Posts: 289
Threads: 42
Joined: Jan 2014
City: Jeffersonville
State, Province, Country: PA
Hi fellas -
I'm working on a PT-25. It's been recapped, new filter caps, repaired speaker, tested and swapped tubes and lubricated volume pot. However, there is clearly audio distortion. Cleaned the tube sockets and installed a few Philco nos tubes but no change. I suspect a resistor is the cause but the schematics I have do not give tube voltage values. I had planned to simply test the resistors but many are stuffed into very small locations with hardly any wire to even clip to.
Tube voltages would definitively reveal if there's a bad resistor correct?
Could there be another cause?
Thanks!
Paul
Posts: 16,495
Threads: 573
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
If you have the schematic, post a link or the image. Nostalgiaair does not have it even though it does have PT-25 entry.
Distortion could be a result of some wrong voltages, possibly due to bad resistors.
But then those radios do not have too many resistors so why don't you just go through them. If the radio is AC/DC (or just transformerless) and there is a input RC filter after the rectifier, see if the large resistors there are ok.
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: 1,259
Threads: 32
Joined: Jan 2014
City: Wellborn Florida
Sorry no voltage reading but everyone can see what you are working on. David
Posts: 289
Threads: 42
Joined: Jan 2014
City: Jeffersonville
State, Province, Country: PA
I'm at work and need to scan the paper copy to post. But David posted exactly what I'm working from.
Thanks!
Posts: 2,118
Threads: 112
Joined: Jun 2010
City: Medford OR (OR what?)
what product did you clean the vol pot with - specifically, if Deoxit, which one?
"I just might turn into smoke, but I feel fine"
http://www.russoldradios.com/
Posts: 16,495
Threads: 573
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
And...have you tried to change the speaker?
Leave all in place, only disconnect the voice coil from the output xfmr secondary and connect a PM speaker to it. See if the distortion persists.
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: 289
Threads: 42
Joined: Jan 2014
City: Jeffersonville
State, Province, Country: PA
I use De-ox-id contact cleaner, part # 19-1906-A
There are 7 resistors. A few are pin to pin that seem to require their removal to test so I might as well install a new one.
I haven't changed the speaker. It played when I bought the set and with each replaced cap the audio quality has improved. It's just not at where I know it should be even for a small table top set.
Very much appreciate the help guys. Trying to finish this set up for a Xmas gift for my dad, and move on to a 16B that I've very stoked about starting.
Posts: 1,411
Threads: 72
Joined: Oct 2007
City: Linn Creek, MO
Paul Wrote:
Quote:There are 7 resistors. A few are pin to pin that seem to require their removal to test
Looking at your schematic, all of your resistors can be tested in circuit. The only exception would be the one connected across the dial light, just remove the bulb to test that one.
Steve
M R Radios C M Tubes
Posts: 2,118
Threads: 112
Joined: Jun 2010
City: Medford OR (OR what?)
(12-20-2017, 10:06 AM)Paul Wrote: I use De-ox-id contact cleaner, part # 19-1906-A
There are 7 resistors. A few are pin to pin that seem to require their removal to test so I might as well install a new one.
I haven't changed the speaker. It played when I bought the set and with each replaced cap the audio quality has improved. It's just not at where I know it should be even for a small table top set.
Very much appreciate the help guys. Trying to finish this set up for a Xmas gift for my dad, and move on to a 16B that I've very stoked about starting.
The Deoxit contact cleaner (black label) will damage (remove) the conductive surface on many variable resistors. This will create a lot of noise. Check the control for proper operation with a VOM.
Use the green label "Fader Lube" to clean variables that are not wire-wound.
"I just might turn into smoke, but I feel fine"
http://www.russoldradios.com/
Posts: 5,166
Threads: 273
Joined: Nov 2012
City: Wilsonville
State, Province, Country: OR
Paul, just FYI... De-Ox-ID is a different product and manufacturer (GC) than the products that Phlogiston is talking about made by Caig. I haven't used the De-Ox-ID products
DeoxIT has a line of products that include the D-5 (which is the one Phlogiston mentions that can mess up some variable resistor controls but is good for metal contact cleaning) along with the Fader Lube and others. They come in a variety of delivery forms as well.
Posts: 2,118
Threads: 112
Joined: Jun 2010
City: Medford OR (OR what?)
I've never seen De-ox-id (if I were Caig, I'd look for a lawyer) but the same message applies. Some (most) "contact cleaner" can damage those controls and the result is often garbled audio. Use one that is made specifically for faders.
I cant believe that I am saying this , but WD-40 will work if you just HAVE To spray something on there.
The real truth is that some of these products will help a control that is just a little noisy but the fix is usually temporary (months or less). People have been using these products for a while so it is not unusual to find controls damaged by them.
"I just might turn into smoke, but I feel fine"
http://www.russoldradios.com/
Posts: 5,166
Threads: 273
Joined: Nov 2012
City: Wilsonville
State, Province, Country: OR
(12-20-2017, 03:28 PM)Phlogiston Wrote: I've never seen De-ox-id (if I were Caig, I'd look for a lawyer)
That's what I was thinking Russ!
Posts: 289
Threads: 42
Joined: Jan 2014
City: Jeffersonville
State, Province, Country: PA
Update. Replaced resistor #'s from the schematic #12 (2.2meg), #14(22k), #20(470k) and #21(130ohms)
Also found a .012 cap from previously replaced and should be a .01mfd
Resistor #18 (220k) tested at 223k
Audio is better but still distorted.
Attached pic of electronic cleaner I had been using.
Posts: 16,495
Threads: 573
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
0.012 uF and 0.01uF for all intents and purposes are the same.
Have you tried swapping tubes, one by one?
Starting from 35A5.
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: 5,166
Threads: 273
Joined: Nov 2012
City: Wilsonville
State, Province, Country: OR
Has the set been aligned?
Users browsing this thread: 1 Guest(s)
|
|
Recent Posts
|
|
Road Trip for a Philco 46-480
|
| Good morning, folks! I’ve finished the cabinet and the electrical restoration, and have detailed those in their respecti...jrblasde — 10:56 AM |
|
Studebaker/Philco AC-2687 car radio
|
| Arran,
Thanks for checking you manuals.
I appreciate that. Let me know what you find.
PhilPdouglaski — 08:46 AM |
|
Studebaker/Philco AC-2687 car radio
|
| I have some car radio service manuals, Riders I think (not to be confused with the big blue binders), so I may see if on...Arran — 01:20 AM |
|
Philco model 40-100
|
| Greetings;
Here is an update, I found a listing on fleabay for a similar chassis to yours, and it has a photo of what...Arran — 12:58 AM |
|
Philco model 40-100
|
| Greetings;
I think I may have found a clue as to what is missing, from a search I made, there is a rear view of the c...Arran — 12:12 AM |
|
Philco model 40-100
|
| I recently acquired a Philco model 40-100 farm (battery) radio. The radio was in very good condition except the red on f...mhamby — 05:59 PM |
|
Studebaker/Philco AC-2687 car radio
|
| Hello, Richard
the radio is an AC-2687 Studebaker model. The Philco model is S -5323 and the chassis p/n is S-5523Pdouglaski — 11:52 AM |
|
48-482 rear panel help
|
| The 48-482 is an AC only set as well, featuring a power transformer. While the transformer shouldn’t get “hot”, it is ye...jrblasde — 11:12 AM |
|
Studebaker/Philco AC-2687 car radio
|
| I gave a Chrysler/MoPar car radio from 1954, it was made by Philco, and it uses two chassis, one has the power supply an...Arran — 11:06 AM |
|
48-482 rear panel help
|
| Hello keithchip. You could make a hardboard back for the set, but make sure you provide plenty of ventilation holes in ...GarySP — 11:04 AM |
|
Who's Online
|
There are currently 790 online users. [Complete List]
» 2 Member(s) | 788 Guest(s)
|
|
|
|
 
|
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
