Posts: 4
Threads: 1
Joined: Nov 2013
City: Australia
Hi, a Philco shouldered 16B, code 125 tombstone landed on my workbench in need of restoration. I'm quite certain it is a Code 125 variant once I found a circuit etc. Tested and found all the tubes to be OK. There was a Type 37 fitted in the OSC socket so I replaced it with a spare 76 I had. The chassis is pretty much dead so I got the power supply up and running OK. Now for the fun bits.. There is no sign of any station signal on any band. I noticed that there is a wire coming from pin 3 of the RF 78 that is floating and not connected anywhere. I followed the circuit and all the 78 Grids are connected as indicated on the circuit. So I have a mystery wire. Connected a sig gen to the grid of the first DET and swept across the IF centre frequency and it appears to be peaking at around 440Khz... So the alignment may be a little off. BTW the OSC appears to be working..
I'm at a stage where I need to resolve the mystery wire issue. It would be appreciated if anyone has an under chassis photo of the wiring around the 78 RF section so I can compare with mine...
Also, is it a must to deal with the Philco Block Condensers?
In the mean time I will look for other issues.
Any help appreciated
Regards
Rob
Posts: 4,612
Threads: 51
Joined: Sep 2008
City: Sandwick, BC, CA
The Bakelite block condensers have paper condensers inside of them, they were commonly used in Philco sets from about 1930 through 1936 and were slowly phased out in favor of the more usual tubular types till just before the war. So the newest ones are now over 70 years old and pretty much have to be replaced. The Bakelite blocks also act as terminal strips so they pretty much have to be cleaned out and restuffed with new condensers, or replaced with a terminal strip, sort of six of one and half a dozen of the other. Some on here are very good at restuffing them, they can undo the screw, flip the block over, remove the old condenser, and replace with a new one, all without disconnecting most of the wires.
While you are at it I would check all of the old carbon composition resistors, any that are more then 20% out, replace them.
Regards
Arran
Posts: 4
Threads: 1
Joined: Nov 2013
City: Australia
Hi Arran,
Thanks for the tips.. all block caps done now..
Regards Rob
Posts: 4
Threads: 1
Joined: Nov 2013
City: Australia
Found some additional info on the WWW and proceeded to rebuild all the Philco Block Condensers and replacing out of tolerance resistors as I went along. Quite a lot of R's had drifted high well over 20-30% and some were double their value.
The radio is now receiving stations on the broadcast band after doing a quick IF alignment but not very loud at full volume. So I may still have an issue somewhere.
The RF alignment requires tweaking a hexagon nut which is down below the surface of the can.
Just wondering if it's OK to use an appropriately sizes tube spanner on these nuts?
The shadow meter starts narrow and widens as the set warm up but it will not open and close when changing stations. Coil is OK and vane moves freely. Plenty of Web info suggesting that it may be related to signal strength, weak tubes or improper alignment. Have decided to leave it alone till I work out how to do the RF alignment.
Cheers
Rob
Posts: 4
Threads: 1
Joined: Nov 2013
City: Australia
I found a suitable Hex tool to adjust the IF's and other trimmers and proceeded to do a full alignment as per the service sheets. All I can say is that the settings were way off.. The radio now booms in loud and clear with only a short aerial of a few feet. The shadow meter also worked better after the full alignment. Another project completed and satisfied owner.
