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Model 70 - Printable Version

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Model 70 - n9vu - 01-22-2006

Hi Guys and Gals,

Putting the finishing touches on a model 70. In the process here's what I have so far and it's sort of baffling, at least to me.

When connecting an antenna wire to the proper post, there is little or no reception. When touching the wire on the grid cap of the 24 tube, 2nd one facing the front of the chassis, reception comes to life and fairly well. When I say touching, this is with my hand only. I notice that reception also comes to life if I touch the can that surrounds the coil underneat. Some abrupt jarring of the enclosure causes reception to be bit intermittent, but not enough to bring the set in or out of comission.

My thoughts, coil issue, either intermittent or something about to happen or perhaps alignment of the receiver. Any other thoughts? Ideas? Suggestions? I appreciate the assistance, and thank you all again. GB.

- Chuck Schwark - 01-23-2006

Sounds like you may have an open antenna coil or open RF coil (just before the 1st. Det tube). Inspect the solder lugs on the coil forms for corroded or green spots where the fine wire connects to the lugs. Any greenish areas in the windings also indicates where corrosion has taken place. Coils can easily be re-wound. See this Service Tip on my site for guidance.

PHILCO SERVICE HINTS & TIPS - NUMBER 36
Rewinding Philco RF Coils

- Ron Ramirez - 01-23-2006

Hi Gary

Assuming you're working on an early 70 (without AVC), here's what I would check:

- n9vu - 01-23-2006

mrphilco Wrote:Hi Gary

Assuming you're working on an early 70 (without AVC), here's what I would check:
  • Antenna coil (2) and RF coil (6);
    ALL wiring from tuning condenser to the various points under the chassis;
    tightness of the screws on the sides of the tuning condenser;
    the RF amp tube, Type 24.[/list:u]
    I think it's probably a combination of bad antenna coil (2) and/or RF coil (6) and wiring/screw tightness issue on the tuning condenser.

    The second Type 24 tube from the front is the mixer tube, so your problem has to be ahead of that. The wiring/screw tightness on the tuning condenser can cause lots of intermittents.

    Hope this helps. Happy troubleshooting! Icon_smile

    (edit) Well, Chuck and I answered at almost the same time, so now you have two votes pointing to those coils. Take a look at them right away. Good luck.

Thanks Chuck and Ron for the advice. I've also noticed one of the 24's, the one in the very front may be bad just by it's looks, but this is a big maybe. The inner components are leaning to one side, not loose, but wondering if this is causing any malfunction in the receive as well. That's kind of a simple resolution. With the tube tester I have and a spare tube or two I'll see if this resolves anything.

Thanks again,

GB

- n9vu - 01-27-2006

n9vu Wrote:
mrphilco Wrote:Hi Gary

Assuming you're working on an early 70 (without AVC), here's what I would check:
  • Antenna coil (2) and RF coil (6);
    ALL wiring from tuning condenser to the various points under the chassis;
    tightness of the screws on the sides of the tuning condenser;
    the RF amp tube, Type 24.[/list:u]
    I think it's probably a combination of bad antenna coil (2) and/or RF coil (6) and wiring/screw tightness issue on the tuning condenser.

    The second Type 24 tube from the front is the mixer tube, so your problem has to be ahead of that. The wiring/screw tightness on the tuning condenser can cause lots of intermittents.

    Hope this helps. Happy troubleshooting! Icon_smile

    (edit) Well, Chuck and I answered at almost the same time, so now you have two votes pointing to those coils. Take a look at them right away. Good luck.

Thanks Chuck and Ron for the advice. I've also noticed one of the 24's, the one in the very front may be bad just by it's looks, but this is a big maybe. The inner components are leaning to one side, not loose, but wondering if this is causing any malfunction in the receive as well. That's kind of a simple resolution. With the tube tester I have and a spare tube or two I'll see if this resolves anything.

Thanks again,

GB

After taking the set down, I noticed the wire coming out of the coil to the secondary 24 has an open spot in it, just bare exposed. Could this be the problem of the grid cap wire to the coil?

- Ron Ramirez - 01-27-2006

As Bugs Bunny would say, "Mmmmmyyeahhh, could be..."

Icon_smile

- n9vu - 02-05-2006

mrphilco Wrote:As Bugs Bunny would say, "Mmmmmyyeahhh, could be..."

Icon_smile

Hope the heck it is, LOL. By the way, what a difference some tubes made in this receiver. Picked up a half dozen 24's at ARCI today, replaced some trashy looking tubes in the 70, now getting reception with no antenna. Still an intermittent issue with the coil housing. I think once I straighten this out this is going to be one sweet old radio. Thanks again for your help.