Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12) x

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

48-475 signal injection
#8

(10-02-2015, 10:27 PM)Raleigh Wrote:  OK, here is a silly question.  Troubleshooting for section 2 says to use an audio signal.  Just to be sure, are you using an audio signal or an audio-modulated RF signal?

If you don't get any audio out of test point A, try walking your probe past C207, the volume control, and C210.  At some point you'll get a signal, because you already know you get strong output from the 7C6 grid at point D.  Then you'll have a good idea what was wrong between points A and D.

Ditto if you walk the audio signal from point A up to the IF transformer.  If you are supposed to hear audio injected at point A, then you should hear it if it's injected anywhere along that path.

Is there a particular problem you are trying to solve?  If you hear audio injected at point D, then you know the AF path works from the speaker back to that point regardless of your indication at point B, so I wouldn't sweat that for now.  What do you hear when you turn the radio on and try to get a station, or if you put modulated RF on the grid of the IF tubes?

The original problem was no signal from the IF. So I just thought I'd try the troubleshooting steps, instead of just going to the IF coils. I did find that the volume control pot is flaky. I was able to finally get a good audio signal on the left of R205 (100K), but very weak on the  test point A side. Is a 100K resistor going to reduce the audio that much? Then I discovered that I got no signal from terminal 1 of TB400, so none of the trimmers did anything. I disassembled the 3rd IF can, and found a bad mica cap. So I'm just going to check all three IF cans out, but I had to order more mica caps and fish paper, as the original insulation was stuck like glue to the insides of the can.

So it will be a week or 2 before I attack it again. But I've got a Deforest Crosley 1621, a Midwest 181, a Philco 41-608, a Philco 37-660, and a Philco 38-3-3XX  staring at me waiting for restoration. I'll hit the Deforest Crosley first.


Messages In This Thread
48-475 signal injection - by Patrick - 09-27-2015, 02:34 PM
RE: 48-475 signal injection - by Patrick - 09-29-2015, 02:47 PM
RE: 48-475 signal injection - by Radioroslyn - 09-29-2015, 06:11 PM
RE: 48-475 signal injection - by Patrick - 09-29-2015, 06:41 PM
RE: 48-475 signal injection - by Raleigh - 09-29-2015, 07:53 PM
RE: 48-475 signal injection - by Patrick - 09-29-2015, 08:54 PM
RE: 48-475 signal injection - by Raleigh - 10-02-2015, 10:27 PM
RE: 48-475 signal injection - by Patrick - 10-04-2015, 01:00 AM
RE: 48-475 signal injection - by Patrick - 10-09-2015, 02:44 PM
RE: 48-475 signal injection - by Patrick - 10-09-2015, 01:23 PM



Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
HiFi (Chifi) tube amp build - but my own design.
Well, maybe - maybe not  :lol: It's been an interesting project so far! Something so simple, yet so cranky. The 1st one ...TV MAN — 05:12 PM
1949 Motorola 5A9M
Haven't thought of Burgess batteres in a while  https://www.radionostalgia.ca/lib/Images/battery/us/burgess1D.jpgi ...Vlad95 — 03:50 PM
Philco Model 16 wiring question
Measure the voltages first, just in case.morzh — 02:19 PM
1949 Motorola 5A9M
Haven't thought of Burgess batteries in a while Mr. Fixer. Boston Edison always used Burgess in their Bright Star yellow...Paul Philco322 — 02:17 PM
1949 Motorola 5A9M
Thanks Sam. I'll let you know. I can probably scare some up from the local radio club.klondike98 — 02:07 PM
Philco 89 Code 123 Osc Coil
Hello,  I thought I would post my findings on my bad oscillator tickler coil. There were 27 turns on the outer coil b...dconant — 12:38 PM
Philco Model 16 wiring question
Thanks Morzh. So it appears I did wire it incorrectly and I have to switch the wires between pins 2 and 4.bobclausen — 09:24 AM
Philco 46-1209 strange behavior
No, it's not a problem, just during certain condition it could show up. Yes, an internal tube short could do that too. ...morzh — 09:13 AM
HiFi (Chifi) tube amp build - but my own design.
You sound guys are never satisfied. :crazy: :clap:RodB — 09:10 AM
HiFi (Chifi) tube amp build - but my own design.
I got some new ceramic octal tube sockets installed and also tried some different coupling caps.  The results:  The go...TV MAN — 08:42 AM

[-]
Who's Online
There are currently no members online.

>