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 Post subject: Filament winding center tap
PostPosted: Feb Sun 24, 2013 4:02 pm 
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Joined: Feb Sat 02, 2013 10:30 pm
Posts: 52
Location: Brecksville, Ohio
I am installing a replacement transformer in a five tube Delco 1105. The secondary for the filament voltage (6.3V) has a center tap. The tap consists of two lacquered solid wires sharing a common sleeve.

When the two tap wires are joined, no-load voltage across the filament leads is 7.3v.

Should the two tap wires connect to chassis ground? Or just tied together and insulated.

Thanks!
Ralph


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 Post subject: Re: Filament winding center tap
PostPosted: Feb Sun 24, 2013 4:10 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 5899
Location: Cleona, PA
The voltage will drop to normal once the load of the tube heaters is on the transformer. Wire it the way the original was, if it had a center tap. If original had none, insulate the center tap wire as you said.

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Reece


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 Post subject: Re: Filament winding center tap
PostPosted: Feb Sun 24, 2013 4:17 pm 
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Joined: Jan Thu 31, 2008 7:19 pm
Posts: 1425
Location: Okie Land
You might want to look up the tubes and see how much current the tubes draw, and compare to the rating of the transformer. Just to make sure the transformer can handle it ok. Like Newton said, voltage will drop. It'll be 6.3V near the rated current of the transformer.

_________________
-- John R.

"What does matter is the size of your heart and the strength of your character."
--Herman Munster

In a short time we may speak of three or six crystal sets, the same as we speak now of a three or six tube set.
-- Hugo Gernsback, 1924


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 Post subject: Re: Filament winding center tap
PostPosted: Feb Sun 24, 2013 4:34 pm 
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Joined: May Sat 06, 2006 4:03 am
Posts: 1840
Location: South of Richmond, VA 25 miles down the pike.
Hey Ralph,
The advice on this label should help too. Likely not your trandformer, but note about your twisted pair is same for yours.
Bill J.




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 Post subject: Re: Filament winding center tap
PostPosted: Feb Sun 24, 2013 4:45 pm 
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Joined: Jan Thu 31, 2008 7:19 pm
Posts: 1425
Location: Okie Land
Having two separate filament secondaries are sure handy. You can connect them in series to double your voltage, or parallel to equal the voltage of a single winding but it doubles your current. Tied together end-to-end in series is exactly the same thing as a center tap, electrically.

_________________
-- John R.

"What does matter is the size of your heart and the strength of your character."
--Herman Munster

In a short time we may speak of three or six crystal sets, the same as we speak now of a three or six tube set.
-- Hugo Gernsback, 1924


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 Post subject: Re: Filament winding center tap
PostPosted: Feb Sun 24, 2013 8:34 pm 
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Joined: Mar Mon 17, 2008 5:05 am
Posts: 3853
Location: Palmerston North, New Zealand
Some tube audio pre-amps used centre-tapped heater transformers - the centre tap was wired to ground in an effort to reduced hum induced into cathodes. Others used a low value potentiometer with the wiper to ground and each end to either side of the non-grounded heater wiring - the pot was tweaked for minimum hum.

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Cheers - Marty ZL2MC


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 Post subject: Re: Filament winding center tap
PostPosted: Feb Sun 24, 2013 10:30 pm 
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Joined: Feb Sat 02, 2013 10:30 pm
Posts: 52
Location: Brecksville, Ohio
Bill and Reece,

Thanks, the tag verifies twisting and insulating. The P6006 is similar (see my specs below). The “P” number on mine is P9201. The original transformer was replaced long ago so I am not quite sure what the original looks like. I’m replacing the replacement.

(a little background info.. viewtopic.php?f=6&t=216332 )


John R.,

Ya got me thinking about the power capability of this transformer. I just took for granted that it would be OK because of the 5y3 hookup (see below) and the same physical size.


Marty,

That makes sense about the audio application. Thanks for the explanation. Now I have to search on that and see why hum is cancelled.


Ralph



Below are a few pics and voltage readings of what I have. There was a long winded commentary that I omitted because you guys covered most everything whilst I was typing.

I’m not 100% sure that this transformer has enough power capability other than the transformer was wired to a 5Y3 which I think is comparable to a type 80.

The tubes in my circuit are type 80, type76, two 6D6 and a 6B5.

Here are the transformer specs:

117v/60cycles
235-235 40ma
5V 2A
6.3V 2A


Image


Image

Image
Image


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 Post subject: Re: Filament winding center tap
PostPosted: Feb Mon 25, 2013 12:44 am 
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Joined: Jan Thu 31, 2008 7:19 pm
Posts: 1425
Location: Okie Land
Hi Beljum; the 6B5 has a 6.3v 800ma filament, the others (except the 80, which is 5v) are all 300ma. So that comes to 1.7amps, so you're good there. I reckon there's a different transformer for the 5v for the 80 tube, and the B+, that's OK? I can see it in the schematic.

_________________
-- John R.

"What does matter is the size of your heart and the strength of your character."
--Herman Munster

In a short time we may speak of three or six crystal sets, the same as we speak now of a three or six tube set.
-- Hugo Gernsback, 1924


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 Post subject: Re: Filament winding center tap
PostPosted: Feb Mon 25, 2013 12:57 am 
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Posts: 22858
Location: Maryland 20709, USA
tack wrote:
You can connect them in series to double your voltage, or parallel to equal the voltage of a single winding
Or you can leave them separate, as intended.

- Leigh

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http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: Filament winding center tap
PostPosted: Feb Mon 25, 2013 3:21 am 
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Joined: Jan Thu 31, 2008 7:19 pm
Posts: 1425
Location: Okie Land
Maybe it was intended for this particular transformer, I don't know. But there's plenty around where the intention is to choose only one or both separated, or tied together series or parallel. Like the ones with two 6.3v windings that can be shunted together for more current or placed in series for 12.6v. I'd make sure that the 2A rating is for each winding first and not two in parallel. Or use one for the 6B5 and the other secondary for the other tubes. Use your judgment. Let use know how it turns out! Keep the smoke in them there wires :D

_________________
-- John R.

"What does matter is the size of your heart and the strength of your character."
--Herman Munster

In a short time we may speak of three or six crystal sets, the same as we speak now of a three or six tube set.
-- Hugo Gernsback, 1924


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 Post subject: Re: Filament winding center tap
PostPosted: Feb Mon 25, 2013 11:30 pm 
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Joined: Feb Sat 02, 2013 10:30 pm
Posts: 52
Location: Brecksville, Ohio
Thanks everyone!

I went ahead and tied the filament CT wires together and insulated them. I suppose the filament secondary is now one coil which gives me 6.3V as the original design shows. There is a separate set of wires for the 5V rectifier element which seems fine. My drawing above is not very good.

I was able to find a bit of info on filament CT and as stated already was mainly with audio-type circuits and also tube guitar amp circuits. I have to look into the back of my Fender Blues Jr.!! Most of the discussion was over my head at this point so I gave up easily.

Ralph


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 Post subject: Re: Filament winding center tap
PostPosted: Feb Mon 25, 2013 11:34 pm 
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Joined: Jan Thu 31, 2008 7:19 pm
Posts: 1425
Location: Okie Land
So you're about to fire it up? :)

_________________
-- John R.

"What does matter is the size of your heart and the strength of your character."
--Herman Munster

In a short time we may speak of three or six crystal sets, the same as we speak now of a three or six tube set.
-- Hugo Gernsback, 1924


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 Post subject: Re: Filament winding center tap
PostPosted: Mar Fri 15, 2013 1:42 am 
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Joined: Feb Sat 02, 2013 10:30 pm
Posts: 52
Location: Brecksville, Ohio
Not quite ready to fire 'er up yet :) . Not too much longer though.

Here is a quick update.
I received all the caps and resistors after some were on backorder so progress resumes. A few roadblocks were overcome thanks to help from good folks on this forum.
It appears that the loudspeaker transformer is not stock so I wonder how it will work out. I have a book from the library by a fellow named Hallmark “How to Repair Old Time Radios” and he mentions that the transformer is important and should be rebuilt when possible.
The volume control was not working at all so it was disassembled, cleaned and lubed. It operates very well now, at least measuring with a meter.

Image


Image



bel


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 Post subject: Re: Filament winding center tap
PostPosted: Mar Fri 15, 2013 2:37 am 
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Joined: Jan Thu 31, 2008 7:19 pm
Posts: 1425
Location: Okie Land
Hey, it's shiny! Cleaned up like new!

_________________
-- John R.

"What does matter is the size of your heart and the strength of your character."
--Herman Munster

In a short time we may speak of three or six crystal sets, the same as we speak now of a three or six tube set.
-- Hugo Gernsback, 1924


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 Post subject: Re: Filament winding center tap
PostPosted: Mar Fri 15, 2013 2:50 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 22858
Location: Maryland 20709, USA
OK. Never heard of Hallmark.

Yes, output transformers are important. I've never had occasion to rebuild one, nor would I attempt
to do so. I suppose some folks might, if a replacement was not to be found.

I'm a bit concerned about the complete removal of the wiring. Some radios are sensitive to wire
placement and dress, suffering from bad squealing and such if the wires aren't where they should
be. Try to put the new ones in the same location as the originals, if you have that information.

- Leigh

_________________
73 de Leigh W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: Filament winding center tap
PostPosted: Mar Fri 15, 2013 1:30 pm 
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Joined: Feb Sat 02, 2013 10:30 pm
Posts: 52
Location: Brecksville, Ohio
Quote:
Hey, it's shiny! Cleaned up like new!


LOL!!! I’m really setup well for mechanical refurbish due to my other interests so the clean and shiny part is real easy for me. My goal is to have a “show and go” radio.

Ralph


Quote:
OK. Never heard of Hallmark. Yes, output transformers are important. I've never had occasion to rebuild one, nor would I attempt to do so. I suppose some folks might, if a replacement was not to be found.



Clayton Hallmark “How to repair Old Time Radios” first print in 1979. Seems like a good intro book. I’d buy one if it was still in print.

Your suspicion of my transformer rebuild comment is correct. To clarify/correct my info from Hallmarks book, to quote,

“Since the field coil was matched to the other components in the power supply, it is best to repair the speaker, rather than replace it.”

Hallmark goes on to say..

“The secondary impedance of the audio transformer should be the same as the voice coil impedance (3-4 ohms in some new speakers, 6-8 ohms in others). The primary impedance of the transformer should approximate the load resistance (impedance) of the audio output tube (last audio tube).”

I am not sure if the speaker is original. If history repeats, it is probably not! The output transformer appears non-original (Stancor A-3852).

The voice coil DC resistance is 2.5 ohms
The secondary output transformer DC resistance is 0.7 ohm (#1 and #3 terminals)

Output primary DC resistance is 226 ohms (B+ and P terminals)
Load resistance of last audio tube (6B5) is 7000 ohms per tables in Hallmark’s book.

Field coil is 1067 ohms DC resistance.

I’m gathering that this output/speaker setup is not optimal. Any advice or comments? I’m not against buying something if necessary.


Quote:
Some radios are sensitive to wire placement and dress, suffering from bad squealing and such if the wires aren't where they should be.


Thanks for the heads up. I suspected that the wire routing was important because of a recent post I read commenting on component location. I figured that wires make real good antennas too. I’d guess that 90% of the wire runs were standard and that is all documented with photos and sketches.
I should have kept this project to one thread so there would be a history of events. I foolishly think that every new surprise is the last one!

Thanks for the help.
Ralph


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 Post subject: Re: Filament winding center tap
PostPosted: Mar Fri 15, 2013 2:07 pm 
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Posts: 22858
Location: Maryland 20709, USA
beljum wrote:
The voice coil DC resistance is 2.5 ohms
The secondary output transformer DC resistance is 0.7 ohm (#1 and #3 terminals)
Output primary DC resistance is 226 ohms (B+ and P terminals)
Impedance and DC resistance are two very different things.
Resistance is easily measured with an ohmmeter. Impedance requires a bunch of equipment, and is dependent on the measurement frequency.

Transformers do not have impedances, they have impedance ratios, which is the square of the turns ratio.
For example, if the turns ratio is 5:1, the impedance ratio would be 25:1.
For example, if you have an 8-ohm speaker and the tube wants an 8000-ohm load, you need a transformer with a 1000:1 impedance ratio.

You'll find some output transformers rated by impedance, but the numbers are only an example. A transformer that provides a 4000-ohm load with a 4-ohm speaker also provides an 8000-ohm load with an 8-ohm speaker, or a 16000-ohm load with a 16-ohm speaker.

You can determine the turns ratio of any output transformer by applying a low voltage to the secondary and measuring the primary voltage.
Apply 1 volt (or 0.1 volt) from an audio generator at a frequency of 400 to 1000 Hz. Measure the voltage on the primary with an AC voltmeter.
If you use the 1-volt test signal, the primary voltage = the turns ratio, such as 33:1 or 54:1 or whatever.
If you use the 0.1-volt test signal, multiply the primary voltage by 10 to get the turns ratio.

- Leigh

_________________
73 de Leigh W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


Last edited by Leigh on Mar Fri 15, 2013 2:11 pm, edited 1 time in total.

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 Post subject: Re: Filament winding center tap
PostPosted: Mar Fri 15, 2013 2:11 pm 
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Joined: Jan Thu 31, 2008 7:19 pm
Posts: 1425
Location: Okie Land
Hi Ralph; The match-up between speaker and output transformer is just a loose pairing. The actual, real impedance depends on frequency, and this is Audio at a range from about 50 to 4000 or so for older AM radio. FM would be a lot wider. But regardless, the measured impedance of 4-ohms or whatever would be at a test frequency that is often 400hz. But impedance will be a lot greater at higher audio freqs, and lower at lower freqs. If your voice coil is 2.5 ohms at DC, then it's about a 4-ohm speaker. And the primary impedance will vary also, as it's tied to the secondary. Here's a link to a pdf file of a Stancor catalog: http://www.clarisonus.com/Archives/Trans/Stancor61.pdf your A-3852 is a good universal output rated at 18 watts. If the correct taps are used for the output tube, this transformer is fine. You cannot get an exact match and it isn't expected. But if you get a larger than required output transformer, it'll have more iron in the core and can reproduce the lower frequencies better.

I see Leigh submitted a reply just before I sent mine. I hope mine compliments his :)

_________________
-- John R.

"What does matter is the size of your heart and the strength of your character."
--Herman Munster

In a short time we may speak of three or six crystal sets, the same as we speak now of a three or six tube set.
-- Hugo Gernsback, 1924


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 Post subject: Re: Filament winding center tap
PostPosted: Mar Sat 16, 2013 3:54 pm 
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Joined: Feb Sat 02, 2013 10:30 pm
Posts: 52
Location: Brecksville, Ohio
I really appreciate both of your inputs. I owe you both a Sam Adams Ale if we ever cross paths.
The impedance concept is on my mind (that is why I specified “DC resistance” above) and is a different way of thinking for me. I need to know, even if on a fundamental level, what a wire does before I hook it up. I’m able to move along now until the next bump in the road. If I do run into another problem :shock: , I’ll start a Delco 1105 restoration thread and reference all my scattered posts.

This radio has actually been a very good learning platform because of the modifications and the relatively simple circuit.

Thanks again guys,

Ralph


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