29th Dec 2016, 8:40 pm | #221 |
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Re: My first valve radio project - Philips 462A
As per post#219, also check that any components/wires on tag 3 of the valve holder are not touching any components/wires on tag 4. Valve holders can leak between the tags by leaking across the valve holders body, worth having a close look.
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29th Dec 2016, 9:02 pm | #222 |
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Re: My first valve radio project - Philips 462A
Try disconnecting R6 so that the grid floats.
What are the anode and grid voltages then with the valve in?
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29th Dec 2016, 9:05 pm | #223 |
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Re: My first valve radio project - Philips 462A
I've had a really good look and I can see no touching wires/components that connect to pin 3 that could possibly be contacting wires/componets connected to pin 4. The top and bottom view of the valve holder looks clear between pin hole 3 and 4 and I've given the top of the holder a clean. There is infinite resistance measured between pin holes 3 and 4.
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29th Dec 2016, 9:18 pm | #224 | |
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Re: My first valve radio project - Philips 462A
Quote:
Pin 3 = +30V (+V2) and +214V (-V2) Pin 4 = -400 mV (+V2) and +68mV (-V2) With the Valve in I get closer to the expected values |
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29th Dec 2016, 9:19 pm | #225 |
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Re: My first valve radio project - Philips 462A
"There is infinite resistance measured between pin holes 3 and 4"
That isn't always a valid test for electrical leakage, any breakdown could be happening at a higher voltage than a test meter puts out on ohms range. That said, if there's still a +ve voltage on tag 4 of the valve holder with the valve removed it should be possible to trace the source of the problem, what I would do next is to disconnect the components from tag 3 in order to isolate that tag then check the voltage on tag 4 again. Whoops...post crossed. EDIT: That +ve grid voltage previously measured has almost disappeared since R6 has been disconnected and with the valve removed, a known good C17 should be in circuit, what's the voltage at the junction of R6 and R7? It should be -ve with respect to chassis Lawrence. Last edited by ms660; 29th Dec 2016 at 9:31 pm. |
29th Dec 2016, 9:40 pm | #226 | |
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Re: My first valve radio project - Philips 462A
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With valve removed and pin 3 snipped = pin 4 is still positive at +6V (pin3 has a small +18mV measurement rather than 0) I'll now resnip R6 for your next suggestion |
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29th Dec 2016, 9:49 pm | #227 |
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Re: My first valve radio project - Philips 462A
The bias supply from the -ve end of C25 should be -ve. With V2 removed somewhere along it's route to the triodes grid tag it's going +ve, check the bias voltage at all points along its route from the supply.
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29th Dec 2016, 10:22 pm | #228 | |
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Re: My first valve radio project - Philips 462A
Quote:
Test conditions: R6 + C19 + pin3 all reconnected to original positions. Pin 3 = 19.5V (+V2); 242V (-V2) Pin 4 = -65mV (+V2); 4.5V (-V2) Voltage at R6 - R7 junction (wrt chassis) = +9.5V (+V2); +11V (-V2) |
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29th Dec 2016, 10:27 pm | #229 | ||
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Re: My first valve radio project - Philips 462A
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Voltage on the other end of R7, the end that connects to the junction of R19 and R20 with V2 removed. Lawrence. |
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29th Dec 2016, 10:43 pm | #230 | |
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Re: My first valve radio project - Philips 462A
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Hold on ... I've seen the path to the grid too... C25 also goes via R20 to R7 to R6 and then onto the grid tag (pin4). The voltage on the R20 side of R7 is -1.6V. On the other side of R7 it's +8Vs This is where is goes from neg to pos. Last edited by indigo.girl; 29th Dec 2016 at 10:56 pm. |
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29th Dec 2016, 10:57 pm | #231 | ||
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Re: My first valve radio project - Philips 462A
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EDIT: Yes C21 does connect to the triodes anode and not the triodes grid. Lawrence. |
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29th Dec 2016, 11:08 pm | #232 | |
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Re: My first valve radio project - Philips 462A
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29th Dec 2016, 11:22 pm | #233 |
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Re: My first valve radio project - Philips 462A
Is that with everything connected apart from the top end of R6?
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29th Dec 2016, 11:26 pm | #234 | ||
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Re: My first valve radio project - Philips 462A
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Lawrence. |
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29th Dec 2016, 11:28 pm | #235 |
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Re: My first valve radio project - Philips 462A
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29th Dec 2016, 11:31 pm | #236 | |
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Re: My first valve radio project - Philips 462A
Quote:
And yes my other meter does do higher resistance measurements up to 20 or 2000Mohms. I'll try it now. Correction: My other meter needs an extra attachment for high resistance measurements - so no I can't measure it. So its possible its gone very high resistance (I presume not completely open circuit else snipping it out would have given no different effect but it did). I'll have to see what I have knocking around to see if I can replace it tonight.... Last edited by indigo.girl; 29th Dec 2016 at 11:52 pm. |
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29th Dec 2016, 11:48 pm | #237 |
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Re: My first valve radio project - Philips 462A
My apologies, I had annotated the schematic I have with the values of R6 and R7 but I wrote them in the wrong positions
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29th Dec 2016, 11:53 pm | #238 |
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Re: My first valve radio project - Philips 462A
If your testmeter is limited to 2Mohm, put a known value in parallel (470K, 1M or why?), take measurement and then calculate correct value for your 2.2Mohm suspect. formula: 1/Rx=(1/R1+1/R2).
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30th Dec 2016, 12:01 am | #239 |
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Re: My first valve radio project - Philips 462A
Keep at it Lawrence and Nicola, its getting quite exciting.
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30th Dec 2016, 12:04 am | #240 |
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Re: My first valve radio project - Philips 462A
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