Tektronix 7704A power supply question

It was during exercises. One group was training heavy-ammo tank attacks and for some reason one went way in the wrong direction and towards us. It made a crater. Problem was, the doc was too young to recognize that you must send soldiers to the hospital right away for a constant blood thinner IV, he sent me back to the barracks for the weekend. Monday he became quite worried and sent me to an army hospital but by then the chances to fully recover the hearing had dropped to 20% or so :-(

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Regards, Joerg

http://www.analogconsultants.com/

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I think he was responding to Fred. Anyhow, it's 1mH and that should result in 30kHz. Which makes the 20usec periods out of the PWM chip a bit weird. I've never driven a series-resonant converter that far "to the side".

This 7000-series scope supply module was a bit disappointing. Looks slapped together, not the cast-iron Tek quality I was used to see in their older gear.

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Regards, Joerg

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Jim Thompson wrote in news: snipped-for-privacy@4ax.com:

I just added my post at the bottom of what you posted,keeping continuity in the thread. Note how you left text from the previous poster between your last comment and your name,creating the confusion.

My newsreader assigns different colors for different posters.

(I also filter out posts using "invalid" and other stuff spammers use,so I didn't see Fred Abse's original post.That's why I replied to your reply.)

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Jim Yanik
jyanik
at
kua.net

Ahh.. You missed something: 1 mH and .03uF resonate at about 30kHz (29 actually), but they're in series with the leakage inductance of the transformer, which is significant. The combination, with the transformer loaded goes at about 25kHz.

The transformer construction is similar to a TV flyback, and we all know how much leakage inductance they had :-(

I've not had chance to check up, yet, but I think the trigger circuit fires every half-cycle, which would explain the 20usec period.

The result is pretty close to 25kHz. There's enough of it gets where it shouldn't to put low-level pips 25kHz either side of the carrier on a spectrum analyzer plugin in a 7000A series mainframe. There's some spurious phase mod of one or more of the LO's going on. The non-A models don't do it, so I suspect it's something to do with the separate HV generator being driven up those long cables from the main PSU and ground loops.

7L12, 7L13, 7L14 all do it on the 7704A, the 7904A, and, to a much lesser extent on the 7104, which also has a separate HV unit. They don't do it on either of the plain 7904s I have. The 7603 storage doesn't do it, but that's got a "cooking" line frequency PSU.

I'm inclined to agree that they're not that pretty, but the performance is fabulous. At least I can pick one up and carry it, unlike some of the earlier stuff.

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
                                             (Stephen Leacock)

Is that patentable?

That'll larn ye!

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
                                             (Stephen Leacock)

Whoops, that much leakage?

Looks like that REG OUT signal goes straight to the drive transformer for the H-bridge bases. But again, the waveforms are very faint in the PDF file I have, hard to decipher. Probably they were red or something and the scanner didn't pick them up too well.

Those modules are a bit hard to find and often pretty pricey. At least when I was in the market for one they were more expensive than a nice PC-controlled scanner, so ...

True, unlike after the HP4191 repair my back did not ache when I was done repairing the Tektronix.

--
Regards, Joerg

http://www.analogconsultants.com/

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snipped-for-privacy@giganews.com:

V .

Joerg will be soon able to notice that there is ,-)

innews:KZ-dnYGRzOqFrTnUnZ2dnUVZ snipped-for-privacy@giganews.com:

Schematic is for the 7704A, scope is a 7704A. What would be the problem? Anyhow, it's fixed, works again :-)

Since you are a Tek expert, do you know how easy it is to replace the first mixer in a 7L12 or 7L13 with something off the shelf like Mini-Circuits? It would be nice to add that module to this chassis but many of them had their inputs fried and the sensitivity is shot.

--
Regards, Joerg

http://www.analogconsultants.com/

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