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 Post subject: Detrola model 148 radio
PostPosted: Jan Wed 03, 2018 8:06 pm 
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Wondering if someone has a more detailed schematic for this radio other than the nostalgia air one. The radio has a sellium rectifier for tube 235z5 and I am first looking for tube voltage for that tube.Thanks from a0e 1k0 nl canada


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Wed 03, 2018 10:23 pm 
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Also testing the tubes and tube 76 is gone and I do not have one nor a 37 but can I use something else thanks.


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Wed 03, 2018 10:39 pm 
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Both sections of the 25Z5 are used separately. Did someone add two selenium rectifiers? Was a dropping resistor added to replace filament of 25Z5?

37 and 76 are interchangeable in your radio. Could use a 6J5 or 6C5 with adapter? Since one 76 is wired as a diode detector you could use other tubes. What tubes do you have with 5 pin bases that draw 300 ma filament current?

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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Wed 03, 2018 10:57 pm 
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Location: Mountains of Mourne. Ireland.
Selenium rectifier!

A voltage table for Sentinel model 83UE can be seen here...
http://www.nostalgiaair.org/Resources/291/M0018291.htm
...a similar radio, albeit with eye-tube 6G5

For any component value queries, see Detrola model 100 or 100A

Greg.


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Wed 03, 2018 10:58 pm 
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First there is only one selenium rectifier added. Next where would dropping resistor be placed? I know that the filament did not light up in radio when the guy who gave it to me plugged it in.


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Wed 03, 2018 11:00 pm 
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Also what would be the best way to figure out what 5 pin tube draw 300 ma filament currents.


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Wed 03, 2018 11:15 pm 
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Dropping resistor is placed after the selenium rectifier. Between the rectifier and filter capacitor. Usally around 100 ohms 5 watg resistor will work

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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Wed 03, 2018 11:24 pm 
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There is a 33 ohm 2 watt attached to pin 3 of rectifier and c-18 24 mfd electrolytic.


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 12:00 am 
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Tubes like 36, 38, 39 can be made to work as a 76 diode. Looks a little strange since they have grid caps. This is an AC/DC radio. Filaments are wired in series. Any tube removed and non light.

Need to check out modifications to this radio. The original 25Z5 was arranged as a voltage doubler. A single selenium rectifier won't operate that way. Maybe they operated the radio on lower B+ voltage?

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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 12:34 am 
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I checked the voltage on the rectifier at first but I think it was around 100 dcv on the rectifier but will confirm tomorrow. What pins will have voltage now that it has a single selenium rectifier and how much should the voltage be?


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 1:14 am 
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Detrola 148 that I found is a different circuit. It uses 25Z5 as a voltage doubler so you won't have the same values. Figuring B+ as 100 volts seems reasonable.

http://www.nostalgiaair.org/pagesbymode ... 003891.pdf

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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 1:21 am 
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Yes I have that schematic but it is very hard to read but if someone has a better one that would be great. Also which pins on the rectifier will have voltage with this set up the way it sits now.


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 1:54 am 
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Not sure what they modified on the rectifier tube? You can't have a doubler with single selenium rectifier. There should be a + mark on selenium rectifier. B+ starts there.

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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 2:12 am 
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I will look at it in the morning and post voltages on rectifier. Should they be all dcv ? Also should I remove the other tubes for now so I do not blow anything has the electrolytics have not been done yet because I am not sure what to do with the recap process until we figure out what is done with chassis.


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 2:49 am 
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Dennis wrote: Whatever you do, never switch that rear AC-DC switch into the DC position unless you like loud noises.
Post subject: ID a Detrola? viewtopic.php?p=1778832#p1778832

:shock: Greg.


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 12:37 pm 
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The ac dc switch has been removed. Also could I use a tube 56 for a 76 for now.


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 12:46 pm 
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The voltage for the selenium rectifier is
pin1-0
pin2-120acv
pin3-140dcv
pin4-120acv
pin5-0
pin6-0


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 3:02 pm 
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spsquires wrote:
The ac dc switch has been removed. Also could I use a tube 56 for a 76 for now.

Yes, with a different filament supply.....
https://frank.pocnet.net/sheets/127/7/76.pdf

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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 3:04 pm 
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spsquires wrote:
Also what would be the best way to figure out what 5 pin tube draw 300 ma filament currents.

Look up the tube data sheets

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"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Detrola model 148 radio
PostPosted: Jan Thu 04, 2018 3:16 pm 
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I do not understand what you mean.


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