[deshawn]

I just noticed something odd with the output tube on my 50-922. The one I have is obviously burned out. I ordered the new tube from the schematic. The schematic says that it is a 50L6GT tube. When the tube arrived today, there is quite a discrepancy in size. So I looked at the old tube. It's a 50C5.

So... Lesson learned: look at the actual tube before ordering!

It appears that there was room on the chassis for a 50L6GT socket, but a conscious decision was made at some point (by Philco, because this socket is riveted to the chassis) to replace it with the smaller 50C5 socket.

So I have a couple of questions:

1) How common was this practice of replacing tubes? The nostalgia air schematic shows runs 2 and 3 of this radio with a couple of different parts, so the design seems to have evolved over time. Is this an evolution that might have shown up in a later service manual?

2) Do I just order the 50C5 and assume this was a design change?

Thanks again! It's great to have this forum with so many of you so willing to share your knowledge!

[codefox1]

Happens all the time. Just have a look at the actual wiring. There was also a 50B5 which pins out differently, so beware. Hang on to the 50L6, you can swap it or use it in the future.

[deshawn]

Thank you, codefox. Yes, I'm going to hang onto the "oops" tube I bought. I think I found my next project on eBay, and it appears to have the 50L6 output tube. This is pending winning the auction, which, if the price spikes, I don't really want to do.

[deshawn]

The parts for my 50-922 will hopefully arrive today and my teen-aged son and I will be re-capping/re-resistoring it tomorrow. As I was going through the schematics and diagrams, I seem to be missing a capacitor.

Here's the radio schematic from nostalgiaair: [Admin note: bad link removed. Good link below in thread.]

I cannot, for the life of me, find C9. It appears in the parts list and it appears on the schematic diagram. It does NOT appear on the parts diagram (on either the run 2 or run 3 version) and it likewise does NOT appear anywhere on the radio itself. It's just. not. there.

What do I do in this case? I can determine where it SHOULD be based on the schematic and put it in, but as I recently read, it worked once or it would be in a landfill somewhere. Should I stick to what is actually physically there, attached to the chassis or should I believe the schematic?

Thanks!

[Olden Broak]

Here is a good link to the schematic http://www.nostalgiaair.org/Resources/702/M0013702.htm

Rob

[deshawn]

Oops! Sorry about the bad schematic link. That is the one I have been using. I still can't find C9 anywhere on the radio though... Thoughts?

[Ron Ramirez]

DeShawn

I just checked Nostalgia Air to confirm that their schematic is the same as the original Philco factory schematic...it is.

From the 1950 Philco Home Radio Yearbook:

PRODUCTION CHANGES

Code 122, Run 1

The 50L6GT tube was replaced by a 50C5, with the necessary wiring changes.

So that answers the 50L6/50C5 question.

As for C9. It is the AVC filter, and the set's AVC will not work correctly without this capacitor. Add it in by all means. I do not know why it is not shown in the parts diagrams. Philco's draftsman may have just forgotten to draw it in. It is known to have happened before, in other Philco chassis drawings. This service information, after all, was compiled by imperfect human beings and now we, equally imperfect, are attempting to make sense of the info.

[deshawn]

As I pulled caps tonight, I found C9. There are two C3s listed on the diagram. One of them was actually C9. Now to sort out R13-R15... They're not in the "right" places because of the output tube change.

Once I have that figured out, it'll be time to get everything put back together and power this thing up (with my dim bulb tester, of course) and test it out.

It's fun to be back into a "hands on" project like this. It's been a while. Since I'm a software guy professionally, I don't usually get to actually touch what I'm working on.

[deshawn]

The radio has been put back together and I powered it up with a dim bulb tester. It doesn't appear to have any shorts or other obvious problems. When it powered up, it just barely started to put out some audio--just the beginnings of some static, and then went silent. All of the tubes lit up. There's no smoke or hot-smelling components under the chassis. I think it's time to probe around and check voltages to isolate the problem, though I believe it may be another tube that I need to replace. The 50C5 was completely dead and the radio didn't show any signs of life until that one was replaced.

I now have an EICO 666 tube tester, so I'm going to test all of the tubes I didn't replace. However, one of the tubes doesn't show up on any of the EICO tube charts--not even on the latest (1978) version I downloaded from BACA. Anyone out there know how to test a 14B6 on an EICO 666?

[codefox1]

One wierd set you are working on.

Well pinout is same as 7B6 or 7C6 if you have specs for it, just need to set filament voltage to 12.6. A rewire to the octal world using the readily obtanable 12SQ7 is one workaround should you not be able to find suitable replacement. Also, if the triode section is working ala buzz when you touch the center terminal of the volume control with volume turned up all the way, you can bypass the diode sections with 1N34 diodes. Kind of hard to kill some of these old buggers though.

[deshawn]

I found an older version of the EICO 666 tube data sheets and it has settings for the 14B6 that, after looking at the data sheet for the 14B6 and reading through the procedure for testing tubes not listed in the data sheets, actually seems to make sense. When I get home tonight, I'll give it another shot.