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Old 16th May 2019, 9:33 pm   #1
trabant
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Default PHILCO SCHEMATIC NEEDED MODEL U-1 no one seems to have seen one

Ok I have a Philco model U-1 it appears to be a late 1930s AC/DC set with a barretter. I've recapped the whole set and I'm 99% sure everything's where it should be however on start up absolutely nothing sound but valve heaters working hence I'd really like to find a schematic for this set
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Old 16th May 2019, 9:45 pm   #2
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Default Re: PHILCO SCHEMATIC NEEDED MODEL U-1 no one seems to have seen one

Was it working at all before you worked on it?
I can't see the barreter lighting in your picture, yet I can see valve heaters.
Can you post a full picture of the set please and list all the valve types in the set, there will be a similar set using the same valves and circuits.
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Old 17th May 2019, 11:42 am   #3
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Default Re: PHILCO SCHEMATIC NEEDED MODEL U-1 no one seems to have seen one

No it wasn't working it just had the hum of doom
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Old 17th May 2019, 12:36 pm   #4
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Default Re: PHILCO SCHEMATIC NEEDED MODEL U-1 no one seems to have seen one

I'd regard hum as a good sign. Check the HT voltage, then the voltages round the output valve, working back towards the aerial.
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Old 18th May 2019, 11:32 am   #5
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Default Re: PHILCO SCHEMATIC NEEDED MODEL U-1 no one seems to have seen one

Radio Museum lists several Philco sets with the same valve line up.
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Old 18th May 2019, 11:52 am   #6
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Default Re: PHILCO SCHEMATIC NEEDED MODEL U-1 no one seems to have seen one

I've checked the 1280 circuit and it does have a 400R resistor, but it's the cathode resistor for the output valve.

The only reason I can see for connecting a resistor to the barretter is if it's wired across the scale lamp/s. A bit of reverse engineering is called for.
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Old 18th May 2019, 12:24 pm   #7
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Default Re: PHILCO SCHEMATIC NEEDED MODEL U-1 no one seems to have seen one

Ok the 290 and it's variants are rather different to this. I have now tested the output TX and speaker those work I'm relatively sure it's a lack of HT will have a prod about later.
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Old 18th May 2019, 2:59 pm   #8
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Default Re: PHILCO SCHEMATIC NEEDED MODEL U-1 no one seems to have seen one

Not relating to you current fault but be aware of the black rectangular box object with the three terminals on the top. Philco put this object into most of their radios of that era. It contains typically two 0.015uF capacitors connected from two of the terminals to ground. These terminals typically connect to the line power input on the primary of the power transformer, when there was a transformer at least. In transformer-less sets its just usually on the two mains power line feed terminals. Be aware these can spontaneously fail, much like an X2 cap.

There were other oddities Philco were prone to do. One was, on the first IF transformer they had an additional single turn winding in series with the suppressor grid if the IF valve.

Another thing they liked was to fix bias the audio output valve, typically in transformer sets derived from the center tap of the power transformer secondary.

Generally the designs of their sets were more creative than most with clever AGC circuits. Their sets also had elaborate and detailed dials.

It might be necessary for you to copy out the schematic by hand if you cannot find the exact original schematic. The easiest way is to initially document the valve bases and electrodes, it speeds up the process.
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Old 20th May 2019, 7:37 pm   #9
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Default Re: PHILCO SCHEMATIC NEEDED MODEL U-1 no one seems to have seen one

Set now working turned out it was a duff smoothing choke
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