I just got one of these off ebay, can't wait for it to come in! This is gonna be a very useful video, thanks so much! Crazy to think this thing just turned 70, my grandfather only has three years on it.
I'm fond of this vintage hp gear. A full cosmetic restoration is one thing, but for the most part, you just rip out and replace all the bumblebee and black beauty caps and the thing will start working just fine.
Nice unit. I just picked 2 of these up for free. An HP innovation at the time, the light bulbs were used for amplitude stabilization during fluctuations in temperature, line voltage etc...
This is obviously when HP was well established. I have had an HP 200B that is from before they started marking serial numbers. A few years ago I noticed pretty bad distortion and replaced the tubes. Seemed to help some. But earlier this year I found it really bad (had not used it in between), including 120 Hz ramble - not called hum any more. So I opened the bottom side and saw some black pitch that had leaked out two dry capacitors, both rated 600 V DC. Obviously a big repair was called for. I found that also a coupling capacitor from one anode to next gate was leaky and probably for that reason resistors feeding the screen had suffered a violent death. The odd thing was that also the lower resistor in the divider was blown open. Oh yes, the two-section metal case electrolytic capacitor was off value, although still with quite low ESR. After all the replacements, no more hum and the distortion is around 0.5%, still not as good as it should be. But my main concern is that I cannot make the frequency dial track properly. One of these days I’ll have to take yet another look at that. Until then, my newer (ARB) generators have to do.
changing all electrolytic and coupling capacitors would be a good idea. The signal was still distorted a bit in the end. Trusting those 50 years caps is like going to sleep with a live grenade in your hand. You never know when it will explode.
Pop Tibi Yup those bumblebee caps are bad news, but I don't have any replacements on hand and this old signal generator sees very little use. It gets turned on a couple of times a year. Now that it is putting out a correct sinewave it may see a little more. I do have that digital generator which is good for most applications.
Those small incandescent bulbs are actually part of the oscillator circuit. They provide a sort of automatic gain control. Do a search on Wien bridge oscillator if you'd like to learn more.
I was just gonna say the same thing, lamps like this were commonly used in these early signal generators to allow like you said "automatic control" of the feedback gain. As the lamp heated up the resistance increased which controlled the positive feedback so in a way it is "kind" of a limiter but not for current. when he said "current limiter". the only time i have seen current limiter lamps used in how he described was in my Hickok tube tester.
mjr1999 I hadn't looked at the schematic when I shot this but correct they are in the amplitude control connected between the cathode of the rectifier tube and the grid on the oscillator. To provide agc. They are connected in series and are used basically as a resistor. The resistance of the tungsten filament changes with the heat in the filament this providing a automatic gain. This is actually the first one of these I have opened.
Frank Scarano At first I thought they may be there to protect against a overload condition say, if the signal output was connected to something putting a voltage back into the circuit, thus protecting the tubes from damage, but correct they are in the oscillator circuit as the schematic shows. For amplitude control as the tubes age.
I highly suggest taking an air compressor to the inside, especially that tuning gang! All that foreign matter in the cap plates and tuning caps can cause issues. Its generally the very 1st thing i do before i start working on something like that.
I used to calibrate test equipment and we bought a lot our test gear used. One thing I've seen more than once is someone substituting 6V6's for the 6F6's this unit was designed for; that can cause distortion and in some cases will make the unit act like a relaxation oscillator. The two tubes use the same basing but the plate impedance is very different. The tubes last a very long time but the electrolytic caps should be replaced every couple of decades.
Scrape, scrape, scrape. Is the dial rubbing on something or is it just some bearings that could use a bit of lubrication? That noise would drive me nuts. It sounds like the tuning cap in one of those radios of similar vintage that shango066 would dig up out in the desert after who knows how many decades.
Did not use mine for ages, sitting on my top bench for same ages, next to my Tek 453... I have absolutely no use for both, but well, you can't throw them out.. :D
There is an ice cream truck that comes through my neighborhood *well* after dark. I'm positive he's really selling shrunken heads and black tar heroin or something like that.
Mark Anderson I have 2 old hp device's. This and the old scope. I should set that old scope up as my crt vector clock again. It looks so good, but draws so much power and the fan is so loud I don't run it much.
killmore75 Which one? I have a few versions. When I ran those longer ones people whine about them being too long. They will come back from. Time to time.
Jérémie Faucher-Goulet My kids used to call them pedo-mobiles in reference to the news stories of a convicted child molester that was found driving one around.
It would have been nice if you could have seen you calibrate the actual unit, rather than looking at the oscilloscope the entire latter half of the video. Couldn't see what you did.
I did show which controls I was turning, and then the scope results. I shoot single camera, so I have to do re shoots to show both. Had I not showed the tweaking on the scope and just showed my hand turning a screw, you no doubtfully would have bitched about that too,
@@scottmartinezguitarandbass Can't please everyone. Doesnt matter what I show someone is going to complain. Hands in the way is the biggest. Sorry but when I am repairing something I have to see first what I am doing. I don't have a camera operator manning the camera and if my hand blocks an adjustment so be it. I generally show which controls I am turning and then show the screen or scope to show the effect. I take constructive critism all the time but most of it is people bitching about something and I have no patience for the trolls. They are either ignored or their comments nuked.
