RCA WO-91C Oscilloscope - Page 1
Forum section: electronics / repair

author: vastargazer
author_rank: Newbie
timestamp: October 01, 2015, 02:53:39 am
content: Hello all:I am new guy to the site and forum. So far my experience here has been very positive in getting feedback on buying my first hobbyist level oscilloscope. So, some time ago I had picked up an RCA WO-91C Oscilloscope on Ebay. At the time it was just for a "mad scientist lab" at a Halloween party. But now I got to thinking, maybe I'll try to see if I can get it working. To that end, I am trying to find a .pdf of the manual. I found one for the WO-91A but can't seem to find one for the WO-91C. The 91A manual has a schematic included so I'm hoping I can find a 91C manual with schematic as well. If anyone has any suggestions please let me know. I have tried Google in a variety of search permutations but so far no luck.Any suggestions most appreciated.Cheers,mark

author: oldway
author_rank: Super Contributor
timestamp: October 01, 2015, 04:04:14 pm
content: There are certainly very few differences , if none, between schematics of WO-91A and WO-91C.Why are you looking for service manual of WO-91C ?I recommend :- look for bad electrolytics and wax capacitors and replace them.- clean all the contacts with contact cleaner.- for the first power on, use a variac with a starting voltage of 50% of nominal voltage and increase this voltage of 10V every 15' (up to 110V nom).Look for anything wrong (for example, tube with hot red anode or hot electrolytic capacitor)Check the 300V power supply.Check all the controls. (vert amplifier, time base, intensity, focus, ...)NB: I wonder if it is still possible to use such an old (and simple) oscilloscope even for a beginner.There are people on this forum who think even a sophisticated analog scope is not adequate.Why not buy a modern analog scope as these ?

author: vk6zgo
author_rank: Super Contributor
timestamp: October 02, 2015, 01:37:43 am
content: This is a quite primitive instrument.Although RCA were still trying to flog it off in the late 1960s,it is pretty much the sort of design you wouldhave found in the late 1940s as far as the triggering facilities,etc.It did have better maximum bandwidth than a '40s 'scope,though,at 4.5MHz for low level signals & 1.2MHz for high level.There isn't any real "triggering" as in more sophisticated Oscilloscopes-----you set the timebase to "free-run".&adjusted the "sync" control,till it hopefully "locked".A contemporary of this unit was the Telequipment "Serviscope",which had 10MHz bandwidth,& real triggering,although it did use a smaller CRT.RCA were really trying to get as many sales out of an obsolete design as they could!All that said,if you want to fix it up "for the fun of it",there is nothing wrong with that.Itisstill a usable instrument,providing you understand its (quite substantial) limitations.

author: dan3460
author_rank: Frequent Contributor
timestamp: October 02, 2015, 02:18:35 pm
content: I have a RCA scope older than that. I made it to work, but it is only a display piece. I would not even think on using it for real work. Calibration is probably difficult and probably very limited bandwidth. Depending on what are you doing (learning, making a few projects, etc) you can get a "modern" oscilloscope in the $50-$100 range from ebay or Craig List.I just got a used Tektronix 2465 for $25, I had to refurbish the power supply and one IC on the main board.