Forums

Amplifer Design

Started by Cursitor Doom October 13, 2019
Cursitor Doom <curd@notformail.com> wrote:
> On Sun, 13 Oct 2019 13:17:04 -0700, jlarkin wrote: > >> I couldn't see that at useful resolution. > > I know; it's a PITA but there's nothing I can do as I pulled it off a > website myself. I've posted 2 versions, so you might see it better with > the enhanced one where I've tweaked things up a bit.
FWIW, <right mouse click> on the image and then choosing "View Image in New Tab" from the popup menu, made the schematic readable for me. YMMV. Thank you, 73, -- Don Kuenz KB7RPU There was a young lady named Bright Whose speed was far faster than light; She set out one day In a relative way And returned on the previous night.
Cursitor Doom wrote...
> >Greetings, gentlemen, > > This is the schematic of the CRO x-amplifier I've been investigating > lately. It's supposed to provide sufficient potential difference to the x > plates in the tube so as to sweep the electron beam left to right in > accordance with the timebase setting: > > https://yandex.com/collections/card/5da36a58f05bf23ffde0742e/
What scope model did it come from? -- Thanks, - Win
On Sun, 13 Oct 2019 14:03:39 -0700, Winfield Hill wrote:

> What scope model did it come from?
To be strictly accurate, it's actually an HP865A RF spectrum analyser. Not that it makes any difference to the question in this instance. In fact the y-amp uses *exactly* the same board as the x; something I'm hoping will assist me in identifying the faulty component. So rarely does something like that arise which can actually be invaluable in fault tracing! -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.
Cursitor Doom wrote...
> >On Sun, 13 Oct 2019 14:03:39 -0700, Winfield Hill wrote: > >> What scope model did it come from? > > To be strictly accurate, it's actually an HP865A RF spectrum analyser.
Can you recheck that HP model number? -- Thanks, - Win
On Sun, 13 Oct 2019 16:25:52 -0700, Winfield Hill wrote:

> Can you recheck that HP model number?
Sorry, Win, it's actually 8565A. -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.
Cursitor Doom wrote:
> Greetings, gentlemen, > > This is the schematic of the CRO x-amplifier I've been investigating > lately. It's supposed to provide sufficient potential difference to the x > plates in the tube so as to sweep the electron beam left to right in > accordance with the timebase setting: > > https://yandex.com/collections/card/5da36a58f05bf23ffde0742e/ > > At first I thought this was operating as some kind of complimentary pair > chain of stages, but it's only quasi-complimentary and I can't fully > understand how it works. The signal path is shown in slightly heavier > lines. It starts off conventionally enough, with a sawtooth sweep > waveform of approx half a volt applied to the base of Q10, but then why > does it then passed to the *emitter* of Q15? This is the part I'm > struggling to understand most. > > What is the name for this type of configuration and why is the input > signal to Q15 being applied to its emitter rather than its base?
* Q10 / Q15 is a differential pair; Q11 is the current source.
> Thanks. > > > (if it were *truly* complimentary/push-pull then I'd have thought there > should be a *minus* 158V supply for the final stage of the lower chain, > but it states +158V which makes no sense to me). > > >
On 13.10.19 23:02, Cursitor Doom wrote:
> On Sun, 13 Oct 2019 20:08:02 +0100, Piglet wrote: > >> Q10 and Q15 are a diff-amp or long-tailed pair. Q11 is the tail current >> source. > > Well I did suspect that initially, Erich, but the input signal is shown > only applied to the base of *one* of those transistors! >
That's how a diff pair is supposed to work, see e.g. Win's excellent book. -- -TV
On Mon, 14 Oct 2019 10:36:35 +0300, Tauno Voipio wrote:

> That's how a diff pair is supposed to work, see e.g. > Win's excellent book.
I shall! Thanks, all. -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.
Tom Gardner wrote...
> > On 13/10/19 19:40, Cursitor Doom wrote: >> Greetings, gentlemen, >> >> This is the schematic of the CRO x-amplifier I've been investigating >> lately. It's supposed to provide sufficient potential difference to the x >> plates in the tube so as to sweep the electron beam left to right in >> accordance with the timebase setting: >> >> https://yandex.com/collections/card/5da36a58f05bf23ffde0742e/ > > Why do you post that on a Russian company's servers, > rather than dropbox?
There's a 236MB file of the HP 8565A Operating and Service Manual, dated 1977, 424 pages, on the web. Unfortunately, it's locked, so I could not extract the pdf schematic page. But I expanded it, and made an image of the HV output amp. https://www.dropbox.com/s/o4tybr81cefbk5n/8565A_amp.GIF?dl=1 The 1st diff-amp stage has 562R emitter and 2k15 collector resistors for G=3.8. The 2nd stage has 750 + 500-ohm trim emitter resistors and a current output. The HV output stage has a 19k6 feedback resistor, for G = 15 to 26, 19 nominal. A 1pF feedback cap would set the video bandwidth at 8MHz. I imagine Zout is less than 1k. Push-pull PNP & NPN BJTs, running at 7mA, and dissipating 1 watt, go from 2V to 140V. There are two complementary amps, for two deflection plates. -- Thanks, - Win
On Mon, 14 Oct 2019 05:59:23 -0700, Winfield Hill wrote:

> There's a 236MB file of the HP 8565A Operating and Service Manual, > dated 1977, 424 pages, on the web. Unfortunately, it's locked, so I > could not extract the pdf schematic page. But I expanded it, and made > an image of the HV output amp. > > https://www.dropbox.com/s/o4tybr81cefbk5n/8565A_amp.GIF?dl=1
And a splendid image it is too. You're obviously way better than me at enhancement.
> The 1st diff-amp stage has 562R emitter and 2k15 collector resistors > for G=3.8. The 2nd stage has 750 + 500-ohm trim emitter resistors and > a current output. The HV output stage has a 19k6 feedback resistor, > for G = 15 to 26, 19 nominal. A 1pF feedback cap would set the video > bandwidth at 8MHz. > I imagine Zout is less than 1k. Push-pull PNP & NPN BJTs, running at > 7mA, and dissipating 1 watt, go from 2V to 140V. There are two > complementary amps, for two deflection plates.
It seems odd to me that there's no minus 158V supply for the final voltage amp. It looks like they're relying solely on attracting the electron beam from side to side with positive voltages swapping back and forth between plates rather than a combination of attraction and repulsion as I would have intuitively expected. :-/ -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.