[jrblasde]

I’ll note that I observed in my 48-482 that this same cap had been replaced. I can’t help but wonder if it blew due to such a fault… But the newer replacement was rated for 1000V.

[HarryWeatherford]

Very nice - Thanks! Any thoughts on running a flat pair of 300 ohm cable to make a "T" cabinet dipole or either a single loop around the interior with 300 ohm cable and set to the wavelength of 116" (if my math is correct) ?

[HarryWeatherford]

That makes sense about the inductance instantly dropping and getting big voltage spikes - gets a lot of CEMF from that (link detaching any inductive load). Normally that is a disaster with a dc circuit - I imagine the same here.

[HarryWeatherford]

I can see where detaching that inductive load could give very big voltage spikes. It would generate a voltage V_L = L * di/dt. So the inductance times the rate of change of the current (from trying to break the current - from the detached load) would cause the inductance's changing magnetic field to collapse quickly, changing the voltage drastically in an attempt to maintain that same original current. The rate of change of the current (di/dt) is the real thing that causes the voltage to go through the ceiling forcing the inductance field to collapse. Thanks guys - you made me think in my retirement years.

[HarryWeatherford]

My FM Cabinet Dipole for the 46-480 was removed. (I'm new to this group and this may be the wrong place to ask this question I also saw a thread about the cabinet dipole for the FM. It had a link ( https://www.rfcafe.com/references/radio-...l-1947.htm) for a folded dipole. The thread was closed and I have a couple questions for anyone with 46-480 experience. Can I run a single loop ( 300 ohm cable) around the perimeter of the console frame shooting for a wavelength of about 116"? If I use the flat 300 ohm pair cable, will it mess up the reception if the shape is not exactly a "T" (by following the inner shape of the cabinet)? I'm asking this because the cabinet dipole has been stripped out.

[klondike98]

I can’t answer your question but this is the right place to ask it.

[MrFixr55]

Hi Harry,

Those of us who are HAMs (I am not, yet) may be better versed in answering this question, but my $0.02 would be that a single length of twin lead would not work. Since the input is balanced, what is picked up by the 2 conductors would be in phase, in other words, common mode and would be cancelled out. It would be best to make the T antenna, similar to the original.

The quickest (and dirtiest) method is to get some lamp cord (Zio Cord) that is long enough to go from the antenna terminals of the receiver to the middle top of the cabinet plus 2 1/2 feet. Separate the first 2.5 Ft of the zip cord and staple from the center of the cabinet down the sides. this gives you a 5 ft center fed dipole that is approximately half wave.

You can make a more proper "folded dipole" out of 300 Ohm twin lead, but by the time you buy the twin lead and spend the time, you can order one from eBay or Amazon for $6-$8 plus shipping.

[jrblasde]

Good morning! I can't say that I've tried using 300-ohm conductor, but I suspect it would work fine! 

I was lucky to have the original dipole in the cabinet. I'll tell you, it's just a couple of pieces of 20 AWG stranded wire. The brown wire is about 28" long, and the white one is about 6" longer. You can see that they connect to the two backmost connections on that J400 socket.

   

   

[MrFixr55]

Great! Philco took the quick and dirty route!

[RodB]

I don't have photos but you can duplicate the late 50s early 60s German FM radios by using two pieces of heavy aluminum foil about 6 x 20 inches fastened to the interior top of the cabinet so the ends are about a half inch apart. Fasten each wire of a 300 ohm twin lead to each aluminum panel using brass wood screws. The other end of the wire goes to the FM input. I've seen some with a small coil of wire between the panels. I don't design antennae but it's probably to modify the electrical length of the dipole.

[HarryWeatherford]

WOW! That is really great information! The picture of the actual Cabinet Dipole is really helpful ( I think 28" is half wavelength for the nominal freq). I have just spent the past day tracing connections and components. I have designated Terminal Lug numbers and on the prints - I'm having to label every connection, just so I don't miss anything. The guy that worked on this unit before really did some changes. He added two terminal lug strips and rerouted and added a number of components. One strip went to an RC circuit hooked in where the ground should be on Z301 - so it did not have a true chassis ground on the secondary winding. I have no idea what he was doing. Another 0.01 uF cap, 1000V was added but he ran both ends of the cap to chassis ground (???). I think there was noise and he tried to design a filter on the 2nd IF Amp. It has been a painful task of redrawing component layouts and then tracing them point by point on the actual schematics. It is fun but very challenging. On a separate note - I just finished working on a 46-1226 ( my hobby). I had poor reception on SW (bad tuning cap - replaced) and there was a lot of noise on AM. I made my own tube extender (breakout box) for the 7AF7 to access tube waveforms. I took many scope pictures and used ChatGPT to create me a troubleshooting document. It clearly shows noise, that ended up being poor connections on the IF Amps. That AI really helped a lot to build the document (30 pages) Should I create another chat to post that? It may be helpful for someone else.

[HarryWeatherford]

jrblasde: Would you share your KiCAD schematic? I need a way to document all of the connection points (terminal lugs) and wire colors so I can fully reconstruct this unit - and figure out what "extra" components added should be removed. Right now, I'm checking the schematic and reconstructing a component layout. Thanks - in advance

[HarryWeatherford]

What a battle! The person working on this unit before, tried all kinds of 'tricks'. I found two extra lug strips for added components - stripped all that stuff out. Traced out the entire circuit and found missing connections to C305 and the connection between C305 to R304. Found an "extra" connection made to R300. R300 was open (severe overheating) - probably from that added connection. The FM was not working. After replacing the open R300 and restoring the proper wiring - FM now works. I've also had to change a Loctal socket. I noticed on both IF Amps, pin 3 had issues (??). AM Alignment is done. Something that surprised me was, for some reason, I thought the pushbuttons were for FM stations. I also had to return a number of open connections to the pushbuttons. The pushbuttons are actually for AM stations - makes sense now considering that era. At first I thought I had bleed over and then I realized that it was for AM stations. I still need to do a full FM alignment. I did the first steps of alignment to 9.1 MHz. My generator only goes to 20 MHz, so I have one on order. I'm doing this to give this to my son. Next I need to do some touch-up work on the cabinet (I am not a carpenter or cabinet maker).

[Arran]

I don't think that I have seen presets for FM stations on any early FM set, those pushbuttons are basically switches, and they switch into the AM broadcast front end. I think that I may have seen a high end Grundig that had presets for one or two FM stations, but that was an electromechanical system with a motor drive, the party selling it thought the set was worth money given the dumb fleabay prices, and once I noticed a tweeter being missing I completely lost interest in even making an offer. The high end Saba sets also had motor drive but I think they worked like a shutter dial brand Z set with a lever for forward, and reverse, up and down the dial rather then actual presets.
Yes, the weekend servicemen were a menace, too many would pick up a Popular Science/Mechanics/Mechanix Illustrated magazine and really make a mess. These days it's half baked online stuff. A lot of people don't understand that wiring colour codes actually mean something, it's not because the guys making the set thought it looked pretty.
Regards
Arran

[HarryWeatherford]

I dialed in the small chokes to tune in a station (for the small LC circuits), then I set the band switch to AM and I picked up the same strong station that I did for the pushbuttons. After checking the frequencies, yes they are for AM. For some reason, I thought the buttons were for FM. I learn something every day. I imagine I'm just use to seeing FM pushbuttons these days. I didn't really think about that era - AM was probably more common. Yes - "weekend servicemen", I basically had to trace and reverse engineer everything , replacing missing connections, removing "extra" components and removing interconnections that should not be there. Fun but frustrating at the same time.
Regards,
Harry