Philco 650 motorboating - Printable Version
+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: Philco 650 motorboating (/showthread.php?tid=1034)
+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: Philco 650 motorboating (/showthread.php?tid=1034)
Philco 650 motorboating - BDM - 03-24-2008
I've posted this on ARF also. Figure I'll see if those on both sites may know something I obviously don't.
Well, this isn't a big issue. But it annoys me at times. Right around 7/mc it starts to motorboat depending how much antenna is connected. I've tried using a weak 6A7 for less gain, this helped but, it still persist. The vid kind of tells the story. All caps and any out of tolerance resistors have been replaced. Set plays fine other than this. Also, it only occurs from about 6.5/mc straight up to 7.5/mc. No other band does this occur.
http://www.youtube.com/watch?v=FLgucsVPHz8
So, what do you guys think? Thanks gents.
- Texasrocker - 03-24-2008
Brian, Thanks for the video!! You most definately have one or more *microphonic* bad (still working tubes) in the set somewhere on the chassis. Tapping easily on top of each tube separately with a pencil while set is on should isolate the defective tube (s).I have found motorboating is usually a caused by a defective coupling-capacitor somewhere out to chassis ground , possibly one missing from the past before you restored the chassis? Doublecheck your schematic, possibly someone removed a cap before in a prior repair job and forgot to replace it? The antenna wire most probably needs at least 20' or so to do a good job. It is easy to *overload* the longwire antennas sometimes also by using too much length in these old sets!! You can try using a 250 pf (uuf) ceramic disc cap in series with your longer antenna wire at the ant term sometimes helps balance the outdoor longwires? Randal
- BDM - 03-24-2008
Well see this is what's funny. I can use about 1' of wire, and it does this. Then I connected 6', and it's gone. Then I connect up to my 150', and it does it. I can add 20' to the long wire and it's gone. I've done this several times playing with antenna wire length and it changes depending. Also operating with no antenna it gets really bad! I haven't tried the tube tap yet. But when it operates properly(again, depending on antenna length) it doesn't have this microphonic sound when tapping the chassis. I should note the shadow meter is out of the set. Could this effect the load on the AVC possibly causing this? Also I'll check the schematic over next time I have it out. Someone did get their fingers in this set and performed a couple of not so good repairs. You could be right.
- Texasrocker - 03-24-2008
Hello again Brian. The shortwave bands will most definately need more than 1' of antenna wire to work properly. I have found about 25'-30' of outdoor antenna wire seems to balance well on all my old sets, incl all different brands of TRF type sets of the late 20s- late 30s that have no factory balanced ant system, both on AM & Shortwave bands. I also have a much longer outdoor longwire ant (such as your longest one also), that I use for my LPAM transmitter only. What is happening, is your 1' isnt long enough for SW, even though it make work well on AM from your local powerful AM stations signals. By trying to use your 100' or more outdoor antenna, you are most definately overloading to much antenna to the receiver for either AM or Shortwave Bands! Way to much! Extra long outdoor LW antennas build-up capacitance on their own. A way to "balance" the extra long outdoor antenna wire can be done by adding a adjustable "antenna-trimmer" in series to your radios! If you have a old parts chassis laying around with a good variable tuning condenser you can rob, (either 2 gang or 3),.. you could mount it to a piece of flat wood and attach your extra-long outdoor ant wire to the frame of it. Then, off the opposite side of the tuner, attach a jumper wire from one of the oscillator screws and attach it to your radios ant terminals. That way, by turning the tuning-shaft on your variable cap mounted to the board, you can "match-up" & "peak" your extra-long antenna to balance perfectly to any set, and works great on AM for *DX-ing* those long distant stations as well!! Just make sure the frame of the "added" inline (series) variable tuning cap doesnt contact the radio chassis. Ala,... by adding the 2nd tuning condenser, you would have a way to "tune" your extra long outdoor antenna for best reception & balance on *any* vintage radio set!! I still think you also have a microphonic-tube (s) somewhere also, intermittant? Just tryin to help!! Good luck!!
Randal
- Texasrocker - 03-24-2008
BDM, I just took a very quick look at the schematic for your Philco 650 over at the nostalgiaair site. You mentioned the shadowmeter was removed from the set. The resistance coil of the shadowmeter appears to be a 5K ohm resistor (wirewound type on shadowmeter). If the shadowmeter wires have been cut loose, then you definately need to sub-in a resistor ( guestimate 5 watter power type resistor) would be OK in place of the shadowmeter coil, until you get the orig shadowmeter coil (if still good) re-installed? I have found in the past, that a missing or defective shadowmeter coil assembly usually completely shuts-down a mid late 30s Philco. I havent worked on a 650 in a long time. Perhaps Ron or Chuck can take a look at the schemat also and provide more info. I am currently restoring 2 vintage radios at the same time, a Radiola mod 80 TRF, & a 36 Truetone D-723 for separate customers. Both were *hacked* pretty bad, but I have both getting audio now, so Im headed in the right direction on both restorations. My heads kinda fuzzy reading schemats right now. (hee hee)
Jus tryin to help 
Randal
- BDM - 03-28-2008
Randal, I'm sure you read what I've found. Two .05 caps coming off both the Ant & RF coils for SW were just too close together.
- Texasrocker - 03-29-2008
Congrats on isolating the prob in your set!! I have never had that prob before. Guess I got lucky in my recaps, and they were still close to orig underchassis locations? Enjoy your Philco!!!
We all learn something new everyday!! Thats what makes this hobby Great!! Randal