05-26-2018, 08:49 AM
April 9.
Having completed the main part of the tuner chassis except for replacement of the interconnect cables, it was time to turn my attention to the part I dreaded most - the RF unit.
I have said this before - if I had my way, I would bring David Grimes back from the dead and sentence him to a lifetime of having to service the RF units of every higher end 1937 and 1938 Philco which used his awful RF units.
His invention was, in my opinion, one of the worst things Philco ever came up with. The RF units of the lower end models aren't too bad, but any RF unit with an RF amplifier stage is extremely difficult to service. Add to that the oscillator control tube as used in this radio, and you have a very complicated, very poorly thought out unit (from the perspective of the person who has to service it).
But to understand just why Philco went with Grimes' RF unit idea, we have to look at radio history in context.
RCA had developed what it called "Magic Brain". This, too, was a separate RF unit which could be removed from the main chassis for service. Unlike Philco's "Unit Construction", however, RCA's Magic Brain has wiring which terminated in a plug. Remove four screws, remove the plug, and remove the Magic Brain. Simple.
With the Philco RF unit, one must unsolder up to 12 wires - and then it can be H**l to get the RF unit pulled from the chassis.
Any mistake can seriously damage an RF unit. I damaged this one in removal. I forgot to unsolder one wire, and that cost me RF coil (14). This is why I was advertising for a coil a month or more ago.
So...I purchased an entire 38-116 chassis from the auction site just to get another RF unit so I could replace that coil.
I know...I probably should not have even mentioned it...but look, we all make mistakes.
Anyway...
Here are the two RF units side by side.
[Image: http://www.philcoradio.com/images/phorum...90_053.jpg]
[Image: http://www.philcoradio.com/images/phorum...90_054.jpg]
You can tell that the original 38-690 RF unit has one damaged tube shield base, and one missing. People did that so they could use metal and/or GT tubes in the Philco sets designed only for use with G (taper-top) tubes.
And notice in the second picture above - the 38-690 tuning condenser is rubber stamped 38-116.
The RF units of both radios are identical.
Having completed the main part of the tuner chassis except for replacement of the interconnect cables, it was time to turn my attention to the part I dreaded most - the RF unit.
I have said this before - if I had my way, I would bring David Grimes back from the dead and sentence him to a lifetime of having to service the RF units of every higher end 1937 and 1938 Philco which used his awful RF units.
His invention was, in my opinion, one of the worst things Philco ever came up with. The RF units of the lower end models aren't too bad, but any RF unit with an RF amplifier stage is extremely difficult to service. Add to that the oscillator control tube as used in this radio, and you have a very complicated, very poorly thought out unit (from the perspective of the person who has to service it).
But to understand just why Philco went with Grimes' RF unit idea, we have to look at radio history in context.
RCA had developed what it called "Magic Brain". This, too, was a separate RF unit which could be removed from the main chassis for service. Unlike Philco's "Unit Construction", however, RCA's Magic Brain has wiring which terminated in a plug. Remove four screws, remove the plug, and remove the Magic Brain. Simple.
With the Philco RF unit, one must unsolder up to 12 wires - and then it can be H**l to get the RF unit pulled from the chassis.
Any mistake can seriously damage an RF unit. I damaged this one in removal. I forgot to unsolder one wire, and that cost me RF coil (14). This is why I was advertising for a coil a month or more ago.
So...I purchased an entire 38-116 chassis from the auction site just to get another RF unit so I could replace that coil.
I know...I probably should not have even mentioned it...but look, we all make mistakes.
Anyway...
Here are the two RF units side by side.
[Image: http://www.philcoradio.com/images/phorum...90_053.jpg]
[Image: http://www.philcoradio.com/images/phorum...90_054.jpg]
You can tell that the original 38-690 RF unit has one damaged tube shield base, and one missing. People did that so they could use metal and/or GT tubes in the Philco sets designed only for use with G (taper-top) tubes.
And notice in the second picture above - the 38-690 tuning condenser is rubber stamped 38-116.
The RF units of both radios are identical.
--
Ron Ramirez
Ferdinand IN
