HP1741A 'scope - some tweaks needed

[RussellSher]

Hi all
I was recently given an HP1741A 'scope. (State of the art for the time it seems.)
It seems to work, but needs a couple of tweaks and I thought I would ask on the forum in case there are any of you who may recognize the symptoms as being (semi) typical.
I have downloaded the user/service manual.
I get a trace with the calibration signal as input.
Both channels seems ok. I have disabled the storage functions for now (the 'CONV.' push button on rear is set to 'conventional' use)

The signal only seems to trigger when the Trigger Level knob is set to around the 2 'clock position, regardless of input waveform vertical positioning
as set by POSN knob. Symptoms are the same for both channels.

The Beam Intensity setting only produces a visible trace if set between anywhere between the 10 o'clock and 2 o'clock positions - the actual brightness doesn't
change much, other than fades out at the limits of those settings mentioned above.
The overall condition seems good and I imagine it may just need calibration and cleaning of the pots and switches. The CRT doesn't seem to have been abused - no signs of burning.
73
Russell

[Radio Wrangler]

Originally Posted by RussellSher

I have disabled the storage functions for now (the 'CONV.' push button on rear is set to 'conventional' use)

Take care. Using the Conventional mode on an HP storage scope is how mesh burns are created.

It is safest to use the variable persistence mode turned down to short persistence. In this way, if you wind up too much beam current you will see blooming.

You can use the short persistence mode to set the beam vurrent to a safe level, then switch to conv, but you'll find it too dim for every day use, but this is the max current you should be using if you want to get good tube life.

At the same beam currents you'd see nothing out of the ordinary in 'Conv' but the mesh is being damaged.

If you want a normal, non storage scope, I'd recommend you have a second instrument, a non-storage one. View a storage tube scope as a specialist bit of kit not a general purpose instrument.

The plant where those tubes were made was torn down in the early nineties and the ground ritually salted to make sure no more tubes were made. There doesn't seem to be any spares left and there are people looking. The ordinary tubes survive quite well, though the common fault with them is the scale illumi9nation flood gun filament being open circuit.

David (ex-HP design engineer)

[RussellSher]

Hi - and thanks for the reply. Ah - so my thinking was incorrect: I thought the CONVentional setting was the 'safe' option because the scope doesn't store anything. Ok, so if I keep CONV off (to unconventional ) that's safer.
Yes, I would look at one of the newer storage 'scopes for my typical use. Even the PC based 'scopes seem quite useful.
Is is my imagination, or does HP not provide a very comprehensive user guide? Eg. in trigger view (as a '3rd channel'), the the trigger view is a copy of the input when triggered - not quite sure what that is about? I though trigger view was just the DC trigger level that was set at the time. Perhaps you could explain if you don't mind.

[Radio Wrangler]

I've never used 'trigger view' What I saw whenever I pushed that button didn't seem to do anything I needed. One more bullet for the marketing brag sheet, I suppose.

The 1740 family are very nice scopes and unlike the Tek 465, you don't have a fan whirring away. Because folklore says no HP scope has ever triggered for any user under any circumstances, you can pick them up cheaply.

David

[RussellSher]

Thanks David. One for the marketing dept. I guess
regards
Russell

[RussellSher]

Further to the above discussions: Switching off the CONV mode as you suggested, seems to iron out some the issues regarding triggering and brightness. So maybe that was user ignorance from me. It seems somewhat normal now.

[Radio Wrangler]

Aye, that's not unusual. There's a significant learning curve for old school storage scopes and a lot of problems come down to 'finger trouble' Once you've got over the hurdle of knowing how to drive the CRT so you don't damage it, you should be OK.

The business of damaging CRTs is not covered in explicit terms in the manufacturer's manuals. I think they didn't want to admit it was possible. Your car steering has no protection to stop you driving into a wall or over a cliff, but electronic gizmos are expected to look after themselves.

The problem is that protection would limit the beam current when very high beam currents are needed for very fast writing speeds. So the scope unprotected is much more capable, but also rendered vulnerable. It would have been better if they'd explained it to the users, though.

David