voltage, then it turns off.  There are several geometries of switching regulator, some of which, if the switching element is turned on, will draw a lot of current.

The problem in a switching regulator (or one that has two transistors driving a transformer as an inverter), is the question:  What happens when the input voltage is too low?

Some turn on and try to build a proper output voltage.  Some may not operate until they get enough input voltage to work properly.

The problem with some of them is that they draw a LOT of current before they start to operate properly (and switch on/off).

Tektronix uses both switching and linear supplies, and the switching supplies may or may not "like" low input voltages.

I have brought up scopes using a variac, but I have monitored the input current.  I've seen it go over the proper rating and then go back to a lower voltage when the supply starts to switch.

I've seen them work into a short (and the tick mode/overcurrent mode) not work well.  You find that out by monitoring the current the scope draws as the voltage goes up.

Each supply/scope may be different.  You'll need to watch what each one does.

I have a sencore unit that has an isolation transformer and a variac.  It measures both leakage current from the supply lines to ground (not neutral) and the input voltage, output to the UUT, and current.

It's been useful.  You could make one if you wanted, with the exception of the leakage current measurements.  Not sure how they did that.

I'd seriously recommend simultaneous output voltage/output current monitoring, but on this one, I know where the variac will put out full voltage, and can still monitor the current.

Harvey

On 5/28/2020 6:39 PM, ciclista41 via groups.io wrote:
Still great advice for later when I'm working on a DUT with a SMPS. :-)

On Thu, May 28, 2020 at 03:34 PM, <ciclista41@yahoo.com> wrote:

Excellent advice, Eric!

Now I'm glad I just put that incandescent bulb in series when I turned it on
the first time. Not that I have a variac (yet).

Bruce

On Thu, May 28, 2020 at 12:53 PM, Eric wrote:

I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one transistor
so far that has "kind of" failed that one took a 576 to find it, was out of
a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac.
The 400 series have switching power supplies they are not the linear
supplies
They can over current when the line voltage drops to low to regulate and can
be damaged. Slow up on a varic is ONLY good for linear power supplies.


Re: probe.

Jim Ford
 

I stand corrected. Sometimes you can teach an old dog new tricks! ;)

Thanks, Raymond!

Jim

------ Original Message ------
From: "Raymond Domp Frank" <hewpatek@gmail.com>
To: TekScopes@groups.io
Sent: 5/28/2020 1:31:23 PM
Subject: Re: [TekScopes] probe.

On Thu, May 28, 2020 at 08:36 PM, Jim Ford wrote:


I was able to adjust the probe to get a nice flat response when connected to
the calibrator on the 54504A. Fortunately it also looked flat with the
calibrator on my Tek 7904.
Hi Jim,
The artifacts that I was referring to don't show up on standard 'scope calibrators. Those only allow you to adjust "LF" behavior with a 1 kHz square wave (flat top).
I meant fast-edge behavior, like that visible with <=1 ns steps in the first few ns or in the edge itself. That's where the differences are. You won't just see a flat or single-curved top but all kinds of ripples, resonance-like behavior etc. I know about only one "classic" Tek 'scope that offers that kind of fast step: the 485 in addition to a nice 1 kHz square wave. It allows LF adjustment *and* HF adjustment. The latter is done with separate adjustment regulators in the compensation box of the probe, underneath the plastic cover. *And* you need a well-matched input to the probe, like a probe-shaft-to-BNC adapter
The calibrator's edges in the 7904 are no faster than 250ns so they are useless for showing the differences between e.g. the P6139A and P6137, much less perform the HF adjustment I was referring to.


And I'd check the input capacitance of the scope (7 pF in the case of the 54504A) versus the output capacitance of the probe (8 pF in the case of the P6139A), and
if they are close, you will probably get good results when you connect the probe to the calibrator and adjust it for flatness.
That's not correct: 8 pF is the nominal *input* capacitance of the P6139A and they don't have to be nor will be equal. Otherwise, you wouldn't be able to adjust an 8pF or 1.5 pF FET input capacitance probe to several different 'scopes, like the 2465B with its 15pF nominal input capacitance or a 7A26 with 22pF nominal. It's all about RC times, probe input, cable, probe output, 'scope input. The publications I referred to show it all.

Nothing to worry about for general 'scoping in the sub-100MHz domain though. Who said that 100 MHz actually is DC?

Raymond



Re: Advice about buying a 7904

Chuck Harris <cfharris@...>
 

Issues and features that I recall:

7904 has lots of tantalum caps, and a couple are bound to blow.
They are easy to find and fix.

7904 has a weak power supply that can't handle many of the digital
plugins, such as the logic analyzer and spectrum analyzer plugins.

7904 always ticks 3 times when it is turned on after being off for
a while.

7904 has at least one "blue" harmonica connector that will have
ossified by now. If you touch it, it will crumble to dust.

Fortunately, the so-called Dupont connectors are compatible.

7904 has a united power supply transformer that has everything
from the low voltage windings through the EHT windings on the
same core. It is reliable, but repair isn't likely.

7904A Has few tantalum capacitors.
7904A has a separate EHT transformer... but because that was too
reliable, they drove it from an AC tap on the main transformer.

Why do I care? If the main inverter goes full tilt on, the HV
and filament voltage for the CRT doubles.

Specs that matter are the same for 7904 and 7904A.

7904A has a noisy fan. 7904 has none.

7904A uses hypacon connectors on its many, many hybrids.

All this said, I prefer the 7854 as my go-to scope.

-Chuck Harris

Reginald Beardsley via groups.io wrote:

I have a 485 and a 7104. The fragile CRT of the latter discourages regular use unless needed. Reed refurbished my 485 and obviously it's a really fine instrument.

I'm mulling over getting a 7904 for more routine work because I find the overshoot on DSOs very annoying. My 1.5 GHz LeCroy has a spec of 17% overshoot. I don't consider anything above 2-3% acceptable. I've asked Tek for a step response for a 3 or 4 series 1 GHz DSO using one of Leo's pulsers or similar. After my adventures with Keysight's MSOX3104T and the Rohde & Schwarz RTM3104 I don't want to get a demo unit unless it has an acceptable step response. It will be interesting to see if I get one.

I've never touched a 7904 and have no knowledge of them other than what I've read on TekWiki.

So some questions:

which is the best choice from a long term support basis, 7904 or 7904A?

what plugins? 2x 7A19 and 7B92 + ???

common issues (e.g things like the 576 transformer problem)?

anything else?

Thanks,
Reg




Re: 475 questions

ciclista41@...
 

‎Hi folks,

Here's my proposed parts order on Digi-Key, except that I haven't decided between the first or second set of tantalums. The caps below those are to replace the large C1412, 14, 42, 52, 62, and 72 capacitors. I tried to go up a bit on the rating of both the capacitance and the voltage, but was hampered somewhat by a lack of choice when only purchasing one or two of each. I'd had Nichicon recommended to me, so I stuck with them where I could. Apparently, Nichicon sold their tantalum capacitor manufacturing to AVX. I don't know about Kemet, but couldn't find Nichicon near those specs. Also, I haven't yet received the circular PCB's, so I assumed from the photos of them that they can accommodate a range of lead spacings. Just thought I'd run it by you all before I place the order in case I'd be advised to change anything.

478-1870-ND‎
‎TAP225K025SCS‎
AVX Corporation
CAP TANT 2.2UF 10% 25V RADIAL
Immediate
0.46400
$9.28

or

478-8972-1-ND‎
‎TAP225M035SRW‎
AVX Corporation
CAP TANT 2.2UF 20% 35V RADIAL
Immediate
0.63500
$12.70

‎493-17708-ND‎
‎UBY1K102MHL‎
Nichicon
CAP ALUM 1000UF 20% 80V T/H
Immediate
3.34000
$3.34

‎493-17783-1-ND‎
‎UBY2A361MHL6TN‎
Nichicon
CAP ALUM 360UF 20% 100V T/H
Immediate
3.18000
$3.18

‎399-19618-ND‎
‎ALC70A562BB040‎
KEMET
SNAP-IN HIGH CV 85C 5600UF 40V
Immediate
5.10000
$10.20

‎493-14637-ND‎
‎UBY1V512MHL‎
Nichicon
CAP ALUM 5100UF 20% 35V RADIAL
Immediate
5.44000
$5.44

‎493-14660-1-ND‎
‎UBY1V302MHL1TN‎
Nichicon
CAP ALUM 3000UF 20% 35V RADIAL
Immediate
3.02000
$3.02

Thanks for your input!

Bruce


Re: Advice about buying a 7904

Dave Daniel
 

My email should have read “no well-known problems”.

I had both a 7904 and a 7904A; I gave the 7904 away to a good home when I moved across the country, reducing my collection to five 7xxx ‘scopes.

If you get a 7854 you will also want the keyboard that goes with it. Like I wrote, rabbit hole.

DaveD

On May 28, 2020, at 19:05, Dave Daniel via groups.io <kc0wjn=gmail.com@groups.io> wrote:

The 7904A is easier to wotk pne because it has the “kickstand” feature where one can split the display section up off of the lower section to make repairs. I’ve never compared the specs of a 7904 and 7904A. I imagine they are quite similar. I’d probably buy a 7904A if I had to choose. As far as I know there are well-known problems with either ‘scope.

If it were me, I’d also consider a 7854.

Selecting plug-ins is a pretty deep subject. 7A26s with 7B92s is a good choice for general purpose work. IIRC, 7A19s are 50 ohm input only.

Once you get a 7xxx ‘scope you will probably want to get a differential amp, pulse and counter plug-ins as well. It’s a rabbit hole.

DaveD

On May 28, 2020, at 18:50, Reginald Beardsley via groups.io <pulaskite=yahoo.com@groups.io> wrote:

I have a 485 and a 7104. The onlyfragile CRT of the latter discourages regular use unless needed. Reed refurbished my 485 and obviously it's a really fine instrument.

I'm mulling over getting a 7904 for more routine work because I find the overshoot on DSOs very annoying. My 1.5 GHz LeCroy has a spec of 17% overshoot. I don't consider anything above 2-3% acceptable. I've asked Tek for a step response for a 3 or 4 series 1 GHz DSO using one of Leo's pulsers or similar. After my adventures with Keysight's MSOX3104T and the Rohde & Schwarz RTM3104 I don't want to get a demo unit unless it has an acceptable step response. It will be interesting to see if I get one.

I've never touched a 7904 and have no knowledge of them other than what I've read on TekWiki.

So some questions:

which is the best choice from a long term support basis, 7904 or 7904A?

what plugins? 2x 7A19 and 7B92 + ???

common issues (e.g things like the 576 transformer problem)?

anything else?

Thanks,
Reg




Re: Advice about buying a 7904

 

On Fri, May 29, 2020 at 12:50 AM, Reginald Beardsley wrote:


which is the best choice from a long term support basis, 7904 or 7904A?

what plugins? 2x 7A19 and 7B92 + ???
Hi Reginald,

Advantages of the 7904A over the 7904:
- Newer, so possibly less failure-prone
- Easier to service because of split construction
- Front panel layout very much like the 7104 (or is that a disadvantage?)
- Internal construction and components very much like the 7104
- More modern look (to some at least)


Advantages of the 7904 over the 7904A:
- Fewer hard-to-get components
- No fan (a huge advantage according to some)
- Backlit Vertical Mode and Horizontal Mode buttons
- More versatile calibrator, includes current loop
- Can be had for very little money

Make sure that in either case, you buy one with the Alphanumeric screen-readout, which is standard.

It's very difficult to determine the better choice on long term support aspects: Do you want a younger and therefore possibly slightly more reliable instrument with more expensive, hard-to-get components or do you want an older, slightly less reliable instrument with fewer and cheaper hard-to get components? If you have room to spare, have 3 7904's for the price of one (or 2) 7904A's.

As regards plugins: For general-purpose work, put in a 7A26 (Hi-Z, 200 MHz) and a 7A19 (Lo-Z, 50 Ohm only) or, preferably, a 7A29 (resettable overvoltage protection, continuously variable attenuation), a 7D15 counter in the A Horizontal slot and a 7B92A into the B horizontal slot. Make sure you have all the other plugins nearby (7A13, 7A22, a sampler system for > 1 GHz).

Both have a switching supply. Apart from the well-known lifetime-driven weaknesses like electrolytic (mains voltage buffer) caps and tantalum (bead) caps, I'm not aware of any structural vulnerabilities.

I concur with Dave D. re. the 7854. It's more complicated and therefore more vulnerable but it's also one great piece of equipment, especially if you use sampling plugins.

Raymond


Re: Tek 4041 GPIB Controller

Monty McGraw
 

We can get the 4041 service manual scanned from the vintagetek.org microfiche library of all Tektronix documentation - after COVID-19 is over. Right now Oregon is still in lockdown. They only charge $25 an hour for scans.


Re: Advice about buying a 7904

Sean Turner
 

Reg,

As you may know from our prior conversations, I have both a 7104 and a 7904A. The 7904A is definitely my workhorse because, as you mention, I want to preserve and protect the mcp tube in the 7104. As Dave mentioned, the chassis is different between the 7904 and 7904A. The 7904A is going to be easier to work on from an access perspective. One thing the 7904 has that I wish the 7904A carried on is a current loop calibrator for current probes. Oh well. Another thing to keep in mind is that the 7904A uses the hypcon packaged hybrids like the 7104 in the vertical amp[1], while the 7904 does not.

As far as reliability, I would imagine both have tantalum capacitors. Since these scopes have a switch mode power supply, it's easy to tell when you have a short because you get the infamous clicking as the supply tries to turn off then shuts down. Finding the short is another matter, though fortunately for me the short my 7104 developed when I got it home from the auction house turned out to be super simple and not tant related at all.

As far as plugins go, the 7A26 is a perfect vertical option for general purpose work. There's a couple different revisions hanging about. Some have a 20 MHz bandwidth switch and some do not. I have examples of both. Honestly, the one that doesn't have it has a sharper trace all around in my experience. Use two of them and have a full on 4 trace scope. The 7A19 is a good match for the mainframe if you want a vertical with a dedicated 50 ohm input. Keep in mind that unlike the 7A29's circuit breaker arrangement, the 7A19 uses fuses for input overload protection. Still useful for specialty probes that expect 50 ohms, such as current probes. Another vertical plugin in find indispensable for low frequency work is the 7A22 differential amplifier. Even single ended with a 10X probe, you can get down into microvolts/div ranges and the adjustable bandpass filter is very useful for isolating signals in noise. I have a 7B15 and a 7B92A as timebases in mine; no complaints.

[1]: http://w140.com/tekwiki/wiki/7904


Re: Advice about buying a 7904

Dave Daniel
 

The 7904A is easier to wotk pne because it has the “kickstand” feature where one can split the display section up off of the lower section to make repairs. I’ve never compared the specs of a 7904 and 7904A. I imagine they are quite similar. I’d probably buy a 7904A if I had to choose. As far as I know there are well-known problems with either ‘scope.

If it were me, I’d also consider a 7854.

Selecting plug-ins is a pretty deep subject. 7A26s with 7B92s is a good choice for general purpose work. IIRC, 7A19s are 50 ohm input only.

Once you get a 7xxx ‘scope you will probably want to get a differential amp, pulse and counter plug-ins as well. It’s a rabbit hole.

DaveD

On May 28, 2020, at 18:50, Reginald Beardsley via groups.io <pulaskite=yahoo.com@groups.io> wrote:

I have a 485 and a 7104. The onlyfragile CRT of the latter discourages regular use unless needed. Reed refurbished my 485 and obviously it's a really fine instrument.

I'm mulling over getting a 7904 for more routine work because I find the overshoot on DSOs very annoying. My 1.5 GHz LeCroy has a spec of 17% overshoot. I don't consider anything above 2-3% acceptable. I've asked Tek for a step response for a 3 or 4 series 1 GHz DSO using one of Leo's pulsers or similar. After my adventures with Keysight's MSOX3104T and the Rohde & Schwarz RTM3104 I don't want to get a demo unit unless it has an acceptable step response. It will be interesting to see if I get one.

I've never touched a 7904 and have no knowledge of them other than what I've read on TekWiki.

So some questions:

which is the best choice from a long term support basis, 7904 or 7904A?

what plugins? 2x 7A19 and 7B92 + ???

common issues (e.g things like the 576 transformer problem)?

anything else?

Thanks,
Reg



Advice about buying a 7904

Reginald Beardsley
 

I have a 485 and a 7104. The fragile CRT of the latter discourages regular use unless needed. Reed refurbished my 485 and obviously it's a really fine instrument.

I'm mulling over getting a 7904 for more routine work because I find the overshoot on DSOs very annoying. My 1.5 GHz LeCroy has a spec of 17% overshoot. I don't consider anything above 2-3% acceptable. I've asked Tek for a step response for a 3 or 4 series 1 GHz DSO using one of Leo's pulsers or similar. After my adventures with Keysight's MSOX3104T and the Rohde & Schwarz RTM3104 I don't want to get a demo unit unless it has an acceptable step response. It will be interesting to see if I get one.

I've never touched a 7904 and have no knowledge of them other than what I've read on TekWiki.

So some questions:

which is the best choice from a long term support basis, 7904 or 7904A?

what plugins? 2x 7A19 and 7B92 + ???

common issues (e.g things like the 576 transformer problem)?

anything else?

Thanks,
Reg


Re: 475 questions

teamlarryohio
 

IIRC, only the 432, 434, and 485 had switchers.

The 485 was much like a 7K with the Tek-made controller chip. The 43X's
were discrete.

-ls-


Re: 475 questions

ciclista41@...
 

Hey guys! Look at me with my newly acquired acronyms! ;-)

On Thu, May 28, 2020 at 03:39 PM, <ciclista41@yahoo.com> wrote:


Still great advice for later when I'm working on a DUT with a SMPS. :-)

On Thu, May 28, 2020 at 03:34 PM, <ciclista41@yahoo.com> wrote:


Excellent advice, Eric!

Now I'm glad I just put that incandescent bulb in series when I turned it on
the first time. Not that I have a variac (yet).

Bruce

On Thu, May 28, 2020 at 12:53 PM, Eric wrote:


I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one
transistor
so far that has "kind of" failed that one took a 576 to find it, was out
of
a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a
variac.
The 400 series have switching power supplies they are not the linear
supplies
They can over current when the line voltage drops to low to regulate and
can
be damaged. Slow up on a varic is ONLY good for linear power supplies.


Re: 475 questions

ciclista41@...
 

Still great advice for later when I'm working on a DUT with a SMPS. :-)

On Thu, May 28, 2020 at 03:34 PM, <ciclista41@yahoo.com> wrote:


Excellent advice, Eric!

Now I'm glad I just put that incandescent bulb in series when I turned it on
the first time. Not that I have a variac (yet).

Bruce

On Thu, May 28, 2020 at 12:53 PM, Eric wrote:


I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one transistor
so far that has "kind of" failed that one took a 576 to find it, was out of
a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac.
The 400 series have switching power supplies they are not the linear
supplies
They can over current when the line voltage drops to low to regulate and can
be damaged. Slow up on a varic is ONLY good for linear power supplies.


Re: 475 questions

ciclista41@...
 

Hi Eric,

Must they be removed from the circuit to get decent readings? If so, I'll do it. This thing seems to have been designed to make it easy to remove them once the large caps are removed.

Bruce

On Thu, May 28, 2020 at 12:53 PM, Eric wrote:


I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one transistor
so far that has "kind of" failed that one took a 576 to find it, was out of a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac.
The 400 series have switching power supplies they are not the linear supplies
They can over current when the line voltage drops to low to regulate and can
be damaged. Slow up on a varic is ONLY good for linear power supplies.


Re: 475 questions

ciclista41@...
 

Excellent advice, Eric!

Now I'm glad I just put that incandescent bulb in series when I turned it on the first time. Not that I have a variac (yet).

Bruce

On Thu, May 28, 2020 at 12:53 PM, Eric wrote:


I would test the rectifiers the silicon is usually pretty resilient and
normally grossly fails "open or short". I have only run in to one transistor
so far that has "kind of" failed that one took a 576 to find it, was out of a
fluke 5200A. However do NOT bring up a 400 series scope slowly on a variac.
The 400 series have switching power supplies they are not the linear supplies
They can over current when the line voltage drops to low to regulate and can
be damaged. Slow up on a varic is ONLY good for linear power supplies.


184 Time-Mark Generator lamp

Sean Turner
 

Hi all,

I recently acquired a rather nice shape 184 for the princely sum of $70. After some good burn in and exercising the controls following by a few adjustments, it ticks along perfectly except for the HF oscillator (but that's beyond the scope of this topic) and the green power lamp (above the oven lamp, which is working), which is burned out. I was surprised to find the bulb is one assembly that plugs into the socket. I assume these are probably unobtainium, but would be interested in being contacted off list if someone has one they are willing to part with.

Thanks!

Sean

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