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 Post subject: Re: Philco 41-300
PostPosted: Mar Mon 09, 2020 7:22 am 
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Location: SoCal, 91387
I would suggest trying the set upstairs, on ground level or if you have a second floor, up there, if all you are using is the internal antenna.

AFA the tubes, they are not specific to any particular band, and it's not imperative that you replace them, unless this set is going to be used often. Using new ones will simply add to the sets sensitivity.

What do you mean by the term, "blurry", BTW? Fading in and out, coming in with a high noise floor, what?

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 Post subject: Re: Philco 41-300
PostPosted: Mar Thu 12, 2020 3:34 am 
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Location: Portland, Oregon 97027 USA
Dumb question but I don’t have a VTVM but I have a digital one. Can I use a digital one to align? I don’t really see why not, it should still provide a reading that’s higher or lower right? Also it says to connect the negative terminal to any point on the AVC circuit but I have no idea how to tell what part is a part of the AVC. One of the pins of 7c6?

In response to the above question, the few stations I get don’t fade in or out, but it’s just sort of garbled and not clear. However as I said previously broadcast comes in crystal clear and very well. I was getting more in tonight (still in the basement though as the sets quite large to drag upstairs until I get these other issues figured out).


Last edited by delco1946 on Mar Thu 12, 2020 4:08 am, edited 2 times in total.

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 Post subject: Re: Philco 41-300
PostPosted: Mar Thu 12, 2020 3:42 am 
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Posts: 270
Location: Portland, Oregon 97027 USA
Also my signal generator says to disable a radios avc circuit to avoid the output being “sufficiently attenuated” but the radio schematics don’t mention anything about this.....What do I do?


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 Post subject: Re: Philco 41-300
PostPosted: Mar Thu 12, 2020 4:04 am 
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Location: Portland, Oregon 97027 USA
And I still have a low level hum which is the bane of my existence. What can I do to get rid of this? As I stated previously I replaced all 3 electrolytic capacitors and all paper caps. The hum doesn’t change with the volume, so does that suggest it’s from a certain stage?


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 Post subject: Re: Philco 41-300
PostPosted: Mar Thu 12, 2020 8:22 am 
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Location: SoCal, 91387
delco1946 wrote:
Dumb question but I don’t have a VTVM but I have a digital one. Can I use a digital one to align? I don’t really see why not, it should still provide a reading that’s higher or lower right? Also it says to connect the negative terminal to any point on the AVC circuit but I have no idea how to tell what part is a part of the AVC. One of the pins of 7c6?

In response to the above question, the few stations I get don’t fade in or out, but it’s just sort of garbled and not clear. However as I said previously broadcast comes in crystal clear and very well. I was getting more in tonight (still in the basement though as the sets quite large to drag upstairs until I get these other issues figured out).

The only dumb question is the one not asked.

A VTVM won't load the circuit down, but it's main advantage is that it has an analog needle pointer so that it's easy to peak the signal level. With a DMM, you have to rely on trying to hit the highest number as they are jumping around. I only align by ear. It's easier than fiddling with a meter, and gets me close enough to peak position.

AFA the Automatic Volume Control, or AVC, it kicks in when there is a strong local signal, to equalize the volume. The best way to deal with it is to simply adjust your generator's output to as low a signal level as possible that can still be heard. That way the AVC shouldn't be triggered.

delco1946 wrote:
And I still have a low level hum which is the bane of my existence. What can I do to get rid of this? As I stated previously I replaced all 3 electrolytic capacitors and all paper caps. The hum doesn’t change with the volume, so does that suggest it’s from a certain stage?

It may not have been mentioned to you before you did surgery, but the best course to take is to follow the same component placement and wiring paths that the factory used, in order to defeat hum. If you took a picture of the underbelly of the chassis before doing anything, compare it to what you have now, and move wiring and components to their original places.
If not, with the radio on it's side so you can get into the underside, turn it on, put one hand in your lap, and use a non-metallic probe, such as a nylon alignment tool, wood pencil, wood or plastic chopstick, crochet needle, etc., and probe. Gently move wires and components to see if you can affect the hum.

I had a situation one time where I had recapped a Sonora AM/FM set, and managed to introduce hum, where there had been none before, so I knew it was something I had caused. I probed, and found that in moving a mica capacitor that was soldered across an IF can outward just a tiny bit, solved the issue.

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 Post subject: Re: Philco 41-300
PostPosted: Mar Thu 12, 2020 10:17 pm 
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Location: Portland, Oregon 97027 USA
Thanks for the feedback! Also, i just realized that i replaced all traditional paper caps, but I did not replace the brown/black box that should have 2 caps in it that connect the power cord to the chassis. What is their purpose, and can i replace them with normal mylar/polypropylene caps?

This seems rather dangerous..... Are these what i've heard called safety caps and would this impact my hum at all?


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 Post subject: Re: Philco 41-300
PostPosted: Mar Fri 13, 2020 12:48 am 
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First of all, it's only dangerous when it's plugged into AC power, so always make sure you see the AC plug out of the wall socket before doing any underside work.

Yes, the line cord safety caps should definitely be replaced, and they could be the source of the hum, so that may be your next step. No, you do not use DC capacitors.

Sal sells X2 and Y2 AC safety caps. IDK if it matters which type you use, so maybe someone smarter than me on the board will offer advice on that, or you could message and ask him. They're expensive, 20 and 25 cents each. :wink:

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 Post subject: Re: Philco 41-300
PostPosted: Mar Fri 13, 2020 4:26 am 
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Location: St. Louis, MO
delco1946 wrote:
Thanks for the feedback! Also, i just realized that i replaced all traditional paper caps, but I did not replace the brown/black box that should have 2 caps in it that connect the power cord to the chassis. What is their purpose, and can i replace them with normal mylar/polypropylene caps?

This seems rather dangerous..... Are these what i've heard called safety caps and would this impact my hum at all?


The purpose of the original caps were line filters. Like their name, they filter out noise coming from the line, AKA the power cord.

Safety caps are something different. A safety cap is a special kind of cap. They're designed to fail open if they do fail. That's very useful for capacitors that run line-to-line or line-to-ground... like line filters. When the old capacitors fail, they usually fail closed. If a cap that runs line to line or ground failed closed, it could shock the next person to touch the metal case or even start a fire. X safety caps are for line-to-line and Y safety caps are for line-to-ground. Safety caps that are rated for both uses will be marked as such. Safety caps come in ceramic and film types. Films can do higher farads.

At the end of the day, a safety cap is still just a cap. You can use them for other purposes too if you have nothing else on hand.


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 Post subject: Re: Philco 41-300
PostPosted: Mar Sat 21, 2020 8:18 pm 
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Location: Portland, Oregon 97027 USA
Success wrt the hum. I just installed two new safety caps and my hum is gone. I’m now attempting an alignment but I’m wonder if there is a standard a and b for aligning, some of my IF transformers have an A and a B , and the schematic specifies an order. Problem is I don’t see anywhere on the schematic that tells me which adjustment is a or b? How do you know which is which??


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 Post subject: Re: Philco 41-300
PostPosted: Mar Sat 21, 2020 9:39 pm 
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Location: Portland, Oregon 97027 USA
I just went for it using an iterative process. Didn’t seem to make much difference as it seemed pretty well peaked. This is my first time using my signal generator and none of my manuals make it very clear , when should I be using AF versus rf? My radio picks up both loud and clear.


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 Post subject: Re: Philco 41-300
PostPosted: Mar Sat 21, 2020 10:00 pm 
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Location: St. Louis, MO
delco1946 wrote:
Success wrt the hum. I just installed two new safety caps and my hum is gone. I’m now attempting an alignment but I’m wonder if there is a standard a and b for aligning, some of my IF transformers have an A and a B , and the schematic specifies an order. Problem is I don’t see anywhere on the schematic that tells me which adjustment is a or b? How do you know which is which??


I ran into that issue on the Rider instructions for a 40-160. It's there, you just have to look hard. Right center:
https://www.tubesandmore.com/sites/defa ... pg12-4.png

An iterative process works too. You'll usually want to go back and double check all 5 to make sure each one is peaked.


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 Post subject: Re: Philco 41-300
PostPosted: Mar Sun 22, 2020 1:43 am 
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Location: Portland, Oregon 97027 USA
Well I have that same diagram but it still doesn’t point to anything. It basically is saying that 36a and 36b are in part 36. I already had that haha. Either I *think* I alighted it correctly. It wasn’t really out of alignment. And I still don’t really receive and shortwave or police. I get the Denver 10mc time station wwv, but it’s still buzzy / lots of static like a weak distant station. It’s upstairs now too. Am comes in like a champ. What do I look at now? Also when I touch the xxl tube that is second in from the outer edge it really negative affects the sound. Is this normal? I don’t have any tube testers I trust to be accurate, but would a bad tube be to blame? Just seems odd that both xxl tubes are used by all stations and that they would behave so differently on different bands.


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 Post subject: Re: Philco 41-300
PostPosted: Mar Sun 22, 2020 1:47 am 
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Location: Portland, Oregon 97027 USA
Went back to earlier posts and noticed recommendation to get new xxls and 7b7s. Mines may be original or are at least Philco brand still. Of I think of this after the sale ends yesterday :(


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 Post subject: Re: Philco 41-300
PostPosted: Mar Sun 22, 2020 1:51 am 
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Location: St. Louis, MO
You'll never get police band on those old frequencies. The spectrum was changed since that face plate was printed. You may get AM expanded band there now however.

It could be a bad tube. It could be a bad socket as well if touching the tube affects it.


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 Post subject: Re: Philco 41-300
PostPosted: Mar Sun 22, 2020 4:12 am 
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If you are not using at least a 10 foot length of wire as an external antenna, your S/W reception is gonna be mighty limited. I would suggest trying that, before purchasing any tubes.

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 Post subject: Re: Philco 41-300
PostPosted: Mar Sun 22, 2020 5:06 am 
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Location: Portland, Oregon 97027 USA
Also, when I made a loop and used that with the signal generator, all bands picked that up rather well, so doesn’t that suggest all bands are amplifying signals when present? As for an external antenna, please walk me thru this. So the external connection has one ground and two other connections ( what do you call these? Hot antenna, non ground???) So do I need a loop to connect to one of those , and then connect to the ground - like what the internal antenna does? Do I need to connect to both? Which one? Does an antenna even need to be a loop?


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 Post subject: Re: Philco 41-300
PostPosted: Mar Sun 22, 2020 8:34 am 
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Sorry delco old boy, but since you've been here since 1969, thought you knew all that, LOL. OK first, since you were able to get WWV, we know that the SW band is functional.

AFA the antenna, simply get a length of wire, ideally at least 10 feet or so, lay it out on the floor straight, and connect it to one of the three terminals. Tune the radio to pickup WWV, then try the wire on each of the other terminals, and leave it on the one that picks up the station the best. You only need one wire antenna connection. You can also connect a ground wire in order to see if that helps. Initially, you can simply connect a lead to the keeper screw on an AC wall outlet plate.

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 Post subject: Re: Philco 41-300
PostPosted: Mar Sun 22, 2020 12:06 pm 
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I've been doing this stuff for 60 years and I still don't understand antennas......but that never seems to stop me from answering questions...;)
Put a piece of wire in the path of an E-M wave and a current will be generated. Depending on the configuration, that current can come from electrostatic or electromagnetic effects---or both. Regardless of the messy details, the current has to flow in a closed circuit in order to do anything useful---such as causing your radio to make some kind of sound.

In the old-fashioned sets, a current would flow from antenna to ground through a coil in the radio. This coil would then be coupled in some way to the first active circuit---eg the grid of a tube. The most common configuration was an "antenna transformer" with a tuned secondary. Current flow in the primary causes a voltage on the secondary---which is highest when the secondary circuit is at resonance.

Does the traditional configuration require a "ground"? Maybe......the current I described above has to have a closed path. If the set is operated from the building power system, then the pathway is there as soon as the set is plugged in. It just might not be the BEST pathway.

Some years ago, a member posted that he had made a really good antenna by laying a bunch of wire on his basement floor---covered with a carpet. NO---he had made a really good GROUND. His antenna was now the building power system.

All that matters is that you get the right currents going through that first coil.....One day, someone realized that that coil could also be the antenna

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 Post subject: Re: Philco 41-300
PostPosted: Mar Sun 22, 2020 3:13 pm 
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Lol sorry about that. I discovered this site when I was in 8th grade or so. My very first email sent was about asbestos in old radios - sent from the library while waiting for my parents to pick me up after school ( my mom was getting very nervous about my new hobby lol ). I learned some in high school but never did get real diagnostic equipment. Then went to college and all this went on hold. Finally have a house a job etc and a bit more time to clean out a section of my basement to turn into a radio workbench. But you forget a lot in 15 years, and I’ve devolved into one who just replaces all caps without really remembering the “why”.

And I stayed up late last night reading my schematic. This set definitely has the antenna transformers which sounds like a fascinating concept. It’s one of the older sets I’ve ever worked on so this has been an education. I’ve been trying to examine shared band components as in my mind that what would be the problem since AM is working. However Each of my bands seems to use a lot of band -specific parts ( such as antenna transformers) so I’ll start with an antenna!


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 Post subject: Re: Philco 41-300
PostPosted: Mar Sun 22, 2020 4:13 pm 
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Location: Portland, Oregon 97027 USA
Well I just connected an antenna , 20 feet or so. It functions better not being connected to the antenna ground. It didn’t make much difference, but the wwv comes in a bit better buttttttt it was starting to squeal on it and it also was squealing on another very strong AM station at the lower frequency. I thought I read somewhere that that means that there’s a problem with the oscillation or maybe I didn’t align it well?

Next idea? :lol:


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