I've got a philco radio 41-280 model and I just changed all the caps and replaced some of the tubes...It works, but I can't get rid of the distortion. What could be causing distortion, I've changed both 41 tubes and the 7C6 tubes, thinking that might be the problem. But I also discovered that there is a cap that is .005 when the schematic says it should be a .002MDF.... could that be the problem. Has anyone come accross this problem with this radio, is there anything else I should be looking for? I ordered new .002 caps and should get them soon. I'm hoping that's the problem but if it isn't, I've run out of ideas.
Nah that cap is not going to do it. Triple check your wiring of the caps that you replaced and any bad rubber wire. Make sure you've got plate and screen grid voltage on the 41's
Terry
7estatdef Wrote:Nah that cap is not going to do it. Triple check your wiring of the caps that you replaced and any bad rubber wire. Make sure you've got plate and screen grid voltage on the 41's
Terry
Sorry, but I'm not electronically inclined...I'm not sure what you mean by having plate and screen grid voltage on the 41's... after replacing the capacitors, I have better volume, but still have distortion. I also found that there were 2 resistors connected to the 41 sockets that were suppose to be 1 Megohm, and actually was 1.341 and 1.234 ohms... so in the middle of ordering new ones. That cap I was talking about, is also connected to both 41 sockets, pin 2, that's why I'm changing it..
I will double check all the wires again and replace as necessary..
If you can, let me know how to check plate and grid voltage if that's not too much trouble.. thanks.
Ok pull out one of the 41 tubes and look at the bottom. You will see an arrow that is between two fatter pins. Starting at the fat pin to the left of the arrow is pin 1 counting clockwise ending at the other fat pin which is pin 6.
What you want to do is measure voltage at the socket with all the tubes in place and on and running. - lead to the chassis + lead measure the voltage on pins 2 and 3 of both 41 tubes. Should have about 200vdc on all four of these pins. Do you?
Terry
7estatdef Wrote:Ok pull out one of the 41 tubes and look at the bottom. You will see an arrow that is between two fatter pins. Starting at the fat pin to the left of the arrow is pin 1 counting clockwise ending at the other fat pin which is pin 6.
What you want to do is measure voltage at the socket with all the tubes in place and on and running. - lead to the chassis + lead measure the voltage on pins 2 and 3 of both 41 tubes. Should have about 200vdc on all four of these pins. Do you?
Terry
I'll get back to you tomorrow and let you know.. Thanks
OldJack1969 Wrote:7estatdef Wrote:Ok pull out one of the 41 tubes and look at the bottom. You will see an arrow that is between two fatter pins. Starting at the fat pin to the left of the arrow is pin 1 counting clockwise ending at the other fat pin which is pin 6.
What you want to do is measure voltage at the socket with all the tubes in place and on and running. - lead to the chassis + lead measure the voltage on pins 2 and 3 of both 41 tubes. Should have about 200vdc on all four of these pins. Do you?
Terry
I'll get back to you tomorrow and let you know.. Thanks
*
Ok, if I'm doing this right, I have one lead on the chassis and one lead to pin 2 and then 3 right? I'm getting 129 Volts and 124 Volts and on the other tube I'm getting 124 V and 112 Volts....
Ok Seems good at worst maybe a little low but not too concerned. How about pins 4 and 5 on both tubes?
Terry
I just re-checked both tubes... and it does fluctuate, Pin 2 (126.7VDC), Pin 3 (131.7VDC), Pin 4 (-00.4) Pin 5 (00.0 )
The other tube Pin 2 ( 127.8V) Pin 3 (114.4 V) Pin 4 (-00.7) Pin 5 (00.0)
I'm almost thinking from reading forums that my low voltage is due to possibly #84 tube?
I can't test it, but I could just go and buy another.
Thanks for all yor help, by the way, it is appreciated.
Ok The problem is you have no grid bias. Pin 4 should have about -10vdc on it. At the junction of the two 1meg resistors 53 and 54 what voltage do you have there? Is the negative side of 62 ground to the chassis?
Terry
I just changed that ECap (62) 12 MDF... and the + side is grounded to the chassis.
I'm not getting any reading at the junction of the 2 / 1meg resistors and the other lead is to ground. 000 I just ordered those resistors because the value's were high... 1.324 and 1.232 but I haven't received them yet.
So there is your problem! 62 should be connected + to pin 4 of the 84 tube. - connects to the junction of 61 and the green yellow wire from the power transformer. Replace 62 as it probably is damage from have the polarity reversed. Measure from chassis with the - lead from the meter and the + lead from meter going to the - side 61. Should read -10v or so and you'll have your grid bias back/ distortion gone.
Terry
(1)Are you serious, your right because the schematic shows it connected that way, what else is wrong in this stupid thing... I don't know how to identify pin 4 on the 84 socket! And I cant find the green yellow wire at 61....
I've attached a picture... I can send you a clearer picture by email if you'd like.
(2)OK, I FOUND WHICH IS PIN 4 AND IT HAS THE + SIDE OF 20UF ECAP...! AS SEEN IN THE PICTURE.... I LOOK AT THE UNDER SIDE OF OTHER UNITS LIKE MINE, AND THEY ARE ALL DIFFERENT. I'D LIKE TO WIRE IT THE RIGHT WAY!
(3) Ok...I rewired the thing according to the schematic, sounds much better and hardly no distortion.... what I did is copied what the previous owner had without really looking at the schematic, put you opened the door and I saw many problems, including they have a 8mdf ecap instead of a 12mdf ecap and a 20mdf instead of a 16mdf as shown in the schematic, so it still works but I'm going to order the right ones and make it perfect... thanks for all your help, couldn't have done without you... very much appreciated.
Note from site admin: Sorry, but the photo which was attached to this post is no longer available.
So it's working properly? Leave the 20mf in replace the 8mf with 10 or 20mf. You'll find when you get the caps fixed up and now that you have the grid bias on the 41 tubes the HV will be more in line with what the manual sez. Without bias on the 41's the plate circuit will draw excessive current thus dragging down the HV line.
Terry
Sorry it took so long to get back to you... yes, it is working the way it should. The schematic shows an 8uf ecap from ground to that 18 ohm resistor, are you sure I should replace it with a 10 or 20uf cap?
OldJack1969 Wrote:Sorry it took so long to get back to you... yes, it is working the way it should. The schematic shows an 8uf ecap from ground to that 18 ohm resistor, are you sure I should replace it with a 10 or 20uf cap?
A 10 will be fine.
Are you in Oregon?