Philco 41-608 Volume and tone control function ++ - Printable Version
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Philco 41-608 Volume and tone control function ++ - Harlan - 01-03-2010
Hi,
In restoring this radio, I had to replace both the volume and tone (Bass) controls. The tone control calls for a 6 meg
but was able to get only a 4 meg. The volume control is a 2 meg with a 1 meg tap which is the same as original.
Since the radio didn't work hardly at all before, I don't really have a comparison available but was wondering if what
I am noticing is normal.
The volume control seems to have an area around the middle of it's travel that makes the tone change to a much
more treble sound... higher pitches, and then back to a more normal tone as it reaches maximum.
Also the tone control starts out with the sound being a bit flat... mostly midrange tones, then increase to a very
prominent treble sound... high pitches, and then finishes off with more normal sound with a bit more bass at max.
These seems a little erratic in that the volume control seems to also be changing the tone and the tone control is
not a very linear change but rather a flat to treble to bass action.
Is this typical or what is anyone's thoughts on this behavior?
When I reach the more bassy end of the tone control, it often makes the audio very muffled and probably distorted.
The speaker seems in pretty good shape. There is no voice coil rub against the core by gently and evenly depressing
the outer edges of the cone. Maybe it is still the speaker or possibly the audio outputs?
A couple more points to ask about ... when finding a distant station that is near the extreme low end of the
AM band, the radio has a varying howl / whistle background sound with the station. So you have to very carefully
try to minimize it or chose the "interference" you can tolerate, by very slightly moving the selector knob.
Question about the "square box" antenna structure that is inside and around the record player. It will rotate
a few degrees inside the limits of the cabinet but I hear little or no change in reception. Wondering what the idea of
this was since there seems to be little or no value (that I'm aware of anyway) and how was one supposed to access
or manipulate this? ... Just by reaching in thru the record player area and getting a hold of it and moving it?
Thanks again for any help,
Harlan
Re: Philco 41-608 Volume and tone control function ++ - Ron Ramirez - 01-07-2010
Hi Harlan
Question: Why did you replace the volume and tone controls? Did you try cleaning them first? Just curious.
I have noticed this same phenomenon in some Philcos with this tone control circuit. The first thing I suggest is that you recheck your wiring. A miswired volume and/or tone control will cause the symptoms you describe. I've had it happen to me before.
Regarding the howl/squealing, recheck your alignment. Check components around the mixer, oscillator and IF circuits. Are the resistors within 20% tolerance? How about those mica caps? Could be leaky?
And on that loop antenna. No, it isn't easy to move, is it? Personally, I reach around in back to move the loop when needed. I think Philco intended for the set owners to find a good spot for average reception and leave the loop there. Of course, they did have that accessory add-on to add an external antenna if needed. I have one of those around here somewhere...it has been temporarily lost in my recent move...I've had some requests to draw a schematic for it, I'll try to honor those requests if I ever find the thing again.
Re: Philco 41-608 Volume and tone control function ++ - Harlan - 01-07-2010
Hi Ron,
Thanks so much for your time and valuable input. I really am trying to restore this unit for a "customer"
and when I got it, it had been previously worked on a few years ago by someone not really knowledgeable but rather
a "tinkerer" (not that I'm a whiz). I don't remember which right now, but he had "cobbed" in a different
control for the volume I believe. It was way off in value and didn't have a "tap" like the original so
that wire was left hanging. Also the tone control, an original, was open... infinite resistance between
ends. (Even opened up the pot and found a cracked carbon track so not much to do to salvage that).
Well I have rechecked my wiring, replaced a couple caps and resistors. I only had ceramic caps on hand
for item 58 (100uufd) and item 56 (.002ufd) but wouldn't think that would affect the sound. I will
check the wiring once again tho to be sure. It's certainly tolerable cuz once you set it where you like it,
it seems fine but it's just that it doesn't seem quite normal to operate that way...guess I get too
fussy about some things and not enough about others, ha.
I will have to do some rechecking on the "front end" again for the howl/squeal problem. I also notice
that our only local AM station which is at 1460 seems to want to come in as an "image" (???) on the
very low end of the dial as well. I don't really have a generator anymore so can't do a proper alignment
so haven't really done much with it other than rock a trimmer back a forth a fraction of a turn and
then leave it where it was.
Sorry, I haven't checked for a response on my other inquiries yet and for making this so lengthy but
would you mind (if you haven't) looking at my post with photos about the "stringing" of the "band"
selector with moving lamp indicator to see if you have a hunch there?
The "Beam of Light" record player is in this unit but as mentioned elswhere, someone has robbed the
transformer that was fastened to the inside of the cabinet (probably the "tinkerer") .
Any suggestions who to check with that may have that item available?
The schematic does't make it clear that there is such an item... just
shows a "pickup".... oh... I see it now... it is the item 54 on the diagram. Guess I had thought that
was some small coil inside the radio I just hadn't tracked down. So... will need that item. Do you know,
was that for some impedence matching or what function did it serve?
Will close it up here now but many thanks for your responses and your invaluable experience as well
as your valuable time. We all have only so many hours in a day and you are appreciated!
Best regards,
Harlan