Saturday, January 12, 2019

CNN Kills Pro-Wall Story From San Diego

This came in the morning email from a friend.

CNN Defends Decision to Spike Local Media Pro-Border Wall Interview: 'This Is a Non-Story'

 

And they wonder why their ratings are in the toilet.....

Thursday, January 10, 2019

Speaker Choices.....

With the rebuild of the Heathkit proceeding apace, I'll need to get some real speakers for it. I have some "P.A. Type" speakers (carpet covered, 8" woofer and a dome tweeter) that I could use, and some Radio Shack/Realistic/RCA "Optimus" mini-bookshelf speakers, but the P.A. speakers aren't really for music (no top or bottom end; all tailored for voice), and I could easily turn the little Optimus speakers into smoking ruins with the Heathkit. Since the amplifier section of this receiver is known for being less than 100% stable with 4 Ohm speakers of current design, and 16 Ohm speakers aren't very common, that leaves me with 8 Ohms as the 'load impedance of choice'.

The amp section is rated at 75 Watts-per-channel with the "Institute for High Fidelity measurement method", and that translates to about 55 Watts RMS, which is much closer to "Real World" than the IHF method. Some of the methods used to measure the power output of an audio amplifier are quite....uh....."creative", and were devised to inflate the RMS power measurement for advertising purposes. I used to chuckle when I read some of the results, as they were grossly higher than what the thing would actually put out.

So, I need some 8-Ohm speakers, rated for around 100 Watts. You can easily spend $2k per speaker, something I'd never do unless that rich Uncle I don't know about kicks and leaves me a few semis full of cash.

So after receiving a $25 discount code from Parts Express, I pulled the trigger and ordered two "Hitmaker MT" speaker kits, along with some bits (like binding posts to connect them!) needed to finish the kits.

They should be here in a week or so, and I'll report on them when they get here.

And since it's going to be raining/sleeting/snowing on Friday, I put the BuddiPole vertical back up. The winds have died down for the present, so it's safe to get it back up in the air.

Tuesday, January 8, 2019

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!

Monday, January 7, 2019

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.

Saturday, January 5, 2019

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.