Philco 38-3 completely redone no reception - Printable Version
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RE: Philco 38-3 completely redone no reception - DuMont - 04-10-2020
Began doing voltage checks on tube pins. So far, they are showing to be much less than they should be. Hmmm......
Philco 38-3 with less than optimal voltage - DuMont - 04-11-2020
Working on a Philco 38-3.
Completely recapped, good tubes, new resistors.
It had been playing fine, now it's not.
Took the meter and ran pin voltage checks vs schematic. Here are the tubes with what they should read on left, and actual read on right:
Output 6Fg (with chassis upside down, this is the output tube on the left)
S 240v 226v
P 230v 198v
H 6.3 vac 6.7 vac
H 6.3 vac .025 vac
Output 6Fg (with chassis upside down, this is the output tube on the right)
S 220v 186v
P 235v 201v
H 6.3 vac 6.6 vac
H 6.3 vac .027 vac
RF 6U7G
P 235v 219v
S 90v -.316 (I thought I had crossed my probe wires here, but I took it several times. Same result)
H 6.3 vac .025 vac
H 6.3 vac 6.5 vac
IF 6K7G
H 6.3 vac 6.5 vac
H 6.3 vac ZERO
P 240v 215v
S 90v -.03 (See "S" under RF 6U7G above)
OSC Control 6N7G
P 180v -1.5 (See "S" under RF 6U7G above)
P 180 Could not reach this without removing one of the bathtub bakelite (all of which were gutted and recapped)
H 6.3 vac .022 vac
H 6.3 vac Could not reach without moving tub above
DET. OSC 6A8G
Osc. Plate 125v -1.65
H 6.3 vac 6.53 vac
H 6.3 vac .025 vac
P 230v 216v
S 90 v -0.32
2ND DET/1ST AUDIO 6Q7G
H 6.3vac 6.5 vac
H 6.3 vac ZERO
P 135v 94v
DISCRIM. 6H6G
H 6.3 vac ZERO
K 6.3 vac 6.5 vac
Now, all of that being said, I did have an incident with the power plug. The screws holding down the AC lines inside the plug came loose, with the result that plugging it in became a little fireworks show at the plug only. The power strip shut itself off, I replaced the plug and this time soldered the screws shut. The power cord goes into one of those oh-so-much-fun to get the goo out of and replace the caps inside bathtubs. In this particular tub where the power attaches I installed a pair of ceramic .015 mf ceramic safety caps. It had originally held a pair of 0.15 wax/paper factory installs that were buried in the tar.
When I had it playing I had alligator clip leads on some components (electrolytic caps that have to be installed in proper pos/neg orientation). I wonder if it's possible I reversed one of those caps when I soldered it together? Did a resistor fail?
I'm just stuck right now.
Thanks!
RE: Philco 38-3 completely redone no reception - Ron Ramirez - 04-11-2020
I merged your two threads together. Please keep all posts about one radio within the same thread.
From the Phorum Rules:
Quote:II. Multiple threads on the same subject not allowed.
When you start a thread, please keep the discussion within the same thread.
Example: "Philco 90 broken"
After you've started that thread, please do not start another thread on "Philco 90 bad resistor" if it is the same Philco 90 being discussed in the original thread. Give others a chance to respond to your questions rather than asking them again in a new thread - please be patient.
These sort of threads will be immediately deleted, to keep clutter to a minimum.
https://philcoradio.com/phorum/showthread.php?tid=4586
RE: Philco 38-3 completely redone no reception - DuMont - 04-11-2020
Oops! Sorry, Ron - Thought I was adding to my original post.
RE: Philco 38-3 completely redone no reception - Ron Ramirez - 04-11-2020
No worries.
Carry on.
RE: Philco 38-3 completely redone no reception - 462ron - 04-12-2020
Dumont, The Nostalgia Air print isn’t clear at all, not sure about some tie point dots whether it’s there or not, but a quick glance at the schematic shows resistor 46, a 1K as a good suspect. Measure for voltage on both sides and measure value of that resistor. Hope this helps!
Ron
RE: Philco 38-3 completely redone no reception - John Bartley - 04-12-2020
Start with an audio signal at the speaker and work back. Once you get to the detector, change to a modulated RF signal at IF frequency and keep working back toward the antenna. Jumping around and guessing will get you nowhere ...... follow the path ..... think like an electron travelling thru the radio
"BE the electron"
RE: Philco 38-3 completely redone no reception - DuMont - 04-12-2020
The 38-3 is up and working. Found an improper value resister in the power circuit, which had burned out. Replaced with proper value, and it's working. How many times do we tell ourselves to double and triple check our own work????
Thanks, all!
RE: Philco 38-3 completely redone no reception - Kestas - 04-12-2020
I am forced to double and triple check my work. This includes sketching out the location of components. Double and triple check values and location against schematics. Then do the same after replacing components. I have to do this because I have few skills with diagnostics.