Low-distortion Audio-range Oscillator

[rsavas]

I used to fix 339A back in the 80's the knobs were cracked even back then. PCB were made in Loveland (PRCD), they liked gold electroplate for some reason or another, I guess because everything else was done that way. Or they did not need solder mask if they gold plated the copper. Probably were all hand solder as well. The 333 series was much better mechanical design from what i can remember. Yes Mr. Marsh you are resurecting a boat anchor, good luck with your efforts.
Cheers
Rick

[RNMarsh]

Originally Posted by rsavas

I used to fix 339A back in the 80's the knobs were cracked even back then. PCB were made in Loveland (PRCD), they liked gold electroplate for some reason or another, I guess because everything else was done that way. Or they did not need solder mask if they gold plated the copper. Probably were all hand solder as well. The 333 series was much better mechanical design from what i can remember. Yes Mr. Marsh you are resurecting a boat anchor, good luck with your efforts.
Cheers
Rick

I am looking for a nice clean sine wave source of variable freq - that i can then run thru a passive filter notch. I plan to use a high quality ADC/DAC system to measure the thd and FFT it in computer. Before that I had 2 fixed freq oscillators from Victor via eBAY. I bought a couple 339A as junk/parts units to cobble into one working unit... but, we shall see. trouble shooting it is easy but time comsuming and not sure I'll have all the parts needed. i did find some NOS of the HA-opamps for $3 each as back up for repair.
Its good we have it noted here for the record for others thinking of doing similar with 339A. Thx-RNMarsh

[rsavas]

Used HP equip from eBay is great stuff. I found these units very affordable.
HP 8656B,8901A,3478A,5316A,436A/8484.
I even have service manuals for them and as you do, buy non-op ones for spare parts. Nothin better than the real deal for spare parts ie. semi's .I know that you can get the ServM from Agilent, have lots but some sch's are hardly readable. I got a spare 8656B from Israel, imagine that $100,$100+ to ship air, still a good deal.
Need a part, I may have it! Good idea Rick, buy junk, remove parts, test,.sell on eBay=$?=Retirement planning. I loved my job at Motorola, fixing this stuff, now i fix PRC low rel. stuff=aweful.
Funny story, bought a HP counter IC on eBay, (Purple side braze w/gold lid/leads) sold as an ornament, pulled from a 5336,works like a charm, I see the same IC being sold on eBay for >100.00
Good idea's about making/sourcing some fine audio oscillators.Thx for that info
Have fun Rick

[DDB]

Richard, I have a 339 off of ebay a couple of years ago and only thing done to it was clean the switches although it could be improved with a recal and the 2nd harmonic mod to the jfet. Victor's boards are a better source I believe. Have you considered installing three or four of them into a 339 hulk and using its atten and switches? They are OK and their power supply is also decent, could be tweaked if desired. Might make a pretty decent oscillator. Dick's links has been posted many times on this thread but it is worth a read to look at a 339 osc and a Cordell SVC osc built into a Heathkit box. #2 IG-18 #2, the BIG-18 #3 IG-18 #3, the IG-339A #4 IG-18 #4, the IG-339B The HP has better shielding, attens, power supply etc so a better base to start from if you dont need continuous tuning and just want to use Victors boards. Larry

[john curl]

I have an HP339 that I just got, and am now baselining. Any input would be appreciated. Are you sure that it is not nickel plated vs gold contacts?

[RNMarsh]

Good ideas. I understand from Demian, the 339A oscillator is better than it's analyzer says it is. So, I expect it is less than .001%, stock. However, if I need a really, really super low distortion source, I have the ones from Victor.... together, they should take care of my needs for a long time. With the 339 mods, and contact cleaning, it should do very well.

[DDB]

A few tweaks I am going to do to my 339 oscillator section when time available:

Add 2nd harmonic mod to jfet.

Remove fuse from sig out line, HP advised some of them caused thermal distortion at low frequencies.

Determine whether better op amps might lower noise from HP/LP filters as Dick Moore suggested.

Improve oscillator +/- 15V power supply to lower noise output from line and PS IC, maybe try super regs with remote sensing. Current limiting nice though in case a tant cap shorts.

Any other suggestions are welcome although I don't want to attempt a major redo of the circuit, that's what Victor's boards are for.

As far as the analyzer section I don't know what improvements are easily made. The power supply for it can probably be improved but its more difficult than the oscillator due to the increased current requirement. Again suggestions are welcome but the need not as great as I also have a hardware SA and use a sound card FFT.

Larry

[1audio]

If the analyzer section is well behaved (doesn't add a lot of its own distortion) its a great front end for a PC sound card. Almost infinite protected dynamic range and the notch extends the distortion floor 20-60 dB depending. A 16 bit sound card, or an 8 bit digital scope adapter even, on the monitor output will show virtually all there is to see.

[RNMarsh]

Originally Posted by 1audio

If the analyzer section is well behaved (doesn't add a lot of its own distortion) its a great front end for a PC sound card. Almost infinite protected dynamic range and the notch extends the distortion floor 20-60 dB depending. A 16 bit sound card, or an 8 bit digital scope adapter even, on the monitor output will show virtually all there is to see.

... and get the auto-nulling which i like better than passive manual. Passive bridged-T might be the last word in measuring lowest thd. But, this comes in a close second and hassel free and a lot more affordable for occassional use.

I plan to do some of the tricks mentioned -- like pot for adjusting null on second harmonic. Its just too easy not to do. Thx-RNMarsh

[RNMarsh]

Originally Posted by john curl

I have an HP339 that I just got, and am now baselining. Any input would be appreciated. Are you sure that it is not nickel plated vs gold contacts?

They probably are nickel... dont know what the base metal is. I will consider soldering the ones that are off the oscillator pcb to other pcb and thru to output. The rest of the contacts (analyzer) can stay as they are.