[joybird]

No RF Audio Fine

I see a difference in schematic and actual chassis. Looks Factory
Bathtub 3615AJ Supposed to contain 2 .05 caps. Parts list states .09 caps
Item 13 is shown as 733mmf and resistor 14 as 15K Item 14 is 8.5K on my chassis

Actually there is also a 56K resistor across 1-6 on Item 9 Bathtub

Looking for any changes in the 90 chassis with 47 in PP
S/N of my chassis is B83449

Anyone have updates on this chassis?

http://www.nostalgiaair.org/Resources/881/M0013881.htm

Thanks
Bob T

[morzh]

http://www.philcoradio.com/tech/images/90c.jpg

Again it has been found repeatedly Philco sch contain discrepancies and downright errors.
If you have 56K that seems factory (and it is 56K resistor, not the value that could creep up) then it could very well be one of the variations.
As for the 0.05uF vs 0.09uF it in this particular case won't make much difference.

I had questions like this in my 90 (2 x 45) plus there was an error in the sch. And one extra cap.

[TA Forbes]

Hello, Bob: everything I have has the caps you mention as being .09uFd, I usually install .1uFds.

Am wondering if the resistor is a throwback to when the color-code was non-standardized? What does the resistor actually measure?

[joybird]

Does not JIVE. The Bathtub Cap involved here is P/N 3615 AJ which contains 2 .05 caps

So how do we end up with .09 on the schematic for Item 9

Bob T

[Ron Ramirez]

Does not JIVE.

Definitely not! The 90 with 2-47 outputs uses the same type of autodyne oscillator circuit as the 71, 91, 19, 89 and a few others. Yup, the very same circuit that has made many a young man's hair turn gray.

That circuit must have the 700 pF cap (13) and a 10K (or better yet, an 8.2K) resistor in place of the factory-designated 15K (14). The det-osc tube (24) will not oscillate without the 700 pF cap, and it most assuredly will not work with a 56K in place of the 15K.

3615-AJ - part (9) on schematic - should definitely be dual .05 uF, not dual .09. I see the schematic on my site erroneously states .09 uF, as does the Rider data (which is the factory data from Philco).

Another "OOPS" moment brought to you by Philco.

[Ron Ramirez]

Addendum:

I just noticed where you mentioned the 56K is in parallel with an 8.5K resistor. This would result in a net resistance of roughly 7380 ohms, close enough to allow the cathode circuit of the 24 tube to oscillate properly - with the 700 pF cap which must be in place as well.

[morzh]

Bob

In this case you can go with whatever. It won't change much at all.
We tried to figure it at some point with my version of 90, and the sch, my chassis and another person's here chassis, all three had different values.
Also the chassis diagram had the capacitors in tin cans swapped.
Also in my case there was a right value cap used in one place but from another item on the sch (another dual cap).
And if you look at this sch (your link, 2x45 version) the cap next to the resistor #47 (on top the osc tube) simply does not exist.

So.....

[Ron Ramirez]

No, no, no, you have to go with the right schematic for the right chassis.

The correct schematic for Bob's chassis is near the end of the link he posted...or may be seen on the link you posted earlier, Mike.

The late version 90 is a very different animal from the earlier 90s which had separate oscillator tubes. The late version (2-47) 90 combines first detector and oscillator functions in a single tube...just like the infamous model 89 and others I listed previously.

[joybird]

Hi Ron
Thank you, Thank You, Thank you
Now it makes sense.

I just pulled Bathtub Item 9 caps still check close .066 and .073
My 700pf is flaky so will get new one. I see now the 56 K added resistor to get Osc to work.
That is problem I had with this chassis Osc not working.
Onward and Upward

Bob T

[Arran]

What was the rational behind Philco using an autodyne oscillator in the later model 90s and the 91, 71, 89 etc? Was this a scheme to cut down on the number of tubes or was it another dodge to avoid paying royalties to RCA? I would have thought Philco would have stuck with whatever worked as a front end rather then re-inventing the wheel, but then again not everything Philco did was exactly rational.
Regards
Arran

[joybird]

OK got that squared away New 700pf Cap and I had misread color code on resistor, turns out to be a 8.2K 1 W As Ron suggested.

NOW a new find, the Primary of the 2nd IF is open, NO easy repair, tried that
Need 2nd IF Coil Philco P/N 04320 . This is 260 KC IF Coil
Any out there on junkers.


Bob T

Nothing is EZ

[Arran]

Oh boy!
Just to make it more fun they decided to use 260 KC IF transformers on the late version rather then 175 KC transformers used in the previous versions?
Regards
Arran

[joybird]

I do not think it helped that last worker Replaced the 2 6MFD @ 450V Filters with
1 18 MFD @450 and the other 80 MFD @ 350.

I may be in store for a bunch of AW SH -- - -

Bob T

[morzh]

No...not necessarily. Epecially the second cap, if it is after the choke (51) it does not really hurt anything, just a waste of lots of microfarads. The voltage could be a bit higher.

[gregb]

Hey Joybird, don't give up on that IF transformer with trying to resolder all of the connections in it first. I just finished a 15X and it had an open primary on one of the IF transformers and a quick resolder fixed it right up. Worth the try.

Gregb