Neutralization of a Philco 87
Posts: 17
Threads: 4
Joined: Jul 2014
City: Topeka KS
I’ve recapped this radio and it works GREAT except for one thing. The two local stations at the high end of the dial come in too well. By this I mean with the volume turned down all the way the volume is too loud. When I tried to neutralize the radio following the procedure in the Philco Library I got all the way to the last step. I can’t get the 1st RF stage neutralized, 2 and 3 adjusted just like they were supposed to. The trimmer doesn’t seem to do anything. I’m using a plastic wrench and did replace the capacitors connected to the trimmers.
Any thoughts?
Thanks in advance.
Posts: 18,427
Threads: 622
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
When I couldn't neutralize a stage with the respective trimmer, I found out I was trying to trim a wrong trimmer.
As long as the trimmer and the coils are good it should neutralize.
PS. I think I used a dud instead of a socket with a disconnected heater pin.
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: 17
Threads: 4
Joined: Jul 2014
City: Topeka KS
I think the trimmer is good, but should I swap it for another one to see if the problem moves? Number 2 for number 1? I’m 99.44% sure I’m adjusting the correct trimmer. I had to rewind the primaries of the other three coils but this one was good. One thing I wondered about at the time was that the primary of this coil has probably twice as many turns as the other three. Might this have something to do with my problem?
Thanks again.
Posts: 18,427
Threads: 622
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Make sure the trimmer is connected on both sides (output and input coils). Also make sure the coils are OK and have continuity on all contacts (including the one where thr trimmer goes to).
If you have a modern trimmer cap you could install it in parallel (or with the original disconnected) and see if it works. Easier than moving the trimmer.
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: 17
Threads: 4
Joined: Jul 2014
City: Topeka KS
The coil is fine and the trimmer is connected. I tried switching two of the trimmers, no change.
I’m starting to wonder if I have some kind of fluke problem. Our station at 1490 comes in way too loud with the volume turned down all the way with no antenna connected.
Posts: 17
Threads: 4
Joined: Jul 2014
City: Topeka KS
Another observation. I had to rewind the primary windings on the three other RF coils. The two stations that are way too strong now were the only stations I could get before I repaired the coils.
Posts: 17
Threads: 4
Joined: Jul 2014
City: Topeka KS
Another observation. When I’m tuning the radio I frequently get a sound kind of like an A-10 airplane firing its cannon. Is this motor boating? If so, is it related to my problem?
Thanks again.
Posts: 18,427
Threads: 622
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
Kirbyc
When you first tried it, you said the radio worked great. Then you said the trimmer was good, then you said you had to rewind three coils.
Why don't you make sure the coils are all OK and are exactly as they were before they went bad, including the tap location etc.
Then make sure you follow the actual procedure and not what you think the procedure is. Like what if instead of trying to achieve the minimum signal the maximum is being achieved.
Your trimmer not working is suspicious.
Check all the tubes.
Make sure the tube used for neutralizing the stages is what it says it should be. Same tube that is either a dud with all structure OK except the filament is open, or a good tube mounted in a transition socket with one filament pin disconnected.
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: 17
Threads: 4
Joined: Jul 2014
City: Topeka KS
Let me reset the timetable. I recapped the radio. When I first fired it up after the recap I could only receive the stations at 1440 and 1490. That’s when I rewound three of the RF coils following the instructions in The Philco Repair Bench. After I rewound them was when the radio worked very well everywhere except it worked too well at the 1440-1490 end. By too well I mean that with the volume turned all the way down the volume is too loud. It is motorboating so I guess isn’t really working well.
I’ve checked the tubes, but I’ll check them again.
I used the procedure from the Philco Library to align and neutralize the set. I used a transition socket and the tube for each stage and a plastic wrench.
I also swapped trimmer 4 and 5 as shown on the Philco procedure with no difference in the outcome.
One other thing. The grid leak resistor should be 750k ohms but is 880k ohms. Could this be a problem?
Posts: 18,427
Threads: 622
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
No I do not think GL resistor would result in this.
In fact I think it is not the gread leak detector but is the plate detector.
Also: you did replace the 0.1uF caps inside the resistors? (co-axial parts 7, 12 and 17)?
And, keep in mind: this is a simple TRF set with no AVC, so strong stations will come very loud and you cannot do much about it.
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: 17
Threads: 4
Joined: Jul 2014
City: Topeka KS
I did replace the capacitors by cutting the wires that went to ground. Should I maybe replace the resistors too?
Posts: 18,427
Threads: 622
Joined: Oct 2011
City: Jackson
State, Province, Country: NJ
No, as long as the resistors are OK (being wirewound they are not likely to drift) you don't have to.
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: 1 Guest(s)
|
|
Recent Posts
|
|
Philco P45-6365 Universal Transformer Instruction Manual
|
| Can anyone guide me to where this may be found?GRG — 03:00 PM |
|
54C Complete Teardown/Rebuild
|
| I don't think that I have encountered a 12Z3 before, curious how it uses one of those but includes a #43, which is a 25 ...Arran — 02:17 PM |
|
HiFi (Chifi) tube amp build - but my own design.
|
| It's the other forum. I'm also in DIY, but mostly read there. Honestly, I kinda jumped into this without much thought to...TV MAN — 10:43 AM |
|
Philco 71 Code 125
|
| Hello,
I am in need of a schematic for this radio. Mine has the three separate circular tube shields and a shadow me...dconant — 08:06 AM |
|
Stromberg Carlson 1500 Squeal
|
| And life just keeps getting more complicated.dconant — 07:57 AM |
|
54C Complete Teardown/Rebuild
|
| Hello Roy,
here is this one
sincerely Richardradiorich — 12:45 AM |
|
54C Complete Teardown/Rebuild
|
| Richard,
Had grabbed it already but thank you just the same. I find myself wanting to find some way to block out the...glyphmon — 12:03 AM |
|
54C Complete Teardown/Rebuild
|
| Hello roy,
here is a link to the schematic .
Sincerely Richardradiorich — 11:54 PM |
|
54C Complete Teardown/Rebuild
|
| Richard,
The Silvertone 2014 also is a transformerless set, so I am incorporating a 1:1 600 ohm audio isolation transfo...glyphmon — 11:37 PM |
|
Preliminary work on wife's Silvertone 2014
|
| Did an alignment today which was interesting. IF alignment went great, almost all was already spot-on. Adjusting on th...glyphmon — 11:35 PM |
|
Who's Online
|
There are currently 1934 online users. [Complete List] » 1 Member(s) | 1933 Guest(s)
|
|
|
|

|