Posts: 36
Threads: 15
Joined: Aug 2007
City: Glendale,AZ
Philco 38-3 has been recapped and all resistors have been checked.
I can pick up 3 or 4 local stations bwt 900 and 1300 but weakly.
The plate voltage on the RF tube 6u7g is a -4.5 volts on bands 1 and 2 but it should be 235v
Band 1 is AM and band 2 is S?W from 2 to 7.5 mhz.
the screen is 74 volts.
when I switch to band 3 the plate voltage jumps to 285 and screen 84volts.
I can RX WWV @ 10 mhz but not very strong.
I think the band switch is faulty because the coils check out.
What Am I missing ?
The schematic is on Nostalgia air.
Posts: 16,495
Threads: 573
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Coil 10 (RF range 2), the one saying 70 ohm, connected to the band switch, is open.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 36
Threads: 15
Joined: Aug 2007
City: Glendale,AZ
Thanks for all your help.
The primary of of rf coil 10 is indeed open...
TKS!!
Posts: 7,300
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Sorry for your loss!
I'll mention a few things. Short of finding a replacement coil you could use a 2.5mh choke to act as the open winding (only it's not open) and use a small cap to couple the rf signal to the secondary of the coil. The primary is untuned. Operating the set on that band with an open plate circuit may damage the rf amp tube's screen grid as there is very little plate voltage. The screen grid at this point is acting as the plate in terms of dissipation and is not designed to dissipate very much.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 16,495
Threads: 573
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Is the open part one-layer or the multi-layer? One layer is easy to rewind.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 7,300
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
So how many feet of 38ga wire = 70ohm?. I would think that it's going to have a lot of turns.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 1,475
Threads: 69
Joined: Nov 2012
City: Kansas city, MO.
Posts: 7,300
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
(07-14-2016, 07:25 PM)KCMike Wrote: about a thousand feet
Nah just seems like it. It's a little less than an ohm per foot so about 80'. That's a lot of turns on a 5/8 form.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 16,495
Threads: 573
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
So then you are outta luck and this is the multi-layer part. Well, make two sides and wind between them,then remove the sides.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
Posts: 1,475
Threads: 69
Joined: Nov 2012
City: Kansas city, MO.
My mistake. I read it as 700 ohms.
Posts: 599
Threads: 24
Joined: Jan 2014
City: Edmonton AB CA
Its possible there is just a bad solder connection, try re-soldering all the connections. That has worked for me a few times over the years.
Gregb
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
