Philco 333 help - Page 4 - UK Vintage Radio Repair and Restoration Discussion Forum

Norman Raeburn · 22nd Mar 2017, 8:05 pm

I also think some of the voltages quoted can be taken with a pinch of salt, the grid supply is quoted in the manual as -6.5v but with my rusty ohms law, if we take the ht current 6ma and multiply that by the resistance of R1/R2 500 ohm I get it to 3v which is what it reads, unless I am doing something stupid again. Norman

Boater Sam · 22nd Mar 2017, 9:10 pm

I can't get my head around the voltage readings either Norman. Ohms law just gives the wrong answers, of course we have the differences between the early meters and modern more sensitive ones. But its still a mile out.

Being confused by the fact you have good audio off the grid, and better audio output with a signal generator input to the grid, I question the impedances between the second detector valve and the output. I think there is a big impedance mismatch.
Those resistors on the grid are very high value, the input voltage will be halved by the one in series and the shunt to ground as well.
I would try changing the values and see what difference it makes. Its time for a little experimentation I think.
I would doubt that these sets ever sounded good, they are very minimal all round.
You did well to find another PEN23, did it make a real difference?

Norman Raeburn · 22nd Mar 2017, 10:03 pm

Hi, The new PEN23 made a little bit of difference but not enough. I really don't know how well this ever performed, according to the service sheet it's supposed to be comparable to a superhet! I will experiment with the resistors mentioned. The service manual quotes them as 490k but they have been change to 470k. I feel such a fool at the amount of man hours wasted on this, well not totally wasted as I have learned quite a bit along the way. I think if I can't get this working better by the weekend I will call it a day as I can't really spend any more time on it. Many thanks again for the suggestions. Norman

Silicon · 22nd Mar 2017, 11:00 pm

It would be interesting to know the speaker impedance and the turns ratio of the output transformer.

I can't find any data on the Pen23 but the above information might give us the anode load resistance.

Norman Raeburn · 22nd Mar 2017, 11:11 pm

Hi, The speaker and output transformer are original and riveted together, the transformer primary is marked as 18k. I am at the moment using the original transformer and a replacement speaker as the original speaker looks in poor condition. I have substituted the transformer and the results are worse, probably due to a mismatched transformer. Norman

julie_m · 22nd Mar 2017, 11:35 pm

So, just to recap, you have managed to obtain the proper output valve for the output transformer, it's biased correctly and the performance is better but still distorted? But if you take the signal that is meant for the output valve and feed it to another amplifier, that is undistorted?

If so, that means the fault must lie downstream of the take-off point. So there is the valve, the transformer, the speaker and a few passives. Going by the manufacturers' data, that's R3, R4, R5, R6, C3, C5, C7 and EC1. 470k is a modern preferred value, and is only 4% off 490k. Test them all anyway (with the valves cold), and replace with good quality 1W metal film if in doubt. Capacitors need to be the same value, same or higher voltage (not too much higher for electrolytics).

Have you tried disconnecting the speaker from the transformer secondary, and feeding it from another source? Just to exonerate the speaker .....

If the speaker is good, and you have another speaker transformer from another set (one from a battery set would be best, but almost any output transformer will do if you are desperate -- even a small mains transformer with a 6 - 18 V secondary), you could try connecting that back-to-back with the one from the Philco. Then feed a signal into its secondary, using it in reverse to feed a stepped-up signal into the Philco transformer primary, thence to the secondary and the speaker. This will test the transformer.

Norman Raeburn · 23rd Mar 2017, 12:09 am

Hi Julie, I haven't tried the speaker from another source but will do on Friday. The thing I can't get my head around is that feeding the audio to another amp the sound is ok. If I feed my audio generator into the grid of the output valve it sounds ok and is undistorted checked with my 'scope. I don't know if it's as Boater Sam suggested a mismatch between the detector stage and the output stage. I really am confused by this, if it was my radio it would be on the shelf on display only. Norman

PJL · 23rd Mar 2017, 1:03 am

Do you have an AF modulated RF signal generator? What does the output look like then? Your latest post might point to instability. It would be interesting to try it on batteries.

ms660 · 23rd Mar 2017, 9:43 am

Some waveform pics with peak to peak voltages given, with everything as original might help?

Lawrence.

Norman Raeburn · 10th May 2017, 7:50 pm

Hi Folks, I want to bring this to a conclusion in case everybody thinks I have ran away. I have put this thing back together and I am giving up on it. I have spent ridiculous amounts of time and money trying in vain to get the radio working better. I would like to thank all who have given me guidance through this and although I haven't managed to repair the set I have a better understanding of how it should work. Very many thanks, Norman. PS if one of the moderators would like to close this then please feel free.

22nd Mar 2017, 8:05 pm	#61
Norman Raeburn Heptode Join Date: Feb 2008 Location: Leven, Fife, Scotland Posts: 823	Re: Philco 333 help I also think some of the voltages quoted can be taken with a pinch of salt, the grid supply is quoted in the manual as -6.5v but with my rusty ohms law, if we take the ht current 6ma and multiply that by the resistance of R1/R2 500 ohm I get it to 3v which is what it reads, unless I am doing something stupid again. Norman

22nd Mar 2017, 9:10 pm	#62
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Philco 333 help I can't get my head around the voltage readings either Norman. Ohms law just gives the wrong answers, of course we have the differences between the early meters and modern more sensitive ones. But its still a mile out. Being confused by the fact you have good audio off the grid, and better audio output with a signal generator input to the grid, I question the impedances between the second detector valve and the output. I think there is a big impedance mismatch. Those resistors on the grid are very high value, the input voltage will be halved by the one in series and the shunt to ground as well. I would try changing the values and see what difference it makes. Its time for a little experimentation I think. I would doubt that these sets ever sounded good, they are very minimal all round. You did well to find another PEN23, did it make a real difference?

22nd Mar 2017, 10:03 pm	#63
Norman Raeburn Heptode Join Date: Feb 2008 Location: Leven, Fife, Scotland Posts: 823	Re: Philco 333 help Hi, The new PEN23 made a little bit of difference but not enough. I really don't know how well this ever performed, according to the service sheet it's supposed to be comparable to a superhet! I will experiment with the resistors mentioned. The service manual quotes them as 490k but they have been change to 470k. I feel such a fool at the amount of man hours wasted on this, well not totally wasted as I have learned quite a bit along the way. I think if I can't get this working better by the weekend I will call it a day as I can't really spend any more time on it. Many thanks again for the suggestions. Norman

22nd Mar 2017, 11:00 pm	#64
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,167	Re: Philco 333 help It would be interesting to know the speaker impedance and the turns ratio of the output transformer. I can't find any data on the Pen23 but the above information might give us the anode load resistance.

22nd Mar 2017, 11:11 pm	#65
Norman Raeburn Heptode Join Date: Feb 2008 Location: Leven, Fife, Scotland Posts: 823	Re: Philco 333 help Hi, The speaker and output transformer are original and riveted together, the transformer primary is marked as 18k. I am at the moment using the original transformer and a replacement speaker as the original speaker looks in poor condition. I have substituted the transformer and the results are worse, probably due to a mismatched transformer. Norman

22nd Mar 2017, 11:35 pm	#66
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Philco 333 help So, just to recap, you have managed to obtain the proper output valve for the output transformer, it's biased correctly and the performance is better but still distorted? But if you take the signal that is meant for the output valve and feed it to another amplifier, that is undistorted? If so, that means the fault must lie downstream of the take-off point. So there is the valve, the transformer, the speaker and a few passives. Going by the manufacturers' data, that's R3, R4, R5, R6, C3, C5, C7 and EC1. 470k is a modern preferred value, and is only 4% off 490k. Test them all anyway (with the valves cold), and replace with good quality 1W metal film if in doubt. Capacitors need to be the same value, same or higher voltage (not too much higher for electrolytics). Have you tried disconnecting the speaker from the transformer secondary, and feeding it from another source? Just to exonerate the speaker ..... If the speaker is good, and you have another speaker transformer from another set (one from a battery set would be best, but almost any output transformer will do if you are desperate -- even a small mains transformer with a 6 - 18 V secondary), you could try connecting that back-to-back with the one from the Philco. Then feed a signal into its secondary, using it in reverse to feed a stepped-up signal into the Philco transformer primary, thence to the secondary and the speaker. This will test the transformer. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

23rd Mar 2017, 12:09 am	#67
Norman Raeburn Heptode Join Date: Feb 2008 Location: Leven, Fife, Scotland Posts: 823	Re: Philco 333 help Hi Julie, I haven't tried the speaker from another source but will do on Friday. The thing I can't get my head around is that feeding the audio to another amp the sound is ok. If I feed my audio generator into the grid of the output valve it sounds ok and is undistorted checked with my 'scope. I don't know if it's as Boater Sam suggested a mismatch between the detector stage and the output stage. I really am confused by this, if it was my radio it would be on the shelf on display only. Norman

23rd Mar 2017, 1:03 am	#68
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: Philco 333 help Do you have an AF modulated RF signal generator? What does the output look like then? Your latest post might point to instability. It would be interesting to try it on batteries.

23rd Mar 2017, 9:43 am	#69
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Philco 333 help Some waveform pics with peak to peak voltages given, with everything as original might help? Lawrence.

10th May 2017, 7:50 pm	#70
Norman Raeburn Heptode Join Date: Feb 2008 Location: Leven, Fife, Scotland Posts: 823	Re: Philco 333 help Hi Folks, I want to bring this to a conclusion in case everybody thinks I have ran away. I have put this thing back together and I am giving up on it. I have spent ridiculous amounts of time and money trying in vain to get the radio working better. I would like to thank all who have given me guidance through this and although I haven't managed to repair the set I have a better understanding of how it should work. Very many thanks, Norman. PS if one of the moderators would like to close this then please feel free.