22nd Dec 2009, 1:54 pm | #221 |
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Re: Newb Stumped on a Derwent
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22nd Dec 2009, 1:56 pm | #222 |
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Re: Newb Stumped on a Derwent
heaters read 6vac
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22nd Dec 2009, 2:02 pm | #223 |
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Re: Newb Stumped on a Derwent
Heater voltage is fine.
Bias on the 75 is a bit high. 3 VDC instead of 2 VDC. Did you check the resistance of the 1.8K? You can check it in circuit with the set off, but expect a delay as the 25uF charges. Check the voltage pin 5 to top cap, but don't use the VVM. (both points relate to 75). While you're at it check the voltage pin 4 to pin 5 of the 42. (expect 15V)
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22nd Dec 2009, 2:15 pm | #224 | |
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Re: Newb Stumped on a Derwent
Quote:
no reading on TC avo set to AC signal goes low avo set to DC hum introduced when you say check voltage pin 4 to 5 do you mean the same way i tested heaters one probe on 4 and one on 5, if so 0 reading volume drops greatly |
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22nd Dec 2009, 2:21 pm | #225 |
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Re: Newb Stumped on a Derwent
Try the 42 first. AVO on DCV. One lead to pin 5 (cathode), one lead to pin 4 (control grid) expect about 15V.
Then on 75. Set volume to maximum. AVO on DCV. One lead to pin 5 (cathode) one lead to TC (grid) expect 3V.
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22nd Dec 2009, 2:29 pm | #226 | |
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Re: Newb Stumped on a Derwent
HANG ON!
From post 219. Quote:
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22nd Dec 2009, 2:31 pm | #227 | |
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Re: Newb Stumped on a Derwent
Quote:
Meter reads dc fine checked on the rectifier |
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22nd Dec 2009, 2:34 pm | #228 | ||
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Re: Newb Stumped on a Derwent
Quote:
using the AVO does not register could this mean the AVO can read High DC but low DC no might be the problem I was having the other night perhaps the AVO is faulty. THAT cap is brand new Last edited by oldticktock; 22nd Dec 2009 at 2:42 pm. |
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22nd Dec 2009, 2:40 pm | #229 |
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Re: Newb Stumped on a Derwent
I'm beginning to suspect the test gear. Check the voltage with the AVO. Then, if you've seen a positive reading, disconnect THAT capacitor from pin 4 and try again. You should see zero volts.
Then connect the meter between chassis and the disconected end of THAT capacitor. Again expect to see zero volts.
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22nd Dec 2009, 2:46 pm | #230 |
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Re: Newb Stumped on a Derwent
I've just noticed that OTT is measuring voltages with an AVO 7.
An AVO 7 is not an ideal instrument for measuring voltages in valve circuits as it is a 1000 or 500 ohms per Volt instrument depending on settings. It will provide low, inaccurate readings unless it is used on a high voltage range. John |
22nd Dec 2009, 2:50 pm | #231 | |
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Re: Newb Stumped on a Derwent
Quote:
Why can i not use the VVM to measure and forget the avo |
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22nd Dec 2009, 2:52 pm | #232 |
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Re: Newb Stumped on a Derwent
We'd better stick with the VVM then, but obviously it can only be used for measurements to chassis because of the earthed probe.
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22nd Dec 2009, 2:53 pm | #233 | |
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Re: Newb Stumped on a Derwent
Quote:
only problem is its DC probe socket seems to be a 1/4 jack odd!!!!! just found a 1/4 jack in my box of spares |
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22nd Dec 2009, 2:58 pm | #234 | |
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Re: Newb Stumped on a Derwent
Stick with the Cossor. I'd like to get to the bottom of the voltage on pin 4 (control grid) of the 42. Yesterday you measured 0 volts there which is correct.
From post 115. Quote:
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22nd Dec 2009, 3:00 pm | #235 |
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Re: Newb Stumped on a Derwent
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22nd Dec 2009, 3:01 pm | #236 |
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Re: Newb Stumped on a Derwent
Just remembered when I inherited the test gear, the Cossor VVM's mains lead was naff so i replaced it and I introduced the earth. Guess that was a no no....... damm my stupidity hurts its a 1956 model so guess they would not have earthed it
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22nd Dec 2009, 3:06 pm | #237 |
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Re: Newb Stumped on a Derwent
radio has been on all this time. 42 pin 4 now reads 5vdc
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22nd Dec 2009, 3:06 pm | #238 | |
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Re: Newb Stumped on a Derwent
Quote:
Don't worry about the earth on the VVM, we''l stick with readings to chassis.
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22nd Dec 2009, 3:08 pm | #239 |
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Re: Newb Stumped on a Derwent
42
pin1..6 pin2..260 pin3.270 pin4..5 pin5..15 pin6..6 |
22nd Dec 2009, 3:09 pm | #240 | |
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Re: Newb Stumped on a Derwent
Quote:
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