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 Post subject: Re: Philco 41-300
PostPosted: Mar Sun 22, 2020 4:38 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 220
Location: Portland, Oregon USA
Ah hah! I played with the built in antenna a bit, and ended up disconnecting the Internal AM antenna “hot” ( terminal 2) altogether. I can now get very faint sw now. Still mostly static. I may try the new tubes next unless others have suggestions.

There’s a guy on the Oregon coast who has done some work for me in the past, I see tube tester repairs in his future lol ( too much for me to do it all plus he knows a lot more!)


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 Post subject: Re: Philco 41-300
PostPosted: Mar Sun 22, 2020 11:41 pm 
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Posts: 34875
Location: SoCal, 91387
As I had previously suggested, try replacing the two XXL/7A4's, and the two 7B7's, with NOS (new old stock) tubes. You don't need a tube tester to do that.

AFA the "squealing", lets use the proper term, which is "oscillation". If you have a signal generator, set it to the IF frequency, usually 455 Kc, and go over the IF's to get 'em right on track. If that doesn't do the trick, then put it on the AM station that oscillates, and very gingerly adjust a core to just below when it breaks into oscillation. When you get the new tubes, you'll want to again touch up the IF's.

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 Post subject: Re: Philco 41-300
PostPosted: Mar Mon 23, 2020 2:26 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 220
Location: Portland, Oregon USA
Well I'll wait then before bothering with anything else - i've ordered new tubes (sans 37s and 42s which don't seem to be related to the IF and RF stages) for a mint. Hopefully that fixes my problems! thanks for the help! -Christopher


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 Post subject: Re: Philco 41-300
PostPosted: Apr Sat 04, 2020 3:26 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 220
Location: Portland, Oregon USA
Update: the new tubes didn’t really make a difference. Terry from the forum helped me to align the set correctly (thanks Terry!) and I just strung up a temporary 14 gauge wire that’s about 50 feet to see what it does. I get stations!! My neighbor also said he’s ok with a wire going to a tree in his yard to get some better length and height. My current question has to do with playing with the antenna connections on the back of the chassis. I have an aerial antenna and I also installed a small grounding rod, and I have connected the antenna to the antenna terminal #4 on the chassis and I have connected the ground rod to the ground terminal #3. This is resulted in loud stations coming in. Success.

However on At least one band, if I disconnect the built in antenna and it’s ground wire to the terminals I get bleeding of AM stations on my shortwave. Why is this?? Aka terminal 3 has to stay connected to the built In antenna ground - the grounding rod connection doesn’t make a difference in stopping this bleed over whether it also is connected or not. What gives?


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 Post subject: Re: Philco 41-300
PostPosted: Apr Sat 04, 2020 12:21 pm 
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Location: Annapolis, MD
In principle, changing the antenna connections can upset the tuning of the front end. That said, this set has some unique features in the antenna setup, and I'm not entirely sure how it all works. For example, there are 2 external antenna terminals--does anyone know what kind of external antenna was envisioned? All I can think of is balanced dipole, but i've never seen a consumer set designed for that.
Given that this is a Philco, someone here can probably produce an owner's manual

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"Even if you don't understand Ohm's Law, you are still required to obey it."


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 Post subject: Re: Philco 41-300
PostPosted: Apr Sat 04, 2020 3:28 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 220
Location: Portland, Oregon USA
I have the original owners manual, or at least a brief pamphlet how to use the radio but all it mentions is to go to your local Philco dealer for the external antenna attachment. I can take another peak to make sure I didn’t miss anything.


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 Post subject: Re: Philco 41-300
PostPosted: Apr Sat 04, 2020 4:50 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 220
Location: Portland, Oregon USA
I took another look at the schematic and the owners manual, and neither indicate you use one antenna or the other, seems like you would just use the external in addition to the internal. One other note, is that I seem to just have a lot of background noise. I noticed that by merely connecting to the terminal strip on the back of the site I may be in advertently miss using the radio the way it was designed. It looks like one terminal of the external antenna connects midway to the aerial transformer in the set. Also the owners manual uses the term “aerial” and does provide for a set up similar to the internal loop- two inputs plus a ground. Does all this suggest it was intended we used with an external loop?


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 Post subject: Re: Philco 41-300
PostPosted: Apr Sat 04, 2020 5:21 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 6372
Location: Near Brandon, Iowa
pixellany wrote:
In principle, changing the antenna connections can upset the tuning of the front end. That said, this set has some unique features in the antenna setup, and I'm not entirely sure how it all works. For example, there are 2 external antenna terminals--does anyone know what kind of external antenna was envisioned? All I can think of is balanced dipole, but i've never seen a consumer set designed for that.
Given that this is a Philco, someone here can probably produce an owner's manual


This Philco was set up to be compatible with a "doublet" antenna, which is a semi-obsolete name for a "balanced-feed dipole". Many household radios in the late 30s-early 40s were designed for use with a doublet: Zenith and Philco were the leaders pushing this alternative but there were smaller-name makers who offered the option as well. Philco and Zenith (especially Philco) offered doublet antenna kits as extra-cost accessories which were essentially "plug and play" electrically with their respective radios (although physical installation of the antenna was probably quite the chore).

BTW, the internal loop antenna used by Philco isn't a direct part of the tuning circuit. The set has an antenna transformer and the tuning cap resonates its secondary winding. So the Philco built-in loop for this model year isn't as highly efficient (read: sensitive) as later sets in which the antenna loop was an integral part of the LC tuning circuit. With these sets an external longwire antenna (or doublet, if desired) will provide superior performance compared with that provided by just the built-in loop.


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 Post subject: Re: Philco 41-300
PostPosted: Apr Sat 04, 2020 9:53 pm 
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Location: SoCal, 91387
I would suggest experimenting with all the options, and using that which works best. I'm sure an outdoor long wire will pull in the best reception, although the noise floor will also be higher.

You might try experimenting with orienting the outdoor wire in different directions, i.e., north/south or east/west, to see if one or the other gives better reception.

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 Post subject: Re: Philco 41-300
PostPosted: Apr Sun 05, 2020 6:14 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 220
Location: Portland, Oregon USA
I’m investigating the doublet antenna and will likely try it out over the next week after ordering some parts online. Meanwhile a resource indicted that doublets benefit from a tuner before the radio to match impedance. That got me thinking.....I bought an RCA tv antenna tuner/ amplifier “thing” in high school not really knowing what the heck it was or if it’s still useful. It has an off, vhf, and uhf setting and a dial to span the old channels (3-83 or whatever it’s supposed to be). I haven’t taken in a part or bothered with it in 15- 20 years ( even was thinking about just junking it as I have too much stuff I don’t need, don’t know how to use, or have no way to really use it these days). I collected anything old and free/ cheap as a kid haha.

Anyway, this has connections for 300 ohm wire in the back for a tv antenna hookup. Any chance this could somehow be used to complement my new shortwave antenna and make it tunable? It has tubes and a transformer so it must amplify signals but other than that I don’t really know what it was for, but it seems like it could be used to amplify radio signals too. It would be nifty to use this as the tuner and also avoid having to gut an old radio for its actual tuner mechanism.


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 Post subject: Re: Philco 41-300
PostPosted: Apr Sun 05, 2020 8:20 am 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 6372
Location: Near Brandon, Iowa
It's no trick to fabricate a doublet to match the impedance of the radio. Once this is done no further impedance-related mods are needed.

What is a bit tricky about a doublet is that it is both frequency (wavelength) sensitive and directional. So, having an effective doublet installation calls for some advanced planning vis a vis the primary band that it is most desired to receive; and knowledge of the geographic orientation of broadcast stations of interest with respect to your antenna installation.

A doublet can be operated as a straight longwire antenna. Doing so would tend to offset some of the above characteristics of the doublet, perhaps making a greater number of stations in more directions available, but at lower signal levels presented to the receiver. The changeover can be done at the antenna terminal board in the rear of the chassis.

I doubt that your TV antenna amp will be of much use: it is designed to amplify at a much higher frequency range than is used by shortwave radio... and probably won't provide any signal gain at the lower radio frequencies. Besides, the 41-300 already has an RF gain stage between the antenna port and the converter tube.


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 Post subject: Re: Philco 41-300
PostPosted: Apr Thu 09, 2020 2:04 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 220
Location: Portland, Oregon USA
So I was able to find a hand drawn schematic for the aerial coupler the Philco made in 1941 to go with this set. How ever Im overthinking the angle of perspective on this - I need help knowing if the inductor connects to the midpoint of aerial transformer or if the 6pf cap does. The rest will fall or place- Resistor to ground etc. also my 6 pf cap has yet to arrive so I don’t have this set up perfectly yet but when I connect the inductor to terminal 4 of the built in my #37 tubes start emitting a high pitched ring/ screech. I’m sure if I were 60/70/80 I probably couldn’t even hear it, it’s that high pitched. once I disconnect the exterior aerial with inductor they stopped making this noise after 3-5 seconds. What’s going on?


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