Heathkit AR-15 Progress

Been chugging along on the Capacitor Replacement Train here for the last week, and as of tonight, all fifty-four of the printed circuit board mounted electrolytic capacitors have been replaced.

These boards are (from left-to-right) the Multiplex Board, which handles the special process of reconstructing separate left and right channels out of  what's broadcast, then two identical Power Amplifier Driver Boards, which take the selected audio stream and amplify it enough to drive the four power transistors mounted on the heat sinks. Above those two boards is the Power Supply Board. This board provides mounting space for the main power rectifiers, as well as the circuitry for several other regulated supplies.

The circuit board with all the control shafts jutting into free space at the top of the picture is the Control/Preamplifier Board, which selects the input you want (Phono, Tuner, Tape, Aux), processes the audio for Bass, Treble, Balance, and Volume, and then sends it to the Power Amplifier Driver Boards.

In the picture below you can see how all the pots (potentiometer) the shafts are connected to are soldered onto the Control/Preamplifier Board. I wound up having to take this thing a lot further apart than I wanted to, but it was the only way to get enough access to the Control/Preamplifier Board. At least it gives me a chance to clean both sides of the dial glass!

This is the "top" of the component side of that board, as seen looking towards where the front panel normally is, with the old caps in place.

And this is the "bottom" of the component side with the new caps installed.

Besides replacing the caps, I cleaned all seventeen controls, the Input Select rotary switch, three slide switches, and seven rocker switches. Some of the controls I could only get at from the top, and the rest I could only get from the bottom, so cleaning them was a multi-day affair, depending on what side of the chassis I was working on.

On the Tuner Board, I replaced all the electrolytic caps, and cleaned and lubed the bearings in the tuning capacitors. The two rectangular grey boxes are 10.7MHz crystal filters. These give this receiver razor-sharp tuning, even in crowded Metro areas with 50kW stations all over the place.

And I disassembled the heatsinks, cleaned them to get all the old silicone grease off, and them reassembled them with new thermal pads instead of using mica washers and grease. That's a new 3-wire grounded AC cord temporarily strapped to the chassis.

After doing these heinous things to this old war horse of a receiver, I rounded up the usual suspects to interrogate them.

As expected, they knew nothing....Off to the landfill with them! I've seen used parts like this for sale on eBay. Seems people are looking to reproduce "Vintage Tone", and as all the Audiofools know, you need Vintage Parts to get Vintage Tone! Seriously.......

Now I'm In Work coming up with some mounting bracket to use with the replacement power supply filter. The OEM cap was 8,000uF @ 90VDC, and even though the new one is 10,000uF @ 100VDC, it's considerably small in diameter; 2" vs 3".

So even though she's a stripped-down hulk right now, work is progressing, and I'm looking forward to doing the alignment on it with my new test gear.

Have fun, be safe, and Carry On!

Windy!

Been running right around 35~40MPH sustained, with (predicted) gusts to 65~70MPH.

Be careful out there, especially if you're out on the highways.

Workshop Adventures

Since it's been too blasted COLD to do much out in the garage, I turned my attention "inward", and spent a bunch of time this last week down in The Dungeon, a.k.a. the basement.

I went through all my bookshelves and cleaned them up, sorted them, and found 45 books that I no longer have need of, mostly "prepper" and "Post Apocalypse" type books. Those will be going to one of the numerous second-hand bookstores we have in town. I'd rather give them to a book reseller and have them make a few $$ on them than toss them in the recycling bin.

And removing those books freed up two complete shelves for other use.

Then I turned my attention to the little Krohn-Hite Function Generator that was sitting on the shelf awaiting repair.

It's a decent generator, but had a problem (I thought) with the negative power supply.

I replaced both electrolytic capacitors, both 75 Ohm current-limiting resistors, both transistors, the blackened Tantalum capacitor that got cooked by the burning resistor, and added new heatsinks with some thermal grease to keep the transistors cooler.

And along the way, I found a "repair" done very sloppily by someone in the past. The soldering was OK, but to not clip the leads on the new parts you just installed is pretty poor workmanship!

After I was done, I checked the negative and positive power supply lines for shorts, and RATS! There's still a 3.2 Ohm short on the negative supply, probably what took out the parts I just replaced. One thing I noticed was one of the other Tantalum capacitors had gotten hot enough to melt the wax on a ceramic cap, so I replaced that cap, but no joy.
 

One of the "Old Radio" forums I frequent had a repair thread about this generator, and consensus is that either the 741 Op Amps used as error amps in the supply are bad, or another of the numerous Tantalum caps on the negative supply line are shorted. I have some 741's, so when I get another round tuit, I'll swap those out. If that doesn't fix it, I'll start lifting component leads on the negative supply until I find the failed part.


So the little Kron-Hite went back on the shelf, and I dug into my HP 8601A RF Sweeper.

The crank knob to set the frequency was really stiff and hard to turn, so I had to do a bit of fettling on it, cleaning the old grease out, and relubed it with some synthetic gun grease I had. The freq adjust knob now spins freely, but yow....this thing is WAY off in calibration. I mean like EIGHT MHz off from what the dial displays compared to what my counter and spectrum analyzer read. Since I have the manual, I started running the performance checks, only to run into a wall because I don't have any SMC connector adaptors so I can connect my spectrum analyzer to the connectors on this module:

And then peak the little 200 MHz Reference Oscillator coil, which is the white tubular component in the picture below.

So the HP RF Sweeper is also back on the shelf until the adaptors get here so I can make the measurements.



And the capacitors for my Heathkit AR-15 arrived from Mouser.

Here's a before shot of the power supply and power amplifier driver boards with the "As Built" capacitors installed:

And here's the after shot with the new parts installed:

Leaving me with a rapidly filling bag of OEM capacitors.

Some of the new capacitors are smaller in physical size than the old ones, but with increased ratings, and some are the same size as the originals, but with greatly increased ratings.

I also bought new thermal pads for the TO-3 case transistors. The "As Built" configuration uses mica washers with silicone thermal grease. While this was accepted practice in the late 1960's when this receiver was built, technology has advanced, and the new parts are cleaner, easier to install, and have comparable heat transfer characteristics to the old system.

Tonight I'll replace all the caps on the Tuner Board, the Phono Input Board, and get started on the Multiplex Board. I wasn't careful when I had the bottom cover off, and when I was wrestling this 25 pound lump around on the bench, my thumb hit one of the filter inductors on the Multiplex Board, and snapped it. It's made of phenolic, kind of like wrapped paper dipped in varnish, and after 50 years was pretty brittle.

I haven't decided if I'll fix it in place, or remove it from the board to repair. I'll see how robustly it's mounted to the board tonight as I'm working on other sections.

I'm just getting rolling on this receiver, and it'll be interesting to see how it turns out. I'm going to need some decent speakers for it, and Parts Express has some nice kits for reasonable prices, so it looks like I'll be ordering one of them soon.

Happy New Year!

It's 13* and snowing, with an expected low tonight of -3*.

We're staying in, as temps under 10* don't agree with us.

"There Was A Time...." when I would have been out hootin' and hollerin' on New Years Eve, but now I'd rather stay in, let the youngsters do the hootin' and hollerin', and tinker away on something.

Be careful if you're out and about tonight. There were many time I shouldn't have been driving, but did anyway, so watch out for the other guy.

What's On The Workbench?

Had a couple of "small" projects I knocked out before going into my next "big" project.

The first was the installation of an LED light kit for my Yaesu rotor control head. The OEM incandescent bulb is a non-serviceable part, and one of the cottage-industry Ham guys came up with a  nice little PCB with three white LED's on it. Took about 30 minutes to install it, it's much brighter, and will probably never "burn out".

The second project was rebuilding my #2 Drake MS-4 speaker with AC4 power supply. The original speaker is old and dried-out, and the electrolytic capacitors and rectifier diodes in the power supply are old tech, and better modern components are available.

In the same space, you can now have capacitors with higher voltage ratings (good for reliability), and more capacitance (better filtering), with a higher temperature rating (better reliability again), and better manufacturing processes. The rectifiers also have higher voltage and current ratings, and their surge capability is far higher than the old type rectifiers the supply was manufactured with. And all the new components mount on a convenient PC Board.

The supply looked like it got into a bar fight at some point in it's life, but since this is an aluminum cover, I should be able to make most of the dents go away.

Pretty clean inside, though....

But, yow....I haven't seen rectifiers in a "Bullet Case" package since high-school! These are 1N3194's, rated at 400V and 750mA. The replacements are rated at 1000V and 1A, a nice upgrade.

So most of the old capacitors, and all of the rectifiers get removed. The two big can capacitors were left on 'for looks'.

Then the new PCB gets mounted, wired in, and a couple of cable ties added to keep the wiring neat.

And the speaker gets replaced.....

Testing revealed 790VDC no-load on the HV, and 275VDC on the B+. Bias (for the 6DQ5 final PA tubes) is adjustable from -25VDC to -65VDC, all well within specs.

So bolt it all back together, and put it back on the shelf next to the one I did a few weeks ago.

Yes, they're sitting quite differently. The one on the right has the "short feet" on the back of the enclosure, tilting the panel back slightly, while the one on the right has same size feet, making it sit level.

Next up on the project list.....my Heathkit AR-15, soon (actually already is) to be On The Bench.

Merry Christmas To All

 Couldn't find a pic of Santa being pulled by eight Supras, so this'll have to do.

Helping the wife clean up the place. The Kids and The Little One will be by on Christmas Day for dinner and opening presents.

Still no snow, and NOAA is predicting a 30% chance for Wednesday.

Hope you all have a very merry and joyous Christmas!

Random Musings.....

Not too  much going on here. Took the wife's oldest son back to DIA the other night after his 4 day visit.

And the wind is blowing pretty good today, but the fence gates are staying shut, and aren't buffeting at all. NOAA is saying sustained winds of 30MPH with gusts to 50MPH. Dropped the vertical antenna the other night when I saw the forecast. Even though the shock-cord whip I used is rated (barely!) for this level of wind, I don't want to see the whip, with a $140 replacement cost, turned into scrap aluminum.

And I've been busy making up a bunch of BNC patch cables. The best test equipment in the world is useless if you can't connect it to anything, and that's what the patch cables are for. Yes, I could buy them pre-made, but they cost anywhere from $15 for a 3' one, up to $25 for a 10' one.

And that's each, not for a 4-pack!

I quite literally have boxes of connectors, and a couple of hundred feet of the cable, so by making up these cables, I'll "save" around $200, and use up some of the things I've been collecting over the years.

On to the random musings, sent by a buddy on the Iowa.....


I was thinking:

If only 11 million people have Obama-Care, how will 24 million people die if it is repealed? Will an additional 13 million people be randomly shot?

I was thinking;
If Donald Trump deleted all of his emails, wiped his server with Bleach Bit and destroyed all of his phones with a hammer, would the mainstream media suddenly lose all interest in the story and declare him innocent.

I was thinking;
If women do the same job for less money, why do companies hire men to do the same job for more money?

I was thinking;
If you rob a bank in a Sanctuary City, is it illegal or is it just an undocumented withdrawal?

I was thinking;
Each ISIS attack now is a reaction to Trump policies, but all ISIS attacks during Obama's term were due to Climate Change and a plea for jobs.

I was thinking;
We should stop calling them all 'Entitlements'. Welfare, Food Stamps, and WIC, are not entitlements. They are taxpayer-funded handouts, and shouldn't be called entitlements at all. Social Security and Veterans Benefits are entitlements because the people receiving them are entitled to them. They were earned and paid for by the recipients.

I was thinking;
If Muslims want to run away from a Muslim country, does that mean they're Islamophobic?

I was thinking;
If Liberals don't believe in biological gender then why did they march for women's rights?

I was thinking;
How did the Russians get Debbie Wasserman Schultz and the DNC to steal the Primary from Bernie Sanders? How did Russia get Donna Brazile to leak debate questions to Hillary Clinton in advance of the debates?

I was thinking;
Why is it that Democrats think Super delegates are fine, but they have a problem with the Electoral College?

I was thinking;
If you don't want the FBI involved in elections, don't nominate someone who's being investigated by the FBI.

I was thinking;
If Hillary's speeches cost $250,000 an hour, how come no one shows up to her free ones?

I was thinking;
The DNC is mad at Russia because they 'think' they are trying to manipulate our election by exposing that the DNC is manipulating our election.

I was thinking;

If Democrats don't want foreigners involved in our elections, why do they think it's all right for illegals to vote?

I'm going to quit thinking for a while.  All of this makes my head hurt.

New Gear Here!

After watching the FedEx progress of my new/used test gear, and seeing it "stuck" in Henderson, CO after taking 4 hours to get there from Commerce City, CO, I figured since the shippers didn't pay for "Saturday Delivery", I'd get it Monday.

Surprise, Surprise! Heard my wife downstairs talking to the delivery guy about 0930, and got dressed and went down to see this on the front porch.

Got the them inside.....

They were both "Foamed In Place", and excellent way to ship fragile items. This is the signal generator. The top section of the foam is off to the left.

And the spectrum analyzer was just as clean and nice as the eBay pix indicated.

So, out with the old.......

And in with the "new"......

I plugged the generator in and let the oven for the time base warm up, and after an hour or so to warm up and stabilize, my counter read within 8Hz of what the generator was set to. The counter had a 'fresh' calibration when I bought it umpteen years ago, and it's nice to see it that close to a good quality generator with a 'fresh' calibration.

The spectrum analyzer also agrees with the generator, both in frequency and amplitude, so the spec a also looks to be on-the-money.

With these accurate, high-quality instruments, I should be able to make any measurements I need to repair/adjust/modify just about any piece of radio gear, or other test equipment, that comes through here.

I've got an RF Sweep Generator and a Function Generator that are "INOP" at the moment, so these will be used to get those two items back on-line. I probably don't need the RF Sweeper as I think I can set this generator up to sweep, but it's a piece of "classic" HP gear that I bought for a specific purpose (swept I.F. Stage Alignment), so I'd like to get it running again.

Now to get that bench cleaned up, and this mess of a "workshop" organized!

R.I.P. Greg Lake

Bummer.....I just heard Greg Lake passed away on December 7th.

I was a huge ELP fan for a big chunk of my life, and this is my favorite ELP song.

Thank you, Mr. Lake. You made many, many people happy.

Test Equipment Status

This is turning into one of my down-the-rabbit-hole adventures.......

This all kinda-sorta started out when we moved here. I didn't pack my signal generator (at all), and it slid around inside the trailer I was pulling, breaking off an input level adjustment knob, and bending the other.

I was pretty sure I could fix it, but I'm glacially slooow doing this (take it apart, see what broke, find the parts, order the parts, etc, etc) kind of work, and I really wanted a newer generator with more features, so I looked around and bought a nice used one which should be here Friday.

But not knowing if my "old" generator still functioned, I set up my frequency counter and Spectrum Analyzer so I could measure the output.

I've been seriously using Spectrum Analyzers since 1982 when I went to work for Hughes Aircraft. They're a very powerful tool for radio work, allowing you to make accurate, repeatable measurements in a fraction of the time it would take using "classical" methods. I understand them pretty well, BUT......I always get things all scrambled up when going between units made by Tektronix, and units made by HP/Agilent. The HP units are very intuitive to use while the Tektronix units are more like your practical for a Master's Thesis. And the controls are not laid out in a logical grouping, and many features I'm used to having are not available on my Tektronix 494 unit. So naturally, when I first powered it up I had forgotten how different it was, and proceeded to get it into a state where it couldn't even see the internal CAL signal.

Hey, I hate this old clunker anyway, so why not go shopping for another unit, and this time buy an HP.

So I did.....

It's an HP 8594E model, and "only" goes to 2.9GHz, but that's plenty for my needs. Has a nice, bright trace....

And in general is very clean.

It's been a "Bench Unit" it's entire life, unlike some of the ones I've dragged around/banged around the ships for Sea Launch!

And even though I paid $40 for shipping, my total was $988, about half of what these go for from a Test Equipment Store.

So anyway....after buying this last night, I went back downstairs to shut things off, and gave the old 494 one last try.

Yep, the damn thing works! Here it is displaying a 100MHz signal from my old generator.

It's drifty for a least an hour after turn-on, but after that it seems stable. The Pilot Induced Problem was that I had the reference level and input attenuator set wrong, essentially making it "deaf" to the signal levels I was trying to monitor.

And the generator only has a 100HZ error at 100MHz......

I'm assuming my counter to be "accurate" as it has the best timebase on-site (one of those nifty HP Ovenized Crystal Oscillators), and it had a current calibration when I bought it some years ago.

I have a known-good Rubidium Frequency Standard with a 10MHz output, so as soon as I get that fired up, along with my HP "GPS Clcock/Timebase", I should be good-to-go for accuracy.

Having any instrument that makes measurements of time or frequency connected to a "Master Timebase" or "Master Clock" keeps them all synchronized, and helps reduce measurement errors.

So at long last, my Radio Lab will have a Tektronix Oscilloscope and an HP Spectrum Analyzer as God and the Chief Radio Engineer have commanded.....

Tonight's project is to finish up the Drake MS-4/AC4 speaker/power supply. This will get the bench cleaned up so I can make some BNC patch cables in 3~6' lengths.

Having fancy test gear is nice, but without patch cables to hook it all together, you can't do much with it. Making accessories like patch cables is a good way to save a few $$, too. I'd rather buy my connectors "By The Dozen" and a spool of cable than pay $12~$25 EACH for a cable. My cost of parts is probably less than $5, so that adds up on 10 cables. It's mindless radio 'grunt work' and not as glamorous as tuning up transmitters or bringing a dead receiver back to life, but it's relaxing and keeps me out of bars.......

New Toy On The Way **Updated**

My trusty old Systron-Donner Model 1702 signal generator took a hit to the front panel on the move out here. 100% my fault for not securing a 75-lb item properly, allowing it to slide around on the floor of the trailer. This one doesn't have rack handles, so there's about 18" of front panel that's pretty exposed, and the knobs slammed into something on the trip out here.

The level adjust pot for an external modulation source sheared off, and the level adjust pot for the internal modulation source is bent, and spins freely. These pots had 1/8" shafts on them, so I'm pretty sure they use a sub-miniature "instrumentation" sized pot, which used to be readily available. If Digi-Key/Mouser don't carry them, then Google is my friend, but these were standard parts for decades.

I'm just really, really, happy, happy that the thumbwheel switches used to set the output frequency survived unscathed. These things were unusual in their day, and even the surplus dealers are probably out of them by now.

So, *if* I can get the parts, is it "worth" repairing? These generators typically command $750~$1k on the used market, a bit less than I paid for this one almost 20 years ago. And they're ruggedly built, rock solid, low phase-noise (quiet!) generators that seem to never wear out or fail, unless some dolt doesn't pack it properly for shipping.....

So, yes, to me it's worth fixing. Even if the pots cost $25 each, I'll have a good signal generator for fifty bucks!

BUT.......what to do in the meantime.......?

Why, get another generator, what else? Besides, there are some very valid (and interesting) RF measurements that require two generators.

I wound up with this one, an HP 8657B, OPT1, OPT3. Option 1 is the world famous HP OCXO ovenized crystal oscillator, called the "High Stability Timebase", and Option 3 is improved noise performance/switching time in certain kinds of pulsed modulation, something I doubt I'll use.

There were several available in my price range (< $1k), but this one had several advantages.

First, the installed "High Stability Timebase" is about the best crystal oscillator HP ever made, and they were used in many, many critical applications where an "External Reference" was not available. In some factories I've worked in, it was the highest precision 10MHz source on-site, and wound up being distributed throughout the plant as the "Master Reference".

It's also the "heart" of the various GPS Disciplined Oscillator designs out there that not only give you the superb short-term stability and spectral purity of a crystal oscillator, but also the long-term stability of an "Atomic Clock". That's a whole 'nother post that I'll be doing since I want to get my GPSDO running again to use for my own 10MHz Master Reference. This way my frequency counter, signal generator, and spectrum analyzer will get the enhanced accuracy and stability of a high performance (or used to be) Master Reference.

Secondly, it had the standard front panel output jack. Many of these instruments were used in Automatic Test Equipment racks where everything was under PC control on the HP-IB or IEEE-488 bus, and the operator was along for the ride, and to load/unload modules and hit "Enter" when prompted. All the normal front panel RF out put jacks were "optioned" out to the back panel because the "Back of the Rack" was where everything happened in ATE, signal routing wise.

Thirdly, the place is an ISO-everything certified Calibration Lab, and the instrument has been tested for 100% functionality, and comes with a fresh calibration.

Oh, and it came with FREE shipping, a $75~$150 expense otherwise.

And I (finally) finished the towel rack project in the upstairs "wife's" bathroom.

One down, countless to go.....

Update on the generator..... 

The generator has an output corresponding to where the thumb switches are set, and the output attenuator (think 'Volume Control')  works correctly.

The control with the bent shaft also appears to work, at least according to the display that goes active when you select that function.

However......when I tried to look at the generator output on my Spectrum Analyzer, I see.....nothing. I tried using a different signal source, which I can read on my frequency counter, but I can't see that signal, either.

And finally......I can't even see the built-in 100MHz "CAL" signal, which also drives the frequency counter.

If you can't see the signal from the built-in CAL source, you're SOL. Looks like I'll be buying another Spectrum Analyzer sooner than I thought......