Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
Hi everyone! I hope everyone is well and staying safe.
I have a problem that I have never run into before. Although it does sound like I've said that before. Anyway, I replaced all the caps, checked and replaced any resistors over 20% out. All the tubes check good and it has been aligned. Here's my problem: with the original loop antenna (it has continuity) the only thing I can pick up is my SStran, about 8 feet away. If I connect my long wire to the antenna connector it sounds great and picks up all local stations.
Any ideas where to look?
Thanks,
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 120
Threads: 15
Joined: Aug 2017
City: Fort Worth
State, Province, Country: TX
Did you adhere to the comment about a connection to chassis when loop antenna is used? See top left corner of schematic. Just a guess on my part.
Posts: 93
Threads: 20
Joined: Aug 2014
City: Greenville, TX
Assume you connected the wire with the lug on it to the chassis per schematic when the external antenna is not used.
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
That’s correct. Never disconnected it.
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 16,476
Threads: 573
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Is your loop antenna intact? Can you disconnect and make sure it at least shows continuity?
The reason I am asking, you might be receiving the SSTRAN even withour it, the signal is strong enough.
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: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
It has continuity. I even tried some loops that I had sitting around. One of them Worked a little better but still no good.
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 1,119
Threads: 44
Joined: Feb 2015
City: Roseville, MN
Is the secondary of T1 good? If so, there should be AVC voltage at the control grid of the 7A8. Also, check to make sure that C12 is connected between the AVC and B-. C12 is the signal ground for the first 2 amplifier stages.
Rod
Posts: 7,294
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
>If so, there should be AVC voltage at the control grid of the 7A8.
To be picky generally the control grid would be the one closest to the cathode. In pentigrid converter circuits it's use in the oscillator portion. The rf input is actually on grid 4 (pin 6). This where the avc voltage should be found. Grid 1 would have some - voltage on it if the oscillator is preforming properly.
In reality the pentigrid has two inputs. It's like having a triode on the bottom half. Cathode, control grid, and plate (grid 2). And a tetrode or pentode on top. Grid 3 acts as a screen grid speeding up the eletrons. Grid 4 is the 2nd input (control grid for the pentode on top) Grid 5 is the screen for the pentode section. And finally grid 6 is the suppressor grid which is internal connected to the cathode.
Happy Hunting!
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: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
Ok, Terry, thanks for the info, but it was way over my head. I did check all the voltages On the 7A8 according to the chart that came with the schematics and they check ok.
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
Hey Rod,
Here's a good one. C12 was the problem. It wasn't there! I installed one and it works!
Thanks, everyone for your help.
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
Posts: 7,294
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Not a problem. The reader's digest version of Rod's post abt the avc is that on pin 4 of the 7A8 you should w/a strong station -10vdc or so. With a weak station the voltage is going to be less - so maybe -5vdc. The less - it is the more the mixer tube (7A8) and the 7B7 IF amp tube will conduct. When they conduct more weak signals become louder. And vise versa.
I'm thinking that it's a open ant coil or IF transformer. Both of these could pass some signal but not all giving poor performance. A weak tube or a stage miss aligned could be the issue too.
Just for grins if you happen to have spare tuning cap try connecting one section in parallel with the ant section in the set. Tune the added cap to see if there is a peak in signals.
GL
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
(This post was last modified: 05-05-2020, 03:13 PM by Radioroslyn.)
Posts: 1,119
Threads: 44
Joined: Feb 2015
City: Roseville, MN
Excellent, on to the next issue. It's after noon, time for a brew to celebrate.
Posts: 825
Threads: 113
Joined: Aug 2012
City: The Villages
State, Province, Country: Florida
You said it!
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
(This post was last modified: 05-05-2020, 04:37 PM by Eric Adams.)
Users browsing this thread: 1 Guest(s)
|
|
Recent Posts
|
|
Philco 42-345 Restoration/Repair
|
| Today I've been reading through the site trying to learn more about this radio. I also soldered the lose power cord cabl...osanders0311 — 08:24 PM |
|
Philco 610B oscillator wiring
|
| Thanks David! I do have that same later prodution model 610 schematic. I've also studied the Philco service bulletins fo...Tubester — 08:12 PM |
|
Philco 610B oscillator wiring
|
| Some info from Beitmans says late production. David David — 06:06 PM |
|
Restoring Philco 96
|
| Oh wow! Just found this thread. Brings me back to early days on this phorum. I did a 96 back in 2017. Thread here:
...rfeenstra — 06:05 PM |
|
Philco 610B oscillator wiring
|
| Thanks for the replies. It's not the really the hum that I am after. Just trying to understand why only the shortwave ba...Tubester — 04:01 PM |
|
Restoring Philco 96
|
| 70 and 90 are Superhets, but at least the 2x45 model of 90 uses the Plate detector (and so does 70).
Also the Atwaters,...morzh — 03:28 PM |
|
Restoring Philco 96
|
| Morzh, Prayers for your mom. I am sure that there was enough pain living through the Holocaust as a child. I pray dail...MrFixr55 — 02:19 PM |
|
Philco 610B oscillator wiring
|
| Hi Dan,
Divide and conquer. First off trry to differentiate between 60Hz and 120 Hz hum. 120 Hz hum has a higher pit...MrFixr55 — 01:49 PM |
|
Restoring Philco 96
|
| Yes, other than takin a toll on your back, they are undeed way more repair friendly than many other Philcos.
To me, som...morzh — 01:04 PM |
|
Philco 610B oscillator wiring
|
| If the wires look like they were this way from the factory (very neat and very dull soldering joints), I'd leave them be...morzh — 12:58 PM |
|
Who's Online
|
There are currently 1560 online users. [Complete List]
» 1 Member(s) | 1559 Guest(s)
|
|
|
|
 
|
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
