Antique Radio with Electromagnet on speaker

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I got an old 1930s Crosley AM radio. It needs to be recapped and a few
other things, such as a dial string and new power cord. Anyhow, after
chopping off the bad power cord, I applied a temporary cord and the
radio does get sound and radio stations. (Along with the hum from the
weak filter caps).  

This radio has a beautiful old wooden cabinet, so I am going to restore
it completely.  

Anyhow, someone replaced the old electromagnet (Field coil) speaker with
a permanent magnet speaker. But what they did is sort of odd. I know
that speaker coil served as a filter choke, in the power supply, on
those old radios. What they did, was saw off the rear of the old
speaker, and mount it to the chassis, with that magnet loosly sitting on
top of the sawed off rear portion of the old speaker.  

What I now have, is this large magnet sitting next to the audio output
tube, and very close to the power transformer as well. That magnet is
quite powerful, in fact I magnetized a screwdriver with it.  

My question is whether that magnetism is going to affect that tube, as
well as interfere with the power transformer's function?  

If this is a problem, how to I determine what size filter choke to buy
to replace it? (Or isn't that real critical)?
If it's not going to cause any problems, I may likely just leave it as
it is, except to apply some sort of adhesive to prevent that magnet from
falling off the sawed off steel piece. Because as it sits now, if I set
the radio on edge, that magnet will fall off and could smash tubes in
the process. I have never seen this sort of thing done.... Very strange!

By the way, the audio output transformer appears to be glued on to the
speaker frame, but it is tight, so I am going to just leave it.



Re: Antique Radio with Electromagnet on speaker
On 2018/12/18 3:21 PM, snipped-for-privacy@myshop.com wrote:
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The field coil will not affect any tubes (in your type of usage) unless  
it falls on them...so make sure it is secure and that it doesn't get hot  
enough to heat up the wood cabinet.

John :-#)#

--  
(Please post followups or tech inquiries to the USENET newsgroup)
                      John's Jukes Ltd.
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Re: Antique Radio with Electromagnet on speaker
On Tuesday, December 18, 2018 at 6:21:29 PM UTC-5, snipped-for-privacy@myshop.com wrote:
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A few things:

a) As this is a 1930s radio, be careful not to add too much additional capa
citance when replacing the filters as you do not want to raise the B+ beyon
d specified levels. This is hard enough in any case as it is likely that th
e line voltage today is higher than it was when the radio was new. You coul
d add a bucking transformer on an outside receptacle - you want to be somew
here around 115 V or so - or you could run everything off a Variac, again i
f your wallplate voltage is over 120 VAC.  

b) An outboard choke would be ideal. "Back in the day" those chokes would b
e anywhere from about 1 H to about 5 H, and rated from about 20 ma to about
 60 ma, at a B+ of about 350 VDC or so. Pretty much as anything is better t
han nothing, as long as your replacement choke will handle the current (dep
ends on the output tubes), even a lower-value choke will help. One-of-many  
links is here for one-of-many chokes that will handle what you have, and th
en some, but is readily available:

http://www.classictone.net/40-18003.html It may be mounted anywhere that
 is convenient and safe.  

c) Stray magnetism will not affect any part of the radio. Placement of said
 parts should be a matter of convenience and safety.  

d) If it is your intention to retain the old field-coil for its value as a  
choke, I would strongly suggest that you replace the entire speaker with a  
(new/different) unit, and remove the stray coil. It carries the entire B+ s
upply - a lethal voltage at lethal current levels - and it is neither secur
e as you describe it, nor designed for that sort of installation. If you ar
e going to retain the PM speaker, use an outboard choke properly mounted an
d secured. There is no shame in that, by the way. Just as there is no shame
 in putting modern oil in a vintage vehicle.  

Best of luck with it!

Peter Wieck
Melrose Park, PA

Re: Antique Radio with Electromagnet on speaker
On Wednesday, 19 December 2018 13:20:44 UTC, snipped-for-privacy@aol.com  wrote:
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e:

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pacitance when replacing the filters as you do not want to raise the B+ bey
ond specified levels. This is hard enough in any case as it is likely that  
the line voltage today is higher than it was when the radio was new. You co
uld add a bucking transformer on an outside receptacle - you want to be som
ewhere around 115 V or so - or you could run everything off a Variac, again
 if your wallplate voltage is over 120 VAC.  
Quoted text here. Click to load it
 be anywhere from about 1 H to about 5 H, and rated from about 20 ma to abo
ut 60 ma, at a B+ of about 350 VDC or so. Pretty much as anything is better
 than nothing, as long as your replacement choke will handle the current (d
epends on the output tubes), even a lower-value choke will help. One-of-man
y links is here for one-of-many chokes that will handle what you have, and  
then some, but is readily available:
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at is convenient and safe.  
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id parts should be a matter of convenience and safety.  
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a choke, I would strongly suggest that you replace the entire speaker with  
a (new/different) unit, and remove the stray coil. It carries the entire B+
 supply - a lethal voltage at lethal current levels - and it is neither sec
ure as you describe it, nor designed for that sort of installation. If you  
are going to retain the PM speaker, use an outboard choke properly mounted  
and secured. There is no shame in that, by the way. Just as there is no sha
me in putting modern oil in a vintage vehicle.  
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Secure the choke, there's no reason to remove it. Replacing things without  
reason on prewar equipment is bad practice.

I don't know what you do/don't know. Valve rectifiers have tight max capaci
tance specs, radios put as much C on them as they can. Don't increase C or  
it will overload the valve. There was good reason in the choke setup rather
 than just using a bigger cap.


NT

Re: Antique Radio with Electromagnet on speaker
On Wednesday, December 19, 2018 at 10:45:45 AM UTC-5, snipped-for-privacy@gmail.com wro
te:
 There was good reason in the choke setup rather than just using a bigger c
ap.

Some historical perspective from this side of the pond, where 300,000,000 "
valve" radios were manufactured from about 1913 to about 1963.  

a) Low-cost, permanent-magnet speakers did not become common or reliable un
til well into the 1940s, and much of that was driven by war-time research.  
Sure, small speakers for portable radios were common, but larger speakers d
esigned for severals-of-watts of power, not so much. And big, honking speak
ers such as were on large consoles, even less so.  

b) Making the choke a (costly) necessity to provide a magnet for the speake
r. Not a convenience. And, with that in mind, many manufacturers then cut b
ack on the size of the transformers to save costs. Leading to the limitatio
ns on capacitance - which protects both the choke (limiting B+) and the tra
nsformer (current). Some AC/DC radios used half-wave rectifiers for their v
oltage-dropping properties.  

c) One may, pretty much, used as much capacitance as one wishes _AS LONG AS
_ the B+ remains withing spec. And this can be a close-run thing. Note that
 in the days of potted paper caps, some of the earlier consumer radio manuf
acturers such as Atwater-Kent were quite specific in their service literatu
re that capacitance values were NOT to be exceeded, again referring to B+ v
oltages, not rectifier or transformer overloads. And, as it happened, these
 radios tended to have very large chokes, weighing several pounds in copper
 alone.  

c) When repairing (vs. a museum-quality restoration), you have options not  
available to the OEM, as well as knowledge and materials unknown to them ba
ck when all this stuff was "New". What this means is that you may, without  
sin, make upgrades or make repairs based on present-day technology to repla
ce compromised elements of/within the original item. The only valid endorse
ment of what is or is not 'good practice' is whether the radio functions pr
operly, safely and without danger to its users into the foreseeable future.
 That it uses as many as is safe and practical of the original elements is  
a good thing. But, if it does that by means of compromising its safe and co
ntinuing use, to that extent, it is a failure.  

There are sources for field-coil speakers. There are those that will rebuil
d existing field-coil speakers. If that level of restoration is your goal,  
go for it. Whatever else, enjoy it!  

Peter Wieck
Melrose Park, PA  

Re: Antique Radio with Electromagnet on speaker
On Wednesday, 19 December 2018 18:14:43 UTC, snipped-for-privacy@aol.com  wrote:
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 cap.
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 "valve" radios were manufactured from about 1913 to about 1963.  
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until well into the 1940s, and much of that was driven by war-time research
. Sure, small speakers for portable radios were common, but larger speakers
 designed for severals-of-watts of power, not so much. And big, honking spe
akers such as were on large consoles, even less so.  
Quoted text here. Click to load it
ker. Not a convenience. And, with that in mind, many manufacturers then cut
 back on the size of the transformers to save costs. Leading to the limitat
ions on capacitance - which protects both the choke (limiting B+) and the t
ransformer (current). Some AC/DC radios used half-wave rectifiers for their
 voltage-dropping properties.  
Quoted text here. Click to load it
AS_ the B+ remains withing spec. And this can be a close-run thing. Note th
at in the days of potted paper caps, some of the earlier consumer radio man
ufacturers such as Atwater-Kent were quite specific in their service litera
ture that capacitance values were NOT to be exceeded, again referring to B+
 voltages, not rectifier or transformer overloads. And, as it happened, the
se radios tended to have very large chokes, weighing several pounds in copp
er alone.  
Quoted text here. Click to load it
t available to the OEM, as well as knowledge and materials unknown to them  
back when all this stuff was "New". What this means is that you may, withou
t sin, make upgrades or make repairs based on present-day technology to rep
lace compromised elements of/within the original item. The only valid endor
sement of what is or is not 'good practice' is whether the radio functions  
properly, safely and without danger to its users into the foreseeable futur
e. That it uses as many as is safe and practical of the original elements i
s a good thing. But, if it does that by means of compromising its safe and  
continuing use, to that extent, it is a failure.  
Quoted text here. Click to load it
ild existing field-coil speakers. If that level of restoration is your goal
, go for it. Whatever else, enjoy it!  
Quoted text here. Click to load it


A couple of points to pick up on there. If you look at valve rectifiers, th
ey come with specs on max C. This should not be exceeded. There is good rea
son for that.

And no, it is not good practice to re-engineer antique radios without even  
having a reason. Not a bit. If you want modern junk there's plenty about, g
o buy it. Too much historic stuff is ruined & destroyed by people with insu
fficient clue what they're doing.


NT

Re: Antique Radio with Electromagnet on speaker
On Wednesday, 19 December 2018 19:38:41 UTC, tabby  wrote:
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er cap.
00 "valve" radios were manufactured from about 1913 to about 1963.  
Quoted text here. Click to load it
e until well into the 1940s, and much of that was driven by war-time resear
ch. Sure, small speakers for portable radios were common, but larger speake
rs designed for severals-of-watts of power, not so much. And big, honking s
peakers such as were on large consoles, even less so.  
Quoted text here. Click to load it
eaker. Not a convenience. And, with that in mind, many manufacturers then c
ut back on the size of the transformers to save costs. Leading to the limit
ations on capacitance - which protects both the choke (limiting B+) and the
 transformer (current). Some AC/DC radios used half-wave rectifiers for the
ir voltage-dropping properties.  
Quoted text here. Click to load it
G AS_ the B+ remains withing spec. And this can be a close-run thing. Note  
that in the days of potted paper caps, some of the earlier consumer radio m
anufacturers such as Atwater-Kent were quite specific in their service lite
rature that capacitance values were NOT to be exceeded, again referring to  
B+ voltages, not rectifier or transformer overloads. And, as it happened, t
hese radios tended to have very large chokes, weighing several pounds in co
pper alone.  
Quoted text here. Click to load it
not available to the OEM, as well as knowledge and materials unknown to the
m back when all this stuff was "New". What this means is that you may, with
out sin, make upgrades or make repairs based on present-day technology to r
eplace compromised elements of/within the original item. The only valid end
orsement of what is or is not 'good practice' is whether the radio function
s properly, safely and without danger to its users into the foreseeable fut
ure. That it uses as many as is safe and practical of the original elements
 is a good thing. But, if it does that by means of compromising its safe an
d continuing use, to that extent, it is a failure.  
Quoted text here. Click to load it
build existing field-coil speakers. If that level of restoration is your go
al, go for it. Whatever else, enjoy it!  
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they come with specs on max C. This should not be exceeded. There is good r
eason for that.
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n having a reason. Not a bit. If you want modern junk there's plenty about,
 go buy it. Too much historic stuff is ruined & destroyed by people with in
sufficient clue what they're doing.
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I've just realised it's you again. You'll never see sense so I won't bother
 continuing.


NT

Re: Antique Radio with Electromagnet on speaker
snipped-for-privacy@gmail.com says...
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Yes, the tube rectifiers do have a maximum filter capacitor value.  
Adding much more capacitance will not raise the voltage in most cases.  
It is the excessive current that is hard on the rectifier tube as the  
capacitor charges and discharges during each cycle.


Re: Antique Radio with Electromagnet on speaker
On Wednesday, 19 December 2018 23:09:37 UTC, Ralph Mowery  wrote:
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mean i is the same, but peak i is higher & conduction angle narrower.


NT

Re: Antique Radio with Electromagnet on speaker
On 2018/12/19 3:09 PM, Ralph Mowery wrote:
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An example - the 5U4GB (RCA) is recommended to have no more than 40UFD  
on the Input To Filter. The note on this value says:

"Higher values of capacitance than indicated may be used, but the  
effective plate-supply impedance may have to be increased to prevent  
exceeding the maximum value for peak plate current."

 From the RCA Receiving Tube Manual - RC-30 - 1975.

I have a nice assortment of tech books on tubes as we fix tube amps  
regularly for jukeboxes.

Hmm, tube amps...I wonder if we should install them in pinball  
games...that would be a hoot!

John :-#)#

--  
(Please post followups or tech inquiries to the USENET newsgroup)
                      John's Jukes Ltd.
We've slightly trimmed the long signature. Click to see the full one.
Re: Antique Radio with Electromagnet on speaker
On Thursday, 20 December 2018 01:20:57 UTC, John Robertson  wrote:
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My 1924 set has all of a few 2uF paper caps on the supply line. They cheated though - it's for dc mains. I've seen rather less than 40uF on some ac mains sets.


NT

Re: Antique Radio with Electromagnet on speaker
On Wednesday, December 19, 2018 at 6:09:37 PM UTC-5, Ralph Mowery wrote:

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Only in direct relationship to the actual load. Assume the cap is sized pre
cisely to the anticipated maximum load - then, theoretically, it should dis
charge 100% and recharge 100% on each cycle.

Assume that the cap is sized to 100% more than the anticipated load - then,
 theoretically, it will discharge to 50% and recharge to 100% on each cycle
.  

Also assuming that the power-supply is capable of delivering the full load  
+ some additional amount of current.  

Overloading the transformer will occur if the load increases due to the add
itional capacitance. If it remains the same, not so much.  

The analogy is a number of individual cells in parallel. The amount of curr
ent they can deliver increases. But a 5 watt lamp will remain a 5 watt lamp
, no matter what *could be* delivered. And that DC motor will not spin any  
faster if it is fed its design voltage and amps. What is a capacitor other  
than an ultra-fast battery? All sorts of (usually bad) things happen when t
he voltage increases, however. And that is why, by specific reference, the  
likes of Atwater Kent warned against excessive capacitance in their mains-d
riven radios - mostly with potted paper caps of 2-or-less uF.

Peter Wieck
Melrose Park, PA  


Re: Antique Radio with Electromagnet on speaker
snipped-for-privacy@gmail.com says...
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This is one of he dumbest statements I have ever heard about how a  
capacitor works in a power supply.  In the normal tube or simple diode  
supply the capacitor never discharges anywhere near 100 %

As a capacitor discharges to any percentage and then recharges, the  
ammount of capacitance determins how much peak current will be drawn  
from the transformer and through the rectifier.  That is what is hard on  
the rectifier tubes and why they sp;ecify a certain maximum capacitance.

Re: Antique Radio with Electromagnet on speaker
On Thursday, December 20, 2018 at 11:33:27 AM UTC-5, Ralph Mowery wrote:

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Let's go back to first principles.  

Back when AK designed their power-supply, they used 2uF paper caps. Which d
id discharge to nearly zero at each cycle. And, they designed "onward" acco
rdingly. And they warned specifically about increasing capacitance. And the
y used other means to clean AC out of the line, typically by way of a massi
ve choke.  

Not so much time later (about 4 years, in their case), they moved onto almo
st exclusively electrolytic caps for filtering, typically at about 10uF, wh
ereupon their field coils got much smaller (same size speaker) and they sto
pped warning about increased capacitance. In most cases, they still used th
e 4-pin 80 tube as their rectifier. Rated at about 10uF. Note that in the H
andbook, the 80 will accept much higher capacitance values "if voltage and  
current are controlled" - which is entirely the point.  

Now, taking what you state - a larger capacitor will draw a larger charge.  
True *upon first charge*. After which, it will cycle just as with any other
 cap based on downline draw. If the downline draw is not excessive, no mate
r the size of the capacitor, current through the transformer will not be ex
cessive - assuming voltage and current are stable.  

Now, moving into semi-modern times - one of the most popular hacks for the  
venerable Dynaco ST70 is to greatly increase capacitance - some times as mu
ch as 200%. The theory behind it is to increase peak response and reduce cl
ipping. That particular unit uses the 5AR4/GZ34 rectifier, nominally rated  
at 60uF,  Power-supplies using this rectifier using 4-section caps totallin
g as much as 320uF are common. The downline draw is not changed on-average,
 the output transformers prevent any stray DC from reaching the speakers, a
nd there is some momentary additional peak-response capacity.  

A note here from a discussion on chokes vs. caps vs. input size vs. output  
side and so forth:

Probably because the d.c. output voltage from the same transformer-rectifie
r system will be higher when a capacitor is added in front of a choke-input
 filter. This neglects transformer heating, which is higher for the same d.
c. power output with capacitor input than it is with choke input, even thou
gh the output voltage is lower with choke input.

Leading to the point on voltages.  

This is straying away from the original discussion on modifying a vintage r
adio. But, there it is.

Re: Antique Radio with Electromagnet on speaker
On Thursday, 20 December 2018 17:59:59 UTC, snipped-for-privacy@aol.com  wrote:
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 did discharge to nearly zero at each cycle. And, they designed "onward" ac
cordingly. And they warned specifically about increasing capacitance. And t
hey used other means to clean AC out of the line, typically by way of a mas
sive choke.  
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most exclusively electrolytic caps for filtering, typically at about 10uF,  
whereupon their field coils got much smaller (same size speaker) and they s
topped warning about increased capacitance. In most cases, they still used  
the 4-pin 80 tube as their rectifier. Rated at about 10uF. Note that in the
 Handbook, the 80 will accept much higher capacitance values "if voltage an
d current are controlled" - which is entirely the point.  
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. True *upon first charge*. After which, it will cycle just as with any oth
er cap based on downline draw. If the downline draw is not excessive, no ma
ter the size of the capacitor, current through the transformer will not be  
excessive - assuming voltage and current are stable.  
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e venerable Dynaco ST70 is to greatly increase capacitance - some times as  
much as 200%. The theory behind it is to increase peak response and reduce  
clipping. That particular unit uses the 5AR4/GZ34 rectifier, nominally rate
d at 60uF,  Power-supplies using this rectifier using 4-section caps totall
ing as much as 320uF are common. The downline draw is not changed on-averag
e, the output transformers prevent any stray DC from reaching the speakers,
 and there is some momentary additional peak-response capacity.  
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t side and so forth:
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ier system will be higher when a capacitor is added in front of a choke-inp
ut filter. This neglects transformer heating, which is higher for the same  
d.c. power output with capacitor input than it is with choke input, even th
ough the output voltage is lower with choke input.
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 radio. But, there it is.

so Peter still doesn't understand the issue. What's new.


NT

Re: Antique Radio with Electromagnet on speaker
:

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Tabby:

What I understand is that there is no issue. That which is being discussed  
here is on the separation of flyshit from pepper, not the restoration-to-fu
nction of a vintage radio. That there are those here chasing after miscella
neous squirrels within the piles is a sideshow.  

Peter Wieck
Melrose Park, PA  

Re: Antique Radio with Electromagnet on speaker
On Thursday, 20 December 2018 19:08:03 UTC, snipped-for-privacy@aol.com  wrote:
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d here is on the separation of flyshit from pepper, not the restoration-to-
function of a vintage radio. That there are those here chasing after miscel
laneous squirrels within the piles is a sideshow.  
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You should tell all the valve mfrs why their specs don't matter. Why don't  
I think they'll find your argument convincing.


NT

Re: Antique Radio with Electromagnet on speaker
Ralph Mowery wrote:
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   ^^^^^^^^^^^^  CORRECT!!!!!!!!  ^^^^^^^^^^^^^^^^^^

Dave M  



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