Philco 40-180 - Resistor Burnout
Posts: 8
Threads: 1
Joined: Apr 2019
City: Germantown
State, Province, Country: Maryland
Posts: 1,114
Threads: 14
Joined: Feb 2013
City: Irvington, NY
Check the wiring to the 6J8 tube socket. There should only be two connections to pin 6. One will be the 4.7K resistor 29 and the other should be the 250 pf cap 22 going to the push button switch. If you have any additional connections there is a miswiring problem.
With the 6J8 out of its socket, the only other part connected is the 250 pf cap and that should not draw any current to overheat the resistor. You must have a short in the associated wiring or something is miswired.
Posts: 8
Threads: 1
Joined: Apr 2019
City: Germantown
State, Province, Country: Maryland
Hi Mondial.
Thank you for the reply!
I had to replace the 6J8 tube socket as you may be able to see in the picture.
I also happen to have four other 40-180 radio chassis, of which, 2 are complete and work fine, and the other two are in line for renovation. So, I have quadruple checked the 6J8 wiring and cannot see a problem. I did find that I miswired cap 10 to the 1235, but after correcting this, and firing up the unit, resistor 29 still smoked.
Stumped.
Posts: 358
Threads: 4
Joined: Aug 2015
City: Monteith, Ontario CA
One of the ways to find a persistent short is to start immediately after the resistor that is getting warm, with the schematic beside you, then follow and disconnect one wire, one component at a time, followed by a test each time. If nothing changes, reconnect the wire or component and go to another branch of wiring. If the resistor stops overheating, keep following that particular path. Don't skip any wire or component. Just disconnect, test, reconnect until you find the short.
Posts: 8
Threads: 1
Joined: Apr 2019
City: Germantown
State, Province, Country: Maryland
That sounds like a plan - thanks John!
Posts: 1,114
Threads: 14
Joined: Feb 2013
City: Irvington, NY
Looking at your photo of the 6J8 socket. I see pin 6 connected to the 4.7K resistor and a red wire. What does the red wire connect to? It should only connect to the 250 pf cap, nothing else.
Its hard to tell from the photo but it looks like the red wire connects to a terminal with more than one connection (brown wire?). The red wire should only connect to the 250 pf cap.
As John said, disconnect anything associated with the 4.7K which gets hot. Start with the red wire connected to pin6 of the 6J8 and follow it to the terminals it connects to.
Posts: 8
Threads: 1
Joined: Apr 2019
City: Germantown
State, Province, Country: Maryland
I disconnected the red wire and the resistor does NOT get hot.
The red wire connects to a terminal that has a 150 ohm resistor connected to it. The other end of the 150 ohm resistor connects to a terminal that has the 250 pf (#22) cap connected to it. This design is seen on all of my other 40-180 units.
Bad #22?
Posts: 8
Threads: 1
Joined: Apr 2019
City: Germantown
State, Province, Country: Maryland
Forgot to mention that the 150 ohm resistor and 250 pf cap are connected to the pushbutton switch. This connection was never touched...
Posts: 8
Threads: 1
Joined: Apr 2019
City: Germantown
State, Province, Country: Maryland
It was difficult, but I disconnected the 250 pf cap (#22) from the unit. It tested okay.
I reconnected #22 to the 150 ohm resistor which has the red wire attached at the other end.
I tested the unit and #29 resistor was operating fine.
I cleaned the junction where I disconnected #22, reconnected #22, rearranged some wires...
IT WORKED!
Attached the antenna, and was able to tune to numerous stations.
Burn-in is next...
Thank you all for the assistance! Much appreciated!
Posts: 990
Threads: 40
Joined: Feb 2015
City: Roseville, MN
So, I've been following along and it's nice that the problem is resolved but I don't see any 150 ohm resistor in the schematic where he describes it. The only 150 ohm resistor near by is the cathode bias resistor. What's happening?
Posts: 1,114
Threads: 14
Joined: Feb 2013
City: Irvington, NY
Seems that a 150 ohm resistor was added in series with the 250 pF cap connected to pin 6 of the 6J8. Appears to be an undocumented production change as it does not appear on the schematic.
Posts: 8
Threads: 1
Joined: Apr 2019
City: Germantown
State, Province, Country: Maryland
Rob - you are correct. There are no other 150 ohm resistors in the schematic besides the cathode bias resistor. I currently have 6 of these radios and they all have this 'extra' 150 ohm resistor where I indicated! I can only speculate that it was a mid-stream manufacturing change that did not get into the schematic, or, the schematic I have is an earlier (or later) version then what my radios have.
Someone smarter than me will have to deduce why this design was implemented.
Posts: 1,114
Threads: 14
Joined: Feb 2013
City: Irvington, NY
According to the Philco service data the resistor appears as a production change in run 3, but it never made it to the parts list or schematic.
https://philcoradio.com/library/download...20Book.pdf
Posts: 8
Threads: 1
Joined: Apr 2019
City: Germantown
State, Province, Country: Maryland
Excellent find! Mystery solved.
Users browsing this thread:
|
Recent Posts
|
1930s Stromberg-Carlson Tombstone Radio need help identifying model number
|
Hi Cap'n Clock,
Unfortunately, I do not have this radio. This is a shame because this should be a good performer. 2A5...MrFixr55 — 06:48 AM |
American Bosch Model 802 auto radio
|
I think it would come under either American Bosch or United American Bosch. American Bosch made sets for the American We...Arran — 05:53 AM |
trying to identify this wire type
|
Thanks to all for the feedback. As Arran said, it is probably an older replacement and yes it has a grid cap so I will ...georgetownjohn — 09:32 PM |
trying to identify this wire type
|
It's possible that the red wire, actually a grid cap lead, is a very old replacement, I can't remember seeing a pre 1939...Arran — 09:18 PM |
Gilfillan Brothers Car Radio?
|
Hi everyone,
Special thanks to Joe Rossi for tracking down this obscure radio and thanks to others who took up the hun...Antipodal — 08:15 PM |
trying to identify this wire type
|
Here's one source for your wire of many.
Take care and BE HEALTHY! Gary
P.S. Can't get the right color you need? I ...GarySP — 06:40 PM |
trying to identify this wire type
|
...and modern wire of the appropriate gauges and insulation V-rating (300V minimum, usually shown right on the wire) is ...morzh — 05:47 PM |
1930s Stromberg-Carlson Tombstone Radio need help identifying model number
|
I have a question about this radio, is there anyone that has access to this radio that has an intact unmolested speaker ...captainclock1988 — 04:28 PM |
1930s Stromberg-Carlson Tombstone Radio need help identifying model number
|
Well what makes me confuse all of those companies is that all three of those companies (Setchell-Carlson, Stromberg-Carl...captainclock1988 — 04:21 PM |
trying to identify this wire type
|
The red wire is rubber covered wire.
The others are cotton braid over rubber often in colors or a tracer, also strand...Chas — 02:43 PM |
Who's Online
|
There are currently no members online. |
|
|