Hi all,


I bought a 576 from eBay with a Tektronix cal from Dallas which expired 01-DEC-10. Everything was going well and I was learning how to use the instrument...until today.

I was attempting to characterize 6C33C tubes when smoke began to emanate from the top array of ventilation ports on the machine's left side. Immediately, I attenuated the Variable Collector Supply and switched the machine off.

I did not observe any POP or other sound in connection with this event.

Now that I've recovered, somewhat, my equilibriium -- I'm writing the post to ask this august group if there is anyone, any resource in my neck of the woods -- San Diego, that can take a look at my beloved Tek 576 CT.

Please, let me know.


Very best regards,

Sam

 

I have the following Plug-Ins that are excess to my needs:

7A11

7A13

7A15

7A22 (2)

7B50 (2)

7B51

7B53A

7B85 (2)

7B87

Take your choice, $15 each, pick-up ONLY in Vail, AZ

20 miles SSE of Tucson

73, Dick, W1KSZ

Chuck, Would you take on the task of re-winding the high voltage transformer in a
647A? I have a near mint condition unit which runs for about 45 min until the
transformer gets hot and the fuse in the 2N3055 collector blows. - George



________________________________ From: Chuck Harris <cfharris@erols.com>

Also, can anyone tell me in what order one would rate the power
dissipation of these 'scopes (e.g., which ones get hotter than the
others)?. My 7904A and 7854 don't get very hot. The 7104 and 7934 have
failed power supplies, so I don't know if they run noticeably hotter.
The four 'scopes I am speaking of are

7104
7904A
7934
7854

Cheers,
DaveD

On 4/13/2013 6:39 PM, Dave Daniel wrote:

Has anyone had any problems running 7xxxx 'scopes stacked two high? I
am thinking of stacking my 7104, 7904A, 7934 and 7854 in a 2 x 2 pile.
I'm not sure if I would need two 'scopes running concurrently. The
fans, where they exist, move air horizontally. Perhaps the bigger
problem would be that one shouldn't have them side-by side?

Cheers,
DaveD

Has anyone had any problems running 7xxxx 'scopes stacked two high? I am thinking of stacking my 7104, 7904A, 7934 and 7854 in a 2 x 2 pile. I'm not sure if I would need two 'scopes running concurrently. The fans, where they exist, move air horizontally. Perhaps the bigger problem would be that one shouldn't have them side-by side?

Cheers,
DaveD

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

Anyone up for a look at something just a bit overpriced? EPay 230881279002

Craig

The other humorous (maybe not so) point is the shipping policy. Like many other small surplus resellers, this company states that they will" gladly ship nearly anywhere in the world".

What many of these small companies fail to check out is that all technology is subject to export classification from the USA, and some items such as this digitizer, are actually extremely controlled, requiring an individual export license be obtained for each sale to other than a tiny handful of "friendly" countries. Even when sold to one of these, you had better have strong evidence that the digitizer is being purchased to really be used in that country, and not be an agent who will pass it on to a banned country. The fines for noncompliance are pretty steep – they would essentially put most small companies under.

While some may say this is just other example of government over regulation that harms small business, I don't agree. The export classification system in the US is relatively easy to follow, and if I were a surplus dealer, I would weigh the relatively small potential for export business with the hassle of checking each item for export restrictions. As an alternative, you could easily specialize in one of the majority of categories that have no restrictions.

In the case of the 7912AD, its main application while Tek sold it was to the government labs for nuclear weapon design testing. While the technology is somewhat dated by today's standards, the digitizer has many features that simplify data collection in this application. I really would not see these going to countries with rogue regimes that would use them for developing their own weapons.

Steve

What can I actually do to increase the HV output apart from replacing the
rectifier-diodes into silicone-types (already done) and replacing the tubes of the
HV Supply (too) or rewind the transformer (what is too expensive for me at the
moment.

ben

From: Chuck Harris Sent: Saturday, April 13, 2013 3:02 PM To:
TekScopes@yahoogroups.com Subject: Re: [TekScopes] Re: Any advice on 547 power
supply repair?


That is, of course, why tektronix added the screen grid clamping diode to the
later model 547's... one of many indications that they knew that the epoxy
impregnated transformers were very lossy, and likely to get worse... Another
indication is the previously unnecessary balancing winding for the asymmetrically
distributed 5642 filament load. And another is the cutout in the bottom of the
plastic HV box for an unused transformer core heatsink. And yet another is
lowering the oscillation frequency from 65KHz to 50KHz... and there are still more
indications if you look at other scope models that inherited the 547's HV
compartment.

I have found that new rewound beeswax impregnated transformers result in screen
voltages around 65V vs. good epoxy impregnated transformer's 100V.

-Chuck Harris

Albert wrote:

Hi Ben,

An indication for that (or for a weak oscillator tube) would be a very high
screen voltage of the oscillator tube, probably clamped at 125 V. Normally that
voltage is well below 100 V.

Albert

Hm, I think then it was one of the less degenerated. I can imagine, that this
is also the reason why the HV still don’t reach it’s specified value.

ben

--- Some transformers that are only mildly affected by the epoxy degradation
will reduce their leakage after being heated, but even at their best, a good
epoxy impregnated 547 transformer is about 10x more lossy than one of my
transformers impregnated with beeswax. --- -Chuck Harris

David,
Thank you for your comments.

I have a FP-502 which I've never used. I also have a precision 50 ohm
sampling termination which I can attach the scope probes to at the
generator output.

Would you care to suggest initial settings of the PG in order to check
the scope probe bandwidths to 100 MHz? I would think I should use the
.1 nsec range for a 10 MHz period.

Ray, W4BYG

On 4/13/2013 3:16 PM, David wrote:

If you have a fast transition time reference pulse generator then you
can test them while connected to the oscilloscope. The bandwidth may
not exactly match but if the transient response is flat, I would
declare victory.

The cheap Chinese 100 MHz x1/x10 Aidetek brand probes I picked up have
worked fine when tested on every oscilloscope I have used them with so
far.

On Sat, 13 Apr 2013 12:05:52 -0400, Ray <w4byg@att.net> wrote:

Fascinating article and comments. It brings up a question for me.

My SC-504 was bought used in good condition, but did not come with
original probes. It supposedly has an 80 MHz BW.

I have tended to use on it my probes from my 465 or probes made by
Leader, model LP-101X, both of which are supposedly 100MHz probes. Both
have adjustable compensation at the scope end of the cables and both
seem to compensate the reference square wave OK.

I'm now wondering how compatible these really are at RF frequencies for
the SC-504?

Your attention is appreciated.

Ray, W4BYG