2017-10-15 Royal Transistor Radio Making Battery Contacts

I have had to make several contacts for the Zenith Royal 500 transistor radios, and I’m only on the second radio refurbishing.  Most of the problems have been mechanical – worn volume controls, tuning capacitor shorted because the screw for the trimmer capacitor was grounding, and bad battery contacts.  The battery contacts have been horribly corroded, to the point where they are disintegrated or fall apart.  There was nothing to repair.  So I have been replacing them with sheet steel I cut from a tin can lid with scissors.

The first two I made were single thickness, and work okay.  The third one I made this morning by folding the sheet in half and flattening it, then bending it to shape and drilling a hole for the screw.  The spring is twice as strong but it seems to work okay.  Since it is two layers, the battery liquid will go between the layers and quickly corrode it.  It will have to be replaced even more often.  But these radios were made around 1960 and have lasted more than 50 years, so I don’t think that’s a big problem.

I made this double thickness contact in the wrong order.  The right order is the following.

Cut the steel lid a bit wider than the original contact.  The excess will be trimmed off later.  It should be about 2-5/8 inches long.

Use a hammer and pound the sheet flat on a smooth, flat surface.  File off the sharp edges.  Then using sandpaper, sand off any paint or varnish.

Measure and fold the sheet in half.  Flatten with the hammer.

Make the 90 degree bend farthest from the folded end.  Then make the 170 degree bend close to the folded end.

Drill the hole for the screw in the 90 degree end.  This hole should be slightly bigger than the 2-56 screw.  Check the size and trim excess with the scissors.

Before putting the screw in, put the solid copper wire through the hole and solder it to the contact.  After it has cooled, secure it with the 2-56 by 3/16 inch screw and nut.

Repeat as necessary.  So far I’ve only had to replace the contacts closest to the bottom probably because the battery juice runs downward.


2017-10-13 Fri 13 More Telephone Tales

FB Telephone group

My least favorite part of the job was doing the crossconnects after new underground cables were installed.  The contractor’s guys had punched down the cables and spread icky pic all over everything, walls, backboards, blocks, everything!  I’d do some work and go to lunch and have to wash that jelly off from all over!  Messy, messy, messy!  And then after lunch another bath in the stuff.  People must’ve thought I was weird!


2017-10-12 Telephone 66 Blocks

More from FB Telephone group.  Continued from yesterday’s thread.

Yeah, those numbers sound familiar.  When we cutover to the digital PBXs, all those key systems were abandoned, and all of the hundred pair cables between bldgs were only partially used.  I pulled of most of the crossconnect wires, so there wasn’t much need for more pairs.  I just had to remember that all those bare 66 blocks were bare *for that reason*.

And then there was the time when they built an addition into the main bldg where the MPOE was.  The foundation contractor augured through the conduits and phones in other bldgs went dead.  Since they goofed and I wasn’t dealing with underground cable, they got a contractor to fix the cables.  Oh, well…


2017-10-11 Telephone PBXs and Heat

From FB group Bell Telephone 

Yeah, that’s the problem.  Them fans whining all the time, and having to rinse out the filters in the bathroom every 6 months to keep the PBXs from overheating.  I had to get the a/c guys to come to the phone room often and blow out the mold clogging the condensate drain pipe.  There was a float switch that shut off the a/c, and the water would back up and shut down the a/c.  In an hour or so we’d get complaints from users of dead phones, and I’d go to the MPOE and find it 100 plus degrees inside.  Sometimes I could get a fan to blow some outside air into the room and get things running again.  It’s always the weakest point that causes big problems.  “For want of a nail, the race was lost.”

Another comment 

I started seeing  correlation between the fields of the various colors of the mushroom holders and the way things were done with digital configuration.  I never had to learn what all those meant because the key equipment was abandoned when I took over.  But like when we moved into the old Wells Fargo Bank bldg on the corner of Main St (Broadway) and Santa Clara in Santa Ana, each floor had a closet with 20 linear feet of backboard covered with green, blue, pink fields of 66 blocks.  Most of the copper cables had been scrapped, so I did a lot of demolition just so the crossconnects could be removed.  Made it a lot easier to track down problems.

Another comment

The only thing I noticed was the 66 blocks were different.  Some were 6 across, and were great for punching down phone lines going to multiple bldgs.  But there were mostly ‘split’ 66 blocks, 25 pair on each side.  One time I punched down a 25 pair, and then found out the block was all four pins connected across.  Aww, spit!  I had to repunch it down to another split block.  😥
Pac Bell did the installation of the key system in a bldg complex in Centennial Park.  I took over the support in 1990.  I found that a whole bunch of 100 pair underground cable was not being used, and the unused part was always on the right side of the blocks.  But I could get dial tone on them.  Short story is the 66 blocks they installed on the far end were not split, so the lines were going from the MPOE to the far end on pairs 1 thru 25, and going thru the unsplit blocks and back to the MPOE on pairs 51 thru 75!  So half the 100 pair couldn’t be used because someone screwed up and used the unsplit blocks! 


2017-10-07 9V Battery Substitute – FB

posted to FB group Vintage Transistor Radios today.

I got tired of spending a lot of money on new 9 volt batteries, so I built a dc-to-dc converter, that takes two AA or AAA batteries and converts 3 volts to 9 volts DC.  One problem is that I got it to put out about 10 milliamps or 90 milliwatts, so it’s not powerful enough to run a 9 volt radio. But it works great for digital multimeters and other small test equipment.  The converter fits where the 9V battery goes, so I had to put the battery holder on the outside of the case.

These have cut down my costs for 9V alkalines.  But the converter draws some current when the meter is off, so it needs its own on/off switch.  Another solution to low current 9V battery is to use three CR2032 coin cells in series.  This gives 9V at a few milliamps, and will fit inside of the battery compartment.  It’s not for long term use.  I had some CR123 cells, so I connected three in series, and these can power a radio, which might take 20 to 30 milliamps.  But CR123 cells are expensive.

One thing I’ve noticed is that I’ve never seen an alkaline button cell leak.  👍


2017-10-02 Ripped Off By eBay Seller?

I bought a few Arduino Nano plus breakout board “kits” from an eBay seller in Las Vegas, Nevada.  The seller seems to be a coin dealer.  They advertised the Nanos as Mega328, but the ones I got were Mega168, which have half as much memory.  I don’t know if the seller knew they were inferior (could be the seller is clueless), but the goods were not what was specified in the advertising.

I filled out a return request and received a free shipping label, and shipped them back to the seller.  What makes me angry is this is the second time in a month I have had to return the goods to the seller because the goods did not meet the advertising.  These bloody sellers are trying to rip off the customers, and I hate it.

Another thing that bugs me is that I can choose to return the goods, but the return cancels the sale.  There is no way to give the seller a negative rating.  If I decide to keep the goods and give the seller a neutral or negative feedback rating, then I’m stuck with the goods and I don’t get my money back.

When I request the return, they allow only a few choices of reason for the return.  Some returns don’t fit into any of the choices.  You have to lie to make up a reason.  They allow a few lines of text to describe, but it’s difficult to squeeze that reason into a few lines.  I don’t remember having these many problems years ago, I think it’s gotten worse over the years.  Maybe someone will fix this, but I’m not holding my breath for that to happen.

Update Thu Oct 5 – This Afternoon I got an email from eBay saying the seller had refunded the money to my PayPal account.  The seller must have received the package back.  The seller didn’t give any further information.


2017-09-30 Zenith Royal 500 Radios  Pt. 02

Posted to FB group Vintage Transistor Radios  Oct 7 and after.
Yeah, it’s a bit confusing because the number of IF transformers is one more than the number of transistors.

When you work on IFs, what do you use for alignment?  I got Zenith Royal 500s that the previous owner apparently fiddled with the IF cores.  I guess I need a sweep generator.

Phillip Grace replied 

Yes, a simple fixed frequency generator is all that is needed, along with a DMM to read the DC voltage at the detector that drives the AGC circuitry. You can also use a generator with AM modulation along with the DMM set to AC to measure the audio level, or a scope. A sweep gen can come in handy when tuning sets that have wide bandwidth IF stages, but not necessary.
Me:  Thank you for the informative replies.  I read some docs online about alignment of AM radios.  I have done FM alignment with a sweep generator.  One of the radios tuned in 640 kHz with the tuning cap set at 780, so I retuned the LO coil to get it back down to 640.  Another one looks like the cores on the IF cans have been messed with, so I think that may be the problem.  But many of these have a bad volume control, so I’m going to work on those to get the audio stages working.  Just getting the battery holder contacts restored is gonna take a lot of time.  So I have to do a lot of TLC that will take time.


2017-09-29 Zenith Royal 500 Radios Pt 01

I bought a bunch of Zenith Royal 500 and similar AM transistor radios from an eBay seller.  These were made in the late ’50s to early ’60s.  They all use air variable capacitors like the 5 tube sets.  They all use four AAA cells for power.  The cases on some say unbreakable nylon, but there are chips and cracks.  They are relatively easy to work on.  I got fifteen for about $15 apiece.

The seller did not put enough packing around the radios, but they survived the shipping.

So far I have downloaded several schematic diagrams for them.  I have an old Zenith TransOceanic Royal 1000, but I had never seen these smaller Zenith radios until now.  They have an RF amplifier stage, oscillator, mixer, IF, driver and push-pull output stages.

I opened most of them up.  The first one I worked on was the one with the oval speaker in the upper left corner.  Most of the problems seem to be mechanical.  The battery holders have corrosion from leaky batteries.  And the volume controls get worn out from use. 

I couldn’t power up the radio because the negative battery contact was mostly eaten away.  The other contacts were in much better shape.

I disassembled the radio, unscrewed and unsoldered the battery holder and drilled out the rivet holding the negative contact.  I cut out a similarly shaped contact out of a can lid, using a pair of scissors.  I used a 2-56 small screw and nut to hold the replacement contact in the battery holder, and reconnected the battery holder to  the circuit board.  Using a power supply, I powered up the radio and found that the volume control was defective – it was dead until turned nearly fully on, and then the radio was playing full blast.  So I unsoldered and removed the volume control, and tried to clean it.  But that didn’t help.  I opened it up and found the carbon element was falling apart.  It had to be replaced.

I spent hours looking for a replacement potentiometer.  I quickly found a guy on eBay who machined replacement pots, but he sells them for $26 apiece, which is nearly twice as much as I paid for each radio.  Someone suggested trying Parts Express, but they didn’t have anything close.

I tried Mouser’s search engine to see if I could find something close.  They have all those filtering  choices so I limited my choices, and it came back with nothing found.  I had to turn off one filter after another, and finally it gave me a few poor choices.  So essentially Mouser doesn’t stock anything like it.

 I tried DigiKey.  They had lots of filtering items to choose from, but the most important, the risistance, wasn’t anywhere to be found.  That was really dumb!

I thought I might be able to use a 10k slider pot, so I looked in my box of potentiometers and I found some 10k miniature pots with the 1/8 inch diameter shaft.  The threaded shaft was extra long for mounting in a very thick panel.  So I decided to try one to see if it would work.  I had to saw off and file the D shaft to get it to fit into the knob.  After a few times of adjustments to get it to fit, I soldered the wires on and powered it up.  It worked, but there is no on/off switch.  It was a linear taper, so to “delinearize” it, I put a resistor between the wiper and common.  I tried some values and found that about 680 ohms seemed to work good at making the volume spread out over its rotation.  I will explain this in my blog in the near future.

I tried to tune in some stations but I heard very little.  I found one strong one on about 820 on the dial.  I listened for awhile and heard 640 KFI, but it was way off.  I think someone had played with the adjustments.  I used a tiny screwdriver to adjust the RF osc coil to get this 640 station back to 640 on the dial.  That helped, but it still needs the other adjustments adjusted.  It needs to have a realignment like they would do at the factory.  


2017-09-23 Cellphone Charger Secret Circuit

Posted to FB Arduino group Sep 23

Mbihi Oliver

Four hours is twice as long as 2 hours with the correct charger.  Here is a secret many don’t know:  Smartphones don’t necessarily charge at maximum, especially if they’re charged by a charger not made for their phone.

Smartphones often have a sensing circuit that checks to see if the plug’s two data pins are connected a certain way, such as two resistors to + and -.  If so it tells the phone that it’s the correct charger and it will accept full current, 1.5 amps or more.

But if these pins are open or the wrong resistance, then it charges at a half amp, because the original USB port is only specified for 0.5 amp.  So it won’t blow out the USB port on your MoBo.

Does your homemade charger have this??  😱  😈


2017-09-21 Kid Was Totally Into Telephone Central Offices

Posted to FB Antique Telephones group as a reply to Kevin J. Fitzgerald 

I helped some students in our computer lab, and one high school kid, I think his name was Robert, was totally into phones.  He had written a Basic program that printed a list out, with the various exchanges in the 714 area code, and what type of exchange they were.  He could tell me what type of equipment the CO had, etc., etc.  He knew, just by listening to the call progression what it was.

I called him up one time, and put “dial tone” on the line, and he didn’t know that I had built two oscillators 350 and 440 Hz, that generated the dial tone.  But he tried the touch tones, and when nothing happened, he figured out that I was making the dial tone.  😄

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