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Offline jcrubin

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My HP 331A distortion analyzer thread
« on: November 27, 2015, 07:16:16 AM »
This thread is to chronicle my HP 331A repairs.  So far, in the inspection stage no power yet applied.
Found 2 bad solder connections on the power supply board and one of which was a sad C4 capacitor.
Both Filter caps measured about 200uf and had an ESR of 0.22OHMS.     I still think they are ready to go.



















Power supply board



Bad solder joint



Burned capacitor C4



Serial
« Last Edit: November 27, 2015, 01:15:04 PM by jcrubin »
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Offline jcrubin

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Re: My HP 331A distortion analyzer thread
« Reply #1 on: November 27, 2015, 07:38:53 AM »
First thing is to check the component chagelog in appendix C to see what steps have been done. Mine include steps 9 through 18





Mine might be exempt from Step 9 as well

« Last Edit: November 27, 2015, 07:43:09 AM by jcrubin »
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Offline jcrubin

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Re: My HP 331A distortion analyzer thread
« Reply #2 on: November 27, 2015, 01:14:31 PM »
Many of the single pin connectors to the board are loose, a light crimp should fix them.  Not too worried about the capacitors on the other boards.
Though they will be tested as well, Ive pre-ordered replacements for all electrolytic on the main power board











On the ESR tester


« Last Edit: November 27, 2015, 01:17:19 PM by jcrubin »
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Offline jcrubin

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Re: My HP 331A distortion analyzer thread
« Reply #3 on: December 08, 2015, 01:58:39 PM »
Capacitors replaced, power supply is good




The following photos are before any calibration, and just testing the operation and controls of the unit.

Coax to unshielded alligator clips, no 600ohm terminating resistor

THD = .21% at 1KHZ 1V



THD = .205% at 5KHZ 1V


THD = .215% at 10KHZ 1V


THD =.315% at 20KHZ 1V


THD =1.2% at 40KHZ 1V


THD =2.2% at 50KHZ 1V using x10K * 5


THD =2.2% at 50KHZ 1V using x1K * 50


THD = 3.6% at 60KHZ
« Last Edit: December 08, 2015, 02:25:09 PM by jcrubin »
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Offline radhaz

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Re: My HP 331A distortion analyzer thread
« Reply #4 on: December 08, 2015, 04:01:18 PM »
Thanks for posting this. I have a 331 as well, but I bought a Panasonic VP-7723A audio analyzer shortly after that, and the 331 is on the shelf.
The 331 is very easy to use, and I love the feel of the switches and the tuning capacitor.
What are your plans for using the 331? checking audio amplifiers?
 

Offline oldway

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Re: My HP 331A distortion analyzer thread
« Reply #5 on: December 08, 2015, 11:54:11 PM »
I also have a 331 and I like it.  :-+
It is great as most of HP test gears of those times.
First thing I have done is to change the ac power connector by a standart one.
For more precision, I measure output voltage with a true rms multimeter because analogic display of 331 is NOT true rms.
It is usefull to check tube audio amplifiers (adjust of bias for instance) and sine wave oscillators.
« Last Edit: December 08, 2015, 11:57:48 PM by oldway »
 

Offline jcrubin

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Re: My HP 331A distortion analyzer thread
« Reply #6 on: December 09, 2015, 01:00:51 AM »
Thanks for posting this. I have a 331 as well, but I bought a Panasonic VP-7723A audio analyzer shortly after that, and the 331 is on the shelf.
The 331 is very easy to use, and I love the feel of the switches and the tuning capacitor.
What are your plans for using the 331? checking audio amplifiers?

Here is a collection of videos of my current project.  I generally work on Dyna equipment
http://www.youtube.com/playlist?list=PLK_zQ6_j4TF13qvrS3i2fw-p9trdjUhVm
« Last Edit: December 09, 2015, 01:03:51 AM by jcrubin »
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Offline jcrubin

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Re: My HP 331A distortion analyzer thread
« Reply #7 on: December 09, 2015, 01:07:31 AM »
I also have a 331 and I like it.  :-+
It is great as most of HP test gears of those times.
First thing I have done is to change the ac power connector by a standart one.
For more precision, I measure output voltage with a true rms multimeter because analogic display of 331 is NOT true rms.
It is usefull to check tube audio amplifiers (adjust of bias for instance) and sine wave oscillators.

Interesting... If its not true RMS what is it exactly?
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Offline oldway

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Re: My HP 331A distortion analyzer thread
« Reply #8 on: December 09, 2015, 01:20:14 AM »
Like multimeters, it measure the average value of the rectified ac voltage.
 

Offline dom0

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Re: My HP 331A distortion analyzer thread
« Reply #9 on: December 09, 2015, 01:56:53 AM »
Only the later versions (339A for example) have a RMS converter.

I think these have a residual / monitor / filter (whatever it is called on the unit) output, so you can connect an external RMS meter (e.g. 3400A, DSO, DMM) anyway.
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Offline AF6LJ

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Re: My HP 331A distortion analyzer thread
« Reply #10 on: December 09, 2015, 02:35:29 AM »
Good Thread Thanks for starting it.
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Offline oldway

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Offline TimFox

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Re: My HP 331A distortion analyzer thread
« Reply #12 on: December 09, 2015, 10:02:13 AM »
I relied on a 334 for many years, until I obtained a 339.
The 333 and 334 have an extremely useful auto-balance function, which servos the fine frequency and fine phase controls to achieve null.
The 339 is great:  a very low distortion generator built in, and the analyzer automatically tunes to that frequency.  Most importantly, if the signal level changes within the selected range, the percent distortion function automatically re-normalizes and gives the distortion.  With the 331 to 334, if you are adjusting for minimum distortion you need to re-check the input level (manually adjusting for 100%).
 

Offline jcrubin

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Re: My HP 331A distortion analyzer thread
« Reply #13 on: December 09, 2015, 01:55:09 PM »
Voltage portion of the calibration this evening........



-25V rail    +/- .25v     violet





+25V rail   +/- 1v         red   (adjusted by negative rail)





-11.3     +/- .1v            A2TP1     Problem here....  adjusting pot A2R3 has no effect.    Pot tested good on resistance



+8.2     +/-  .5v           A2TP2




+2.65     +/- .2v          A3TP1





-20.2   +/- .3v              A3TP2




The next board to work on......













« Last Edit: December 09, 2015, 02:21:04 PM by jcrubin »
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Offline Vgkid

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Re: My HP 331A distortion analyzer thread
« Reply #14 on: December 09, 2015, 02:03:55 PM »
It is impressive that those rails are still in spec. Though something is amiss with the -11v rail.
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Offline jcrubin

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Re: My HP 331A distortion analyzer thread
« Reply #15 on: December 09, 2015, 02:22:57 PM »
They weren't... that was post cal.    They were off, out of spec, but nothing terrible
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Offline AF6LJ

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Re: My HP 331A distortion analyzer thread
« Reply #16 on: December 09, 2015, 02:34:17 PM »
It will be interesting to see what is wrong with the -11V source.
Sue AF6LJ
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Offline jcrubin

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Re: My HP 331A distortion analyzer thread
« Reply #17 on: December 09, 2015, 02:39:34 PM »
See my post again....   Its probably C4 or C14 or Q1-4


My guess is C4 or Q1
« Last Edit: December 09, 2015, 02:41:42 PM by jcrubin »
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Offline AF6LJ

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Re: My HP 331A distortion analyzer thread
« Reply #18 on: December 09, 2015, 02:50:09 PM »
See my post again....   Its probably C4 or C14 or Q1-4


My guess is C4 or Q1

I am thinking C-4 leaky or shorted.
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Offline jcrubin

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Re: My HP 331A distortion analyzer thread
« Reply #19 on: December 10, 2015, 01:08:41 AM »


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Offline AF6LJ

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Re: My HP 331A distortion analyzer thread
« Reply #20 on: December 10, 2015, 02:26:04 AM »



As I remember the asterisk means the transistors are selected for specific performance properties.
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Offline jcrubin

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Re: My HP 331A distortion analyzer thread
« Reply #21 on: December 10, 2015, 09:00:14 AM »
lets hope its a capacitor.

That being said.   And granted I only work on tube equipment,   there must be a transistor that meets or exceeds the specification of the ones in the device
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Offline dom0

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Re: My HP 331A distortion analyzer thread
« Reply #22 on: December 10, 2015, 09:06:56 AM »
Most certainly. But sometimes they are not as easy to come by, for example HF Si-PNPs were common when Germanium transistors faded... but today they aren't really common anymore.
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Offline fivefish

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Re: My HP 331A distortion analyzer thread
« Reply #23 on: December 10, 2015, 09:35:33 AM »
Thanks for posting. I'll be following this thread... also have a 331A, sitting unused at the moment.

Got the 331A but then found a deal on a 8903B so the 331A never got turned on beyond checking that it's working.
But would like to at least maintain and calibrate my 331A.
 

Offline AF6LJ

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Re: My HP 331A distortion analyzer thread
« Reply #24 on: December 10, 2015, 11:20:15 AM »
lets hope its a capacitor.

That being said.   And granted I only work on tube equipment,   there must be a transistor that meets or exceeds the specification of the ones in the device

I am confident one could be found.
A friend I know on the radio has an old Collins 75-A4 receiver from about 1954 or so. He had overhauled the radio back about 30 years ago replacing all the parts that are known for failure in said receiver. The other day he was using it and had to change to another set up because the receiver started developing problems.
The trouble was a ceramic disc cap that had gone open. He was reminded by a friend that "there are no good 60 year old caps".

While the distortion analyzer isn't that old... (yet) My experience tends to lead me to the passives before considering transistors when the problem is not obvious, but marginal like this one....
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