Best AM FM Stereo RF Generator for a Newbie

[George S.]

Been reading and looking at equipment. Just ordered a cheap and dead HP3325A to repair and play with. Does sweeps and markers.
The frequency and output range is key when looking at RF sweep oscillators. Lots of HP units out there that have no practical application for AM/FM tuners due to the frequency range.
The 3325A is technically more of a function generator, but we'll see how well it works for RF. I'm mostly concerned about the output.
For RF work the output needs to be dialed down vanishing small.

 

[George S.]

Got the HP3325A on the bench. It's better than expected.
Boots with no error, but two power supply rails are way over voltage, fan is noisy needs cleaned and lubed, one of the "West" keys doesn't click like the others, original caps, etc.
Just what I was looking for.
This will be a good project and keep me busy.

 

[Gepetto]

Got the HP3325A on the bench. It's better than expected.
Boots with no error, but two power supply rails are way over voltage, fan is noisy needs cleaned and lubed, one of the "West" keys doesn't click like the others, original caps, etc.
Just what I was looking for.
This will be a good project and keep me busy.

Those HP keys are notorious for that George...one of the weaker points of otherwise excellent equipment.

 

[George S.]

Been reading up about them Joe. That's the good thing about HP test equipment. There's lots of info out there and a devoted highly educated community.
World of difference between the consumer grade gear I've been working on and HP test equipment.

 

[Gepetto]

Been reading up about them Joe. That's the good thing about HP test equipment. There's lots of info out there and a devoted highly educated community.
World of difference between the consumer grade gear I've been working on and HP test equipment.

I just live with it on my HP8903B, it is a major effort to tear down the front panel. The buttons work fine, they just feel funky on several of them.

 

[laatsch55]

How old is that stuff?? As we all know , switches dont last forever..

 

[laatsch55]

George, I was looking for a manual for an RCA 519A VOM the other night and found the " bama archive" ever heard of it?

 

[George S.]

Sure have Lee. Got my Triplett VOM download there.
They have a file of scanned but unsorted documentation. I've dug deep in it many times.
I was last in it months ago looking for TrueTime XL-DC receiver documentation for my GPS disciplined 10 MHz oscillator.

 

[George S.]

How old is that stuff?? As we all know , switches dont last forever..

Lee, they're the "Bill West" switches named after the HP engineer who invented them.
They bridge the gap directly on the gold plated boards.
My unit was probably made in the early 80's, and is now overdue for service.
Here's a good link where knowledgeable and experienced guys discuss servicing these switches.
https://groups.io/g/HP-Agilent-Keysight-equipment/topic/repairing_hp_s_iconic_beige/87421785?p=

 

[laatsch55]

Interesting stuff there George, thanks..

 

[George S.]

Making progress. No issues with the power supply. I was incorrectly measuring the feed back rails.
The fan motor is burnt toast with a scored shaft, have a NOS replacement headed my way.
Thought the unit had attenuator issues until I read about impedance matching and the need to terminate the output into a 50 ohm load. Added a "T" and 50 ohm load at the scopes input and now the generators output is correct on the scope.
I need to see if I can do this internally on the DSO, if it has a 50 ohm input setting. The old HP CRT scope does have such a setting for the inputs.
Going to pull the face plate today and clean the switches, facia, and straighten a bent rack bracket.

 

[George S.]

Here's a good photo of the switches. The flat metal spring is clearly visible. All appear to have good springs. Replacements can be cut from shim stock or feeler gauge.
Now that I see them, think I'm doing the alcohol bath, carefully blow them out and dry the board with low pressure compressed air. Then give each a small spritz of DeoxIT Gold for lubrication. I have a large unused can of it in the garage.

 

[George S.]

The switches turned out amazing. They all now have very good and equal tactile feel.
Was very worthwhile servicing them.
I pulled out the heat gun and evaporated the remaining alcohol rather than chance disaster with compressed air. They felt very good after the alcohol bath, and the DeoxIT Gold made them even better with the lubrication.

 

[laatsch55]

Good job George!

 

[NavLinear]

Here's the HP push button patent. There are some good renderings of the device.

 

[laatsch55]

Way to get in the weeds Navo!!!!!!!!!!!!

 

[George S.]

Thanks Nav, those drawings answer some questions.
When I got the 3325A, depressing a key resulted in a slight resistance and a audible "snap" before the key bottomed. All the keys were like that except for #4, so I thought #4 was bad.
Not the case. Key #4 was the only key operating properly.
After service there are no more "snaps" and the keys operate like a desktop computer keyboard. I'm so happy there was no damage and all keys now operate as designed.
So far all the functions seem to work correctly. I've done some sweeps, but need to learn how to use the markers and X-drive on the scopes. Lots to learn about and how to use it.
The pass transistors mounted on the right rear rail run hot, so waiting on the replacement fan before I do more with it.

 

[George S.]

Peter, I see no difference on the scope between using the HP3325A or the cheap Koolertron DDS Signal Generator for the sweep parameters in the Yamaha manual.
The only real difference is the HP will sweep at a maximum rate of 0.01 second, the Koolertron has a maximum of 0.1 second sweep.
The old HP equipment is DEFINITELY more fun to use!

 

[Peter S]

Hi George and all, I hoping I can get away without a sweep generator for now. Most of the gear that comes my way seems to be 70's and newer. As you may have mentioned, non adjustable crystal IF filters may reduced the necessity of a sweep generator(?).
Christmas again! I got a nice deal (at least before exchange, shipping, and import duty) on a 520 MHz Frequency Counter, to satiate my Leader addiction for a little while.
By coincidence, I seem to be attracting sick FM tuners lately. A sansui T 80 with a partially functioning digital display and weak reception. That turned out to be simply a bad 5 V regulator. A Pioneer SX-737 with decent FM reception and no stereo. The centre tuning meter was off to one side between stations. This called for the adjustment of the lower core of T6. I have puchased a set of 'Aven' plastic diddle sticks from Digikey but the required size was either not included or poorly manufactured. The required size is 5/64" (0.078") but the plastic Allens in the kit are 0.071" and 0.73" After considerable googling with no luck, I did the unthinkable; made one out of a steel Allen key. Of course, inserting the key affected the adjustment but it did not take long to take this into account and get the meter centered when the key was withdrawn. Got lucky again, FM stereo loud and clear.

 

[George S.]

Nice work Peter. Good to see you having a go at this.
In regards to sweep generators. I doubt many shops, hams, and hobbyists had good functioning sweep generators back in the day.
Most got by just peaking the oscillators to highest output by using their ear, signal strength meter, or in some cases a millivolt meter.
During 31 years in trucking, I've been in "CB Shops" all over the country. The majority did "peak and tunes" by adjusting the receiver oscillators for highest signal strength reading on the units S meter, and tuned the transmitter portion for highest readings on a cheap watt meter and 50 ohm load.
We're lucky and reaping the awards of this old test gear finding it's way down market to us hobbyists!