I am in the process of restoring a 1939 Standard Jukebox. I have replaced all the caps and tube and the amp powers up and work except I have a 60 Hz hum. If I pull the 76 tube the hum go away. I have checked the DC voltage and it looks ok. Have two 76 tubes and they both have the same problem. Anyone have any ideas ?
I am attaching the schematic. Thanks.
I am attaching the schematic. Thanks.
Attachments
Have all ready done both of those. The hum level is low and once music starts you do not notice it. The schematic shows the plate voltage is suppose to be 165 V and I am reading around 88 V. I have the 245 on the high side of the 30 K resistor and the resistor ohms out ok.Short the input and see if it is still a problem with the 76 tube in place. It could be a pickup problem if the hum goes away. Also make sure the ground on the cathode resistor is good.
Checked that already.Have you got the electrolytic capacitors the right way round?
Some caps have the negative marked some have the positive marked.
NB make sure you discharge the supply before you touch anything!
Regards
M. Gregg
Checked the cap polarity and all the resistor values. Shorting the input has no effect. The only thing I have found is the plate is suppose to be 165 VDC but I only have 88 VDC. I have the correct voltage on the high side of the 30K plate resistor.Have you got the electrolytic capacitors the right way round?
Some caps have the negative marked some have the positive marked.
NB make sure you discharge the supply before you touch anything!
Regards
M. Gregg
Checked the cap polarity and all the resistor values. Shorting the input has no effect. The only thing I have found is the plate is suppose to be 165 VDC but I only have 88 VDC. I have the correct voltage on the high side of the 30K plate resistor.
What voltage do you have on the last supply cap feeding the anode of the 76?
Its fed via a 30K.
Regards
M. Gregg
Found the problem. I must have missed measuring the cathode resistor. Found it is 80 ohms instead of 3500. Thanks to everyone for your input.
Great!
Regards
M. Gregg
Slightly off topic,
Does anyone know as shown in the diagram a modern substitute for the PH3055?
Sorry back to the thread..
Interesting circuit..
Regards
M. Gregg
Check with Mike LeFevre at Magnequest.. He has made this sort of phase splitting transformer/choke in the past. Possibly also Electra-Print. Not sure someone in the EU could not replicate this at a reasonable cost.
Is yours a Rock-Ola ST-39 or DE-39?
I have a 1939 Rock-Ola Deluxe (DE-39) which seems to have this same F-2 version of the amplifier. I am gradually launching into a restoration and documenting on youtube. iIt would be great if you could add any lessons learned to the radiomuseum.org site.
Jukebox 39 Standard Luxury Light-Up C-Series ST39 R-Player R
https://www.youtube.com/channel/UC-7q18lW8R2BDTVZVOq6AcQ
I have a 1939 Rock-Ola Deluxe (DE-39) which seems to have this same F-2 version of the amplifier. I am gradually launching into a restoration and documenting on youtube. iIt would be great if you could add any lessons learned to the radiomuseum.org site.
Jukebox 39 Standard Luxury Light-Up C-Series ST39 R-Player R
https://www.youtube.com/channel/UC-7q18lW8R2BDTVZVOq6AcQ
This may be suitable. However there is a conflict between specified inductance and secondary impedance.
http://www.hammondmfg.com/pdf/560N.pdf
http://www.hammondmfg.com/pdf/560N.pdf
This may be suitable. However there is a conflict between specified inductance and secondary impedance.
http://www.hammondmfg.com/pdf/560N.pdf
That looks interesting,
I have never seen this done before, have you ever had any dealings with this type of splitter? How good/bad its is..I'm just surprised they didn't drive the primary of an interstage and split with the secondary can you see any reason for the design being done like this?
Regards
M. Gregg
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