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Old 20th Dec 2009, 7:04 pm   #81
MichaelR
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Default 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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Old 20th Dec 2009, 7:15 pm   #82
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Default Re: Newb Stumped on a Derwent

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Originally Posted by MichaelR View Post
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.

Mike
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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Old 20th Dec 2009, 7:23 pm   #83
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Default 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
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Old 20th Dec 2009, 8:03 pm   #84
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Default 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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Old 20th Dec 2009, 8:43 pm   #85
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Default Re: Newb Stumped on a Derwent

Quote:
Originally Posted by electrogram View Post
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
Rectified the error and the following

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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Old 20th Dec 2009, 8:59 pm   #86
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Default 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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Old 20th Dec 2009, 9:08 pm   #87
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Default Re: Newb Stumped on a Derwent

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Originally Posted by electrogram View Post
remove the 50uf altogether, measure the resistance between pin 5 on the 75 and chassis, then switch on again, see what happens
50uf removed
5000ohms reading on 75's pin 5
switch on, same fade off
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Old 20th Dec 2009, 9:14 pm   #88
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Default 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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Old 20th Dec 2009, 9:21 pm   #89
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Default 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.
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Old 20th Dec 2009, 9:23 pm   #90
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Default Re: Newb Stumped on a Derwent

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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.
confused ..... too right
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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Old 20th Dec 2009, 9:26 pm   #91
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Default 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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Old 20th Dec 2009, 9:26 pm   #92
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Default Re: Newb Stumped on a Derwent

Quote:
valve 42 readings

pin 1=about 24 (Heater)
pin 2=255 Anode)
pin 3=320 (G2, screen grid)
pin 4=45 (G1, Control Grid)
pin 5=35 (Cathode)
pin 6=0 (Heater)
Pin 4 should read zero volts to chassis. Is the 45 volts you're measuring here positive or negative with respect to earth? ie with the black lead of your meter to chassis and the red lead to pin 4 does the meter read forwards (positive voltage) or backwards (negative voltage)? If it's positive you need to check THAT capacitor which connects the control grid to the previous stage. If in doubt disconnect it at the control grid end and measure the voltages on the control grid and the disconnected end of the capacitor

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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Old 20th Dec 2009, 9:29 pm   #93
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Default 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.
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Old 20th Dec 2009, 9:29 pm   #94
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Default Re: Newb Stumped on a Derwent

Quote:
510k it is
it is on pin 4 of the 42 with the other end on chassis
snip
pin 4 cannot get the meter to read even on the 1meg range with Q
In that case the 510K resistor or the wires feeding it are open circuit.

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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Old 20th Dec 2009, 9:34 pm   #95
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Default Re: Newb Stumped on a Derwent

Quote:
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
I think that's because confusion arose between pin 5 of the 75 and pin 5 of the 42. The positive end should be connected to pin 5 of the 42 and the negative end to chassis.
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Old 20th Dec 2009, 9:39 pm   #96
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Default Re: Newb Stumped on a Derwent

Quote:
Originally Posted by Station X View Post
Quote:
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
I think that's because confusion arose between pin 5 of the 75 and pin 5 of the 42. The positive end should be connected to pin 5 of the 42 and the negative end to chassis.
Spooky just done that before reading the post, maybe i'm picking something up. above chassis photo now wrong does not show 50uf back in place. By the way its 50wv is that ok
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Old 20th Dec 2009, 9:47 pm   #97
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Default Re: Newb Stumped on a Derwent

Yes. 50 Volts Working is OK.
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Old 20th Dec 2009, 10:10 pm   #98
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Default 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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Old 20th Dec 2009, 10:16 pm   #99
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Default 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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Old 20th Dec 2009, 10:26 pm   #100
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Default Re: Newb Stumped on a Derwent

Quote:
Originally Posted by Station X View Post
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.
yes AVO reads it as 510k
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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