Posts: 365
Threads: 76
Joined: Oct 2014
City: Winter Haven, FL
Without going into too much detail, I can inject an RF signal at various frequencies down to 500Hz (with var. cap fully meshed), and tune to that frequency, at which point I can adjust both the 1st and 2nd IF cans. But I get nothing when I try to inject the 460 Hz IF.
Can something be preventing me from hearing anything below 500Hz? Only tried it by ear so far.
I'll post a schematic if needed, but I thought this just might be a general question.
Thanks.
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Do you mean hz or khz?
Would connect the generator to the grid cap of the 6A7 and set it for 460kc w/modulation. Adjust IF transformers for max signal. If there is no signal check voltages at the plate and screen of the 6A7 and 78.
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: 04-02-2021, 12:01 PM by Radioroslyn.)
Posts: 365
Threads: 76
Joined: Oct 2014
City: Winter Haven, FL
Khz. Cap of 6A7 is where I fed the signal in. No IF. Voltages are good. Can receive stations.
(This post was last modified: 04-02-2021, 12:08 PM by Patrick.)
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Ok voltages @ the 6A7 and 78?
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: 365
Threads: 76
Joined: Oct 2014
City: Winter Haven, FL
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
So the problem is you can't align the IF but the receiver works?
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: 365
Threads: 76
Joined: Oct 2014
City: Winter Haven, FL
Yes. Well...I can align by using an existing station, but not using the IF frequency. And I know my sig gen works.
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Ok sounds like a generator problem. Would check by listening for the 2nd harmonic of 460kc (920kc) on a modern digital receiver. Don't know what you are using but could have a dirty band switch or out of alignment on that band.
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: 365
Threads: 76
Joined: Oct 2014
City: Winter Haven, FL
Nope. I'm using an HP 8657A. Tried it on other chassis. Works fine. 'Tis a mystery.
Posts: 15,819
Threads: 554
Joined: Oct 2011
City: Jackson, NJ
Are you sure 6A7 is good?
Increase your IF signal a whole lot if possible.
Make sure your cap on your 6A7 soldered well.
Check IF coils for continuity.
Try bypassing 6A7: inject the 460kHz right into the IF xfmr (6A7 plate) via a capacitor and put a Zener in parallel to the generator output to protect it from initial surge of Plate voltage.
PS. Have you UNPLUGGED the Grid Cap wire from 6A7 Grid Cap? If not, it should be unplugged.
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.
(This post was last modified: 04-02-2021, 02:04 PM by morzh.)
Posts: 365
Threads: 76
Joined: Oct 2014
City: Winter Haven, FL
Yeah, I tried 2 other 6A7's. First thing I did was check the IF coils. One thing that was puzzling, is that the primary of the second IF should be 11.5Ω, but it measures 39Ω. Pulled the can off, and everything LOOKS fine, but still 39Ω. All the other coils are spot on. Haven't bypassed the 6A7 yet.
Posts: 15,819
Threads: 554
Joined: Oct 2011
City: Jackson, NJ
But you did disconnect the wire to the 6A7's cap when applying the signal to the cap?
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: 365
Threads: 76
Joined: Oct 2014
City: Winter Haven, FL
Posts: 15,819
Threads: 554
Joined: Oct 2011
City: Jackson, NJ
I cannot explain it.
If it were not disconnected, there is the wavetrap. It attenuates 460kHz.
If you used good high levels of 460kHz and it does not show at he output, I would disconnect the filters and put the signal directly through them, trying to align them to it.
Keep the input is under the plate voltage, so if using a solid state generator, use a capacitor and a zener in parallel to the generator's output (i use it all the time, I described it a few years ago.)
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: 15,819
Threads: 554
Joined: Oct 2011
City: Jackson, NJ
How sure are you your generator is good?
I am asking because if you used it to align other radios it will work with them then.
Do you have a counter that could confirm the accuracy of 460kHz?
Also, is it possible you simply have not found the spot in the IF cans where the signal would go through? It could be simply really badly out of IF alignment, so one of the filters would always block it.
I think now even more, it is time to disconnect the filters and align them one by one; start from 27 first, then solder it back and align the 21.
then try to inject the 460kHz via the 6A7's cap.
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.
Users browsing this thread: 2 Guest(s)
|
|
Recent Posts
|
|
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 |
|
trying to identify this wire type
|
| Greetings Phorum members,
Hope you can help me identify this type of wire in the photo I have attached. I am not sure ...georgetownjohn — 01:53 PM |
|
Who's Online
|
| There are currently no members online. |
|
 
|
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
