29th Dec 2016, 12:50 pm | #201 | |
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Re: My first valve radio project - Philips 462A
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29th Dec 2016, 12:51 pm | #202 |
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Re: My first valve radio project - Philips 462A
I would check out the resistors in post#194 and by association C22.
EDIT: Woops...post crossed, ignore this one. Lawrence. |
29th Dec 2016, 3:44 pm | #203 | |
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Re: My first valve radio project - Philips 462A
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R6 = >2M (2.2M spec) R7 = 100-400K (470K spec) R14 =109K (100K spec) R13 = 113K (100K spec) |
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29th Dec 2016, 4:33 pm | #204 |
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Re: My first valve radio project - Philips 462A
"Here are the resistance readings. Basically all on spec except for R7 which seems to have a variable resistance ranging from 100-400K ohms - so I suspect has a fracture in it somewhere.
R6 = >2M (2.2M spec) R7 = 100-400K (470K spec) R14 =109K (100K spec) R13 = 113K (100K spec) R7 does look dodgy looking at your measurement, I would replace it, R14 and R13 look ok. When say ">2M" do you mean greater than 2M, if so how much, or does it mean that your meter isn't designed to measure over 2M? Lawrence. |
29th Dec 2016, 4:37 pm | #205 |
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Re: My first valve radio project - Philips 462A
Well here's an interesting observation....
I wanted to replace R7 (470K) but only had a 1M ohm variable resistor to hand. So I set it to 470k and soldered it into the circuit. No real change. I then, of course, decided to see what would happen when I varied the resistance and I found a significant increase in volume at the zero resistance. So I removed the variable resistor and replaced it with a continuous wire. I now get a much higher peak volume and this slowly reduces to silence across the WHOLE span of the volume control. Exactly what I was wanting. How do you explain that one! PS: my dodgy R7 resistor is <2M because 2M is the max my multimeter will measure to. |
29th Dec 2016, 4:54 pm | #206 | |
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Re: My first valve radio project - Philips 462A
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Meanwhile do post the voltage measurement suggested first so there's an idea as to what's what, all this might sound like a long way round but it's important to do one step at a time when learning to troubleshoot. Lawrence. |
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29th Dec 2016, 5:41 pm | #207 | |
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Re: My first valve radio project - Philips 462A
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I'm still getting the same voltage from the V2 triode anode (pin3) of 18V. I have measured a few more voltages annotated on the figure. In this set up R7 is now the variable resistor preset at 470 Kohms. I have also replaced C22 with a new cap - although I heard no differences before and after changing C22 but of course I didn't measure voltages. |
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29th Dec 2016, 5:54 pm | #208 | ||
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Re: My first valve radio project - Philips 462A
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It might have been a typo but the triodes grid is called the control grid, there is no screen grid in a triode. Lawrence. |
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29th Dec 2016, 6:07 pm | #209 |
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Re: My first valve radio project - Philips 462A
Hi
On a slight tangent, can I ask a silly question. You said the volume on the radio when amplifying your phone is low, is the music source (phone) you are using turned up full. Mike |
29th Dec 2016, 7:09 pm | #210 |
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Re: My first valve radio project - Philips 462A
I've found some valve data for the ECH21 using the triode as an AF amp, they all state that with an HT (Vb) supply of 250 volts the anode voltage computes to 50 volts with an anode load resistance of 200k with a grid bias voltage of -ve 2 volts.
Lawrence. |
29th Dec 2016, 7:30 pm | #211 | |
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Re: My first valve radio project - Philips 462A
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Last edited by indigo.girl; 29th Dec 2016 at 7:35 pm. |
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29th Dec 2016, 7:34 pm | #212 | ||
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Re: My first valve radio project - Philips 462A
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Lawrence. |
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29th Dec 2016, 7:39 pm | #213 |
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Re: My first valve radio project - Philips 462A
Interesting - so I'm getting the HT supply of about 250V but this is not translating to the higher anode voltage of 50V. The -ve grid bias is a lot higher than -2V also. How do I measure anode load resistance? Is is this referring to the resistor connected to anode (R14) which is 100k in this instance
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29th Dec 2016, 7:39 pm | #214 |
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Re: My first valve radio project - Philips 462A
Last edited by indigo.girl; 29th Dec 2016 at 7:53 pm. |
29th Dec 2016, 7:48 pm | #215 | |
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Re: My first valve radio project - Philips 462A
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If the control grid tag on the valve socket does indeed measure 18 volts +ve with the valve removed then that would suggest a leakage some where from a +ve voltage source to the bias supply for the valve, so to be sure could you confirm again that it's 18 volts +ve with respect to the chassis with the valve removed. Lawrence. |
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29th Dec 2016, 7:55 pm | #216 | |
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Re: My first valve radio project - Philips 462A
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29th Dec 2016, 7:58 pm | #217 |
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Re: My first valve radio project - Philips 462A
Quick reply for Mike - the phone is up full. The problem is not that the audio from the set is too low. At max volume its adequate for listening too. But I have to turn it right to max to hear it. There's nothing to hear at the lower volume setting right up to almost the max position when suddenly lots of volume kicks in. I want a smoother increase
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29th Dec 2016, 8:05 pm | #218 | ||
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Re: My first valve radio project - Philips 462A
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Lawrence. Last edited by ms660; 29th Dec 2016 at 8:11 pm. Reason: word change. |
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29th Dec 2016, 8:33 pm | #219 |
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Re: My first valve radio project - Philips 462A
If that capacitor is ok then it's starting to look like leakage between tags 3 and 4 on the valve holder.
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29th Dec 2016, 8:34 pm | #220 | |
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Re: My first valve radio project - Philips 462A
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Pin 3 = 18V (+V2) and 240V (-V2) Pin 4 = -113mV (+V2) and +9V (-V2) Although when I play via the bluetooth the volume control issue has resolved. I get a high max volume and a nice gradual increase through the range. Last edited by indigo.girl; 29th Dec 2016 at 8:40 pm. |
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