Radio - A look at and attempted repair of the Marconi Instruments 2305 modulation meter

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@cuban9splat 7 жыл бұрын

That is a very nice piece of equipment. Back in the late 50's and perhaps early 60's there was a phenomenon we called the TV repairman gremlin. Our TV would stop working properly and we would call the TV repairman to come out and fix it. This was back when they made house-calls to repair heavy televisions. When the repairman would arrive the TV would suddenly be working when he turned it on to diagnose the issues. Nothing he could do would make it stop working and he would leave while scratching his head wondering why we called him for no reason. However, shortly after the repairman left it would stop working again. You may have similar gremlins at work here LOL. Very neat video, Kevin. Thank you for sharing it with us. 73 DE K7RMJ Frank.

@rlmillr 7 жыл бұрын

LOL exactly

@piranha32 7 жыл бұрын

The "Sync" line in the OCXO is used to fine tune the reference. Internally it is connected to a varicap diode, which adds some extra capacitance loading the crystal. By applying voltage to this pin you can pull the frequency of the generator up to a few 10s of Hz one way or the other. It is used to adjust the frequency of the reference during calibration process.

@loughkb 7 жыл бұрын

Yep, Rick already pointed that out a couple of comments down. But I have a feeling I'll be hearing about it a few more times. What's life if you don't learn something every day? I don wonder why they call it, "sync" and not "adj" or "tune" though.

@piranha32 7 жыл бұрын

YT comment system is hopeless. I noticed Rick's comment after writing mine :) I guess they called it "Sync" meaning that it is used to bring the frequency of the generator in sync with a master reference. On other OCXOs I've seen this pin is simply called "ADJ". On more modern instruments the pin is driven from a DAC and tuning is done by changing tuning setting.

@rlmillr 7 жыл бұрын

This was running from a rubidium standard and I simply forgot to switch it to internal before I shipped it. I had it aligned to the standard but when the issue was present it should shift several khz. I touched the 15 Volt lead and it would lock on perfectly and stay there. A few days later I would notice that it was off frequency again. It was aligned to less than .1hz a few months ago so if it is working it should be very accurate. The HP was always reliably

@loughkb 7 жыл бұрын

OK Rick, I'll have to put it aside and let it run for a few days. I guess I got that sync line wrong. Oh well, it's still a pretty neat circuit. I like the way they handle the heater. It's such a simple circuit, that I'm perplexed by what would cause that type of failure. Unless one of those resistors in the oscillator has drifted way out of tolerance. But I wouldn't expect it to snap back in that way. Very odd. Still a very interesting exploration into the guts of the device.

@Jimwill01 7 жыл бұрын

Rubidium and Cesium standards. If I remember the Cesium is more accurate than the Rubidium, but I could have that backwards! Thanks for showing us the insides of that cute beast!! jim KF5AQF

@ElmerFuddGun 7 жыл бұрын

0:31 - Sorry but it wasn't made in the '60s or '70s. LCDs weren't commercial until mid '70s or so and yellow LEDs later than that. Those nice push buttons with the built in LEDs were mid '80s I believe as I remember looking up the pricing for them back then. They were quite expensive so I didn't use them! So my guess is mid 1980s when this came out. 12:40 they are NOR not NAND gates. AND gates are flat at the inputs and OR gates are round at the inputs. Looking forward to watching the follow up video.

@loughkb 7 жыл бұрын

+ElmerFuddGun Thanks for the additional info. I knew it was somewhere near the seventies or eighties ,makes sense. I knew they were nor Gates I don't know why I said and, but they were just used as drivers and an inverter to provide a inverted version of the 10 megahertz reference.