The 600 ohms mentioned on the meter low side print is only there for defining what dB reference they are talking about. There are several more or less "standard" references in use. You can use something defined at 50 ohms, for example. It just uses the power at resistance rather than direct volts or millivolts, for example. The meter input resistance is 10 Meg, if I remember. The only effect the terminator (attenuator) would be to match the output (i.e. input to the 3400) to the signal source, in case it expects a 50 ohm load, and you want to use the generator meter as your reference.
Hey! Nice job there! Its been a nice hour spent watching this restoration. I just love this. I’m absolutely not an expert, and that’s why I’m always looking for videos like this, I’m learning so much! Towards the end of the video you talked about the impedance matching input-ouput and said something I believe was wrong. The input impedance of the HP I think is 10 MOhm not 600 ohm. The 600 ohm is just the reference for how the db scale is calibrated on the meter due to the “audio frequencies” those meters can work on. So if you don’t terminate your generator into 50 ohm you’re gonna see double the voltage as measuring an open circuit. I learned this myself when I started playing with mine, a Racal 9300F. I got confused initially. On mine though the input impedance is 1Mohm. So please correct me if I’m wrong in what I just said. Thank you and congratulations again on your work there!
Yes what I said may have implied that. The actual input impedance is not 600 ohms. I used a 50 ohm terminator in the video match the 3400A to my signal generator. Thanks for the comment.
I have this meter as well, even has the same prefix on the serial number. Mine seems to work just fine with the exception of the slight meter oscillation that seems to stay within 1%. All I have done is calibrate it with my HP 3325A and so far it's been a great addition to my bench.
I have three HP 3400A's. Thank you for posting this. This video is interesting to me as one of mine does not work at all (no needle deflection); the others seem fine. Question: How do you translate the serial number prefix into the data of manufacture, please? Mine has serial 1050 000969 and is marked 'MADE IN GREAT BRITAIN'. There is an article in HP Journal January 1964, volumr 15 No 5, about the 3400A.
Hi there, What instrument did you use to measure the capacitors? Where do you source your capacitors? Thank you for a really great video. I like how you went back and forth between schematic and actual instrument, while explaining your thought process. Cheers Mark
On your Source to 3400A connection the open end of the Y splitter would bring is a bit of noise but the line would still be 50 Ohms terminated. NOT a big deal. Damn I love this old stuff. Still chooching after all these years. The one I have is the most precision measure I have at hand. I can use it to feel happy most everything else I have is within reason.
I have several 3400A's drifting some and your video has given me loads of good advice to get started. THANKS. For giggles, do you have plans to resurect the othe units at some point?
Funny you should mention that. Sometime after I made this video I came across another 3400A for a good price and I snagged it. Turns out it had the later chopper amp board which is completely solid state. I may give that one a go but it’s case was mauled up pretty good. I also have a 419A which I’ll get to working on sometime. Mr. C already did a pretty good video on those but I’ll see what I can do. Thanks for the comment.
I'm totally confused at 32:30, your supplying 5ma to a series connection of your ohmmeter and heater assembly? If that is a Ohm meter how can you force 5ma through it? wouldn't it be better to supply 5ma to the heater and measure the voltage drop across the heater and calculate the resistance?
I’m sure there are other methods that could be used to make this measurement. I was using the method described since I had what was necessary on hand. In the ohms function, a small current is supplied by the meter to the device under test (usually a resistor). The meter uses this current to determine the ohms value and display on a meter. I have the DMM hooked up in series with this to measure the current being supplied by the ohmmeter. I hope this helps. Thanks for the comment.
@@FreeElectron Ok, I missed a key point, that is not a current source, as this time, I heard you say amp meter. So your ohm meter is supplying about 5ma to when you measure the heater, That was convenient. I'm working on one now, It looks like all of the LDRs in the photochopper have about aged out. Neither set passes the >10kΩ test, one is 9kΩ and the other is 2.1kΩ. There are some mods to replace the photochopper, using either a DG403 or an H11F1 clocked with a 555. I'm leaning that direction, if anyone has a good schematic of that mod, let me know.
From W1°23'42.43" · N42°34'33.13" Great job. Just two people, is amazing!
Mr Carlson did a video on replacing the neons with leds and driver circuit. Nice repair.
Yes, I’ve seen his video. I may try something like that but for now the standard neons are working well. Thanks for the comment.
The 600 ohms mentioned on the meter low side print is only there for defining what dB reference they are talking about. There are several more or less "standard" references in use. You can use something defined at 50 ohms, for example. It just uses the power at resistance rather than direct volts or millivolts, for example. The meter input resistance is 10 Meg, if I remember. The only effect the terminator (attenuator) would be to match the output (i.e. input to the 3400) to the signal source, in case it expects a 50 ohm load, and you want to use the generator meter as your reference.
thank you for this extremely thorough and informative diagnostic/repair.
Very informative and precise. Thanks for your work.
Wow, awesome work man! Nice gear! ~Jack, VEG
Hey! Nice job there! Its been a nice hour spent watching this restoration. I just love this. I’m absolutely not an expert, and that’s why I’m always looking for videos like this, I’m learning so much! Towards the end of the video you talked about the impedance matching input-ouput and said something I believe was wrong. The input impedance of the HP I think is 10 MOhm not 600 ohm. The 600 ohm is just the reference for how the db scale is calibrated on the meter due to the “audio frequencies” those meters can work on. So if you don’t terminate your generator into 50 ohm you’re gonna see double the voltage as measuring an open circuit. I learned this myself when I started playing with mine, a Racal 9300F. I got confused initially. On mine though the input impedance is 1Mohm. So please correct me if I’m wrong in what I just said.
Thank you and congratulations again on your work there!
Yes what I said may have implied that. The actual input impedance is not 600 ohms. I used a 50 ohm terminator in the video match the 3400A to my signal generator. Thanks for the comment.
@@FreeElectron thanks for the answer. Cheers!
I have this meter as well, even has the same prefix on the serial number. Mine seems to work just fine with the exception of the slight meter oscillation that seems to stay within 1%. All I have done is calibrate it with my HP 3325A and so far it's been a great addition to my bench.
It’s a great meter. I use mine quite a bit, more than I thought I would. Thanks for the comment.
I have three HP 3400A's. Thank you for posting this. This video is interesting to me as one of mine does not work at all (no needle deflection); the others seem fine.
Question: How do you translate the serial number prefix into the data of manufacture, please? Mine has serial 1050 000969 and is marked 'MADE IN GREAT BRITAIN'.
There is an article in HP Journal January 1964, volumr 15 No 5, about the 3400A.
Hi there,
What instrument did you use to measure the capacitors?
Where do you source your capacitors?
Thank you for a really great video. I like how you went back and forth between schematic and actual instrument, while explaining your thought process.
Cheers
Mark
I usually source from Mouser or Digikey. For checking capacitors I use either an HP 4262 or my handheld ESR meter it’s a DE5000.
On your Source to 3400A connection the open end of the Y splitter would bring is a bit of noise but the line would still be 50 Ohms terminated. NOT a big deal. Damn I love this old stuff. Still chooching after all these years. The one I have is the most precision measure I have at hand. I can use it to feel happy most everything else I have is within reason.
Just watched this video as I have been using mine today. I thought mine was the only one with the broken zero screw!
Haha, I guess there was at least two out there. It’s an easy fix though. Thanks for watching!
I have several 3400A's drifting some and your video has given me loads of good advice to get started. THANKS.
For giggles, do you have plans to resurect the othe units at some point?
Funny you should mention that. Sometime after I made this video I came across another 3400A for a good price and I snagged it. Turns out it had the later chopper amp board which is completely solid state. I may give that one a go but it’s case was mauled up pretty good. I also have a 419A which I’ll get to working on sometime. Mr. C already did a pretty good video on those but I’ll see what I can do. Thanks for the comment.
Excellent teaching!
It's great work but camera work is horrible :( please buy some cheap stand for your camera and do not record all from the hand .
Realy enjoyed this and subbed !....cheers.
I'm totally confused at 32:30, your supplying 5ma to a series connection of your ohmmeter and heater assembly? If that is a Ohm meter how can you force 5ma through it? wouldn't it be better to supply 5ma to the heater and measure the voltage drop across the heater and calculate the resistance?
I’m sure there are other methods that could be used to make this measurement. I was using the method described since I had what was necessary on hand. In the ohms function, a small current is supplied by the meter to the device under test (usually a resistor). The meter uses this current to determine the ohms value and display on a meter. I have the DMM hooked up in series with this to measure the current being supplied by the ohmmeter. I hope this helps. Thanks for the comment.
@@FreeElectron Ok, I missed a key point, that is not a current source, as this time, I heard you say amp meter. So your ohm meter is supplying about 5ma to when you measure the heater, That was convenient. I'm working on one now, It looks like all of the LDRs in the photochopper have about aged out. Neither set passes the >10kΩ test, one is 9kΩ and the other is 2.1kΩ. There are some mods to replace the photochopper, using either a DG403 or an H11F1 clocked with a 555. I'm leaning that direction, if anyone has a good schematic of that mod, let me know.
Prime suspect to me is needing RE CAPPING.