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Cliff Jones
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PostSubject: Transistor Radios   2011-06-01, 3:00 pm

I have a few of those that need repairing.
One is a Zenith 500

This transistor radio is one of the most sought after portables and is highly prized by collectors, and because of that, the prices are way out of line. It has in some cases an added RF section, and 8 transistors. The one good point is that most were hand wired. In My 500 the speaker (I think) isn't in good shape, as it's a little on the tinny side but lots of volume. When I went in the service during the Cuban Missile Crises (1963). I purchased one of these and it would play on the train all the way home. Sure sorry I don't have that one still, but I'll get this one working properly (eventually), and will be just as happy.

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PostSubject:    2011-06-22, 6:22 pm

I will be developing a list for transistor data, substitution, repairs and testing. (as time allows. feel free to contribute)

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PostSubject: Re: Transistor Radios   2011-06-22, 6:25 pm

I did get a dual power supply that can be voltage and/or current regulated and this will make testing transistor sets from smoking if I make erroneous repairs or having shorts. Embarassed Smile

I also have a Beckman Transistor tester to help in troubleshooting and repairs.

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PostSubject: Re: Transistor Radios   2011-06-23, 4:54 am

I've started picking up any AM only transistor sets whenever I come across them. They are harder to come by up here than I thought they would be.

Keep us posted on your progress for sure,

Bob
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PostSubject: Re: Transistor Radios   2011-06-25, 11:44 am

I have been picking more of the transistor radios up in the last several years. Back in the 1970's I worked for a wholesale dist. and sold many of the Channel Master Radios throughout the tri-state area. I have been collecting when I find them and have about 25 different models. Biggest problem I have is with my arthritus. It makes it hard to work on the little guys! I am trying to get the whole set of TSM manuals and only need a few more. If anyone has these to sell please let me know.
TSM 8-9-10-11-12-15-18=157=158
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PostSubject: transistor radios   2011-11-04, 4:30 pm

There are alot of small neat looking battery operated transistor radios on ebay being auctioned off, problem is alot of people are after them which racks up the price quite quickly!
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PostSubject: Re: Transistor Radios   2011-11-05, 4:32 am

[You must be registered and logged in to see this link.] wrote:
I have been picking more of the transistor radios up in the last several years. Back in the 1970's I worked for a wholesale dist. and sold many of the Channel Master Radios throughout the tri-state area. I have been collecting when I find them and have about 25 different models. Biggest problem I have is with my arthritus. It makes it hard to work on the little guys! I am trying to get the whole set of TSM manuals and only need a few more. If anyone has these to sell please let me know.
TSM 8-9-10-11-12-15-18=157=158

I have the same problem. It's kinda like being stuck tween a rock and a hard place. Very Happy My RA kinda forced me to get rid of the big boat anchors due to their weight, and the real smaller stuff isn't easy to work on when the fingers don't wanna cooperate. Rolling Eyes

Cheers, Bob
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PostSubject: Re: Transistor Radios   2011-11-07, 12:45 pm

I recently picked up a complete testing rack for $125 from a local antique mall. Its a Energy concepts test rack, it has two 0-25Vdc supplies, an audio and RF signal-generator, FET Multimeter, along with a variac that can run both a 0-300 Vdc supply and 0- 135 Vac supply. Built in filament transformer 6 or 12Vac and speaker with audio transformer. Turned it on after making sure that every thing is OK and all the lights work and no smoke.I will have to test each unit though and get proper probes and cables. going to have to get my work bench organized to set it on (It so big I wont have room to work on the bench LOL.

Nothing digital on it but I have been thinking to add either analog or Digital displays to it. It should work out well with doing transistor radios. My main objective for getting this. You can see kinda what it looks like from this web page, however those are newer pieces of gear than I have, showing digital readouts, where as mine have no readouts other than the FET Meter.
Mine are mounted in a frame that is horizontal rather than vertical. Strange thing though the RF Generator only goes to 6 Mhz.

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PostSubject: Re: Transistor Radios   2011-11-08, 4:25 am

Nice piece of equipment Cliff!

That has got to be one of the biggest disadvantages of living where I do out here in the sticks. (literally) Finding stuff like that locally. It just doesn't happen. It's probably better this way though, me thinks my budget would always be strained. Laughing

Right now, what keeps my purchases in check are the shipping rates. Rolling Eyes

Cheers, Bob
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PostSubject: Re: Transistor Radios   2012-02-29, 8:23 pm

Just found a Zenith Royal 400 a couple of weeks ago, I mentioned the difficulty of the switch not working, so whoever had it installed a tiny slide switch on the back. I'm going to tear into it one of these days and repair the original switch. If I can do that then I will have to see if I can repair the back cover where the slide switch took up residence. Since its a nylon case, It may be difficult, maybe epoxy. The surprising thing it sounds terrific and tunes well. It looks to have the same speaker as the 500H and circuit card as well, minus one transistor.

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PostSubject: Transistor Zenith   2012-03-01, 12:37 pm

Sounds like a nice radio. I like the small Zenith radios . Good quality and they seem to receive well. I have a Zenith Model 90 and a Model 50. I had a Royal 500 several years ago and sold it on Ebay . Wish I would have kept it now.
Good luck on the switch. With my bad eyes and hands with athritis, it is harder for me to work on these. Would like to hear your adventures in repairing that case when you get to it. I am not very good with any cabinet repairs.
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PostSubject: Re: Transistor Radios   2012-03-09, 12:02 am

Went to my local Goodwill and found a Sony ICF-7600AW, not working, a lot of corrosion in battery compartment. Cleaned it up, still didn't play, so I took the back case off and found a lot of white crud from batteries on circuit card. I used vinegar to neutralize acid and boy did it fizz. Used it in the battery compartment also. Noticed a lot of traces and solder connections all white. I took some Qtips, tooth brush, tweezers to scrape crud. The vinegar stripped off the conformal coating. Used a magnifying glass and my trusty LED snake light to scrape crud off traces and solder connections. Used Isopropyl Alcohol to remove crud with toothbrush and QTips. Used my granddaughter's pink nail polish to coat traces. Assembled and put good batteries in this time Embarassed HeH HeH! And low and behold it came to Life. Took me about an hour from start to finish. Psst! Got the radio for $2.99 What a Face

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PostSubject: Re: Transistor Radios   2012-03-09, 5:37 am

$2.99 and an hours work. Doesn't get too much better than that! Very Happy
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PostSubject: Re: Transistor Radios   2012-04-20, 9:28 am

I am reading a Gernsback book on "How to fix Transistor radios and printed circuits" by Leonard C. Lane. I am having trouble concentrating whilst reading it though. I did run across a couple of things that I can pass along that I didn't know. Most transistor Radios use NPN transistors, with no explanation why. Any one have any info on why?

The grounded base transistor circuit is similar to the grounded tube grid circuit.
The grounded emitter transistor circuit is similar to the grounded tube cathode circuit.
Both amplifiers have very low input impedance's (less than 1000 ohms) and the outputs are High.
The grounded base being several hundred thousand ohms and the grounded emitter is generally less than 50 thousand ohms.
The grounded collector is opposite, in that it has high input impedance of 100,000 to 300,000 ohms and output of just a few thousand ohms.

The grounded emitter is the only circuit that has phase reversal.

The grounded collector transistor circuit is similar to the cathode follower tube circuit.

The amplifier has a gain depending on the input and output resistances.
If the input is 100 ohms and the output 10,000 ohms, the output is divided by the input = 10,000/100 = 100 so the ratio is 100.
So 1ma at 100 ohms gives a voltage of 1/10 of a volt input (I X R)
So 1ma multiplied by the output resistance gives 10 volts so the ratio of input to output gives a voltage gain of 100.

Another aspect is the alpha gain, it is a ratio that is always less than 1 (except in point contact transistors). Its alpha is the ratio of collector current to emitter current.
It should suffice to say that Beta current gain is the ratio of collector current to base current.
It is usually designated in percent. So with an emitter current of 10ma and a collector current of 9ma the alpha is .9 or current gain of 90%

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PostSubject: Started buying Sams TSM   2012-06-26, 10:38 am

I finally decided to start collecting those manuals. Hey only $2 ea. But I forgot when you get 20 of them that's $40 plus postage. WHOO!
I started to realize that I wasn't keeping track of which volumes I had, So I will have duplicates, and will list them as found.
For my cost. Will post them in the for sale topic.
I have started to put them in a spreadsheet for tracking. Now I will have to figure out where to store them Suspect
----------------------------------------------------
I did run across an article on substituting silicon transistors for germanium ones because some of the old germanium transistors are getting rarer than hens teeth. There are ways to modify the circuit, but it takes some experimentation to make satisfactory. Adding resistors and removing capacitors , changing bias etc..

One though that ran through my head was why not OP-Amps?????? Simple to set the gain and will cover the gain range limiting easily. I don't know about bandwidth though as germanium has a smaller bandwidth than silicon, from what I read which could be problematic.
I'll have to root around for a book on OP-Amps.
It should be easier than finding replacement transistors.

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PostSubject: More TSMs coming to me   2012-07-31, 10:46 am

I took a look on ARF and there was an offer for over 100 more, so now I will have about 12 duplicates or more and will probably try to sell them, first here of course then maybe back at ARF. Looks like I will have to get another book case. Very Happy

I also went on EBay and Bid and won a radio I had back in the late 60s for $40 total. I will post a picture if I can, but the Picture is already gone off Ebay. It will be delivered in about a week with the booklets and original box too. Has Wonderful Stereo separation and fidelity, dunno know why I ever gave it up in the first place. Oh well found this one after an exhaustive search and the seller claims it still works. My fingers are crossed, LOL.


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PostSubject: Re: Transistor Radios   2012-08-29, 2:45 am

[You must be registered and logged in to see this link.] wrote:
I am reading a Gernsback book on "How to fix Transistor radios and printed circuits" by Leonard C. Lane.

Hi Cliff, what do you think of that book? Would you recommend it? A while back, I picked up a Zenith 490 real cheap on the ARF. I think it was like 8 bucks? I got it home, cleaned it up, recapped it and aligned it. Now it works great and from central Florida will pick up WSM in Nashville. The volume control is a bit flaky, but not too bad. I'm sold on those old Zenith long distance sets and hope to collect more models. When I do, I'll check with your first for TSM's.

Just for fun, I recently built a 4 foot round loop and put a 6 turn pickup on the zenith 490's ferrite antenna. It really pulls in the DX now! The loop is ugly and was my first try at building one. Now that I know how well they work, I'll be making more and nicer looking loops.

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PostSubject: Re: Transistor Radios   2012-08-30, 11:01 am

Yes It is a Helpful Book, and I do have about 40 Duplicate TSMs that didn't sell at PSARA Parking lot sale. I wanted to sell them as a lot rather than Individuals. I do have some prior claims on a few but, I told them to wait till I got them back. Which should be this evening from a fellow club member.

That's great on the repairs. I still haven't attacked one repair job, forum monitoring, wife's and fathers care, painting the house looking after and transport grand-kids and all.

Whew Just explaining that was exhausting. Sleep

If you feel you can explain, how many caps, resistors, did you use a schematic? How long did it take you to repair?, (would be nice details to know too.)

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PostSubject: Re: Transistor Radios   2012-08-30, 1:11 pm

I used Sams TSM 33. There were only 5 electrolytic caps in the zenith 490 and all common that I had replacements on hand for. I didn't replace any resistors. I did go over some of the solder joints and replaced some of the wiring. The alignment wasn't difficult, but I had to do it twice. When I added a 6 turn coupling on the ferrite rod for my new loop, it changed the first alignment. I lost some tuning range at the top end. 1300 was as high as I could tune to. I went back through the alignment and it fixed it. Someone else told me they had the same problem on an old zenith they tried to couple to an external loop that way. It is over coupled though. When I adjust the loop's tuning capacitor, it varies the radio's frequency a bit. I kind of like that though, since the small tuning wheel on the 490 is touchy. Now, it's like having an extra fine tune control.

Before the alignment, I could just barely hear WSM about 750 miles north. After the alignment, I can get WSM crystal clear during dark hours. That's without the loop. With the loop, the difference is incredible! I've been thinking about taking this old zenith apart and putting it into a new larger case. Maybe replace the tuning capacitor with a better one, vernier dial with some reduction. Maybe I'll fabricate a small cathedral shaped case with some nice veneer? As my zenith 490 sits now, the case isn't in that great of condition. Anyway, it might be a fun project some day.

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PostSubject: Re: Transistor Radios   2013-08-26, 8:01 pm

My first repair job of a Transistor radio since I made a new work bench back in March.

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It was a Channel Master Model 6519, with a leather carrying case and leather pouch for the earphone. I Originally used my HP dual Power supply to power up and had the wires crossed Embarassed switched power wires around and no sound so I started to check the speaker terminals with an ohmmeter, no luck so I checked the tinsel wires going to the solder connections on both the terminals and the fine wires soldered to the coil, with no reading.

I decided to get the schematic before delving into the radio any further. The schematic arrived in about 10 days. So today I decided to remove the speaker and do a close inspection with a magnifying eyepiece. I didn't have enough light to proceed, so I brought out my Multi-LED bench light. That made a big difference in what I could see.

I looked at the solder connections and found some burned insulation so I knew that someone had worked on this puppy before. That's when it dawned on Me that was probably why this one was for sale at the PASARA parking lot sale. They didn't have the skill or patience to find the problem.

On further inspection I found that there was some minor corrosion on the battery terminal's and cleaned those with a wire brush and used Q-tips with vinegar to neutralize the acid. With that in mind I found that the hair fine wires going to speaker coil looked like there was some corrosion on them. Sure enough that was my clue to start digging deeper. I got out my tiny flat blade screwdriver and started Scraping  off the corrosion.

I had to use my magnifying eyepiece in one hand and the screwdriver in the other. I did get the bare copper to show in some places, but since the wire was so fragile I didn't want to break it. Got out my ohmmeter and again tried to do a continuity check. NOGO. So I fired up my soldering Iron and tried to apply a coating of solder. I decided to get out a dental pick to remove the black glue that got burned in soldering. Scraped the glue and in the process I bent a small section of wire (Hmm that shouldn't have happened) well I thought, I must have been heavy handed drats. Then I noticed there was another small section that wasn't connected.

I got some fine wire and tinned it and tried soldering it over the spaces but the solder kept wire from adhering to the wires. So my next Idea was to attack the problem with a big piece of wire, and I thought that wont work for the same reason. Next I decided to use solder DE-wicking braid, I figured that would cover the entire area and heavy enough to not move.

I used my dental pic to hold my pre-soldered braided wick. IT WORKED, YEAH!

Got out my Ohmmeter and there was now continuity!
I measured from the speaker terminals and used my talking RadioShack meter, it stated nineteen point five ohms. YEAH!

I decided to use Elmer's glue over my patch so the speaker wouldn't rattle.
Wired and installed back in the case, hooked up my power supply and it worked.  

It is a 3 band with AM of 540 t0 1620Khz, LW of 150 to 400Khz, and MB of 1.85Mhz to 4.3Mhz.

Yet on the front dial is printed aircraft marine
So it picks up SOS *xxx just below and a little to the right of 2.2Mc Mark and 80 meters and 75 meter bands.

It has a pushbutton dial light and also printed on the dial is # band 10 transistor.
It has a pin plug for a long wire antenna, and a tuning / battery indicator meter. It also has two mini jacks, one for external speaker and the other for earphone. It also has a slide switch that says NAV-NORMAL.
I WONDER IF THATS FOR RADIO DIRECTION FINDING?
It does have a flip down metal lid that contains a metal movable compass. So the nav switch must make the more Directional by either decreasing the sensitivity or voltage, because the volume decreases in the nav position. Any Ideas?

------->  By the way Bill you can get a tuning dial reducer instead of futzing with a better cap (which wont do any thing other than cause a nightmare). I have also seen an old hint of attaching a larger knob an also gluing a small popsicle stick to the knob for more precise tuning control.

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PostSubject: Re: Transistor Radios   2013-08-27, 2:50 am

Nice work on the Channel Master Cliff! I've had my eye out for one of those for quite a while. I think the model 6516 is the one with the nice large ferrite rod antenna. I haven't yet had the pleasure of working on any channel master transistor sets yet, but from what I understand they have excellent long range receive, similar to the Zenith long distance portable transistor sets.

Thanks for the tip on my zenith 490. I've changed my mind and decided not to butcher that set. Instead, I've built a TRF set using a TA7642. It has a .5x7.5 inch type 61 ferrite rod antenna and a nice low loss ceramic air variable cap. It performs great, as good or better than any commercial set I've tried and from central FL, I can pick up stations as far away as NY. So, that's the set that I will end up eventually putting into a home brew arch top tombstone type cabinet. I recently started teaching myself to veneer and about half way done with my first veneer covered wooden radio cabinet. After I do this one, I'll try making the nice tombstone version. I thought it might be wise to practice on something first, hi.

Good luck with your projects!

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PostSubject: Re: Transistor Radios   2013-08-27, 1:41 pm

I had the opportunity of setting up a sound system for a local church that had a youth choir of about 70-100 participants that went on tour and they had a couple of Huge Voice of the theater Speakers. The Horn was mounted on top of the cabinet, it look pretty grungy and was pained all black, so every time it was toted around, of course it would get scrapes and scratches.

I removed the horn and installed it in side of the horn port. I stapled a speaker cloth that covered the entire front side of both cabinets. I put on a black walnut grained Formica on all sides with contact cement. I used brass corner protectors over the top of brass channel on each edge.

It looked very high end when finished.

So you might think about sheet Formica as a veneer.
After I applied the Formica I did use a router to smooth all edges of course.

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PostSubject: Re: Transistor Radios   2013-08-28, 3:17 am

I bet it looked real nice when you got finished with it Cliff! Learning how to apply real veneer on your own isn't as easy as I thought it would be. I'm starting out simple though. Covering a large wooden cigar box with walnut burl veneer with no backing. It will house that TA7642 MW set I mentioned earlier. The big 7.5 inch long ferrite rod just barely fits inside, but that was the intent.

I've got the 2 sides glued on and did the bottom yesterday. I've already learned some lessons, one is to watch out for excess glue. What a pain it is to have to scrape that away, so the veneer edges come together nicely. Veneer is so brittle, even using a product called super soft 2 veneer softener, I've still managed to break off tiny bits of the corners.

I also learned that it's a lot easier to veneer a sheet of plywood before you cut it. Trying to cover a pre-made box means cutting each side to fit and takes a lot longer. My next veneer project will be much better doing it that way! I'll try and remember to post some pictures. Maybe other forum members might want to try veneer too?

So, what else you working on now Cliff? Got any good projects going? Lots here, too many, hi. I'm still trying to finish my AC-1 clone and my MW AM transmitter. Both are so close to being finished. Several other projects going too. I'm rebuilding my DX crystal set, hopefully getting it done before winter when the bands get better. I'm going to wind me some better coils using 660/46 litz on 4 inch styrene forms.

Nice chatting with you again Cliff. Take care, 73. Bill..

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PostSubject: Re: Transistor Radios   2013-08-28, 10:11 am

I'm futzing around trying to get my work bench more organized. I am also collecting PFD files for all my test equipment and then print them out. I have a lot of electronic parts that I have organized but not cataloged yet. So I am going to set up a spreadsheet or database to number each storage parts cabinet and each drawer.

I just took the leather case for the channel master radio I repaired and glued the edges of the case.

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