UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Radio (domestic)

Notices

Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

Closed Thread
 
Thread Tools
Old 28th Dec 2016, 10:05 pm   #181
peter_sol
Octode
 
Join Date: Aug 2003
Location: Welwyn Garden City, Herts. UK.
Posts: 1,906
Default Re: My first valve radio project - Philips 462A

Use 10k resistors in series with your phone outputs otherwise you will overheat the phone's (or other devices) output stage.
You would not connect the two outputs of a stereo amplifier together and then use one speaker would you?
The same applies.
peter_sol is offline  
Old 28th Dec 2016, 10:08 pm   #182
indigo.girl
Retired Dormant Member
 
Join Date: Apr 2016
Location: Loughborough, Leicestershire, UK.
Posts: 754
Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by Ed_Dinning View Post
Hi Nicola, the 2 resistors are to give a small degree of isolation to the stereo channels. They also act as safety resistor if something go wrong on the radio and it will not incinerate your player.

These sets were often designed to run from high output record player cartridges, perhaps up to 1 volt. Do you know, or can you measure (scope preferably) the output of your player?
Does this drop significantly when connected to the radio?
Some players have been used with a small IC amplifier to boost the sound.

Not sure of your circuit, but check to see if the cap in series with the tone control is OK, if it has gone low resistance, it will shunt the output transformer and reduce volume as you describe.

Note that some sets used the on/off switch on the tone, not vol control (to save wear and tear.

Ed
Hi Ed - I've just double checked and in the traders manual is states that the on/off switches S18 and S19 are ganged to volume control R8. Useful to know that they can sometimes be on tone control sometimes.

At the moment I'm connected my iphone via the 3.5mm jack but ultimately I want to use a bluetooth device. I have used a bluetooth device on a radiogram to get wireless audio playing through the radio input in it (to complement the existing grams and radio functions). So its the output of the bluetooth device that I need to consider. I have plugged in my BT device to the mains and sent audio to it from my phone. It has a 3.5 mm jack coming from it so I tried to measure some voltage across the ground and audio part of the jack - can't detect anything. So either its very low signal voltage - or I'm just not doing it right...

So I don't know about voltage but from my experiences last time I know that when I switch off the power to the bluetooth is goes very high impedance and caused lots of buzz from the radiogram - so I connected 47k resistors from each channel input to ground.

https://www.vintage-radio.net/forum/...d.php?t=132236
indigo.girl is offline  
Old 28th Dec 2016, 10:17 pm   #183
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: My first valve radio project - Philips 462A

I doubt if you will get a voltage reading from the signal output of your device, the signal voltage will be low and will be AC, ordinary meters measuring AC won't normally measure audio frequencies very well.

Don't forget the voltage checks mentioned earlier.

Lawrence.
ms660 is offline  
Old 28th Dec 2016, 10:45 pm   #184
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: My first valve radio project - Philips 462A

Hi Nicola, I am sure 2.2k ohm resistors will be sufficient. Just add one resistor in series with each signal (left & right) then combine them together.
Did I see that you had removed the wiring to S16 and R12 (trader) to isolate the point you connected to from the radio circuit. That should stop any stray unwanted volts in the radio from damaging your phone.

Without the resistors you have shorted one channel output onto the other channel output, this is not good practice.

C18 (trader) will give protection from stray DC voltages that may happen in the valve radio, so it may be worthwhile changing it for a known good one of high voltage, just in case a fault develops in V2 triode. (unlikely but just to be safe)

Mike

Last edited by crackle; 28th Dec 2016 at 10:57 pm.
crackle is offline  
Old 28th Dec 2016, 11:50 pm   #185
indigo.girl
Retired Dormant Member
 
Join Date: Apr 2016
Location: Loughborough, Leicestershire, UK.
Posts: 754
Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by ms660 View Post
so far there might be an assumption that those stages are both working as they should, the 1st port of call for that is measure the valves voltages, the triode section of V2 (AF amp) and the pentode section of V3 (AF output) Measure the voltage on V2's triode anode and V2's triode grid (called the control grid) Measure the voltage on V3's pentode anode, screen grid and control grid, the control grid voltages should be -ve, all other voltages +ve, the cathodes of those valves are connected to the chassis so there will be no cathode voltages to measure.

All voltages measured as DC with respect to the chassis.
Lawrence.
Hi Lawrence - here are the voltage measurements for the two amp stages:

V3 pentode:
Anode (pin2) = 260V
Screen grid (g2; pin4) = 240V
Control grid (g1; pin3) = -3.68V

V2 triode:
Anode (a.t; pin3) = 15.1V
Control grid (g1.t; pin4) = 60mV

The control grid for the V2 triode is very small but not negative as you suggested it should be. Is this cause for concern?
indigo.girl is offline  
Old 28th Dec 2016, 11:55 pm   #186
indigo.girl
Retired Dormant Member
 
Join Date: Apr 2016
Location: Loughborough, Leicestershire, UK.
Posts: 754
Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by peter_sol View Post
Use 10k resistors in series with your phone outputs otherwise you will overheat the phone's (or other devices) output stage.
You would not connect the two outputs of a stereo amplifier together and then use one speaker would you?
The same applies.
Based on Peters and Mikes recommendation that I should have a resistor in series on each input channel before connecting to mono I've added a couple as suggested.

I only have 47K Ohms to hand so used those; obviously a bit higher than Peters suggestion of 10K Ohms (and a lot higher than 2.2k Ohms from Mike). I made the assumption that something is better than nothing. I can of cause change these to lower values if I order some in. What is the potential issue (if any) of using a resister that is too high? Will I lose any signal?
indigo.girl is offline  
Old 28th Dec 2016, 11:56 pm   #187
indigo.girl
Retired Dormant Member
 
Join Date: Apr 2016
Location: Loughborough, Leicestershire, UK.
Posts: 754
Default Re: My first valve radio project - Philips 462A

By the way, I have now fitted my bluetooth device to the set rather than my phone - working well (but with the same volume control issue of course).
indigo.girl is offline  
Old 29th Dec 2016, 12:32 am   #188
Lucien Nunes
Rest in Peace
 
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
Default Re: My first valve radio project - Philips 462A

Quote:
What is the potential issue (if any) of using a resister that is too high? Will I lose any signal?
Yes, there may be more attenuation and/or treble cut according to the input load resistance and capacitance of the circuit you feed the mono signal into. The idea of these resistors is simply to stop the two outputs 'fighting' for control of a single point in the circuit, whenever there is a difference between the instantaneous signal voltages on the L & R channels. Some headphone/line outs have sufficient resistance built-in to allow them to be directly paralleled without damage or distortion, others do not.

In theory, with a headphone output designed to work into typical 32Ω phones, the mixing resistors need not be very high - I often use 470Ω when working into a mono line input, so that the source impedance is 235Ω and the load on each output around 1kΩ (i.e. the path from one output through both resistors back into the other output, which we assume has minimal source impedance). Higher values such as those suggested above will work well too provided the input impedance of the mono destination is an order of magnitude higher still.
Lucien Nunes is offline  
Old 29th Dec 2016, 12:34 am   #189
indigo.girl
Retired Dormant Member
 
Join Date: Apr 2016
Location: Loughborough, Leicestershire, UK.
Posts: 754
Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by crackle View Post

C18 (trader) will give protection from stray DC voltages that may happen in the valve radio, so it may be worthwhile changing it for a known good one of high voltage, just in case a fault develops in V2 triode. (unlikely but just to be safe)

Mike
I've replaced old hunts C18 (10nF) with a new cap (47nF @ 400V).
No significant change, although I think there is now some weak audio heard at the lower vol pot positions rather than at all suddenly coming on at the highest pot positions only. Only a slight improvement, with most of the useable volume coming at the end of the turn of the dial.

Why is volume a log pot rather than a linear. Surely a log pot will be prone to giving all the volume at the top end?

I'm still having the strange issue with tone control - it seems to act like a volume control.
indigo.girl is offline  
Old 29th Dec 2016, 1:08 am   #190
Lucien Nunes
Rest in Peace
 
Join Date: Apr 2008
Location: London, UK.
Posts: 2,508
Default Re: My first valve radio project - Philips 462A

Quote:
Why is volume a log pot rather than a linear. Surely a log pot will be prone to giving all the volume at the top end?
You actually need most of the increase in level to occur at the top end, to give an impression of smooth increase in volume. The auditory system has a logarithmic response to enable it to handle a very wide range of levels occurring in nature. Thus there is as much perceived increase in volume from 0.1 watt of sound power to 0.2W, as there is from 100W to 200W. A linear control would put 1/4 maximum power midway on the dial, which sounds almost as loud as full volume, while all the useful range of control would be clustered at the anticlockwise end of the travel.
Lucien Nunes is offline  
Old 29th Dec 2016, 8:23 am   #191
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: My first valve radio project - Philips 462A

Hi
C23 (trader) is the capacitor associated with the tone control. When the tone control wiper is at the bottom (see trader circuit) C23 is in effect connected across the grid of the output valve and chassis. The effect of the capacitor will be to create a path for the higher frequencies to ground thus removing some of the high frequencies, it is a treble cut control. The value .0039uF seems high to me, it may actually be cutting out the high frequencies and also encroaching onto the middle frequencies. If this is a wax type capacitor I would change it, either for a new 0.0033uF capacitor (3.3nF), or you could also try a 1nF rather than the 3.3nF, it would then tend to cut less of the "middle" frequencies and make things sound louder and clearer. If 1nF makes the tone control have too little effect, then try something in the middle, say 2.2nF capacitor. I have often seen the tone control capacitor in my radios as a small value such as a few hundred pF, rather than a few thousands of pF's.

Mike

Last edited by crackle; 29th Dec 2016 at 8:34 am.
crackle is offline  
Old 29th Dec 2016, 10:14 am   #192
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,173
Default Re: My first valve radio project - Philips 462A

Hi Nicola, it may need an oscilloscope to measure the voltage out of your I pad, see if you can borrow one.
An AC millivoltmeter would do, but with a scope you can "see" the actual signal and be sure it is not something else.

Ed
Ed_Dinning is online now  
Old 29th Dec 2016, 10:35 am   #193
PaulR
Dekatron
 
PaulR's Avatar
 
Join Date: Oct 2003
Location: Southport Lancashire, UK.
Posts: 3,221
Default Re: My first valve radio project - Philips 462A

I have just come across this thread having repaired the same model before Christmas. Just one point I would make is that in mine the wiring was all rubber insulated and all the rubber was crumbling. If yours also has rubber insulation I would poke around to make sure it is ok.

In my example the mains transformer had shorted turns and the output one was open circuit!
PaulR is offline  
Old 29th Dec 2016, 11:08 am   #194
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by indigo.girl View Post
Quote:
Originally Posted by ms660 View Post
so far there might be an assumption that those stages are both working as they should, the 1st port of call for that is measure the valves voltages, the triode section of V2 (AF amp) and the pentode section of V3 (AF output) Measure the voltage on V2's triode anode and V2's triode grid (called the control grid) Measure the voltage on V3's pentode anode, screen grid and control grid, the control grid voltages should be -ve, all other voltages +ve, the cathodes of those valves are connected to the chassis so there will be no cathode voltages to measure.

All voltages measured as DC with respect to the chassis.
Lawrence.
Hi Lawrence - here are the voltage measurements for the two amp stages:

V3 pentode:
Anode (pin2) = 260V
Screen grid (g2; pin4) = 240V
Control grid (g1; pin3) = -3.68V

V2 triode:
Anode (a.t; pin3) = 15.1V
Control grid (g1.t; pin4) = 60mV

The control grid for the V2 triode is very small but not negative as you suggested it should be. Is this cause for concern?
According to those measurements V3 pentode voltages are in the ball park... But....V2 triode voltages are out by quite a bit, the anode voltage should be higher, there is no spec for the grid volts in the Trader sheet but I would say that whatever it should be should be -ve, lack of bias voltage on a valves control grid will cause the anode to pass more current, that current has to pass through the anodes load, that means the voltage drop across that load will increase therefore reducing the voltage on the anode.

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.
ms660 is offline  
Old 29th Dec 2016, 11:26 am   #195
indigo.girl
Retired Dormant Member
 
Join Date: Apr 2016
Location: Loughborough, Leicestershire, UK.
Posts: 754
Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by crackle View Post
Hi
C23 (trader) is the capacitor associated with the tone control. When the tone control wiper is at the bottom (see trader circuit) C23 is in effect connected across the grid of the output valve and chassis. The effect of the capacitor will be to create a path for the higher frequencies to ground thus removing some of the high frequencies, it is a treble cut control. The value .0039uF seems high to me, it may actually be cutting out the high frequencies and also encroaching onto the middle frequencies. If this is a wax type capacitor I would change it, either for a new 0.0033uF capacitor (3.3nF), or you could also try a 1nF rather than the 3.3nF, it would then tend to cut less of the "middle" frequencies and make things sound louder and clearer. If 1nF makes the tone control have too little effect, then try something in the middle, say 2.2nF capacitor. I have often seen the tone control capacitor in my radios as a small value such as a few hundred pF, rather than a few thousands of pF's.

Mike
Hi Mike - in my meagre stash of capacitors I have a 330pF (50V wkg). The next one up is 22nF (50V). I have measured the DC voltage across C23 and its only a few mV so I've presumed the low working voltage of 50V will be OK for this position and replaced C23 with the 330pF cap. There is now only a slight decrease in volume as I move the wiper from one side to the other which is good. The effectiveness as a tone control is poor though and I can't detect any noticeable decrease in treble. Perhaps I should experiment with cap values to hit the sweet spot. How good would the tone control have been expected to have been anyway when the model was first out? Pretty basic I should think so I might just leave it as is.

Can you also confirm that my thinking around working voltage is OK and that it is safe to leave the 50V cap in permanently?
indigo.girl is offline  
Old 29th Dec 2016, 11:33 am   #196
GeoffK
Heptode
 
Join Date: Mar 2016
Location: Essex, UK.
Posts: 602
Default Re: My first valve radio project - Philips 462A

As this is no longer a thread about a vintage radio but an audio amplifier shouldn't a new thread in the vintage audio be started. It would have been interesting to know if the radio worked. The anode voltage of the triode section of V2 should be around 40 Volts so the valve could be conducting too heavily. As V1 will never be used again this could be removed, and tried in V2 position.
GeoffK is offline  
Old 29th Dec 2016, 12:14 pm   #197
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: My first valve radio project - Philips 462A

50v cap for C23 should be fine, no real harm can come if it goes faulty anyway, other than loss of audio if it fails shorted.
Have you changed all the wax paper capacitors, in the AF part of the receiver (e.g. C22 & C17 trader) .
Philips sometimes used paper caps covered in black pitch which also need to be changed.

Mike
crackle is offline  
Old 29th Dec 2016, 12:31 pm   #198
GeoffK
Heptode
 
Join Date: Mar 2016
Location: Essex, UK.
Posts: 602
Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by crackle View Post
50v cap for C23 should be fine, no real harm can come if it goes faulty anyway, other than loss of audio if it fails shorted.
Have you changed all the wax paper capacitors, in the AF part of the receiver (e.g. C22 & C17 trader) .
Philips sometimes used paper caps covered in black pitch which also need to be changed.

Mike
The Philips black pitch covered capacitors tend to be quite reliable, I have an older Philips radio still with its original capacitors and it works just fine, though any type can be replaced with a modern polyester for improved performance and reliability. I personally would re-instate the original electrolytic can capacitors for appearances with the replacement electrolytics underneath.
GeoffK is offline  
Old 29th Dec 2016, 12:39 pm   #199
indigo.girl
Retired Dormant Member
 
Join Date: Apr 2016
Location: Loughborough, Leicestershire, UK.
Posts: 754
Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by crackle View Post
50v cap for C23 should be fine, no real harm can come if it goes faulty anyway, other than loss of audio if it fails shorted.
Have you changed all the wax paper capacitors, in the AF part of the receiver (e.g. C22 & C17 trader) .
Philips sometimes used paper caps covered in black pitch which also need to be changed.

Mike
Hi Mike - there are only 5 black capacitors left as the originals now.

C17 (the V2 triode GB decoupler) has already been changed but I will change C22 now also (the V2 triode HT decoupler) as you suggest.

C10 is the AVC line decoupler so I'll change that too.

C24 is the fixed tone corrector - this sounds relevant to tone control so I will replace this also.

C3 and C4 are band pass couplers so I won't bother changing those as they aren't going to be used now.
indigo.girl is offline  
Old 29th Dec 2016, 12:48 pm   #200
indigo.girl
Retired Dormant Member
 
Join Date: Apr 2016
Location: Loughborough, Leicestershire, UK.
Posts: 754
Default Re: My first valve radio project - Philips 462A

Quote:
Originally Posted by Hetrodyne View Post
The anode voltage of the triode section of V2 should be around 40 Volts so the valve could be conducting too heavily. As V1 will never be used again this could be removed, and tried in V2 position.
Good idea.
I get the same reading regardless of which ECH21 is in the V2 position so we can rule out a valve fault.
indigo.girl is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 7:27 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.