GEC/Marconi crystal oven pinout - Page 1
Forum section: electronics / beginners

author: NottheDan
author_rank: Frequent Contributor
timestamp: February 11, 2017, 01:11:42 pm
content: I got acrystal oven with an octal base and no markings on the outer shell(with cork insulation between it and the inner case that probably has all the markings) I know nothing about. Can anyone explain to me how to get it out of the outer case and inside it to get the data or does someone even have just the pinout for it?

author: edpalmer42
author_rank: Super Contributor
timestamp: February 11, 2017, 06:25:51 pm
content: I haven't seen one like that, but there aren't a lot of options. If there are no external screws, it could be glued, but that seems unlikely. A friction fit is possible. Or, maybe the outer part unscrews from the inner part. I can't think of anything else.Remember that it might not have been disassembled for decades so it could be seized.As for the pinout, it should be easy to find the heater. I've seen a couple of ovens that brought out both sides of the temperature switch. For the crystal, you could do an RF sweep and look for the impedance change. A spectrum analyzer with a tracking generator or maybe a noise generator would make that easier. Obviously, if there's no crystal inside, this won't work.

author: NottheDan
author_rank: Frequent Contributor
timestamp: February 11, 2017, 06:44:03 pm
content: You can actually see the screws on the inner case and the greyish-brown stuff between the inner and the outer case is cork used as insulation, so I assume it will not be screwed and the inner case is a normal one you usually see in photos. I just don't want to damage anything trying to get it out but I can't see how I could lever the inner part without causing damage.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 11, 2017, 07:03:54 pm
content: I see what you're saying about the outer and inner parts not being screwed together. That would be a bad heat leak, wouldn't it?I'd plug the thing into a socket, preferably one that's mounted in a chassis. Then grab the top with your hand and see if you can twist and wiggle it to break it free. The socket will spread the force between all the pins and the center post. If it's just being held by friction and maybe bonding on the cork, you should feel some give as you twist and wiggle. If the cork tears, you can always scrape it off and replace it, either with new cork or something with better insulating properties.If you can't take it apart, you can't reuse it. Ultimately, you have to apply force somewhere. If it breaks, you shrug and move on.

author: NottheDan
author_rank: Frequent Contributor
timestamp: February 11, 2017, 08:23:48 pm
content: Found a socket and using a bit more force than I felt comfortable with I managed to pull it out. Seems like whoever put it in did not properly align the screws with the slots in the cork, making this a bit more complicated than it had to. So here are a few photos of what I found inside.Do I understand it correctly that the temperature regulation would be integrated in the heating element?Edit: Duh! Three pins to the heater.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 12, 2017, 01:09:51 am
content: Congratulations! Disassembling some of these antiques can be a bit stressful, both on you and the equipment!I think that the ceramic thing in the third picture is the thermostat. It's thermally bonded to the metal cover, appears to be in series with the heater, and connects to the base via the three sockets in the fourth picture. Rather a complicated structure.The thermostat will be a simple bimetallic thing that clicks on and off. Crude compared to today's proportional control ovens, but still a significant improvement over a room-temperature device. I don't think they realized that crystals have a preferred temperature. I think that came later. They were just trying for a constant temperature, rather than one that varied with the temperature of the equipment.Do you have any plans for the unit or was it just for curiosity?

author: NottheDan
author_rank: Frequent Contributor
timestamp: February 12, 2017, 08:07:27 am
content: Something along the line of 60% curiosity, 40% vague plans. I took the ceramic thing as simply the base of the heating element.I guess the heating elements tales the standard 6.3V filament voltage?

author: edpalmer42
author_rank: Super Contributor
timestamp: February 12, 2017, 06:06:49 pm
content: There's no way to tell what the voltage is. If you had access to a few similar units, you could compare resistance values. A quick check on ebay shows ovens from 6 - 24 volts. I even have a big old Bliley unit that uses 110 VAC! Start at 6.3V and see how it goes. Ideally, set up a system that measures either the current or maybe the voltage across the thermostat. Automatically log the results to a computer and graph the results. If the thermostat never trips, it's not getting hot enough so you have to raise the voltage. Probably the best setting would be if it was on for most of the time while sitting on the bench. Inside a warm piece of equipment, the 'on' time would drop. Precision isn't required. Just don't use such a high voltage that something smokes!

author: NottheDan
author_rank: Frequent Contributor
timestamp: February 12, 2017, 08:27:46 pm
content: Joy!Probably have to do it by hand with a DT830B unless I can set something up with an Arduino. I'm not exactly equipped for automatic logging.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 12, 2017, 09:32:47 pm
content: If automatic logging is too big a pain, just connect a small bulb or LED in parallel with the heater. Then the bulb will turn on and off with the oven. I think that's why they wired out both sides of the switch. Put it somewhere that you'll see it and note the time when it turns on and off. Remember, precision isn't required here.

author: NottheDan
author_rank: Frequent Contributor
timestamp: February 12, 2017, 10:34:11 pm
content: Not so much too much of a pain and more a total lack of experience and equipment for it. I posted this in the beginners section after all. So I'll have to see what I can cobble together for it.