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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 24th Jul 2021, 4:46 pm   #1
davebms
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Default Jewel radio.

hello all i have started to look at the chassis that i got from the forum ,,
changed grid coupling cap, check power transformer , lamp limiter Buzzz
change filter caps (there is a 8uf but tested ok) put meter on HT and the
1.5 volt heaters used variac and dim bulb , slight hum but no stations .after
a long time i found the earth the the tuning cap (solid link) broken fixed that
it works, not very well, normal stuff change waxys, then it stopped working one off the heaters gone open ,, test the ul41 very low emission get replacement valves, df91 all good. ul41 shorts ht to ? kills ht ,,seller sends replacement
re test 3 meters+ variac THE problem is any more than 160 volts ht, the 4.2

string for small valve goes way to high (that was probably the end of df91)
SO with reduced ht 160v 4.2 LT UL41 (old and new)anode 160v. g2 150v. g1 -5.6
cathode 10 volts, sorry for the long babel. all resistors check ok how do i control heater volts
thanks for your time dave
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Old 24th Jul 2021, 5:33 pm   #2
ms660
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Default Re: Jewel radio.

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Originally Posted by davebms View Post
g1 -5.6
Is that cathode to g1 or ground/chassis to g1?

Lawrence.
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Old 24th Jul 2021, 5:38 pm   #3
davebms
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Default Re: Jewel radio.

sorry, g1 to cathode i think thats the way to measure it ?

dave
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Old 24th Jul 2021, 6:27 pm   #4
ms660
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Default Re: Jewel radio.

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Originally Posted by davebms View Post
sorry, g1 to cathode i think thats the way to measure it ?
Yes that's one way to measure the bias, the cathode voltage suggests it's 10 volts unless there's some leakage somewhere, when measuring cathode to grid voltage you should factor in what the meters input resistance will have on the cathode-g1 voltage.

Out of interest does the grid resistor connect to ground/chassis as shown in the schematic?

Lawrence.
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Old 24th Jul 2021, 7:53 pm   #5
Dickie
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Default Re: Jewel radio.

I would certainly run through the wiring and check it all against the circuit. Assuming it's the one you got from me I had to correct 3 wiring errors before it would power up at all. You're a brave man for taking it on!
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Richard, BVWS member
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Old 26th Jul 2021, 8:14 pm   #6
davebms
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Default Re: Jewel radio.

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You're a brave man for taking it on!
no not brave poss daft
yes it is the set from you

Quote:
Originally Posted by ms660 View Post
Yes that's one way to measure the bias, the cathode voltage suggests it's 10 volts unless there's some leakage somewhere, when measuring cathode to grid voltage you should factor in what the meters input resistance will have on the cathode-g1 voltage.

Out of interest does the grid resistor connect to ground/chassis as shown in the schematic?

Lawrence.

yes the the grid resistor goes to chassis ground
i have put the replacement ul41 in , i can put more HT in. before LT goes to high,, anode 180 volt, screen grid 170 g1 -9 but with mains reduced ul41 heater at 40 volt ht 190 volt, meter, Heathkit vtvm /fluke 25 any more volts and LT may pop small valves ?
thanks for the replies.. dave

Last edited by Cobaltblue; 26th Jul 2021 at 8:18 pm. Reason: Fixed the quotes
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Old 28th Jul 2021, 8:31 pm   #7
davebms
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Default Re: Jewel radio.

hello all , i think ive sorted some of the problems ! i took onboard Lawrence.
comment ,Out of interest does the grid resistor connect to ground/chassis as shown in the schematic? well physically it does,, so i removed the screws cleaned all parts fitted a star washer. the junction 100/500R and feed wire for heaters all go to one small tag, took them all of re soldered and put feed wire
to the other end of the same tag much better, re HT,but selenium rectifiers
cut HT down ! (that was the strange aroma ) uf4007 . 4/5 stations MW several on SW LW not so good but its a start

thanks all dave
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Old 29th Jul 2021, 2:57 pm   #8
slidertogrid
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Default Re: Jewel radio.

Quote:
Originally Posted by Dickie View Post
I would certainly run through the wiring and check it all against the circuit. Assuming it's the one you got from me I had to correct 3 wiring errors before it would power up at all. You're a brave man for taking it on!
I remember reading the article Gerry did on these and he mentioned errors in construction saying he thought the sets were all rejects from the first production run. I think he said on one the UL41 valve holder wiring was all backwards..?
Good luck with it!
Rich
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Old 29th Jul 2021, 6:56 pm   #9
davebms
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Default Re: Jewel radio.

yes this set probably was !! most of power supply was re wired by the last owner but its still got problems, when i get the HT/LT sorted
i can look at valve voltages ,,, well thats the plane

dave
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