C39...

I chose the easiest part to remove to get started... C39. First, I documented the original component.

Easiest part to remove...

I also made a little drawing.

Is it art?

There are several ways to do this. Since the connecting wires are of sufficient length, I simply cut them close to the terminals of the capacitor. I did use soldering equipment on one wire. This gave me a sense of the proper temperature setting for those cases where I do not want to clip a lead. The solder used in this beast flows very nicely. Another important consideration is whether the device uses silver solder - which has a higher melting point. You do not want to use lead-based solder in that case. Some of the old Tektronix scopes used a silver formulation, and even included a small length of the stuff mounted inside the chassis.

Choose the proper tip

Since the tabs of the capacitors are flat metal, a chisel-tip was selected - the third one from the left. This will transfer the heat in an efficient manner, promoting complete flow of molten metal in the desired area.

Until the restoration is complete, I mark the component and save it. Sometimes replacements have different dimensional characteristics, so it is handy to have an old one if you don't yet have the replacement. There is one more cap like this one - two sections of 1500uf @ 15 volts. I haven't purchased these yet, so off to a supplier website...

New Project - HP 400L

An HP 400L  VTVM found its way into my collection of amusing, anachronous test equipment.

Click for larger view

It came with the operating and service manual, which was printed in 1963.

This VTVM measures AC voltages in twelve ranges - .001 VAC to 300 VAC, Decibel range -72 to +52, with a frequency range of 10 cps to 4 mc.

It weighs about 18 pounds, or in terms of our cat, 1 Chester Unit.

1 Chester Unit

Unlike a lot of old stuff, this came with the original box. It had been sitting on a shelf, unused, for decades. It is exceptionally clean, so I don't have to deal with rust, dust, or other annoyances.

What's Inside?

The following two images show the jumble of parts.

Left interior jumble...

Tubes!

First up...

Never plug-in and turn on old junk like this. Yikes. Since I dislike refinishing metal and all the cleaning, this is a nice project to work on. To make it operational, I will replace the electrolytic capacitors, a few Bumblebees (another common old capacitor type) and other random components as I check out the circuitry. Unlike the Hallicrafters restoration (see the previous project), I will use modern multi-section electrolytic capacitors.

The Suspects...

Bottom of multisection capacitor C1, with associated resistors

I will take several pictures of each component prior to removal. Each part directly connected to the capacitor will be checked out-of-circuit. There are no tell-tale bulges or evidence of heat stress in this area.

Selenium Rectifier

I will research the need to replace this selenium rectifier - I vaguely recall some post in another restoration forum about these things.

Getting the Stuff Together

Which meter to use...

 I was too lazy to look for the test leads for the tube-based Simpson 303. Is it a shock (so to speak) to imagine I have two of those? Not pictured - the Weston 931...

Solder, desoldering stuff...

The Powerstat - to gently ramp up the voltage for testing - in a few weeks!

Next: Deciding where to start.

New Photography Blog

In addition to restoration of old radios, test equipment, and other electronics, I like to play with film and paper based imagery - cameras that are old, unusual, home-made, or modified in some way will be explored. If you have an interest in film, check out:

http://anachronousphotography.blogspot.com/

 

Self Portrait, San Francisco October 2011

Hasselblad 501CM, Kodak Ektar Film

 

 

 

 

 



Hallicrafters SX-96 Mark 1 Manual

Here's the manual!

There was one discrepancy that I noticed when comparing the parts list with the schematic. For any restoration, it is worth verifying part values and circuitry - this may save time. It is frustrating when you discover that you missed one or two components, and have to make additional orders. There will be surprises along the way; however, I like to minimize the interruptions and take the time to get a good idea of parts needed. This also helps locating parts.

Modifications pose additional challenges. Manufactures sometimes substitute parts - similar components may look different due to manufacturing changes, or substitution of similar parts from another source. Values may differ slightly - note whether the part is within the stated tolerance requirements of the specific circuit location. Manufactures also make changes after the schematics are printed - there may be additions or deletions to enhance performance, or reduce part count to reduce manufacturing costs.

The other changes are the result of someone trying to fix something. Some well-intentioned modifications may be baffling and sometimes dangerous. I've encountered mods that don't do anything at all!

The Tiny Mystery

When comparing the parts list to the schematic, I couldn't locate C-86 (.01 mfd 20% 600 V molded paper - parts list page 20A) on the schematic. From the schematic, I noticed that C-85 ( .01 mfd, in the AC line primary after S3B, schematic page 19B) was not in the parts list. The values matched, the component type matched, and there were no other lost capacitors, so the mystery was easily solved. Trust me - it isn't always so simple!

Click on each image for a larger view.

That's all!

Next - look for the HP 400L Vacuum Tube Voltmeter restoration.

Isolation Transformer for the Hallicrafters SX-96

This is the isolation transformer for the radio. A link to the schematic from the Hammond site: http://www.hammondmfg.com/pdf/EDB169C.pdf

This provides two functions - isolation from the AC source, and reduction of the line voltage via the taps. The local line voltage is 122 vac. This is within the Hallicrafters stated operating range of 105 - 125 vac. Some comments from other restorers mentioned that the power transformer in the radio runs hot with the higher voltage. Waste heat is not kind to any electronics, and since this features 50+ year old electrical bits, I want to give it a break. The radio 'starts up' around 90 vac, runs perfectly at this lower range, so I chose the 105 vac taps on the isolation transformer. The assembly is much smaller than the Powerstat (which does not provide line voltage isolation).

Isolation/voltage reduction transformer.

Click for larger view.

Initially, I was going to put it inside an enclosure. Since it was going to generate heat, I tried to find a ventilated box. To limit size, I decided that the transformer would be fine outside the box, so to speak...

The chassis is also made by Hammond, about 6 by 4 by 2 inches. Since I do not have the proper metal working tools to cut a neat hole for the line output, I simply used the mouse-tail method. A power switch was added, as there is no need to consume electricity when the Halli is powered off. Total current draw with the radio powered on is .58 amps, with an input line voltage of 121 vac and output of 102 vac.

Under the hood...

Click for larger view.

I wanted to preserve the ability to change the line voltage, so all of the taps are available on this connector.

Standoff detail

Click for larger view.

For easiest access to the connections, I mounted the barrier strip on 1/2 inch nylon standoffs. While scrounging through the materials at the local hardware store, I found nylon standoffs that fit into the mounting holes of the 10 position Cinch barrier strip. This illustration is with a different barrier and standoffs that I did not use - in the finished box the standoffs fit perfectly in the mounting holes, providing excellent stability.

The Cinch 8-position barrier picture above will be used for an impedance matching enclosure for my older battery radios.

I will soon add a line fuse for this box - just waiting on a part. The radio runs well on the reduced voltage, perhaps lasting a little bit longer.

Next - I'll scan the entire manual in PDF format for amusement.

Powering up the Hallicrafters SX-96

The last parts to be soldered...

Six caps on the selectivity switch

S2 with old, and new bees...

Click for larger view

The wires leading to the switch were in good condition, allowing replacement without completely removing it. Sometimes old insulation cracks, or wires break. Once the switch was back in place, I started to check the entire area under the chassis. There were a few times when a cut component lead would disappear into the mysterious fray of wire... I was able to find them all with a little help from a bright light and small amounts of compressed air. There were a few solder splashes, mostly from the solder removal process. Other components were inspected for signs of heat stress - color changes, slight bulges, tiny cracks. I randomly measured some resistor values, and they were within tolerance. I had replaced one resistor earlier in the project, as it appeared to have been stressed with heat. Even though it measured within tolerance, such parts should always be replaced.

Almost there...

 The Buzz...

There is a mysterious 8-pin socket on the back that will allow power via DC operation. If you have a DC supply with 208 volts at 105 ma, and 6.3 volts at 4.1 amps, you're in business - add your batteries or supply for the perfect 40 pound bundle for your trip to the park. Don't forget to throw in your speaker - the one in the metal enclosure. Enjoy the broadcast of the game with this great portable set...

I replaced the power cord. The original wasn't too bad; however, this is always a good idea considering the age of the components. I should have installed a fuse as well... there is a hole in the chassis, originally intended for an rf connector. I will install one before releasing it from the quarantine of my work area.

Initial power up configuration...

The audio output has a terminal strip for a 3.2 Ω or 600 Ω speaker. I have an impedance matching transformer that was hooked to the 600 Ω terminals, then connected the 8 Ω speaker. A random length of wire was strung across the floor in the basement, much to the delight of the cat.

The Powerstat was plugged in, and I looked at the point where the AC output would be near the minimum operating voltage of 105 vac. While the label says acceptable voltages range to 125, I figured that something idle for a few decades would be happier with a lower voltage. The radio was then plugged in to the variable AC supply, and the Fluke meter was attached as well to monitor line voltage as I rolled up the AC.

The manual describes two methods for tuning - also noting that it was calibrated with the bandspread dial fully CCW. I set the main dial near an expected local AM broadcast station. The bandspread was not fully CCW, as I wanted some 'room' to rock the adjustment. Volume and sensitivity controls were set near the low end, and other switches selected the AM broadcast band, and the selectivity at 5kc.

Power up

Leakage current?

Old electronics can be dangerous - I used this Simpson leakage current tester to evaluate the radio's safety. I am going to operate the radio with an isolation transformer, and at a reduced AC line voltage.

It's a keeper. All controls and bands work well. The calibration is off a little - it is close enough for now. I don't have the signal generators to go through the alignment procedure.

Next: I'll post the tiny isolation transformer, voltage step-down project.

Also, a separate blog about past restorations, including an Atwater Kent (a 20 Big Box and a 40), a Crosley Trirdyn, and the Grunow will launch at some point.

Hallicrafters SX-96 Component Replacement

Most of the parts to be replaced are easy to get to. I've replaced most of the caps - saving a potentially annoying section for last.


Part of S2 - Selectivity Switch
Click to enlarge

This section seemed like the most annoying, so I saved it for last. There are six bees hiding in and around this multilayered switch. The good news is that it isn't quite as annoying as I'd initially thought it would be. Note the circled area - three bees and a wire are attached to a single point. The primary concern for something like this is the relatively fragile attachment point - these switches may be difficult to find, and repair is not something I care to think about.

S2 Schematic

Click to enlarge 

Since the connection is delicate, a minimum amount of heat is applied to melt the solder. First, I drew a diagram of the mess, in addition to the photo. Next, I cut the wire lead of the bee close to the body of the part - leaving sufficient wire so that it could be grabbed with needle-nose pliers. Carefully heating the joint with the 25 watt soldering iron, I used a spring powered vacuum device to remove a blob of molten solder. I had to heat it twice, since woven component leads make it hard to get enough solder out of the joint to remove the leads. Once the joint was partially clear, it was heated a second time. Wires are bent like hooks in these joints. I used the needle-nose pliers to grasp one of the wires, and moved it around within the connection when the solder was molten. I removed the heat, and continued to move the wire quickly so that the small amount of remaining solder would not tack it to the point again.

Partially cleared tie point...

Click to enlarge

Note the appearance of the remaining solder - it appears dull and rough. This is the result of moving the wires as the solder cooled, the desired effect so that the part wouldn't re-tack itself, allowing easy removal.

Cleared pad

Click to enlarge

The connection is now clear for the new parts.

Next - The switch with new parts.