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 Post subject: philco 90 45 tube chassis. speaker type to get?
PostPosted: Dec Sun 31, 2017 7:12 pm 
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Joined: Apr Mon 11, 2016 1:16 am
Posts: 251
Location: east canton ohio 44730
Have looked on ebay for speakers, absolutely nothing. I can get one for a model 90 console but I think its for a console only and has 3 wires which isnt for push pull 45 tubes, but has a 3200 ohm field coil. So far I think my chassis is missing the filter choke under the chassis and a speaker. Can I make the single ended speaker work if I add the extra wire and transformer? Chassis stamped number is 110250. I thought I would just clean up the chassis and use it like the E H scott radios with no cabinet. I could swipe one out of my not repaired model 20 radios but I think those are also not working with blown windings.


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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Dec Sun 31, 2017 7:26 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 4516
Location: Near Brandon, Iowa
Yes, what you are suggesting should work, provided you replace the SE output transformer on the "new" speaker with a push-pull type that is of the correct primary impedance for the 45 tubes. Outer ends of the primary go to each plate of the 45 tubes; center tap goes to B+.

Output impedance is a bit of a gamble but will probably operate OK even if there is a slight mismatch... most of these early 1930s speakers used low impedance voice coils (a couple of ohms).

Speaker field matching is also important. Using a speaker with a very different field impedance from that the radio was designed for can result in incorrect B+ and bias voltages, or a burned-out field coil.

The missing filter choke coil can be replaced with a power resistor, with a much larger cap on the "downstream" end of the choke than what was originally specified, to minimize hum.


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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Dec Sun 31, 2017 7:43 pm 
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Joined: Apr Mon 11, 2016 1:16 am
Posts: 251
Location: east canton ohio 44730
the rca tube data sheet has fixed bias and self bias for load. not sure which one to use but I would guess 5060 ohms for primary transformer?


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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Dec Sun 31, 2017 8:52 pm 
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Joined: Jan Tue 31, 2012 1:55 am
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Location: Mountains of Mourne. Ireland.
All Philco speakers 1935 four page pdf 757kB
https://dropbox.com/s/hnvhfw5ylc5l22r/A ... 5.pdf?dl=1

Too expensive + the 300 Ohms doesn't sound right?
https://www.ebay.com/sch/i.html?_from=R ... 6&_sacat=0

Greg.


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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Dec Sun 31, 2017 10:28 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
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Location: Near Brandon, Iowa
quartermilecamel wrote:
the rca tube data sheet has fixed bias and self bias for load. not sure which one to use but I would guess 5060 ohms for primary transformer?

Philco 90 version with push-pull 45 tube output uses fixed bias. 5K ohms is about right for output transformer impedance for these tubes in this configuration.


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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Jan Mon 01, 2018 5:00 am 
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Joined: Apr Mon 11, 2016 1:16 am
Posts: 251
Location: east canton ohio 44730
trying to grasp fixed and self bias. Read in another thread that the stancor 125e would work? Its 15 watts, but 45 tubes can output 18 watts. I wonder if theres a stronger one out there


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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Jan Mon 01, 2018 5:30 am 
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Joined: May Fri 01, 2015 2:33 am
Posts: 1174
Location: Roslyn,Pa 19001
>trying to grasp fixed and self bias
Fixed bias has a negative voltage applied the control grid(s) of the output tube(s). Usually developed thru a resistor from the center tap of the hv winding of the power transformer to chassis ground.
Self bias devolopes negative voltage on the control grid from a resistor it the cathode or filament center tap on directly heated tubes powering the output stage.

Terry


Last edited by Radioroslyn on Jan Mon 01, 2018 6:37 am, edited 2 times in total.

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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Jan Mon 01, 2018 6:13 am 
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Joined: Apr Mon 11, 2016 1:16 am
Posts: 251
Location: east canton ohio 44730
egg wrote:
All Philco speakers 1935 four page pdf 757kB
https://dropbox.com/s/hnvhfw5ylc5l22r/A ... 5.pdf?dl=1

Too expensive + the 300 Ohms doesn't sound right?
https://www.ebay.com/sch/i.html?_from=R ... 6&_sacat=0

Greg.

300 ohms??? extremely shorted or missing a zero?? I was thinking about getting the one from same seller for 125 but dont know of any sources cheaper. Also cant tell if thats 3 or a 4 wire one


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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Jan Mon 01, 2018 3:15 pm 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 5015
Location: Mountains of Mourne. Ireland.
You could place a WTB ad in the classified section here at arf.
It gets a lot of traffic.

Notes on (the more readily available) model 20 speaker adaptation...
http://web.archive.org/web/201603181600 ... peaker.htm
Also... See fully notated schematic for model 90 with 45 output tubes.

It's just a pity that off-the-shelf replacements can't be purchased in 2018 as those old Philco cones (like me) must be pretty stiff by now... :)
Greg.

oh... the 300Ω in the ebay listing may be his reading of the output transformer's primary resistance.


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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Jan Mon 01, 2018 4:27 pm 
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Joined: Apr Mon 11, 2016 1:16 am
Posts: 251
Location: east canton ohio 44730
havnt even seen model 20 speakers on ebay in a long time. Yes I have read about the model 20 adaptation years ago but dont remember much.
Not sure I remember how to post a wanted ad on arf or where its at, might try that.


Last edited by quartermilecamel on Jan Mon 01, 2018 4:41 pm, edited 1 time in total.

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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Jan Mon 01, 2018 4:32 pm 
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Joined: Apr Mon 11, 2016 1:16 am
Posts: 251
Location: east canton ohio 44730
just read the speaker link. It describes the change from model 20 to model 90 but single ended application.


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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Jan Mon 01, 2018 5:35 pm 
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Joined: May Fri 01, 2015 2:33 am
Posts: 1174
Location: Roslyn,Pa 19001
>just read the speaker link. It describes the change from model 20 to model 90 but single ended application.

The Philco models 20,21 and 90 w/2 #45 tubes all use the same spkr. All are designed for push/pull triode output tubes. The field coils are rated @40ma. These are known as Philco K style spkrs (K and K1).

The model 70 uses a K speaker too and the field coil is the same as the 20,21,and 90 but the transformer is different because the 70 has one output tube a #47. The plate load impedance of the 47 is about twice what the 45 is. This is why you can use the 20,21 and 90 w/2 #45 tubes by use the whole primary connected to the 47.

In order to use the model 70 spkr you'll need to change the output transformer to one that matches a pair of 45's (also known as push/pull) @ 5000 ohms to about 1.5 ohms (voice coil).

Philco in the mid '30s had a number of sets at used a later style K speaker and also used push/pull triode connected 42's in what they dubbed as their super class A output. Some of the model 16b/116b used this set up. When the pentode tube is wired as a triode it lowers the plate load impedance so to be a good match for your set.

If you go the the Philco Phorum there is a downloadable list of the specs for Philco speakers from the late '20s -late '30s or so.

GL
Terry


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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Jan Mon 01, 2018 7:44 pm 
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Joined: Apr Mon 11, 2016 1:16 am
Posts: 251
Location: east canton ohio 44730
I have 2 model 20 speakers. both of which I think have issues but not sure about testing them yet...........looking for the pin out diagram. I have one model 20 chassis and case which is not too bad. Other model 20 case is fair but its been 15 years and I dont even remember if I have a chassis for that one. One measures 3050 across the 2 large pins. Other one has .210k and .430k from small pin to the pins on both sides of it. couldnt detect a field coil read out on that plug at all


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 Post subject: Re: philco 90 45 tube chassis. speaker type to get?
PostPosted: Jan Mon 01, 2018 11:11 pm 
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Joined: Apr Mon 11, 2016 1:16 am
Posts: 251
Location: east canton ohio 44730
I keep seeing refferences to s e, what is that when looking at speaker wiring?
ad placed for 90 or 20 speaker will see if I even did it right. s e Im guessing is secondary transformer


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