[LedHed]

I am about to start on my next project. The bad news is that someone has been at it before me, and I'm having some trouble deciphering what is going on underneath the chassis as I am pretty new to this. Does anyone have a good photo of the underchassis, either original or recapped correctly? I'm particularly interested in the wiring of the electrolytics.

Here is how it sits now. None of this is my work, and I haven't traced out the replaced caps to make sure they were wired correctly. All values are 22uF @ 450V.

http://i1267.photobucket.com/albums/jj54...6a2764.jpg

http://i1267.photobucket.com/albums/jj54...915944.jpg

[Joe Rossi]

The best way to determine if what was changed underneath is correct is to get the schematic and trace the components. Looking at the photos, I'd say that the person who re-capped did a good job soldering and keeping the leads neat. But get the schematic. Joe

[Arran]

One of the biggest mistakes people make when replacing filter capacitors is assuming that B- and the chassis are one and the same, and of course the set doesn't work properly and hums like crazy. In many cases the set will use a fixed bias network with a series of resistors so one filter cap will be slightly more negative then the other, or one will have it's negative side connected directly to the transformer center tap while the other will have it's negative side connect to the chassis.
According to the schematic found here:

http://www.nostalgiaair.org/PagesByModel...025209.pdf

The set is supposed to have two filter caps, not three, neither filter cap should have it's negative side connected to chassis, C16 is connected to the center tap and C17 should be connected between the 27 ohm and 126 ohm section of resistor R12, which was a wire wound candohm like we can see in the first photo. The field coil of the speaker should be connected between the positive side of the two filter caps with the positive of the output filter also connected to the primary of the output transformer. In short I think you should print out that service data on Nostalgia Air, undo whatever the previous person did in there, and start over, it's hard to tell from the photos everything that was done but what I can see in the power supply section does have some wiring errors, in fact one cap looks like it's wired in backwards.
Regards
Arran

[LedHed]

Thanks for the help guys. I've got the schematic and will do as you suggest. I am a product of digital electronics, and am still getting the hang of the point to point wiring style of these old sets. I suppose that the best way to learn is as you suggest. I'll plan on pulling the old electrolytics out, rewiring the whole thing and then tracing the other caps out which shouldn't be too bad.

[Arran]

One thing to check on, while you are in there, is the candohm resistor I mentioned, sometimes those have a habit of developing open sections, but you have the resistance readings listed on the parts like under R12 so you can see if it's still good. Another area to check on is the speaker plug socket, to me it there does no seem to be enough wires connected to it and there should be at least three. One should be connected to the cathode/filament of the rectifier tube, one should be connected to the positive end of the output filter capacitor and one end of the output transformer, and the third should be connected to the plate of the power output tube.
In some cases they will add a fourth connection to one end of the output transformer rather then sharing one with the output side of the field coil. This set looks like it uses a six pin speaker plug socket, in some of my radios, Rogers made sets in particular, they will use the extra pins for a jumper just to disconnect the input filter capacitor from the rectifier tube filament if the speaker is unplugged. Sometimes they will add another jumper just to disconnect some other portion of the power supply circuit. It would have been nice had Philco included this feature in their model 18/118 sets rather then their traditional four pin plug, those sets use the speaker field coil in the B- circuit so if it is out the B+ will try finding a return through other parts like 1/2 watt resistors.
Regards
Arran

[LedHed]

So... I figured out the electrolytic caps. I used a 10uF and 16uF where the schematic calls for 8uF and 14uF respectively. I also went through and replaced the other paper and wax caps, plus the ones that the previous owner had removed/replaced. I have another chassis I picked up for a 6S203 that I will work on next, so I bounced the schematic off the other chassis (untouched other than electrolytics it would appear) and wired them the same way.

When I am tuned to a strong station, in general, the radio plays OK. Sometimes, it will be have very very poor reception. When the reception is OK and I tune away from a station it starts to motorboat. when the reception is poor, there is no motorboating.

In the event that it isn't motorboating, the reception stinks. If I mess around with the shield, tap on, or remove the cap lead from the 6K7G, it will receive, but also start motorboating. I also have replaced resistors R7 and R6 coming off the 6F6, R4 and R6 from the 6F5, and R3 off the 6K7. What should I start with now? Did I miss a grid load resistor?

EDIT: I swapped the 6A8G and 6K7G with others from my stash. There was no change. I also tried to monkey around with the tube shields to no avail.
I'm really looking forward to getting this one going... I was planning on giving it to my dad for Christmas.

[Arran]

Which set has the motorboating issue? The 6S229 or the 6S203? One thing to check in sets like this that have tubes with grid caps is the grid cap leads. The clip they use to connect the grid lead to the cap often develops a bad join between the lead and the clip either through the solder breaking down or the wire breaking inside. There are other things that can cause motorboating, the main ones being an open ground on a bypass capacitor or an open output filter capacitor. Sometimes the IF alignment being off can cause squealing or motorboating as well, another thing could be the primary and secondary leads of an IF transformer being too close to each other.
Regards
Arran

[LedHed]

Sorry about the confusion. It is the 6s229 with the motorboat problem. The 6s203 chassis is the same, and I used it to help verify my work.

I will take a closer look at the suggested areas.

[LedHed]

Thanks for all the good advice guys. Got it figured out this evening. A previous serviceman subbed in a 100k resistor in place of a 1k for R11. Swapped it out, playing pretty good! I boogered up the alignment trying different things, so that's tomorrow's project. After that, back to the cabinet she goes! I love that part!

[rghines1]

Glad you found it!

Would not have suspected that.

Was the 6A8 plate voltage quite low?

Anyway good practice to make basic voltage checks on all the tubes. May be more surprises.

[LedHed]

You got it, plate voltage was about 3 volts! I checked voltages throughout and all looked pretty good. Added a power resistor to drop line voltage to about 115V and aligned it this morning.

Learned a valuable lesson on this one. I will always check voltages as I bring a set up on the bench from now on. Between the hosed up electrolytics and the resistor issue, plus some other poorly done things I found underneath I think I'm pretty luck that nothing catastrophic happened. Cheap lesson too, it just cost me some of my free time.

[LedHed]

All put back together and playing again!


http://i1267.photobucket.com/albums/jj54...AG0308.jpg




http://i1267.photobucket.com/albums/jj54...AG0309.jpg