I'm having difficulty bringing my Philco 66 back to life. All caps have been replaced, along with out of tolerance resistors. The audio section gives a nice buzz when I touch the grid cap on the 75, and a weak one when I touch the 78, but no indication that the RF/IF sections are working. A voltage check showed everything fine except for the screen voltage (SG-K) which reads under 1 VDC. The Riders info says it should be 85V.

Any ideas of where to look next?

Hi Rush

You do need screen voltage to have the radio operate. The screen is supplied voltage from a resistor divider. Check for an open resistor in this divider.

Also there is a cap (#20, .09 mfd) from screen to chassis. Be sure this cap isn't shorted. It's a bakelite block cap.

If voltage was there before you changed components look for a solder short to chassis.

Norm

:I'm having difficulty bringing my Philco 66 back to life. All caps have been replaced, along with out of tolerance resistors. The audio section gives a nice buzz when I touch the grid cap on the 75, and a weak one when I touch the 78, but no indication that the RF/IF sections are working. A voltage check showed everything fine except for the screen voltage (SG-K) which reads under 1 VDC. The Riders info says it should be 85V.
:
:Any ideas of where to look next?

Thanks, Norm. I want to make sure that I'm following your direction correctly. On my Model 66 schematic, I don't see a .09 cap listed as #20. There are two .05 caps to ground on the 78 and 6A7 tubes that are #9 and #21, respectively. I think those were the caps you meant for me to check. There's only one .09 bakelite block cap, and it's in the power supply (#51). I'll check that, too.

I'll check all three tonight and let you know if that does the trick.

Thanks for the help!

:Hi Rush
:
: You do need screen voltage to have the radio operate. The screen is supplied voltage from a resistor divider. Check for an open resistor in this divider.
:
: Also there is a cap (#20, .09 mfd) from screen to chassis. Be sure this cap isn't shorted. It's a bakelite block cap.
:
: If voltage was there before you changed components look for a solder short to chassis.
:
:Norm
:
:
:
::I'm having difficulty bringing my Philco 66 back to life. All caps have been replaced, along with out of tolerance resistors. The audio section gives a nice buzz when I touch the grid cap on the 75, and a weak one when I touch the 78, but no indication that the RF/IF sections are working. A voltage check showed everything fine except for the screen voltage (SG-K) which reads under 1 VDC. The Riders info says it should be 85V.
::
::Any ideas of where to look next?

I think he accidently looked at the model 60. This radio is practically identical to yours. It's shortwave frequency coverage is from 1.7 to 5.5 megacycles, where-as your's goes from 5.5 to 16. The model 60 has a .09 MFD condenser going from the screen grid of the second IF to ground, and your's has a .05 MFD. Either way, check out this condenser, and check out the resistors that feed power to the screen grids. I think that in your radio both the screen grid of the IF and of the oscillator receive voltage from the same source, so a fault here would not only knock out the IF, but also the oscillator.

Thomas

Hi Rush

Thomas has it right. It's cap #46, .05 mfd in the Philco 66 schematic. The resistor is 37,000 ohms, #47. Either resistor open or cap shorted will cause zero volts on the screen.

Norm

:I think he accidently looked at the model 60. This radio is practically identical to yours. It's shortwave frequency coverage is from 1.7 to 5.5 megacycles, where-as your's goes from 5.5 to 16. The model 60 has a .09 MFD condenser going from the screen grid of the second IF to ground, and your's has a .05 MFD. Either way, check out this condenser, and check out the resistors that feed power to the screen grids. I think that in your radio both the screen grid of the IF and of the oscillator receive voltage from the same source, so a fault here would not only knock out the IF, but also the oscillator.
:
:Thomas

Also to note....in my model 60, the condenser bank (four condensers including the .09 MFD condenser) is in a tin box. The box has cardboard ends, and one end has all the wires coming out of it. Instead of being a bakelite block condenser, this condenser you need to examine in your 66, may be in a similar container.

Thanks for the help, Norm and Thomas!

Since I had already replaced the .05 condenser, so I double checked the power circuit to the grid and found a surprise: it appears that an original cloth-covered jumper wire from the cap to the voltage divider resistore was dropping most of the voltage! I used a jumper with alligator clips to restore the path and the voltage at the grid jumped to ~60V. Still no sign that the RF sections are working, however, so there's more to do.

I'm traveling this week, so I'll update my progress and more details next week. Thanks again for your help!

WOAH!!!!!!!!!!!!!!!!!!!! STOP!!!!!!!!!!!! READ YOUR DIAGRAM THOROUGHLY!!!!!!!!!!!!!!!!!!!!!!

The cap on top of the 78 tube is for the CONTROL GRID, not the screen grid. The control grid, which is the first grid in the tube, NEVER has such high voltages fed to it. It is connected to the secondary of the IF transformer as shown in your diagram. The screen grid of the 78 and the screen grids (tied together within the tube) of the 6A7 are all that should be connected to that high voltage circuit.

When reading your circuit diagram, Philco does not use the little hump in the wiring to show that a wire crosses without touching. When a wire crosses without touching another wire, it is simply shown as two wires drawn over eachother. When they cross and are connected, you will see a dot where they cross.

Also, within Philco receivers, there are actual cloth resistors (one or two). The cloth wire you are talking about is just a regular wire...the one that goes to the cap of the 78 tube. If you see a short piece of cloth wire with bands on it (like a regular resistor), and the wire spirals up on each end, this is a wire wound resistor called a "flex" resistor, and will be labeled as such somewhere either in the diagram or in the parts list. They usually aren't any more than several thousand ohms, and are usually found in power circuits such as cathode and screen grid resistors. They aren't usually more than an inch or two in length. Keep this in mind when looking through your radio. If you ever find a wire that has resistance, check the diagram to see if it is supposed to have this resistance. If you ever find a wire that you suspect has resistance (such as the wire leading to the control grid cap of the #78), test it with your multi-meter to be sure. The wire leading to the grid cap on your 78 does not actually have any large amount of resistance (not more than say .01 ohms). It may have seemed so when at first you perhaps thought that this was the screen grid connection, and you wondered why there was no voltage here. If you check this wire with your meter, however, you will find no resistance to it.

At any rate, be extremely thorough when working on your radio, and examine every detail, and disconnect the control grid of the 78 from the high voltage supply before you blow up the tube.

Thomas

Hmmmmmmmmmmmmmm......or I misunderstood what you were saying.....maybe you meant the electrolytic capacitor, and not the grid cap. In that case, if the wire leading from the electrolytic to the voltage divider network was failing, this would cause trouble throughout the radio. Is this what you meant???? I guess I should remember that some people abreviate the word capacitor as cap. Perhaps you meant this, and you know that the control grid of the 78 shouldn't be connected to the high voltage.

Sorry about that,

Thomas

Thomas,

Thanks for your response, and you're correct ...I did mean capacitor, not the grid cap. The wire I mentioned earlier was not a wire resistor, but your note prompted me to recheck the wire resistors and I found that one (#8) was bad.

I got back into the set last night and replaced the offending wire (and a 200 ohm wire resistor #8), and the set came to life.

Thanks for all of your help. Now I can start on the cabinet!