[morzh]

Question:


I have the sch for codes 121/122.

My Philco has some discrepancies, the first being using 6A5 as the output tubes.

Now while recapping (and I am far from being done) and at the same time checking the resistors where I can I noticed that the resistor 103 (70K) has some other resistor going to Ground that is not there on the sch. The resistor connects where the 103 attaches to the cap 104 (8nF); it is probably the tone control circuit. The value seems to be high and there is that green band in the middle that tells me that it should be high. The circuit is such that I do not expect it to make much of a difference but still would like to know if it is present in some other modifications.

[John R]

The use of 6A5's makes your set a code 125 or 126. Service bulletin
258 shows a 2 Meg resistor was added to prevent clicks when tuning the bass compensator 'tone' control on a very strong carrier. Code 125 is manual tuning and code 126 is auto tuning. Pot 128 is removed and the cathodes of the 6A5's are grounded. John

[morzh]

Thanks John, so I was not dreaming.

Does anyone have the sch for those? Not much difference, I can work off of the 121, but always easier to have a current version handy.

[TA Forbes]

Recommend you get the package Chuck offers. Excellent quality!

[morzh]

Well, I finished all backelites and all tubulars. While I thought the backelites was the pain I really appreciated the easiness of access when I started tubulars. Most of them happened to be in the RF sub-chassis and the access is dismal. And I was and am reluctant to take it off.

I changed some resistors but not many. Only those I thought would be critical. Some are a bit over 20% off but I don't think those matter too much and the access to them is the worst so I decided to take my chances with them.

Now I am down to that tin can block and then electrolytes. I am tempted to bite off the wires off the block and throw the caps over, since I have some tubulars that say Philco on them. But then it's somewhat of a cheating, even if I am the only one who knows. Will see how involved it is and then decide. Got all the tubes except the rectifier 5U4 but this one is already traveling from Ukraine to Canada to be then sent to me.

[codefox1]

I'd probably get 6J5 (metal version) replacement, they are plentyfull and inexpensive. If the readings are so very low, it would be doubtful if they were any good.

Pin 1 of the metal variation is the connected to the metal shield, obviating the need for a separate tube shield. Just check to make sure pin on on the socket is not used as a tag of convience, and do ground it. The 6C5 can sometimes be used as well, so if you have some, no harm in trying.

[morzh]

Codefox

I got all the tubes I need, 6J5, 6D8 and two 6A5s from Bob Dobush 3 weeks ago.

[morzh]

Today the scariest part I kept putting off, the cap 89, the triple one in a box, against expectations turned out to be a snap. That is, almost a snap - I had to first desolder and lift a backelite that was under it.
I was afraid there would be rivets to drill and tabs to desolder but all that there was to it happened to be three snap-locks (two of which were under that backelite) and three wires to cut. The potted part inside is simply wraped in paper so it came out on request, just by pulling the wires, and was held inside by simple bending tabs. Not quite unlike those tin-can rectangular caps in Philco 20. I have the stuffing, so tomorrow will put it in and in the oven it goes

[morzh]

Speaking of that 89 cap. I am not sure I understand why they made it the way it is.

It has three caps inside: two 0.1uF in series, the centerpoint grounded, and the ends connected to a 0.8uF cap. The grounding is done through the lock and spring against the chassis. However instead of putting out just two wires they put three wires. Obviously the connection of one of the 0.1uF cap and 0.8uF one was not done inside, as two wires out of three were connected to the same pin of 490K resistor.

I connected everythiong inside, and only put out two wires connecting them to two of the 490k resistors.

Usually the reason for something like this is that the cap assembly could've been used in some other radio and the interconnect was different. But I don't know that.
Also spring-loaded Grounding is not my favorite way of doing it, I always opt for attaching it with an inclined plane wrapped helically around axis. But then that's me. The spring is a pretty stiff one, so I hope it will provide for good contact.

But if anyone knows the reason for that wire exuberance ikn that cap - I'd love to know.

[morzh]

I was a happy person for a while thinking I was done with re-capping.
Before soldering in place the tuning cap I thought of checking if the wires that go to it still connected as they should (I did not see a couple of them and applied a bit of force...nothing ripped but I'd like to know that everything is copacetic) and the best way to buzz it is to the grid caps of RF 6K7 and MIX 6L7.

Then I realized I could not find the grid caps with the wires.
Then I realized they are not there. And I do not remember de-soldering them. This would be the least likely thing I'd do.
So, now I have to figure where the point is where the caps go.
The bad thing about all this is that the RF chassis is, well, not very convenient to work on. So far I successfully escaped the necessity of taking it out.

Judging by 6A8 OSC they use a spare pin on its panel to first bring the wires to, and then solder the caps from there threading the Grid wire through the panel's rivet.

Another sad thing is, there was one last cap #17, from Cathode to GND in parallel with the Cathode resistor, that I overlooked and have not replaced, that is lurking deep inside. It goes to the Chassis, but that Chassis pin is really inside. Cannotreach it without taking out some coils and I do not want that. And I do know all those caps are bad, so I have to change it. And I am not willing to use another Chassis point as this may potentially be harmful (though not likely). Cap #26 connects to a chassis, may try it.

So, does anyone know where were those grid cap soldering points? It will take me time to figure it out, too much stuff there, too crowded.

[Mondial]

Are you sure you need to change the cathode bypass cap? There is very little voltage across it and unless you are positive that it is open or intermittent I would just as well leave it alone. It is not in a circuit location where failure would do any damage and DC leakage is not an issue.

Typically I do not replace cathode or filament bypass caps unless they definitely check bad or otherwise have to remove them to replace other parts.

[morzh]

Cathode bypass caps will not create fire, sure, but they affect the amplifier performance.

[morzh]

Old age is no fun.
I thought about it and realized that the grid caps should've come from the tuning cap.
Sure enough...found them with dial assembly parts/

Now I have to try to replace that cap. I have already cut it.
But I will not be able to get to another pin without taking the top cove off and the effort is disproportionate, so I will leave the cap dangling and will throw a new one from the cathode to another close Chassis pin.

Oy vey!....

[morzh]

The last piece of the puzzle came: the Soviet 5U4 (5Ц3С) rectifier.

Got three of them. All three test as new or better.
Another refutation of the accusation to my Hickok. It works just fine. After I tested all thhree, I inserted the original 5U4 in, and sure enough it as dead now as it was then.

Well.....close...close am I getting to powering it up.

[morzh]

The silicon grommet that holds back shaft of the tuning cap dried out.
Does anyone sell exact fitting grommets?