HP 333A Distortion Analyzer – Revitalize.

[M-HZ]

     I have been looking for a HP 333A or a HP 334A Distortion Analyzer that would hopefully be in rather good working condition, but realistically I keep my expectations in check. However, I did come across a 333A that is being offered by an individual within my local vicinity. A price range of $100.00/$150.00 is being negotiated and debating on its acquisition. It's in rather good shape, but a quick check reveals that the 333A is functional, rail voltages are fine, but has not been calibrated for some time. I do not have access at the moment to equipment to produce a high quality (?) 100uV, 400Hz sine wave signal nor any other high level calibration instruments that may be needed? Also, the Frequency Range rotary switch may need a cleaning as would the Meter Range Set level per the owners own tests. There appears to be no physical damage (rotate smoothly) whatsoever nor did I see any form of deterioration/burning components and the like. I gather a high quality cleaner would do the trick? It has been a while since I have flipped on my Tek 2236 and various other pieces of equipment, but would not mind undertaking a reasonable project. I would welcome any suggestions/steps for an attempt to bring this unit up to some form of reasonable performance baring any unknown "pitfalls". I will mainly be utilizing it for measuring THD+N in tube amps/guitar and other forms of experimentation along these lines. Again, much appreciate any form of input.   

[nre_admin]

The 333A voltmeter is calibrated using a signal sinewave generator capable of micro-volts output.  The procedure is to check the voltmeter over a range of frequencies with an input set at 300 micro-volts RMS.  The meter, set to 0.0003VRMS peak reading, should not deviate more than +/- a few micro-volts off "3".

The alternative is to assess the distortion residual using an FFT and determine if sufficient attenuation of the fundamental is achieved.  I can provide a few screen shots of that.       

[nre_admin]

FFT of residual output of 333A (blue) and Krohn-Hite 6900B distortion analyzer, same input signal.  The plot is what's left after the fundamental is filtered out.  Note the K-H unit has much lower noise floor.  Input signal signal is 1kHz ultra-low distortion sinewave sourced from Stanford Research DS250 Low Distortion Analyzer, split and sent to each unit.

[M-HZ]

Firstly, thank you very much for a New Years answer which was much appreciated and of great help. I surmised that this may have been the way to go from what research I have done and a previous posting on the net, but was a bit unsure of. No doubt the chart clearly points out the difference between both units – helpful visual! Will assess shortly which way to go, but may have another question or two moving forward. -TY

[M-HZ]

I have managed to purchase a 333A (nearby resident) and a 334A both for a rather fair price. I have tweaked the 333A which of course turns on and is showing rather good signs of functionality.  However, the 334A was DOA. I have done some very basic "continuity checks", visually I see no leaking caps as of yet, but thus far revealed nothing. I'm new to these specific units and inability to track down viable schematics at the moment has me in a bind. No doubt the power supply would be the initial go to point, but any other recommendations would be appreciated.