HP 8620C Sweep Generator with RF Module Acquisition

[Chris K]

I apologize if this should be in the tech instrument section but since it has to do with my recent alignment adventures with post war RCA TVs, I thought I might get better viewership and specific use feedback in this section.

I'll be getting back to the RCA alignment next week so I'm revving up to start that torture again. Meanwhile, I was able to pick up another HP Sweep Generator to see if it could be used in future alignments. It is an HP8620C that has the plug in RF module.





I have the service manual and it looks like it does have some internal marker capability but I'll need to play with it first. I think this was the last of the HP generators without a digital frequency readout. Manufacture date 1975. The basic sweep unit was a few hundred dollars back then but the RF module was insanely priced at over $13,000! The coaxial lines in the module are shielded with solid metal tubes. There are several YT videos on maintenance and repair so I'll be watching them. If anyone has any experience with this instrument, please let me know. As a sweeper/alignment noobie I think it can be used for TV IF alignments but I'm not sure.

[ARC Tech-109]

Not exactly what you would need to sweep a TV IF. I had the older 8690B with the slide in modules and I can tell you these are a bear to work on. The metal coax is known as "semi-rigid" and don't take kindly to flexing or bending. Popular during the space race and early microwave development but a relic today being almost as old as many of the members here including myself.

FYI: Placing the post in the wrong section isn't always going to get more views in fact it may get fewer

[Penthode]

AI have also the 8620. It is good for microwave sweeping. Used to use them at Varian for sweeping travelling wave tube amplifiers at 6GHz.

I haven't used mine yet for TV work because of the complications of adding a convenient marker.

[Chris K]

Interesting because in the HP model line of sweeper generators, this was the model that superseded the 8601 I’ve been using to align the RCA 📺 that’s been giving me grief the past few months. I was under the assumption it would be a similar instrument that would do the same type of work.

[ARC Tech-109]

I've always been a sucker for the older test equipment be it for television or 2-way radio. My main scope is a mid-60's Tektronix 453 (210H) with the nuvister inputs, I'm not much into the gigasamples or choppy waveforms with all kinds of info around them. The only digital scope in the house is part of my Motorola (Gould) R2670 service monitor and it seldom gets used.

[Penthode]

Originally Posted by Chris K

Interesting because in the HP model line of sweeper generators, this was the model that superseded the 8601 I’ve been using to align the RCA 📺 that’s been giving me grief the past few months. I was under the assumption it would be a similar instrument that would do the same type of work.

Unfortunately you initially got a bummer unit. From experience, the alignment of old tvs is far from foolproof. I have tested and used a variety of test instruments to do the job and the 8600a/8601a combo to me has been the most accurate and convenient solution. Nothing is perfect but these devices for what they do come close.

They have done a terrific job on my tvs and communications receivers. I recently aligned my RCA AR88D with them and the receiver is now amazing. The alignment of the RCA CT100 was a breeze and the HP duo identified the subtle tuner bypass capacitor fault which I expect has gone unnoticed by other CT100 owners. I can say the alignment of my CT100 using the HP8600a/8601a is as best as could be.

The key is building up a rapport with your equipment to get a good feel of it's operations.

In your case, you did choose one of the most difficult early TV sets to align! So don't feel disparaged.

[old_coot88]

On the subject of gaining rapport with the vintage electronics avocation, it's worthwhile to study the history of the superheterodyne principle and why the IF was imperative to the performance of receivers. That way, you become "one with" the service gear and the gear you're servicing rather than just 'following a cookbook'. Anybody know some good tutorial material?

[Kevin Kuehn]

Originally Posted by old_coot88

On the subject of gaining rapport with the vintage electronics avocation, it's worthwhile to study the history of the superheterodyne principle and why the IF was imperative to the performance of receivers. That way, you become "one with" the service gear and the gear you're servicing rather than just 'following a cookbook'. Anybody know some good tutorial material?

If you can handle old school learning techniques, Elements Of Radio by Marcus and Horton starts with the absolute basics of understanding simple AC and DC circuits. Lots of information on Tuned Radio Frequency receiver development, but eventually explains why the Superhetrodyn became the ultimate solution. Electronics is one of those disciplines where if you don't get a good grounding in the most basic understanding of circuit theory, you'll never be able to comfortably grasp the more advanced subjects. One really has to be driven to learn those basics or you'll stumble through life wondering why it's all so confusing and mysterious.

[Chris K]

I was able to also pick up an HP8350A with the RF module. This sweep generator has a digital readout for center frequency, setting sweep width and 5 independent adjustable markers built in so I believe an external digital marker will not be necessary. Anyone have any experience with this machine?

[Chris K]

Originally Posted by Penthode

Unfortunately you initially got a bummer unit. From experience, the alignment of old tvs is far from foolproof. I have tested and used a variety of test instruments to do the job and the 8600a/8601a combo to me has been the most accurate and convenient solution. Nothing is perfect but these devices for what they do come close.

They have done a terrific job on my tvs and communications receivers. I recently aligned my RCA AR88D with them and the receiver is now amazing. The alignment of the RCA CT100 was a breeze and the HP duo identified the subtle tuner bypass capacitor fault which I expect has gone unnoticed by other CT100 owners. I can say the alignment of my CT100 using the HP8600a/8601a is as best as could be.

The key is building up a rapport with your equipment to get a good feel of it's operations.

In your case, you did choose one of the most difficult early TV sets to align! So don't feel disparaged.

I'm not and I intend to get back on the RCA this weekend...once I get the Christmas lights strung on the house! I have no issue continuing to use the combo units as I proceed. This switch problem on the 8601 is still a nuisance. The toggle than changes the frequency scale from X1 to X10 is rock solid in the X1 position but results in frequencies jumping all over the place in the X10 position. If I wiggle it around and put it halfway between settings, there's a sweet spot where it works but it's a pain. The first unit I got is now a parts machine but harvesting the switch and replacing the one in my functional unit looks near impossible, at least for me. The switch will, I imagine, eventually fail and I'll have to do something. That's why I hoping to learn how to operate the 8350 in this alignment procedure. Unless I'm way off base, it's a sweep generator with a digital readout and 5 independent internal markers so it should be able to do the same work as the 8601/8600 combo. Fingers crossed. Looks like step one is finding an "N" connector to BNC adapter as the RF output isn't BNC.

[Electronic M]

It's possible that the switch contacts are just dirty. If you can get some contact cleaner into them you should get them to come around. I've seen similar (between the detents) behavior from dirty contacts in TV tuners... Sometimes when I'm feeling too lazy to get contact cleaner in I'll fix the problem by toggling it a bunch and letting the contacts scrub themselves clean.

I think he meant discourage not disparage...you get discouraged by a daunting task, you get disparaged by someone insulting you...

[Penthode]

Funny. Because I used disparaged inferring that the TV mocks us and belittles us as we attempt to repair it.

[Chris K]

Anyone who has followed my relationship with numerous electronic instruments and vintage TVs knows it is very personal! I do feel like these things have a good ole' time with me!

[Chris K]

Originally Posted by Electronic M

It's possible that the switch contacts are just dirty. If you can get some contact cleaner into them you should get them to come around. I've seen similar (between the detents) behavior from dirty contacts in TV tuners... Sometimes when I'm feeling too lazy to get contact cleaner in I'll fix the problem by toggling it a bunch and letting the contacts scrub themselves clean.

I think he meant discourage not disparage...you get discouraged by a daunting task, you get disparaged by someone insulting you...

Looks like DeoxIT did the job. It's been stable for a couple of days now and for long hours of use. It's just a simple toggle so I didn't think the switch contacts would be an issue considering I did work them, albeit without cleaner, multiple times. I imagined all sorts of nightmare scenarios. So far it's been behaving like it should.