20th Dec 2009, 4:03 pm | #61 |
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Re: Newb Stumped on a Derwent
electrogram's post looks good to me.
The 220K resistor and 0.1uF capacitor are a red herring. It's the anode resistor of the 75 and associated decoupler.
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20th Dec 2009, 4:06 pm | #62 | |
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Re: Newb Stumped on a Derwent
Quote:
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20th Dec 2009, 4:11 pm | #63 |
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Re: Newb Stumped on a Derwent
Yes. It is. Chop it out and fit a 500 Ohm one.
I've been looking at other circuits for this era and 500 ohms is about right. Put a 1 Megohm between Pin 4 and Earth. Then try it. Cheers, Steve P.
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20th Dec 2009, 4:15 pm | #64 |
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Re: Newb Stumped on a Derwent
Steve.
It appears that a 500 or perhaps 540R resistor is already wired cathode to earth, but IN PARALLEL with the 510K. So perhaps the 510K is the grid leak, but goes to the wrong pin?
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20th Dec 2009, 4:33 pm | #65 |
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Re: Newb Stumped on a Derwent
Possibly. It would cause a problem. But a new resistor will only work better, as we don't know what value it is. Should be yes, what is is, no. If it's open or high, then it won't do any harm.
When the set works, bring the pliers into play. Cheers, Steve P.
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If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...? |
20th Dec 2009, 4:57 pm | #66 |
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Re: Newb Stumped on a Derwent
Just had a sanity break and i'm up for the next round ..... Oooo my head hurts will just read through and gather my thoughts and make sure I get all your advice clear, bear with me. So appreciative of your help.
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20th Dec 2009, 5:10 pm | #67 |
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Re: Newb Stumped on a Derwent
Sorry guys so much advice came in it's left me a bit lost.
I think its the following 1. cut end of wire that joins 42 pin 4 to 75 chassis tag (as per Steve P) and confirmed by station x 2. cut other end at 42 pin4 and insert a high value resistor ( whats high 10k 20k 100k ) 3 swap 50uf around as its wrong 4 510k resistor should be terminated on pin 4 of 42. Last edited by oldticktock; 20th Dec 2009 at 5:16 pm. Reason: spelling |
20th Dec 2009, 5:12 pm | #68 | |
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Re: Newb Stumped on a Derwent
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20th Dec 2009, 5:16 pm | #69 | |
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Re: Newb Stumped on a Derwent
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20th Dec 2009, 5:17 pm | #70 |
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Re: Newb Stumped on a Derwent
Just steps 1 and 4. See what that does.
Cheers, Steve P.
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If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...? |
20th Dec 2009, 5:21 pm | #71 |
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Re: Newb Stumped on a Derwent
And step 3.
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20th Dec 2009, 5:31 pm | #72 |
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Re: Newb Stumped on a Derwent
can I confirm that the pins on the 75 conform the same standard as the 42 in as much the heaters are the fat pins 1 & 6 so count clockwise round from pin one. Just want to make sure i get the 510 on the correct pin
Last edited by oldticktock; 20th Dec 2009 at 5:37 pm. |
20th Dec 2009, 5:48 pm | #73 |
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Re: Newb Stumped on a Derwent
There is confusion here. The resisitor needs to be moved from pin 5 to pin 4 of the 42.
NOT THE 75.
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20th Dec 2009, 5:54 pm | #74 |
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Re: Newb Stumped on a Derwent
Ok thats about to be done then I will fire it up ...... well lets home not really
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20th Dec 2009, 5:59 pm | #75 |
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Re: Newb Stumped on a Derwent
Here's how the circuit should be.
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20th Dec 2009, 6:05 pm | #76 |
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Re: Newb Stumped on a Derwent
I'm off to work on one of my own radios now. If the fix doesn't work check the DC voltages between chassis and pins 2 through to 5. Also the voltage between pins 4 and 5.
Post the results here.
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20th Dec 2009, 6:12 pm | #77 |
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Re: Newb Stumped on a Derwent
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20th Dec 2009, 6:26 pm | #78 |
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Re: Newb Stumped on a Derwent
Made changes as suggested, exactly the same scenario as before and when I did the avo trick it allows the station to be heard although this time its much more distorted the volume is on full
Last edited by oldticktock; 20th Dec 2009 at 6:45 pm. |
20th Dec 2009, 6:28 pm | #79 |
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Re: Newb Stumped on a Derwent
Oh and voltage checks were the same
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20th Dec 2009, 6:41 pm | #80 |
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Re: Newb Stumped on a Derwent
Actually pin 2 is now 315 instead of 325 and pin 3 is 335 instead of 345
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