Category Archives: Radio Modifications

How to fix the Grundig S350DL’s mechanical tuning drift problem

The S350DL may look like a digital radio, but it’s actually analog inside and tuning is prone to drift.

Many thanks to SWLing Post contributor, Ed, who noted my comments about the Grundig S350DL’s tuning drift yesterday, and shared the following fix found on Jeff McMahon’s Herculodge blog.

Ed writes:

The Grundig S350DL’s mechanical tuning drift problem is reportedly easily correctable with a screwdriver:

(Source: The Herculodge)

[…]The drift on AM was terrible! After 10 minutes, it is jumping all over the place – if you touch the radio, the sound mutes and the display goes nuts. I pack it up to take it back but then I decide to google the problem and find this:

http://groups.yahoo.com/group/Grundig-S350/message/4644

I do exactly what he says – I pull off the cover after unscrewing all of the screws (including the 2 in the battery compartment).

Only the speaker is attached to the front. I remove the three screws from the display and then tighten the two screws on the tuning wheels. They were barely loose – almost not noticeable – so I was not too optimistic. I carefully got it all back together (the plastic pieces that hold the fabric handle on only go back on one certain way and were sort of a pain!). I cross my fingers, plug it in, and wow – a brand new radio. The tuning is perfect. Zero drift on FM and AM. AM sounds excellent.[…]

I have an earlier Grundig S350 that I bought at a hamfest years ago which had an easily-fixed power problem. For $20 it makes a nice bathroom radio and it sounds great, especially on FM.

BTW, I found schematics for it on radiomuseum.org, which is a great resource for radio schematics.

Thanks for the tip, Ed! I think I’ll crack open my S350DL later today and give this a try!

Schematic for the PLL EDUTEC 4-Band Digital Radio Weltempfänger?

Many thanks to SWLing Post contributor, Cezar Vener, who writes with the following inquiry:

I would like to ask you if you can help me with a schematic diagram for an EDUTEC 4-Band digital radio (PLL EDUTEC 4-Band Digital Radio Weltempfänger). It is not broken, but I would like to modify it. Of course, I could spend some time and manually extract the schematic, but I would lose too much time.

While I know that “EDUTEC” is a registred trade mark for technical (“non-food”) products that was sold by “Eduscho Handelsgesellschaft” in Bremen and also I found that it is now owned by Tchibo, well – I would like to kindly ask you for help in this matter? (course, if you can).

It is an old product, probably made in the 90’s and until now, I didn’t find anything on the net about it. I opened it and I found that its core is TA8132AN, and the FM section is made around TA7358AP. The audio stage is built with C1212C, and there is one more integrated circuit there, TA8148S (no datasheet on the net, but I found that is a DC-DC converter for electric tuning – built-in stabilized supply output for biasing VHF tuner variable capacitor / sine wave oscillation).

BTW, I found it also in SONY CFS-W504L 🙂

The PLL chip is soldered with the unmarked side, so I don’t know what type it is.

[See photo at top of post.]

Here is a photo of the rear back stand:

Unfortunately, there is no other model or name written on the radio.

I see there “CENTRON LABORATORIES LTD”, that points to the company with the same name from Gujarat, India. Very interesting :))

In the hope of an answer from you, please allow me to thank you and to congratulate you for the very nice site that you maintain there!

Many thanks, Cezar! It’s readers like you who make this site such a great one!

Post Readers: I hope someone may be able to help Cezar. This radio looks familiar–perhaps I’ve seen it badged with a different company name?  Please comment if you can help Cezar locate a schematic.

Tecsun PL-660 Hidden Feature: FM Calibration

Many thanks to SWLing Post contributor, Rick B, who writes:

I just thought I’d share with you a hidden function I discovered documented on the web for the Tecsun PL-660. It’s how to calibrate the FM band if you have a radio that is off frequency.

As my current PL-660 is accurate on FM, I haven’t had to try this myself. But perhaps it could save someone else from having to return/exchange a radio.

http://kaito.us/miscellaneous/qa/how-to-calibrate-the-pl660-on-the-fm-band.html

“Re-calibrating FM, radio needs to be on and set to FM band. Tune to the desired frequency/station you wish to listen to, press “SYNC” for about 3 seconds back light will flash. Tune up until the frequency/station sounds more clear press “1” to confirm re-calibration. If done correctly the correct frequency/station will be displayed on the display. Keep the battery in for all the time…”

Very cool!  Thank you for sharing the tip, Rick!

Guest Post: The Story And Restoration Of My Hallicrafters SX-42

halllicrafters-sx-42-front-panel

Many thanks to SWLing Post contributor, Arthur Smith, who shares the following guest post:


The Story And Restoration Of My Hallicrafters SX-42

by Arthur Smith

As a junior high student way back in 1978, I had a natural interest in radios. My dad was a ham radio operator, electronics engineer, and designer. We always had cool, exotic radios and electronic gadgetry around the house. He was also in the Korean War, in the US Army Corps of Engineers, with access to a wide variety of equipment. He often told me the story of how he became interested in radio at an early age, and how he saved up for expensive radio gear, with a little help from my grandparents. Back in 1946, Hallicrafters was THE brand to own, and their postwar designs from Raymond Loewy, were catching the eye of many enthusiasts. The SX-42 was being hyped up in Hallicrafters ads as the ultimate radio to own, one that could tune the shortwave and ham bands, and beyond. I don’t know the complete story, but prior to acquiring his SX-42, my dad also purchased an S-38 and S-40. Never satisfied with “good and better”, my father wanted “the best”. All 15 tubes and 50-plus pounds of boatanchor.

Always ambitious and industrious, he mowed lawns, repaired motorcycles, and did odd jobs for neighbors in his suburban Boston neighborhood. He worked smart, and worked hard. And that fall, bought his SX-42.

halllicrafters-sx-42-front2

The radio, we think, was about $279, which would make it the equivalent of almost $3500 in today’s dollars. He heard the start of the Cold War, and the Soviet Union’s Sputnik. And the birth of Rock and Roll on FM! He graduated high school, went away to the Korean War, serving two Tours of Duty. He came back home, and became an electronics engineer. And a licensed ham radio operator.

Moving ahead to 1978, and yours truly had the radio bug, in the worst way. Not as ambitious or as savvy as my father, a classmate, who was also a ham radio operator, told me about a National HRO he had, with some coils, and maybe needing some work. My Dad came home from work, and I just had to tell him about this great opportunity, which of course, would require his financial backing. At this point, the SX-42 and his other two Hallicrafters were seeing “backup” duty, having long since gone solid state in his post. “Hey, I’ve got an idea!” When a Dad says that, a son usually wants to run. Not in this case. “How about we give you my SX-42?!” Gee, twist my arm. I had loved watching those mesmerizing green back lit dials, S meter, and geared tuning knobs. Unfortunately for my classmate, he had to keep his National. Fortunate for me, I had my father’s SX-42!

That radio logged my first 100 countries, including QSL cards from countries and stations no longer in existence. It heard the fall of the Berlin Wall. And, it was at the heart of my school Science Project, which made Science Fair, featuring an experiment on longwire shortwave radio reception.

halllicrafters-sx-42-open

halllicrafters-sx-42-tubes Years later, the focus became family, a child, and a house. The SX-42 and siblings came with me, but this time, in boxes. After having seen a WW2 vintage Hallicrafters S-20R at a consignment shop a couple of summers ago, I thought how cool it might be to have Dad’s radios electronically and cosmetically restored.

The S-38 and S40 were in a box in my damp basement. While intact, they had a considerable amount of rust. Luckily, I was able to find a gentleman with great electronic and mechanical skills. He brought the S38 back to life, working and looking beautiful. And is working still on the S-40. As for the SX-42, that was upstairs in a box in my son’s closet. Dry and somewhat preserved, but with some corrosion on the control panel. And sadly, that iconic lock knob that switches between main tuning and brandspread tuning, had been lost in the move. I had to find someone who could take this project on.

After an extensive search, I found my man. An engineer with his own business, who was moving into retirement, and shutting his business down. He had restored an SX-42 a few years back, with amazing results. I had to lure him out of retirement! Which I did after a few emails back and forth. And, he was within driving distance! First warning was “do not power the radio back up under any circumstance- you’ll fry the wafers on the bandswitch!” I resisted temptation, as I had read online that these were notorious for failure, usually to some original capacitors that leak over the decades.

After 13 months replacing every capacitor, virtually every resistor, and vacuum tube, the iconic radio was coming back to life, in a great way. The transmission and gears in the tuning was re-lubricated. During the restoration process, a date was found stamped on the chassis of October 25th, 1946. Could it be?

img_7367-02-12-16-06-57-1Hallicrafters had advertised in the Oct, 1946 issue of Radio News that “The first hundred are always the hardest to build.” This, coupled with the fact that none of the chassis circuit had been modified, lead my restorer to believe that my radio was one of the first 100 SX-42’s that Hallicrafters had built!

The front panel was stripped and treated, professionally painted and silkscreened. The cabinet and apron bead blasted, repainted, and clear coated. It came back home with me last month. A month after it turned 70.

halllicrafters-sx-42

As you can see here, the radio looks stunning. And, with all the Hallicrafters Service Bulletin mods implemented, sounds and performs better than I remember. Maybe more importantly, we were able to locate a replacement brake lock knob for the tuning shaft, even with the “Lock” decal and arrow showing to rotate it counterclockwise. It just would not have felt complete without that little knob- and, it works!

halllicrafters-sx-42-frontEngaging a set of what essentially are brake pads, you rotate it once to disengage the main tuning and engage the bandspread tuning. Again, and you’re back to main tuning.

halllicrafters-sx-42-ad

This radio will always remain a truly cherished family heirloom, and will be my son’s someday. Complete with the original owner’s manual, and Darth Vader-like R42 Reproducer (speaker).

halllicrafters-sx-42-front-panel

Hopefully to live on for another 70-plus years, and hear more history along the way.

-Arthur Smith Worcester, MA


Wow–!  Thank you so much for sharing your story with us, Arthur. No doubt, your SX-42 will certainly outlive all of us and will hopefully continue to be passed down through your family. What a wonderful story.

Mr. Carlson restores and repairs a Hammarlund HQ-140-X

hammarlund-hq-140xMany thanks to SWLing Post contributor, Moshe, who writes:

Hi Thomas!
You must see this restoration job from Mr. Carlson’s lab:

Click here to view on YouTube.

Thank you for sharing this video, Moshe!  I truly enjoy watching Paul’s videos–no doubt, any radio turned over to him is in expert hands. I love how he explains, in such detail, each action he takes to restore and repair these vintage radios.

Click here to view Mr. Carlson’s YouTube channel.