IARCHS Meeting/Repair Session 9/23/2017

President Dave Perkins brought the meeting to order at 10AM at  Jerry Lange’s home in Dubuque, IA.

Attending: Jerry Lange, Dave Perkins, Jim Coohey, Jerry Rappel, John O’Briant, David Fitkin, Tom Waterman, Al Bailey, Dave Stewart, Doug Spyrison

 

 

 

 

 

 

 

 

 

Treasurer’s report: Total balance of $4137 in our checking and saving accounts

Old Business: The next annual radio auction is set for Saturday April 28th 2018 with radio check in on the 26th and 27th. Same location and format: Hawkeye Downs auction arena, Cedar Rapids, IA, Wears Auctioneering will conduct the auction again. as we approach the auction the usual planning and volunteer requests will be made.

New Business: Webmaster David Fitkin explained the need for an “https” secure website certification to make our website safe to use and encourage more “hits.” The charge is $50/year. Moved, seconded, adopted by consensus.

Newer member Dave Stewart asked about finding repair people. This is a continual challenge for the club. Anyone willing to repair old radios is asked to contact us and be listed on the Repair Service web page. Many repairs are arranged informally.

Having an announced repair topic coverage at the meetings was discussed but is challenging due to the many different levels of skill by attendees. Listing some “YouTube” links (to good instruction videos) on our website will be offered as a partial solution.

Next Meeting is tentatively January 13th or 20th, 2018. A host volunteer is sought. Please contact Dave Perkins to volunteer.

Adjournment to lunch and the repair session 11AM

John O’Briant had brought up a Zenith Walton chassis and speaker. He says it was a great auction buy but had been dropped at the auction. Candohm resistor failure was part of the diagnosis. Jerry Rappel had the Airline bakelight case radio which needed to begin with the basics of tube testing and electrolytic capacitor replacement.

Submitted by IARCHS Secretary Doug Spyrison text and photos.

IARCHS Meeting/ Repair Session June 10, 2017

On Saturday June  10, 2017 a club meeting  was held at the home of Rob Tracy in Des Moines.  Due to schedule conflicts, it was a small gathering.  In attendance were Rob, Al Bailey, Craig Huseboe, Dave Perkins and new member Ron Russel.

Business and Discussion: Craig reported on the April auction.  550 lots were sold with gross sales of $22K   The club netted $462 which is an improvement over previous years. (One expense was still pending as of this report.) The improvement was  primarily due to the reduced advertising expenses this year.   The feedback we got from the crowd and the auctioneer’s staff indicates that our switch to a combination of direct mailing to past participants and on-line promotion away from multiple print ads, worked well so we concluded that we will stick with that for the foreseeable future.   Also, both from the crowd and the auctioneer, it seemed that moving the auction up one week earlier than in the past worked quite well. Craig said that Wears Auctioneers will be available so we decided to set the tentative date for the next auction of April 28, 2018.

In other discussion, a couple of members have commented that the club should be better at keeping the event calendar up to date.  No one person is charged with that task so those that have access to it haven’t always thought to take care of that.  [Note to all, I’m one of those people and guilty as charged, I’ll try to be more diligent and if you see something that should be there but isn’t please ‘ping’ me].  Another very good suggestion is that we should add a prominent link on the web site’s front page to information on the time and place of the next club meeting.    At this point that meeting has not been set.  I will be asking, via a general email, for people to volunteer a location.  As the last two meetings have been in central Iowa, I’m hoping to have someone elsewhere in the state to offer a place.

Repair Session: Rob gave everyone a write up on a simple & handy coil tester which should be posted on the website as a separate post.  Photos: Rob Tracy in the ISU  shirt. Ron Russell in blue, Craig Huseboe in red, Dave Perkins in checks,  photos by Al Bailey (not pictured). 

New member Ron Russel, had acquired a couple radios (a Majestic and a Grunow) a week before our meeting. In the meantime he found and joined our club and  showed up at this meeting with the Majestic,  both to see what it would take to make it play, and to start on the process of learning some about restoration.   After testing the tubes, cleaning the controls and replacing the power supply caps with parts that Rob had on hand, it did play clearly but at a rather low volume.  With some signal injection and tracing and a few more measurements, we concluded that some of the old ‘dog bone’ resistors had drifted  out of spec to higher  values and, most importantly, the volume control resistance was out of spec.  We were able with some jumpers to try some different, resistors but Rob did not have a suitable volume control pot on hand.  So we concluded our troubleshooting session with some ideas on what to look for in the way of parts and hopeful that he could at least acquire the necessary parts.  It was a steep learning curve for someone who’d never looked at a schematic before, so Ron, if you get hung up on your project, keep in mind that you can always bring it & some parts, to the next meeting once I have it set up.

That’s it for now.  Everyone enjoy your summer bargain hunting at flea markets and yard sales, keep cool and watch for an announcement of  our next meeting time & place.

Submitted by Dave Perkins, IARCHS President

WordPress editing, Doug Spyrison

 

 

Coil and Resonance Tester

Synopsis by Dave Perkins: Have you ever been frustrated while working on a set because you couldn’t tell if an IF transformer coil was OK or shorted since the resistance readings for the two conditions is almost the same?   Here is an excellent tech write up on building and using a fairly simple tester that club member Rob Tracy put together and gave to each of those attending the last club meeting.  This is the kind of weekend project that makes your troubleshooting more trouble free and is something that is a valuable addition to your test bench. You don’t even need to use a printed circuit board, this could be built on a piece of perf board.

The Coil Tester  

by Rob Tracy

Measure inductance and resonant frequency

How do you test a coil? Usually, you want to know two things: the inductance and the frequency at which it will resonate with a particular capacitor. This handy tester helps you find both. Connect it to any LC tuned circuit, and it oscillates at the resonant frequency, from below 20 kHz to above 20 MHz. What’s more, at the flip of a switch, you can use the built-in 150 pF capacitor to make a tuned circuit out of any coil and deduce the inductance from the frequency at which it resonates.

You can read the frequency on a frequency counter, calibrated oscilloscope, grid dip meter, or communications receiver. From the frequency, you can find the inductance with the accompanying nomograph or computer program. The tester works with coils over a million-to-one inductance range from 0.2 µH to 0.2 H or more.

The Search for the Circuit

For years I had been looking for an oscillator controlled by a single parallel tuned circuit. The Hartley and Colpitts circuits won’t do because they require, respectively, a tapped coil and a “tapped” (double) capacitor. The Clapp circuit uses a single coil and capacitor, but they’re in series. That’s not good enough. I wanted an oscillator that would take a parallel tuned circuit so I could measure the resonant frequencies of IF transformers and other ready-made tuned circuits. Also, every coil has a self-resonant frequency at which it is parallel-resonant with its own internal capacitance; only a parallel-tuned oscillator will test this directly.
Figure 1. C1 and Lx control the frequency of this source-coupled FET oscillator. S1 removes C1 from the circuit to enable testing of tuned circuits or self-resonant coils.

The circuit in Figure 1 does the job. It’s adapted from a cathode-coupled oscillator described by F.C. Alexander, Jr. in the September 1946 issue of QST, pages 69-70, who credits it to F. Butler. Mr. Alexander reported that the oscillator would really take abuse; he found it would still oscillate at 10 MHz with a 6J6 tube with four volts on the filament and a mere 3 volts (instead of the usual 300) for the plate supply. The FET version was first described by L.F. Heller in Wireless World, September 1969, page 409, but he used an RF choke instead of my resistor R1.

Understanding the Circuit

Think of Q1 as a source follower and Q2 as a common-gate amplifier. The two stages communicate by sharing source resistor R2. Positive feedback goes through C2, and the tuned circuit ensures that the feedback is only effective at the resonant frequency.

The high supply voltage (18 volts) helps extend the frequency range and improves the performance with low-Q tuned circuits. The oscillator won’t work with a crystal, but it will sometimes oscillate with a resistor in place of the coil.

The output, rich in harmonics, is taken across R2 (Photo A). R3 provides some output isolation; without it, a capacitive load-such as the internal capacitance of a long cable-could sometimes stop the oscillation.
Photo A. The output waveform consists of half-sine-waves and is rich in harmonics.

Construction

I built the oscillator on perfboard and housed it in a Radio Shack instrument case. The layout is not critical as long as all leads are kept short. Even the test leads should be short-just long enough to reach out of the enclosure-because their inductance is part of the tuned circuit.

Switch S1 is also part of the tuned circuit; to save lead length, I mounted it through a hole in the circuit board, and the switch itself attaches the circuit board to the front panel (Figure 2). The batteries are held by clips mounted on the back panel (Photo D); the clips are lined with vinyl tape to keep the batteries from slipping out.
Figure 2. To keep leads short, SI mounts in a hole in the circuit board.

Measuring Resonant Frequency

The simplest way to read out the frequency of oscillation is to use a frequency counter. Make sure the reading is stable and is the same with the counter set on more than one range. You can also measure frequency with a calibrated oscilloscope:

Frequency (MHz) = 1 / Length of one cycle (microseconds)

Don’t strive for great accuracy; because of stray capacitances and inductances, your results are bound to be off by a few percent.

You can also determine the frequency by tuning in the oscillator on a communications receiver. No physical connection is needed; just place the receiver close to the coil and look for an unmodulated carrier. When you find it, also try one-half, one-third, and one-fifth of that frequency to determine whether you initially heard a harmonic.

Or you can use the ham’s traditional tool, a grid dip meter. To do this, start up the test oscillator, then use the dip meter as a field strength indicator. That is, set its gain so that it does not oscillate, and place its coil right next to the coil under test. Tune across the band until you get a slight but sharp peak in the meter reading. This is more accurate and more sensitive than testing a tuned circuit with the dip meter by itself.

What’s the Inductance?
Figure 3. Nomograph to find inductance of a small coil from a single frequency reading. Inductances up to 0.1 H can be measured by taking two readings (with and without the 150 pF capacitor) and doing calculation.

To find the inductance of a small RF coil, measure the frequency of oscillation with C1 in the circuit. You can then find the inductance with the nomograph in Figure 3. In fact, you may want to stick a copy of the nomograph to the top of the test oscillator.

The nomograph works as long as you’re dealing with a coil whose internally distributed capacitance is small. Any coil with more than 50 turns is likely to have appreciable distributed capacitance. Fortunately, you have an easy way of measuring this, too-just read the resonant frequency with C1 out of the circuit as well as in it. Then use the BASIC computer program in Figure 4 to do the calculations, or work through the formulas from the program on your calculator.
Figure 4. This program finds inductance and distributed capacitance from frequency measurements. It was developed on an IBM PC but should run in practically any version of BASIC.

The program was written on an IBM PC but should run in practically any version of BASIC. It finds the inductance and distributed capacitance, then prints a table of resonant frequencies and the capacitances needed to obtain them (Figure 5). That’s helpful because usually, hams don’t really want to know inductance for its own sake; they want to make a resonant circuit for a particular frequency.
Figure 5. Sample output from the computer program. These data are from a coil labeled 470 µH, 5%.
Figure 6. Foil diagram.
Figure 7. Parts placement.

If you test an IF transformer, you’ll get an inductance and a distributed capacitance that includes the built-in capacitor. For instance, a 10.7 MHz IF transformer that I tested came out as 3.6 µH in parallel with 60 pF, and according to the table displayed by the program, it will tune 40 meters if I add slightly more than 128 pF.

Improving Accuracy

You’ll notice that the program has variables for the stray inductance (LS) and stray capacitance (LC) of your setup, in henries and farads respectively. In the program as shown, they are set to zero, but you can gain additional accuracy by measuring or estimating them and putting them into the program.

Stray capacitance is hard to measure and is fairly unimportant, since the 150 pF capacitor completely swamps it. As a ballpark estimate, try 1 pF, which you would enter into the program as CS = 1E -12 (i.e., 1 × 10-12 farads).

Stray inductance is more important. It’s likely to be about 0.2 pH. To measure it, wind three or four turns of solid hookup wire into a small coil, then measure the resonant frequency with C1 in the circuit. You’ll probably get something like 20 MHz. Now spread out or unwind the coil to make the frequency rise. You’ll get a maximum frequency around 25 MHz before oscillation stops. Put this frequency into the computer program, and you’ll get back a fair approximation to the stray inductance of your setup. Now modify the computer program to make this number the value of LS (for example, if it’s 0.2 µH, make LS = 0.2E-6).

By the way, this is not the highest frequency at which you’ll ever see oscillation. A high Q tuned circuit can override the low Q stray inductance and make the oscillator run as high as 120 MHz.

An Essential Tool

Two weeks ago I didn’t know an oscillator like this could be built. Now I don’t know how I’d get along without it. The ability to measure inductance and resonant frequency is so fundamental to RF circuit design that an instrument like this belongs in every ham shack.

Parts list

B1, 2 9V
C1 150 pF 5%
C2 33 pF
C3 47 nF
Q1, 2 J310 FET
R1 10 kΩ
R2 1 kΩ
R3 1 kΩ

Courtesy of N4TMI, Michael A. Covington  and

http://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/73/1990/09/page48/index.html

Schematic updates to J310 FET by Rob Tracy

Article submitted/authored by Rob Tracy

WordPress editing Doug Spyrison

2017 Auction Report- Highlights/ Photos/ Prices Realized

IARCHS annual Antique Radio Auction took place on April 29th, 2017 with 91 registered bidders and 8 states represented. Brent Wears auctioneering kept a fast pace through the approximate 600 lots of radios, speakers, parts, tubes etc. Listed below (the photos) are some selected auction highlights with prices realized.

The tentative date for the 2018 auction is April 28th, stay tuned for further information.

(Click on any picture to see a larger view)

 

  • Belmont 6D111 tabletop radio $80.00
  • Philco 20 cathedral $90.00
  • Gloritone Z6P cathedral $80.00
  • Galloway TRF battery radio $175.00
  • Kennedy XV, Type 430 $200.00
  • Hickok 600A tube tester $150.00
  • Magnavox type R3 model B horn speaker $110.00
  • Crosley XJ $135.00
  • RCA Radiola II model AR-800 $175.00
  • Federal Type 61 $975.00
  • Northome model 3 $175.00
  • Tuska Superdyne type 305 $200.00
  • Grebe Synchrophase $200.00
  • Ampex 601 reel – reel tape deck $100.00
  • Pilot TV37U television $150.00
  • Zenith 4B321 tombstone $50.00
  • Three boxes of Sams TSM series service manuals $70.00
  • National NC-100A receiver and matching speaker $100.00
  • Magnavox TRF 50 battery radio $175.00
  • Western Electric 7A amplifier with tubes $650.00
  • Western Electric 10-D horn speaker $70.00
  • Kodel Goldstar C-113 battery radio $100.00
  • Crosley PUP radio $120.00
  • Crosley model 50 $70.00
  • Crosley Type V $60.00
  • Crosley model 148 cathedral $60.00
  • Crosley D25-BE radio $100.00
  • Federal Jr. Crystal radio $130.00
  • Argodyne Crystal radio $90.00
  • A-K model M horn speaker $70.00
  • Beckley-Ralston AX235 battery radio $130.00
  • US Apex 7A cathedral radio $100.00
  • BC-223-AX/TU-17-A military set $60.00
  • Arvin 544 bakelite radio $50.00
  • Admiral Super Aeroscope 15-D15 $80.00
  • Reichmann horn speaker $130.00
  • Bristol Super-S horn speaker $60.00
  • Cabinet of misc. Sprague capacitors $100.00
  • Crosley model 609 Manchu black “Gemchest” $100.00
  • Tung-Sol lighted clock $45.00
  • Pioneer Turntable and Shure cartridge $90.00
  • L-Tatro 6 and 32 volt tombstone radio $70.00
  • Globe 1-tube battery radio $80.00
  • Henry Field Shenandoah 5 battery radio $90.00
  • Salisdyne battery radio $90.00
  • Detrola Desk set radio $250.00
  • Shenandoah Super Six battery radio $160.00
  • Scott Stereophone tube amplifier $175.00
  • Folder containing numerous WHO, WOC radio station brochures $250.00
  • Folder containing numerous KMA, KTNT radio station brochures $100.00
  • Murphy (British) model A26C small console radio $50.00
  • RCA Radiola 30A console radio $500.00
  • RCA Radiola AR-810 battery console $650.00
  • RCA Radiola 28 with loop antenna and 104 speaker $900.00
  • RCA Radiola RC (RADA) $110.00
  • RCA Radiola IIIA in special table cabinet $225.00
  • 15” E.H. Scott speaker made by Magnavox $100.00
  • Box lot of misc. loose E. H. Scott chrome tube shields $55.00
  • Blue Neutrowound model 1927 without tube caps $700.00
  • Philco model 16 cathedral radio $225.00
  • Johnson Viking Valient transmitter $150.00
  • Philco model 38-9 radio $90.00
  • Dewald A-501 catalin radio as found $150.00
  • RCA 9TX Little Nipper catalin radio as found $50.00
  • Coronado 32 volt tombstone radio $45.00

Craig Huseboe reporting

Photos from Dave Perkins Facebook post

Doug Spyrison WordPress editing

 

 

2/11/17 IARCHS Meeting/ Repair Session

A club meeting was held at Dave Perkins’ home south of Marshalltown on Saturday 2/11/17. Dave herded the cats into a line and got the meeting started at 10:15.

Keith Lowe and John Thomas working on the Admiral

Those in attendance included Al Bailey, Keith Lowe, Rob Tracy, David Fitkin, Craig Huseboe and new member John Thomas of Coralville. There was no financial report available for review. Under old business we discussed that the date and other arrangements for this years’ auction is substantially set and, in keeping with our earlier discussion and decision, promotion this year will be almost exclusively on line via social media because of the poor performance of printed ads the last few years relative to their expense. That said, because the informal survey at last years’ auction indicated it was effective, we will be reaching out to past attendees via a direct mailing to remind them of the auction and emphasize the change in date to a week earlier than in past years. Also, because it costs us only reciprocating in our newsletter for their events, Craig will ask the Illinois club to publish a notice of our auction in their newsletter. Craig will be sending Dave the mailing list from last year’s auction and Dave will take care of sending out the notices via mail.

Under new business we discussed how the general effectiveness of social media, especially Facebook, for gathering people with a common interest like collecting, restoring & selling antique radios, continues to increase. Dave reported that there had been quite a number of responses to his post about our auction on 3 radio related Facebook pages, including some that, upon seeing what had sold in the past on our web page, declared their intent to attend the auction. Dave and Keith have posted notices on various pages already and will post reminders as the time for the auction draws closer. On a related point, Dave said that Doug Spyrison (who could not attend due to illness) had suggested that the club create an Iowa based antique radios for sale page on Facebook. These have become rapidly popular as the fees for services like Ebay have increased. We could also use this to draw people to our general club page and website. There was general agreement that this was worth considering. Dave said he will continue to discuss who and how this may be done with Doug.
Finally, David Fitkin floated an idea of how we could use the auction as a basis for extending the reach of our club into the general population, potentially including younger people, something every club like ours desires. The essence of the idea is to approach various organizations in a community such as churches, fraternal organizations, 4-H clubs, the boy scouts etc. and suggest that they could collect radios donated to them and sell them at our auction. Each organization would serve as a single consignor to the auction. In doing this it would provide a unique fund raiser for the group selling the radios beyond the typical bake sales and spaghetti dinner sorts of events AND give us an opportunity to interact with them, making them aware of our existence & purpose and, perhaps, inspiring some people to join. The consensus was that it’s too late to try and do something like this for this year’s auction but it is worthy of discussion for subsequent auctions.

As it happened there were only two sets brought for the groups’ collective efforts to analyze and, hopefully restore them. One of them was a 1956 Harmon- Kardon AM-FM set in which the AM and mono phono amplifier worked fine but with an FM section that remained stubbornly mute thereby addng to Dave’s chronic baldness.

A vigorous team effort ensued and at one point Craig Huseboe and David Fitkin conspiring to suggest that a grounded jumper be place such that a bit of the ‘magic smoke’ was allowed to escape from a power supply resistor. A rapid lesson in smoking cessation relieved that condition with no harm done (the component in question was deemed old enough to legally smoke in any event) then Craig and Rob Tracy teamed up to reach the conclusion that the problem was at least one unreliable, flaky tube socket. So that set was put aside for more detailed attention.

On a happier note, new member John Thomas brought with him his first ever  collected radio, a 50’s era Admiral table set, seeking to learn a bit about

John Thomas, Dave Perkins and Keith Lowe work on the Admiral
Keith Lowe and John Thomas in the shop

 

 

 

 

 

 

restoration. He had no schematic and we were unsuccessful at quickly finding one on line, but undeterred, Keith Lowe helped him dissemble it and visually identified the power supply filter cap. Dave had some suitable caps on hand and while Keith and John replaced them and cleaned the volume control, the tubes were tested and found to be usable. Upon powering the rebuilt set up on a Variac, it came to life and played …… those of us in this hobby know the satisfaction of that moment when your first ever restoration ‘talks’ to you again. It was nice to share in that moment with John and a nice way to bring the meeting to a close.

Dave Perkins

 

New IARCHS Newsletter format coming soon

New IARCHS Newsletter format coming soon

IARCHS-Summer-NewsletterNew IARCHS Newsletter format will appear here soon. Articles will be posted online for members to see and use. Your input is welcome, as we are continually trying to improve our member resources.  If you haven’t registered as a website user yet, it is free for everyone (subject to approval).  We don’t want you to miss any of the new IARCHS newsletter stuff when it starts appearing on the members only portion of this site.