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 Post subject: HP 8601A vs. Wavetek 146 sweep
PostPosted: Aug Tue 17, 2010 7:27 pm 
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Greetings all,

Any opinions regarding these two units?
Will only be used on tube receivers and radios.

Thanks.... Harlan


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PostPosted: Aug Tue 17, 2010 8:00 pm 
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Two very different instruments.

One is a function generator, the other is a RF generator with sweep ability. A function generator will have much more jitter and phase noise than a good RF generator.

If I was forced to chose between only between those two, I would opt for the HP 8601. But remember, it is a very old instrument that is pushing its twilight years. Also, the bands switch at 10.00MHz on the 8601-- right near the common used 10.7MHz IF frequency.

My favorite sweeper is a HP 3336B. But, it is a lot more instrumentation than is needed by most. What exactly are you going to be working on? Consumer AM and FM table radios, or high end commercial or ham gear???? There are other options out there.

Pete


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PostPosted: Aug Tue 17, 2010 8:13 pm 
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Primarily vintage general coverage HF receivers. First in line is a Hammarlund hq-129X I've recently acquired.

Thanks,

Harlan


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PostPosted: Aug Tue 17, 2010 8:24 pm 
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Hello Harlan, and by the way welcome to ARF!

If you go back a few months on the test equipment forum you will find a very extensive discussion of sweep generators by GMCjetpilot. George has gone through several generations of sweepers, including function generators, the HP-8601, HP-3336C, etc. in his quest for the ultimate sweep setup.

The need for sweeping communications receivers was also discussed in the communications receiver forum--I believe that the concensus was that sweep alignment wasn't needed.

Pete


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 Post subject:
PostPosted: Aug Wed 18, 2010 2:00 am 
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You can't go wrong with a HP 8601A.... It is primarily a sweep gen but can be used as a signal gen... surprisingly stable for a sweep. It is all solid state and a light year better than any old tube sweep.

As Peter said the Wavetek 146 is a function Gen.... Even if it was a sweep Gen you need one that goes above 10 Mhz. FM radio IF is 10.7 Mhz typically.

Search the archives for the HP 8601A. They tend to be expensive if in good shape. Expect to pay at least about $200 for a working one in fair to good shape. You can get one that needs some work for half that and cross your fingers you can fix it.

They are mostly discrete (solid state) components but has two proprietary IC chips in it. Mine had issues, but easy to fix. Mostly cleaning and adjustment solved all my issues. I upgraded to a HP 3336C pretty quick because it came up, so I sold the HP 8601A. I have to say the 8601A makes a beautiful sweep but synthetic digital is easier to use and more accurate. I posted some pics of the 8601A in my threads. I also have a HP 8640B signal gen, it is a digital analog hybrid with a PLL function to keep the freq stable. Nice unit.

The 8601A is full range SWEEP Gen that produces a nice sweep from 100 KHz to 110 Mhz. That low range is great because you can sweep the AM radio IF's which are typically 455 Khz or some times 262 Khz. Most sweeps bottom out at 1 Mhz. It has mechanical digital setting that is very accurate, but you still need a Freq counter to be spot on. It is easy to do some basic calibration with basic gear, scope, freq counter. It has an accurate RF meter.

The manual is free on the web and is very complete, although the pictures of the scope traces for trouble shooting are hard to read in the PDF copy.

They were made for a long time from about 1969 to early 1980. They were very popular, so there is a lot of info and people to help you repair them if needed. It should be brick outhouse reliable. However like all HP stuff of the era can have mechanical issues with the gears (for the digital display).

If you search these ARF archives you can find lots of info. I found out how to repair the "Light Pipes" (lights to indicate the decimal point). These are fiber lights that route from the bulb sockets to the front panel. The fiber lights get old and cloudy and stop carrying the light to the panel. It is something that does not need to be fixed, it has nothing to do with operation. The decimal is in one of two position for the 100khz to 11Mhz go 10Mhz to 110Mhz.

I had a Wavetek 1801A sweep which was a fine machine but the HP was better. The Wavetek 1801A almost went to a Giga Hz! Not really needed for radio. If I got a Wavetek sweep the Wavetek 2001 I think best for radio and TV (anlog). The trick of the Wavetek is to get one with all the proper markers built in. The markers are proprietary little modules so it's not easy to add. My Wavetek 1801A I had some markers for Cable TV, like a 5 Mhz comb marker and a 50 Mhz comb marker, not useful for radio.

The sweeps I have now is a the Sencore SG-165 (I have a thread on it and recommend it). It sweeps only FM 10.7 Mhz IF, but has built in markers. It produces nice FM alignments. If you buy one, get one with all the cables, demodulator, output, matching pad, scope cable and automotive radio adapter.

The HP 3336C is "synthetic" or digital signal/Sweep Gen. They can be found cheap (some times). I bought it on a whim. It was about $200. I see them for $500-$1000. It's a signal gen & sweep, very accurate. It has a built in TTL "Z-marker". It's range is 10Hz to 20.999999999MHz. Yes 10Hz and resolution 0.000001Hz for frequencies < 100 Khz, 0.001 Hz for frequencies => 100kHz

I use it mostly to sweep align AM radios, which don't really need to be swept (but it's more accurate and fun). I don't know what to do with all it's accuracy and precision otherwise, but it comes in handy when calibrating things. You can mix it (X-Y) with another signal on the scope and get a "Lissajous figures". Having such exact fine control is nice. No analog signal gen can do that. With that said mine has not been calibrated in 8 years (according to the sticker). How do you calibrate something that is the most accurate thing you have. Sending them out for calibration is not cost effective. I might get some GPS freq standard like the Trimble thunderbolt. The 3336C accepts an external oscillator. I compare all my signal gens and freq counter manually. They are all close enough for me, in the ball park for what I do. One Hz is not going to make any difference. I lucked out, my 3336C is in great shape & works well. Not sure how hard it will be to repair if that time comes. I am sure it has lots of proprietary IC's that are not available. So a parts donor would be needed to repair it if something burns out. That is the nature of old gear.

Getting the 3336C is why I parted with the HP8601A, which I liked because it went to 110 Mhz. I don't have a need to sweep anything above 10.7 Mhz right now. If I did I think I'd look for a synthetic signal/sweep. Once you go digital test gear it's hard to go back to analog.

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on Aug Wed 18, 2010 3:03 am, edited 3 times in total.

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PostPosted: Aug Wed 18, 2010 2:34 am 
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Much of what you'll need for communications receiver alignment is for IF's, and although you can use peak alignment methods with a good degree of success with a regular signal generator thare are some advantages to sweep aligning as I have discovered, such as being able to see the true picture of the response curve on the oscilloscope. The setups are a little trickier and it involves more equipment, but it can yield better results or results more tailored for your listening style IMHO.

Dollar for dollar, I would invest a tiny bit more to get a HP 3336C, 3325A, or 3325B rather than an HP 8601A. (Forget the Wavetek.) These synthesized sweep generators will walk circles around the analog 8601A when it involves communication receiver IF sweep alignment. Why? They give you three very accurate points of reference.

You accurately set the frequency where you want the sweep to start. You set where the sweep ends. You set the amplitude of the signal and the sweep time. Plus, you can set a nice accurate Z axis marker that can show your center sweep frequency in a very narrow sweep range- something about impossible with a generated marker birdie. IMHO, a sweep generator without reference points is basically useless. Another advantage to these synthesized generators is they generate sine waves up to 20 MHz, so you can use them as standard RF generators up to 20 MHz. The 3325B even includes internal AM and FM modulation (A version has external inputs) and B version has setup memory backup during power off. 3325A and B are also function generators, slightly higher noise than the 3336C but the difference is not an issue when using them for IF sweeping- they are a little more verstile all-around bench units, I use my 3325A for a lot of different tasks, its one of my most utilized pieces of equipment.

-Mark-

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 Post subject:
PostPosted: Aug Wed 18, 2010 4:46 am 
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Hi Harlan, welcome to ARF.

I'd also recommend NOT getting a wavetek anything, or most any function generator with the hopes of sweeping IF's, they are not up to the task. Most all are built around R/C oscillators. They typically never stop drifting, have lots of phase noise and are a general PITA to try and work with. Service grade sweep generators, for the most part, certainly aren't much better.

An HP 8601 will work as George mentioned, but if you can swing it, his advise regarding an HP 3336C is right on the mark, they are a good generator and drop dead accurate when running off a good time base. I love mine.


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 Post subject:
PostPosted: Aug Wed 18, 2010 5:03 am 
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Location: San Francisco, California, USA
Thank you all for the advice!

I will begin the search for HP-3336C.

Thank you for the welcome.

I look forward to listening and learning...

Harlan
(in training)


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 Post subject:
PostPosted: Aug Wed 18, 2010 5:54 am 
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harlan1 wrote:
Thank you all for the advice!

I will begin the search for HP-3336C.

Thank you for the welcome.

I look forward to listening and learning...

Harlan
(in training)

Try the 3325A as well as the 3336C
.
What are you going to do? This is a lot of Signal Gen to learn with. Nothing wrong with getting the good stuff from the start. Most get the $25-$30 signal gen and upgrade. However it is not a bad way to go getting a good signal gen to start.
.
The down side of these signal gens is they top out at 21 Mhz. You really need something that can make a signal up to 110 Mhz for FM radio.......

The Sencore SG-165 is the Swiss army knife of signal gens, and a great one to learn on. Cheers.

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


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PostPosted: Aug Wed 18, 2010 12:54 pm 
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It does not seem that anybody has ever come up with the perfect signal generator that does everything one could want--and does it well. So you are probably going to end up with multiple signal generators in any event. Last time I checked, I am up to about 11.

There is actually very little need for a sweep generator in communications receiver alignment, because the IF's are typically only a few kHz wide. In the rare cases where a little sweep is necessary, like the stagger-tuned IF's in a NC-183, have you considered using a FM generator instead?

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 Post subject:
PostPosted: Aug Wed 18, 2010 12:54 pm 
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duplicate post

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Last edited by Chris108 on Aug Sun 22, 2010 10:59 pm, edited 2 times in total.

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PostPosted: Aug Wed 18, 2010 2:04 pm 
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Chris108 wrote:
It does not seem that anybody has ever come up with the perfect signal generator that does everything one could want--and does it well. So you are probably going to end up with multiple signal generators in any event.


So very true. I've managed to keep it down to two that work well, the HP 3325A for radio IF sweeping and audio signal needs, and a Marconi 2019A that I use for any RF needs. The two have been about as far as I want to push the level for hobby needs. I don't want to spend any more for features or performance I have no real application for, yet I am definitely pleased with the way the two synthesized signal generators perform compared to the things I used before I had them.

Most everyone in the hobby has found that attempting to perform sweep alignments with rinky dink sweep generators just isn't worth the bother, and a little more investment here will go a long way if it's something you are interested in doing. The nice thing with the HP 3336C or the 3325's is you can sweep align, or if you decide you just want to peak align a set you can do that too. I even use the 3325A on old broadcast/shortwave household sets. When I'm done with the IF's and such, I'll sweep the whole AM broadcast band and and each shortwave band with a little added modulation and have a listen while moving the dial end to end.

-Mark-

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 Post subject:
PostPosted: Aug Wed 18, 2010 4:00 pm 
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Unless one really, really needs the 50-ohm output, a HP-3336B can be had, as a rule,at much cheaper prices. Same basic intrument, but 75 ohm output, and the unusual odd Telco connector. Removing an internal 25 ohm resistor yields a 50 impedance, as would using a lossy match pad to go between 75 to 50 ohms. Subtracting the known dB error will get you close for RF level measurements. The A/B/C suffixed companion selective RF voltmeters are a different matter.

One other plug for the HP-3336x series--the sweep output is linear, unlike the AC line generated sweeps used in many service grade units. Since the stop and end points are precise, it is easy to simply use the scope or X/Y display gradicules to determine the exact sweep frequency across the sweep, without relying on markers, etc.

Likewise, an 8640 with the companion downconverter can be taught to do some neat sweeping tricks by using driving the external FM deviation input (DC coupled) with a ramp generator. A bit more involved setup procedure, but the end results are the same.

Pete


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 Post subject:
PostPosted: Aug Wed 18, 2010 6:40 pm 
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Peter Bertini wrote:
Unless one really, really needs the 50-ohm output, a HP-3336B can be had, as a rule,at much cheaper prices.
Pete

Good point Peter. My HP8601A was 75 ohms out. It causes no problem injecting into a radio circuit. You can get a matching pad. In the case of the RF output meter it would be off, but some math could correct and estimate that. The 3336C has both 50 and 75 ohm impedance output.

The original poster said they were new. I think this thread (thanks to my "War and Peace" long post) got out of hand with detail. I started out with a handful of TUBE Signal Gens. I out grew them. Now they are all sold and I have the HP gear I have now. I would have missed out on a lot of TUBE learning if I had bypassed the Tube gear. I am glad I did it.

I think for a NEWBIE's first signal Gen, even if they outgrow it, a ubiquitous basic Eico, RCA, B&K, Precision or Hickock tube signal Gen, is a great way to start, something from the 50's not too old.

The BEAUTY of old tube gear is they can be fixed by a Newbie. They are simple, TUBE, no proprietary parts and generally with clean up, new capacitors it will work better than new. Of course even in top shape some old signal gens are kind of lacking in quality RF signal. It is fun to learn how to use them and tune them for max accuracy. With digital stuff you punch it in, DONE. BORING! Ha ha! :roll: That of course is the good part of digital stuff, it saves time, more accurate, stable, consistent, easy to use, almost no skill to set it (good for me). However learning the "TOUCH", how to hold your mouth when you set an old analog tube Eico Freq select knob is kind of an art. The THRILL to get within a few Hz and not have it drift more than 10 Hz is like you won! :lol: If your synth digital Signal Gen is not within a micro Hz you are way off.

There is no perfect signal Gen, as was said. The idea is buy one that you will use and get most use out of for what you are doing. Also the HP 3336( ) or 3325 are not the be all end all; however it is a good deal for an entry level "synthetic" or digital signal Gen. There is a WORLD of signal Gen brands and models. To me most important is to not get a orphan, some rare unit that no one heard or. The more ubiquitous with the most info on the web and forums the better. At some point it will stop working. It will either be repairable, become a $300 door stop or parts for sale in eBay.

_________________
Tube: AM/FM Zeniths, RCA, TrueTone table tops; Transistor: Kaito KA1103, TenTec RX320D, Pioneer SX780


Last edited by gmcjetpilot on Aug Thu 19, 2010 2:26 am, edited 1 time in total.

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PostPosted: Aug Thu 19, 2010 1:27 am 
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As I've grown in my understanding of radio repair, it has brought me to an undeniable conclusion. The old timers, with their tube test equipment, had to refine their technique, to get good alignments. They could do a fine job with less precise equipment than I could hope to. Everybody has heard some story of an old radio tech that could repair anything with just a Simpson and a screwdriver, right ? So, to make up for my lack of expertise , lab grade test equipment, puts me on par with the pros. Besides, I get a tickle out of the visual alignments. Seeing a response curve take shape, is neat stuff! Especially when I swap between a digital sweep alignment, ( using an HP 8663a digital sweeper and a Lecroy 9400a digital scope) and then use an analog set up ( an HP 8601A & 8600A with a Tek 475 scope) All I do is swap the output cable and detector probe from one set up , to the other, with both set at the same db level and vertical gain and I get very similar results! Once in a while, I'll do an alignment with an older setup ( rf gen and a vtvm), just for kicks, but nothing beats good equipment.
I started out 6-7 years ago, with a rusty Eico 221 vtvm, and an Eico 324 sig gen and like the rest of us, I got bit by the better equipment bug. It's a terrible disease, with no cure!
Bruce


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