Philco 87 B+ Current? - Printable Version

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Philco 87 B+ Current? - Guest - 10-04-2005

Anybody know how much total B+ current this radio should pull (as measured right off the #80 rectifier filament pin) ?

I have measured around 120 mA on one of these sets which seems to be working fine, but I don't know if this is normal or if it is too high. I haven't replaced the filter condensers and I really don't want to get into that if I don't have to. I am measuring the current based on the voltage drop across a 0.100 Ohm resistor using a Fluke 189 meter on the DC millivolts scale.

As it is, the power transformer runs a little hotter than I like, and I'm thinking this may be due to excessive load on the B supply. When I plug in a very weak (good filament, zero emission) #80 tube, the transformer runs barely warm, so I'm pretty sure that a good part of the heat is coming from the HV winding load. I just don't know how much is "normal".


Thanks,

DD

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RE: Philco 87 B+ Current? - Chuck Schwark - 10-04-2005

You say the set you measured "seems" fine, but have you replaced all the filter block caps and other wax-paper bypass caps?

• Excessive leaky B+ bypass and filter caps can cause excessive current draw and warmup your transformer and ultimately kill it and the 80.
  
  
• Check for winding to winding or winding to case shorts in the audio output transformer. Bad shorted output tube(s).
  
  
• Check for carbon burns bewtween pins on the 80 socket.
  
  
• Check for shorted filter chokes. #3422 = 200 ohms, #3472 = 1,350 ohms.
  
  
• Check for shorted field coil - should be approx. 3,200 ohms.
  
  
• The filter block caps can be replaced with like-value film caps. They don't need to be electrolytic.
  
  
• It's a good idea to replace any resistors that are more than +/-20% off value as well. Imprpper audio tube biasing can make them draw excessive current. Check resistor #35, a three section wire-wound. The cathode bias section should be approx. 640 ohms.
  

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