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Old 29th Dec 2016, 12:50 pm   #201
indigo.girl
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Default Re: My first valve radio project - Philips 462A

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Originally Posted by ms660 View Post

First thing I would check are R6 (2,2M) and R7 (470k) providing C17 and C18 aren't electrically leaking those two resistors can be measured in circuit with the valve cold.

If those resistors check out ok then check the anode load resistor R14 (100k) and it's decoupling resistor R13 (100k) those can also be measured in circuit providing C22 isn't electrically leaking and the valve is cold.

Lawrence.
Thanks Lawrence - I'll test the resistors and report back before I swap the Caps over.
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Old 29th Dec 2016, 12:51 pm   #202
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Default 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.
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Old 29th Dec 2016, 3:44 pm   #203
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Default Re: My first valve radio project - Philips 462A

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First thing I would check are R6 (2,2M) and R7 (470k) providing C17 and C18 aren't electrically leaking those two resistors can be measured in circuit with the valve cold.

If those resistors check out ok then check the anode load resistor R14 (100k) and it's decoupling resistor R13 (100k) those can also be measured in circuit providing C22 isn't electrically leaking and the valve is cold.

Lawrence.
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)

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Old 29th Dec 2016, 4:33 pm   #204
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Default 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.
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Old 29th Dec 2016, 4:37 pm   #205
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Default 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.
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Old 29th Dec 2016, 4:54 pm   #206
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Default Re: My first valve radio project - Philips 462A

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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.
That does suggest that the bias voltage may be insufficient, two things I would do, set that preset to 470k and measure the voltage at it's junction with R7, there should be some -v voltage at that point with respect to chassis, based on that measurement we might be able to asses the state of R7, however if you have a replacement for R7 I would replace the original as high M ohm value resistors do have a habit of going high.

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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Old 29th Dec 2016, 5:41 pm   #207
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Default Re: My first valve radio project - Philips 462A

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set that preset to 470k and measure the voltage at it's junction with R7, there should be some -v voltage at that point with respect to chassis, based on that measurement we might be able to asses the state of R7,
Lawrence.
I now do get a negative voltage from the triode screen grid of V2 (pin4). Its -93mV.
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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Old 29th Dec 2016, 5:54 pm   #208
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Default Re: My first valve radio project - Philips 462A

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set that preset to 470k and measure the voltage at it's junction with R7, there should be some -v voltage at that point with respect to chassis, based on that measurement we might be able to asses the state of R7,
Lawrence.
I now do get a negative voltage from the triode screen grid of V2 (pin4). Its -93mV.
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.

Attachment 135093
Ok, some -ve grid voltage is good but the anode voltage is still too low, what I would do now is remove V2 and power up, then measure the voltage of V2's anode connection on the valve socket (pin 3)

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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Old 29th Dec 2016, 6:07 pm   #209
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Default 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
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Old 29th Dec 2016, 7:09 pm   #210
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Default 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.
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Old 29th Dec 2016, 7:30 pm   #211
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Default Re: My first valve radio project - Philips 462A

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Ok, some -ve grid voltage is good but the anode voltage is still too low, what I would do now is remove V2 and power up, then measure the voltage of V2's anode connection on the valve socket (pin 3)

It might have been a typo but the triodes grid is called the control grid, there is no screen grid in a triode.

Lawrence.
Without the valve inserted the voltage at pin 3 (anode position) is 240V and at pin4 (control grid) is 18V

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Old 29th Dec 2016, 7:34 pm   #212
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Default Re: My first valve radio project - Philips 462A

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Ok, some -ve grid voltage is good but the anode voltage is still too low, what I would do now is remove V2 and power up, then measure the voltage of V2's anode connection on the valve socket (pin 3)

It might have been a typo but the triodes grid is called the control grid, there is no screen grid in a triode.

Lawrence.
Without the valve inserted the voltage at pin 3 (anode position) is 225V and at pin4 (control grid) is 18V
Is the 18 volts +ve or -ve with respect to chassis?

Lawrence.
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Old 29th Dec 2016, 7:39 pm   #213
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Default Re: My first valve radio project - Philips 462A

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Originally Posted by ms660 View Post
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.
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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Old 29th Dec 2016, 7:39 pm   #214
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Default Re: My first valve radio project - Philips 462A

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Is the 18 volts +ve or -ve with respect to chassis?

Lawrence.
It is + 18V

Here are all the voltages remeasured with the V2 removed for comparison.

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Last edited by indigo.girl; 29th Dec 2016 at 7:53 pm.
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Old 29th Dec 2016, 7:48 pm   #215
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Default Re: My first valve radio project - Philips 462A

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Is the 18 volts +ve or -ve with respect to chassis?

Lawrence.
It is + 18V
Ouch.....Something amiss there, all control grid bias voltages in valves should be -ve only.

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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Old 29th Dec 2016, 7:55 pm   #216
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Default Re: My first valve radio project - Philips 462A

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Ouch.....Something amiss there, all control grid bias voltages in valves should be -ve only.

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.
Yes, its definitely +Vs. This time I get a reading of 14V.
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Old 29th Dec 2016, 7:58 pm   #217
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Default Re: My first valve radio project - Philips 462A

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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
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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Old 29th Dec 2016, 8:05 pm   #218
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Default Re: My first valve radio project - Philips 462A

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Quote:
Originally Posted by ms660 View Post

Ouch.....Something amiss there, all control grid bias voltages in valves should be -ve only.

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.
Yes, its definitely +Vs. This time I get a reading of 14V.
Ok, that gives us something to work on, the only obvious component that I can see in the schematic that, if leaking, would cause some +ve voltage to appear is C19 in the Trader sheet, might be worth disconnecting/carefully snipping one end and see if that makes any difference.

Lawrence.

Last edited by ms660; 29th Dec 2016 at 8:11 pm. Reason: word change.
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Old 29th Dec 2016, 8:33 pm   #219
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Default 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.

Lawrence.
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Old 29th Dec 2016, 8:34 pm   #220
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Default Re: My first valve radio project - Philips 462A

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Ok, that gives us something to work on, the only obvious component that I can see in the schematic that, if leaking, would cause some +ve voltage to appear is C19 in the Trader sheet, might be worth disconnecting/carefully snipping one end and see if that makes any difference.

Lawrence.
Snipped one end of C19 (5pF). No major differences :-(

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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