Thanks for all the help so far.
I have done very little with this set, apart from replacing the candohm and burned out 5.6K resistor today. I am looking around the set for issues and today found a cut ground wire attached to the RF section. See pic. From the parts diagram/layout drawing, this appears to be part 20, a .05 cap that connects to Position 4 of the RF transformer, one side of the shadow meter, and some other parts.
I have looked around this part of the circuit and cannot find a replacement cap; so I am unsure why someone in the past cut this out of the circuit and didn't replace it.
Two questions:
What does this cap do?
Also, would I be able to tie a replacement .05 cap anywhere along this node? Or should I try to keep it as close to the transformer as possible? Getting it in there will be tight, as that transformer is buried in the RF section. I would be easier for me to tie it into the shadowmeter, etc., but don't know if that's kosher.
Thoughts appreciated, thank you!
PS: Turns out the on/off switch is shot. Someone intentionally shorted it out with a soldered in wire, so I'm looking for a replacement if anyone has one. See the WTB section.
Ted
OK, so I got no help on that last question
Here's another. Anyone?
I am going through the radio and found these two .003, 1000V caps (parts 73 and 74) running from either side of the audio output transformer and output tubes to ground. Didn't have any .003 caps in that voltage rating, so for each I ran two .0068, 630V caps in series. Should cover the voltage requirement. But my real question: Is such a high voltage rating required?
Thanks.
Let's examine your first question first.
The .05 uF cap, part (20), is tied into the B+ line feeding the plate of the RF tube (through the appropriate coils, of course), and it looks to me that it acts as a bypass to keep stray RF out of the B+ line.
The second question is more tricky.
1000 volts were specified due to the possibility of voltage spikes at the plates of the audio output tubes. Now, there has been disagreement among experienced collectors/restorers as to whether they really need to be 1000 volts or not. All I can tell you is that I've been using 600/630 volt caps as these plate bypasses for years, and have yet to have one blow up on me. But then again, I do not run my radios at high volume levels. If you run a radio full blast, then it *might* need the 1000 volt rating. YMMV.
Just curious...why are you using a Canadian 37-3670 schematic? Although it should be the same as the USA 37-670 schematic, I think...
(01-26-2015, 04:28 PM)Ron Ramirez Wrote: [ -> ]Let's examine your first question first.
The .05 uF cap, part (20), is tied into the B+ line feeding the plate of the RF tube (through the appropriate coils, of course), and it looks to me that it acts as a bypass to keep stray RF out of the B+ line.
The second question is more tricky.
1000 volts were specified due to the possibility of voltage spikes at the plates of the audio output tubes. Now, there has been disagreement among experienced collectors/restorers as to whether they really need to be 1000 volts or not. All I can tell you is that I've been using 600/630 volt caps as these plate bypasses for years, and have yet to have one blow up on me. But then again, I do not run my radios at high volume levels. If you run a radio full blast, then it *might* need the 1000 volt rating. YMMV.
Just curious...why are you using a Canadian 37-3670 schematic? Although it should be the same as the USA 37-670 schematic, I think...
Ron,
This is the only schematic I could find, apart from the NostalgiaAir one which isn't so great (honestly I did not know I had Canadian version). I have ordered paperwork from Chuck Schwark at the Repair Bench (comes highly recommended as I'm sure you know) but haven't received it yet; just sent payment a few days ago.
Anyway, the schematic appears mostly correct; a few differences, but I have stuck to the original wiring in those cases. Thanks for the info on those .03 caps, 1000V. I'll never crank the radio, so shouldn't be an issue, esp. with running those .0068s in series.
Thanks! Fired up the radio for the first time last night after replacing the electrolytics, AC to ground and some other caps, and got reception. What a sweet sound!
I wonder if the set ever played after the previous restoration. Among other problems, previous person wired electrolytic 86A backwards
he ran the negative to ground; this one has positive to ground.
Cheers, time to go hunker down for the blizzard,
Ted
This is my first Philco and I still have a long way to go on it, but as a collector who has mostly Zeniths, I have to say that this set is pretty impressive. Just finished stuffing the bakelite blocks and replacing all resistors more than 10 percent off spec, plus all paper caps. Haven't got to the caps/resistors in the RF section yet (I will when I remove it) but I am more than impressed with the radio's performance. Without an alignment, after just a partial recap, and in the middle of a blizzard, I picked up many, many SW stations that I am not used to hearing on any of my Zeniths, including my 12S265 and 12S267. And the AM band is very impressive, too. Selective, with great sound and volume. I am really glad I got this radio. Can't wait to get back to it.
Well, after taking out the RF section, replacing some caps and putting the set back together, all H**l has broken loose. Prior to taking out the floating RF, I was getting great reception and volume across all bands. Now, I am getting very weak AM volume and somewhat decent volume (though there's a lot of squealing going on) on the other bands. In AM, I can barely hear it with volume turned all the way up.
When I squeeze the 6A8 Dector/oscillator grid cap wire, the volume increases a good bit. In SW bands, it's very loud, just about what it was before, I think. In AM, its loud though not as loud as it was prior to pulling out the RF section. When I let go of the grid cap wire, the volume dies again. Reception is poor on AM; on the shortwave bands, there is some reception; however there's also a ton of squealing. The 6A8 voltages are pretty much where they should be. Tubes all test good.
Can someone guide me through some troubleshooting? I would love to solve these issues. It's a beautiful set and I'm very discouraged. Could use some expert help.
Thank you.
Here's a clean copy of the schematic. Click on the photo once or twice to zoom all the way in.
http://imgur.com/NozIIBg
(02-02-2015, 11:11 PM)Diverted Wrote: [ -> ]When I squeeze the 6A8 Dector/oscillator grid cap wire, the volume increases a good bit.
Sounds to me like you have an issue somewhere
before the 6A8G control grid. How are the voltages on the 6K7G RF amp?
This sounds very much like the classic bad antenna or RF coil on AM. SW...??? Did you replace caps (8 ), (20) & (21)? Also check resistor (9); if it fails, you lose AVC to the RF tube and the radio will exhibit the same symptoms as open antenna coils.
(02-03-2015, 06:56 AM)Ron Ramirez Wrote: [ -> ]Sounds to me like you have an issue somewhere before the 6A8G control grid. How are the voltages on the 6K7G RF amp?
This sounds very much like the classic bad antenna or RF coil on AM. SW...??? Did you replace caps (8 ), (20) & (21)? Also check resistor (9); if it fails, you lose AVC to the RF tube and the radio will exhibit the same symptoms as open antenna coils.
Found the issue. A stupid oversight on my part.
When I re-installed the tuning condenser, one of the unshielded wire leads leading to the fins ended up getting pushed up agains the side ofthe round access hole on the top of the RF chassis. So the wire was hitting the grounded RF chassis, grounding the fins on the back third of the tuning gang sections. It was just barely touching, but enough. Got home from work, noticed it, desoldered the lead and readjusted ... Bingo. Radio is playing strong and perfect across all bands. Thank god! It was a simple error.