Telequipment D75(?) 'delayed sweep facility'

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Hi

I've acquired an anonymous analogue scope which I think is a Telequipment D75. It all seems to work, at least as far as basic vertical amplifier/timebase/triggering goes. It also has some more mysterious buttons/knobs, which I can't puzzle out at all. The manual for the D83 (apparently very similar) says "...a dual sweep plugin provides the mainframe with a delayed sweep facility to permit close examination of any part of a complex waveform...". Can anyone explain the principals behind this, and what the various knobs/dials do? Please excuse the awful pictures...




Cheers
John

[Bored@Work]

A second time base with delay allows you to zoom in on a part of the signal. The delay is used to adjust where in the signal you start to zoom. The time base speed dictates the zoom level. E.g. a 10x faster second time base compared to the normal one means a 10x zoom of the signal.

[Aldobrandi]

I hope this video will answer your delayed sweep question:

[Monkeh]

Mine is still undergoing a very, very gradual refurbishment, so I can't help you on the operation, but..

Yes, that is a D75. Functionally identical to the D83, in fact many D75s have the D83 boards in them (mine has a mixture). The plugins are identical.

You may want to (carefully, of course) give the EHT board a good looking at. Specifically the resistor chains. They tend to go open.

[w2aew]

I hope this video will answer your delayed sweep question:

You beat me to it (posting the link to my video)!

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Yay! After much fiddling around, I've worked it out. I had seen W2AEW's video, but I couldn't square it with what I was seeing. There were a couple of problems. The first was that the scope seems to turn the intensity way down when you use any of the delayed timebase modes, so that you only see the intensified portion. Once I realised that, I turned the intensity up so I could see the whole wave. The next problem is that, unlike the Tek, the Telequipment doesn't seem to allow you to view both the original and 'zoomed' waveform at the same time. You have to set the portion to be zoomed while in the 'B INT BY A' mode, and *then* hit 'B DEL BY A'. Apart from that it all works like the Tek in delay and timebase terms. There is a 'MIXED' mode which seems to do a half-arsed both-at-the-same-time job, but not as two separate waves.

There's a few things remaining to work out. I still haven't got anything sensible out of the 'B trigger' business. There are also two separate EXT TRIG inputs, one for the A timebase and one for the B timebase. No idea why that would be useful.

On the upside there's both a sweep gate and ramp output (right there on the front panel) and a Z mod input on the rear panel. So that's pretty much full house! I'm very pleased with this acquisition, having suffered Tek-envy brought on by W2AEW's videos.

John

[w2aew]

As for the B trigger, it looks like that button that says IN VAR and TRIG OUT gives you a way of choosing to have the B sweep run immediately after the Delay setting, or to be separately triggerable after the Delay.