Some history; the #75 tube when tube tested came up in the middle, or 50% questionable, and one other tube, the #42 (Output tube) was weak at only 40% or replace. The volume/on off control worked, but seemed weak and scratchy. Presently there is only a loud hum and there is no response with the volume control.
Apparently the # 75 and 42 tubes are related in that a tubular (part 59) .02 mfd cap connects them. I realize I need to replace the 75 tube and probably the 42 tube, but why did everything stop working when I replaced the simplest of things, a cap wire? The volume control never seemed to work very well to begin with but it did (past tense) work
Further does any one know what the volume control is and where I may find a replacement. Please, I am electronically challenged (which is a nice way of saying stupid when it comes to this stuff)
In your opinion what is wrong and how do I correct it. Thanks in advance for your help.
Dave ( a radio repairer wana be)
Presently there is only a loud hum and there is no response with the volume control.
That statement sort of wants to suggest a malfunction in the filtering of the B+ having randomly occurred at some time before that last testing instant, very probably not even being related to your last wiring change, due to its circuitry placement nature.
However, if you want to double check, take an ohmmeter and have the set un-powered and then make a check at the GRID cap wire termination of the #75 as mentioned and see that it is not shorted to chassis ground, and then check for continuity to the wire lead close to the .02 capacitor (43) body as well as the companion 1 meg (53) grid resistor, thereby confirming no mis- wire or continuity mishap in that 75’s grid area.
Then to confirm if the hummmmm….chummmm….. is coming from the power supply or being induced in from a low level audio area…..see if the hum diminishes / disappears when the volume control is turned all of the away down.
Did it ?
Next have the system making its loud hum and take a test jumper wire and have one connection go to chassis ground
and either make connection to either the right side of .02 caps lead wire (59) OR the high leg of 500K
grid bias resistors (58) wire lead OR to the first grid pin (#4 )of the #41 AF output tube.
Do this shorting out action of the 42 tubes 1st grid for but a mere few seconds to see if that mentioned hum cleared for that instant. That then gives direction as to the area of the origin of the hums source.
For the time present , only worry about getting the instrument back to its prior state of functionality.
That volume control is one piece of exotica, so hope that a solvent clean up and oxide overcoat protectant will get it back to working as it was normally.
Standing by….if my turkey doesn’t get me…gobba…gobba….GOBBA !
73's de Edd
:I am restoring A Philco model 620 radio. I replaced all the caps, save two, and the radio worked, but was weak at best. After each change/replacement I would check my results to see that the radio still worked and it would. My last change was to replace the cap wire to the # 75 (2nd det, 1st Audio) tube which is when the radio stopped working. I went back and checked my solder connections, of which there were 2, and they appear to be fine. I do not think I affected or altered any other connections.
:
:Some history; the #75 tube when tube tested came up in the middle, or 50% questionable, and one other tube, the #42 (Output tube) was weak at only 40% or replace. The volume/on off control worked, but seemed weak and scratchy. Presently there is only a loud hum and there is no response with the volume control.
:
:Apparently the # 75 and 42 tubes are related in that a tubular (part 59) .02 mfd cap connects them. I realize I need to replace the 75 tube and probably the 42 tube, but why did everything stop working when I replaced the simplest of things, a cap wire? The volume control never seemed to work very well to begin with but it did (past tense) work
:Further does any one know what the volume control is and where I may find a replacement. Please, I am electronically challenged (which is a nice way of saying stupid when it comes to this stuff)
:
:In your opinion what is wrong and how do I correct it. Thanks in advance for your help.
:
:
:Dave ( a radio repairer wana be)
:
As to the buzz test, nothing, no response. As to the socket voltage what pin is #1? Further the schematic gives me voltage to test for pin position “P”, “SG”, and “K”
What socket pins are they, that is looking at the socket base as a clock where are they located?
Edd.
The B+ filtering, you may be right because I by passed the new wire with a jumper and it made no difference. How does one check the B+ and what should it read for volts. Second, the humm does not change at all with by turning the volume control, but after about 2-3 minutes the loud humm decreases but nothing else changes. As to your test, I will perform them as directed but you said at one point “of the # 41 AF output tube, do you mean the # 42 tube? It’s easy to interchange part numbers with the number on the part!
I agree with you, find this problem and solve it and them move on with the restoration. I will check out the sight reference you mentioned and get some contact cleaner for the volume control.
Tom:
As to the two capacitors not replaced, they are the part 57 .1 mfd capacitor, and part 67, the 8 mfd & 8 mfd Electrolytic. As to properly replacing the other caps, yes I have a chart that converts the numbers for me and a point to be made is that prior to this wire change the radio worked after I changed all the other caps!
How do I check the volume control, what should I set my digital VOM meter to and what should I read?
Finally to all, I have the schematic, tuning information and parts list for the radio so I am following it accordingly. As you can probably discern I am not an radio repair person. I am quite ignorant in these matters and rely heavily on fine gentlemen like your self to help in these matters and I do truly appreciate your efforts and in responding to my inquiries and be patient with the ignorant questions I pose. But know this I am determined, I want to make this radio and others work and will keep at it till it does, so please stay with me.
Finally the most encouraging thing perhaps I can offer you is this. On this day in Bethlehem a child was born which is Jesus Christ the Lord. The true gift of Christmas is the salvation He offers and the forgiveness of our sins, Like old radios we are all broke due to sin and need to be repaired, (born again) in order to work right with God. Guys God loves us, receive His gift of salvation today.
Hope to hear back from you soon, A Merry and blessed Christmas to you all.
God bless you,
Dave
Above is your schematic. What two capacitors did you not replace? Be sure that when you replace capacitors, you are interpreting codes properly. Modern capacitors have code numbers. The first two are actual values. The third tells you how many zeros to add on the end. The value will be in picofarads (pF or MMFD). If you have a 103 cap, then you have 10 and 000. That makes for 10000 pF, or .010000 MFD, or .0000000100000 Farads. I left all of the zeros on the end to give you an idea of the relation. A 102 cap will be a .001 MFD cap. If you put a 102 cap in place of a 103, things might be a bit quieter.
Be sure that you are following the schematic well. You should either be completely disconnecting the original bakelite capacitors, or you should dig the tar out of them and wire in new components exactly as the original ones were wired (recommended).
Weak tubes don't necessarily funcion poorly. Quite often, even in the output stage, a tube will function acceptably even though it tests weak or replace. The rectifier, since it powers the whole radio, is usually better off in the weak to good region.
Try out some new tubes, but also be sure that the radio's alignment is fine. When you tune in a station, adjust the trimmers (not the oscillator trimmers) on the IF and antenna circuits. See if things get louder. If they do, then your radio is out of alignment. It is best to align with a signal generator for accurate tracking, though you can do a reasonable job by ear, provided that noone severely mis-adjusted the trimmers before you.
Check the volume control. It should measure its rated resistance between the end terminals, and the center terminal should smoothly go through the resistance spectrum (minimum to maximum, and vice versa) when tested to each end terminal. Any jumping or missing means that the control needs service or replacement.
Finally, be sure that you are connecting an antenna to the radio. The radio needs a long wire antenna in order to perform properly. Signals received will be very weak if no antenna is connected.
T.
As to the buzz test, nothing, no response. As to the socket voltage what pin is #1? Further the schematic gives me voltage to test for pin position “P”, “SG”, and “K”
What socket pins are they, that is looking at the socket base as a clock where are they located?
Edd.
The B+ filtering, you may be right because I by passed the new wire with a jumper and it made no difference. How does one check the B+ and what should it read for volts. Second, the humm does not change at all with by turning the volume control, but after about 2-3 minutes the loud humm decreases but nothing else changes. As to your test, I will perform them as directed but you said at one point “of the # 41 AF output tube, do you mean the # 42 tube? It’s easy to interchange part numbers with the number on the part!
I agree with you, find this problem and solve it and them move on with the restoration. I will check out the sight reference you mentioned and get some contact cleaner for the volume control.
Tom:
As to the two capacitors not replaced, they are the part 57 .1 mfd capacitor, and part 67, the 8 mfd & 8 mfd Electrolytic. As to properly replacing the other caps, yes I have a chart that converts the numbers for me and a point to be made is that prior to this wire change the radio worked after I changed all the other caps!
How do I check the volume control, what should I set my digital VOM meter to and what should I read?
Finally to all, I have the schematic, tuning information and parts list for the radio so I am following it accordingly. As you can probably discern I am not an radio repair person. I am quite ignorant in these matters and rely heavily on fine gentlemen like your self to help in these matters and I do truly appreciate your efforts and in responding to my inquiries and be patient with the ignorant questions I pose. But know this I am determined, I want to make this radio and others work and will keep at it till it does, so please stay with me.
Finally the most encouraging thing perhaps I can offer you is this. On this day in Bethlehem a child was born which is Jesus Christ the Lord. The true gift of Christmas is the salvation He offers and the forgiveness of our sins, Like old radios we are all broke due to sin and need to be repaired, (born again) in order to work right with God. Guys God loves us, receive His gift of salvation today.
Hope to hear back from you soon, A Merry and blessed Christmas to you all.
God bless you,
Dave
See other posting.
Norm
:Norm :
:
:As to the buzz test, nothing, no response. As to the socket voltage what pin is #1? Further the schematic gives me voltage to test for pin position “P”, “SG”, and “K”
:What socket pins are they, that is looking at the socket base as a clock where are they located?
:
:Edd.
:
:The B+ filtering, you may be right because I by passed the new wire with a jumper and it made no difference. How does one check the B+ and what should it read for volts. Second, the humm does not change at all with by turning the volume control, but after about 2-3 minutes the loud humm decreases but nothing else changes. As to your test, I will perform them as directed but you said at one point “of the # 41 AF output tube, do you mean the # 42 tube? It’s easy to interchange part numbers with the number on the part!
:
:I agree with you, find this problem and solve it and them move on with the restoration. I will check out the sight reference you mentioned and get some contact cleaner for the volume control.
:
:Tom:
:
:As to the two capacitors not replaced, they are the part 57 .1 mfd capacitor, and part 67, the 8 mfd & 8 mfd Electrolytic. As to properly replacing the other caps, yes I have a chart that converts the numbers for me and a point to be made is that prior to this wire change the radio worked after I changed all the other caps!
:
:How do I check the volume control, what should I set my digital VOM meter to and what should I read?
:
:
:Finally to all, I have the schematic, tuning information and parts list for the radio so I am following it accordingly. As you can probably discern I am not an radio repair person. I am quite ignorant in these matters and rely heavily on fine gentlemen like your self to help in these matters and I do truly appreciate your efforts and in responding to my inquiries and be patient with the ignorant questions I pose. But know this I am determined, I want to make this radio and others work and will keep at it till it does, so please stay with me.
:
:Finally the most encouraging thing perhaps I can offer you is this. On this day in Bethlehem a child was born which is Jesus Christ the Lord. The true gift of Christmas is the salvation He offers and the forgiveness of our sins, Like old radios we are all broke due to sin and need to be repaired, (born again) in order to work right with God. Guys God loves us, receive His gift of salvation today.
:
:Hope to hear back from you soon, A Merry and blessed Christmas to you all.
:
:God bless you,
:
:Dave
:
T.