Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Philco 39-7 Alignment Problem
#1

I've completed a rebuild of a Philco 39-7, but there is an issue with the alignment instructions from Philco that I cannot resolve.  Does anyone know how to adjust the "6A" trimmer capacitor that is in parallel with the oscillator coil?  Nowhere do the official instructions from Philco mentioni how to do that.  I've finding the tuning alignment across the dial to be very difficult.  My experimentation leads me to believe that the "6A" trimmer holds the key.  Any ideas?
#2

6A is a 20 pF fixed capacitor used only in model 39-7; 3B is the oscillator trimmer.

The alignment instructions state that both 3B and 3A should be adjusted at 1550 kc.

https://philcoradio.com/library/download...20Book.pdf

--
Ron Ramirez
Ferdinand IN
#3

Very interesting.  On the radio I've rebuilt, "6A" is definitely a trimmer cap from pin 1 of the oscillator coil to ground.  I suspect that someone modified the radio at some point, but there's no indication of any other modifications at all.

Thanks much; that certainly points me in a different, maybe more productive, direction.
#4

The Philco service sheet clearly indicates 3B as the oscillator trimmer. That's all I can say about it.

It's been a while since I owned a 39-7. 6A could be one of those "semi-fixed" trimmers Philco used in some models of around that period (1938-39), which looks like a trimmer cap but was adjusted and sealed at the factory. Why they did this rather than using a fixed mica cap, who knows other than some models needed more or less capacitance?

If this is the case, do not make any attempt to adjust 6A.

--
Ron Ramirez
Ferdinand IN




Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
Philco 91 Speaker Replacement
The spider is glued on the cone and so is the voice coil. I think you can use a cotton swab dipped in acetone and carefu...RodB — 02:42 PM
Restoring Philco 37-604C
Yes I saw that. If I knew, I'd probably try to arrange for getting it myself. But I have just got one. Which does not m...morzh — 01:44 PM
Philco 38-2 Automatic Tuning
When you push the lever, you are supposed to rotate the disk to the desired station. Then the magnetic tuning will acqu...morzh — 01:42 PM
Philco 38-2 Automatic Tuning
I figure out the muting from another picture that helped. Now I need to know how the automatic tuning works. When I push...dconant — 12:11 PM
Philco 91 Speaker Replacement
How would I go about removing the spider from the cone?dconant — 12:04 PM
Philco 38-2 Automatic Tuning
Hello, I am having trouble getting my automatic tuning to stay unmuted. If I play with the tuning handle I can get it to...dconant — 10:51 AM
Does anyone make photofinish replacements?
Here’s the link to the DIY photofinish section of our site: klondike98 — 09:46 AM
Delco car radio Peko vibrator converstion issues
Hi Richard, Thx for posting the schematic.  As I remember as a kid, these were great performers for the time, likely...MrFixr55 — 08:56 AM
Delco car radio Peko vibrator converstion issues
hello mr Fixr, The Electro  Powersupply that I am powering the radio with has a huge choke plus a 10,000ufd electrolyti...radiorich — 10:58 PM
Delco car radio Peko vibrator converstion issues
How about putting a choke in the power supply? The big cap was likely an attempt to stabilize the DC. Kids who cre...MrFixr55 — 09:19 PM

[-]
Who's Online
There are currently 2830 online users. [Complete List]
» 1 Member(s) | 2829 Guest(s)
Avatar

>