HP339A distortion analyser

Hi,

Going by memory only... If it isn't corroded contacts --- there is a fuse and a relay contacts in series with the osc output. One could be open.


THx-RNMarsh
Thanks Mr. Marsh, I will check that fuse and relay, my manual is hiding under tons of other stuff. Its been a few months since I looked at these 339a's but I will get to it soon.

Steven
 
Hi Sync, and Mr. Marsh,

Well I finally found out was is wrong with one of my 339a's. See pix. I think that is Sw4

Steven
 

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Hi Steve,
That's heart breaking! That damage came about from within the instrument.

"Struck by Technician", or someone who calls themself a technician. All you can do now is buy a parts unit to raid that switch from. Either that, or this analyser becomes a parts unit. I'm very sorry this happened to you.

-Chris
 
I don't suppose anyone has one of those wafers or the Sw4 switch they could sell?

If not I guess the set becomes a parts donor, and I may sell the parts, boards, etc. off on eBay, piece by piece, it was a working unit that passed loopback criteria the last time it was used. It is stock, no mods or changes before it got damaged (also no knobs, I replaced them with small metal ones, sorry!).

Steven
 
Hi Steve,
That's heart breaking! That damage came about from within the instrument.

"Struck by Technician", or someone who calls themself a technician. All you can do now is buy a parts unit to raid that switch from. Either that, or this analyser becomes a parts unit. I'm very sorry this happened to you.

-Chris

Thanks Chris, not sure what happened, but I guess I should have put all the front screws back in months ago :yes: ... At least my other 339a is fully intact, I will have to double my efforts to get that one fully working, I tested it recently, on that time it seemed the oscillator was not working but it did give good readings using an external Amber 3501's oscillator.

Thanks,

Steven
 
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Hi Steven,
Well, after you raid the broken one for parts, you might want to keep it for parts. I have two units, one is a backup in case the other one hiccups. I can't be down without it.

I have an RTX-6001 (and I really like it), but it isn't the same as the 339A for some jobs. Again, I'm really sorry to hear you have a broken switch. But since you have non-factory knobs on that one, it takes some of the burn off.

-Chris
 
I took a while to see what the problem is. I keep staring at it thinking this is cleanest looking 339a I've ever seen. No corrosion or dust. After a minute of staring I see half a wafer missing.

What a shame. I tried to find wafers for them with no avail. Close but not quite.
 
I also found a second switch with the center moving contacts pushed out beyond the wafer, I'm guessing these things must be my fault, as the owner, I have been working on the front panel Banana Jack's, two of which, had recent breakage of the plastic mounts, leaving the metal inserts "hanging", also the meter came loose and was moving around.

I don't believe in coincidences, so I'm guilty here. Yup. Too much heavy hand, not enough alignment and gentle, those switches are much too fragile.

HP should have used the blue plastic mil-spec based switches, the one place that HP didn't use the best parts, becomes a true failure mode decades later.

Yes, this set is quite clean inside, looks like new inside, I think both my sets are about the same in that respect. This set has the "toggle" power switch.

Otherwise, I note that it was several plastic parts that failed over time - the knobs, the plastic dual banana mounting parts (both for grounds), and one of the A4 board lift out plastic action lift pieces. Not sure where or when these plastic parts became over-stressed, maybe it is just luck or age, set has mostly 1979 date codes inside. Have to look for date codes in the other unit, that one has the "push" type power switch I think they were made later?

Steven
 
Plastic drys out and become brittle over time. You probably didn't do any wrong with the clips, they just broke. The switch wafers are probably phenolic because of it's high resistivity. phenolic plastic also becomes more brittle with age.

One has to be extra careful with these vintage instruments.
 
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Hi David,
That is true, but I haven't had any problems with phenolic switches or even tube sockets in old radios. A switch wafer will not break without a force directly applied to it. I have seen switches made from other materials also broken. If it is from a shaft forced back, typically all the wafers break no matter what they are made of. Never seen it happen with ceramic wafers.

-Chris
 
HP-339A OSC Output Distortion

I had one HP-339A.

But there is something that I can not understand.

Is there a noise (50Hz, 1K, 2K, 3K, 4K, 5K, 6K ...) in the scope waveform and spectrum of the OSC output as shown in the attached figure?

The Boonton-1120's OSC output is free of normal Sine waveforms and noise.
 

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There is an Asian made clone of the HP-339A now. It does not look exactly like the 339A but similar and has all the same features and controls.

MCP-DTM4120-distortion-meter.jpg

MCP DTM4120 - distortion meter, View distortion meter, MCP Product Details from Shanghai MCP Corp. on Alibaba.com

It is only one range less on THD. So, if cheap enough compared to old worn out and over-priced HP-339's, it could do the job for many, stock. And, maybe we could tweek it a little and get X10 more out of it. Right now, stock, it will read down to < .01% on the .1% range.

I have inquiry in to mfr as to their selling cost.


THx-RNMarsh
 
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