20th Dec 2009, 7:04 pm | #81 |
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Re: Newb Stumped on a Derwent
Just a suggestion but it would be easier and safer if you get a circuit diagram for the radio, you will solve the problem in minutes then.
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20th Dec 2009, 7:15 pm | #82 |
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Re: Newb Stumped on a Derwent
That would have been nice and I would not be in this nightmare if I had one. I don't know what the set is and nobody else does... total mare!!!! I've only done a couple of sets before both were easy and both had trader sheets.
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20th Dec 2009, 7:23 pm | #83 |
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Re: Newb Stumped on a Derwent
As it stands now after changes suggested, with the 510k resistor on pin 5 nothing and the avo trick does not yeild anything, with it back on 4 you get the fade off and the avo trick works.
I'm off outside to stick my head in the foot of snow and suggest the locals take a free kick at my backside for the next hour or so. I've been at this all day and i'm sure you are all bored by a newbs attempt. Shame as i like this set but someone must have played before me with 510 on pin 4, this is where it is at the moment not as the drawing shows valve 42 readings pin 1=about 24 pin 2=255 pin 3=320 pin 4=45 pin 5=35 pin 6=0 Last edited by oldticktock; 20th Dec 2009 at 7:51 pm. |
20th Dec 2009, 8:03 pm | #84 |
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Re: Newb Stumped on a Derwent
in this diagram both ends of the 510k are connected to the wrong place, one end should be connected to chassis and the other end to pin 4 on the 42
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20th Dec 2009, 8:43 pm | #85 | |
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Re: Newb Stumped on a Derwent
Quote:
Radio fired up, station heard quite loud/distorted, fade off starts but this time does not totally go. Stays about the same as when i did the avo bit. If I tune a bit it goes and cannot get it back. however valve voltage readings on pin 2 3 etc are negative so that's gone scew all dc readings want to fire the avo the wrong way. Can only read ac on the ac side of the rectifier, dc side does neg deflection Last edited by oldticktock; 20th Dec 2009 at 8:53 pm. |
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20th Dec 2009, 8:59 pm | #86 |
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Re: Newb Stumped on a Derwent
remove the 50uf altogether, measure the resistance between pin 5 on the 75 and chassis, then switch on again, see what happens
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20th Dec 2009, 9:08 pm | #87 |
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Re: Newb Stumped on a Derwent
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20th Dec 2009, 9:14 pm | #88 |
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Re: Newb Stumped on a Derwent
We're getting thoroughly confused with the valves here. 510K (if that's what it is) should be connected between chassis and pin 4 of the 42.
Going back to the 42, with the set off you should measure 500 ohms from pin 5 (cathode) to earth and 510K from pin 4 to earth.
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20th Dec 2009, 9:21 pm | #89 |
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Re: Newb Stumped on a Derwent
The 50uF is the wrong way around. As the cathode bias appears to be shared by the 75 I am not sure it will work without the 50uF. This seems a very odd arrangement and I wonder if there is something else wrong with the wiring. Did you take any pictures before you started?
You ran the 42 flat out when the 510K was connected to anode of the 75. |
20th Dec 2009, 9:23 pm | #90 | |
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Re: Newb Stumped on a Derwent
Quote:
510k it is it is on pin 4 of the 42 with the other end on chassis pin 5 does meassure 500ohms pin 4 cannot get the meter to read even on the 1meg range with Q Oh and now the 50uf is out all together as previous suggestion |
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20th Dec 2009, 9:26 pm | #91 |
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Re: Newb Stumped on a Derwent
yes, perhaps I am confusing matters, I was thinking maybe the output stage was now ok, In the latest circuit the 50 uf was reverse connected across the 75's cathode resistor(s)
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20th Dec 2009, 9:26 pm | #92 | |
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Re: Newb Stumped on a Derwent
Quote:
If the cathode is at 35V, which is exceedingly high, you should get 35V between pins 4 and 5 of the 42. Check your wiring and component values carefully against the diagram I posted. If the 510K really is 5K replace it with 1M or the highest value you have to hand.
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20th Dec 2009, 9:29 pm | #93 |
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Re: Newb Stumped on a Derwent
Earlier on someone said the 50uf was the wrong way round so i swapped it round now you say its the wrong way round now............... Aggggggggggggg
chassis as it stands now. i'm so confused now. |
20th Dec 2009, 9:29 pm | #94 | |
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Re: Newb Stumped on a Derwent
Quote:
When you say you cannot get a reading I assume that the meter is reading just as if its leads were disconnected and not as if they were shorted?
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20th Dec 2009, 9:34 pm | #95 | |
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Re: Newb Stumped on a Derwent
Quote:
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20th Dec 2009, 9:39 pm | #96 | ||
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Re: Newb Stumped on a Derwent
Quote:
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20th Dec 2009, 9:47 pm | #97 |
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Re: Newb Stumped on a Derwent
Yes. 50 Volts Working is OK.
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20th Dec 2009, 10:10 pm | #98 |
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Re: Newb Stumped on a Derwent
trying to answer pin voltages as per station x request. Only trouble is since putting 510k from pin4 to chassis I can no longer obtain DC readings on any pins or even the dc side of the rectifier, getting negative deflection. If I remove the chassis end of 510k readings return
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20th Dec 2009, 10:16 pm | #99 |
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Re: Newb Stumped on a Derwent
OK. Now you've got the resistor disconnected make sure it measures 510K.
There should be no DC connecton to pin 4 of the 42 except for the 510K grid leak resistor. What else is connected to the 42 pin 4? I would expect to see only a coupling capacitor (THAT capacitor from the previous stage).
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20th Dec 2009, 10:26 pm | #100 | |
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Re: Newb Stumped on a Derwent
Quote:
backing out from pin 4 you hit this pin4...... 0.1uf.... the 0.1 is coupled from pin 2 of the 75 (why does everyone call it THAT) which also has the 220k onto HT rail as mentioned before |
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