[Pepperoni]

The winding on the section of my oscillator coil that has one end connected to the cathode of the 36 Det. Osc. and the other end to the RC circuit to ground is supposed to read 5.25 ohms according to the schematic. Mine was corroded (imagine that) and open.
http://www.philcoradio.com/tech/89evol.htm
So I carefully counted the turns and came up with 26 trying to add in the couple of pieces that broke off while unwinding it. It's rewound taking notice of the direction, start and finish points etc. Now it reads about 2 ohms.

1. I don't understand why the bias for the cathode is going through the oscillator coil. If this is the bias for the cathode.

2. Why with the same amount of turns as the original and using the same gauge wire I only have 2 ohms and not 5.25.

3. The primary and secondary windings of the oscillator coil are much bigger (at least 100 turns each) and they read 5.07 & 5.7 ohms respectively. How can my little tickler coil with so many less turns on the form read about the same on the schematic? Primary & secondary do read about the resistances called out on the schematic.

I believe my oscillator will work just fine with my new winding but can someone answer the puzzles I mentioned above. And as a note I am trying to incorporate as many of the changes as possible to my 89 as pointed out in the notes that go along with the above referenced url that I imagine were drawn up by Ron R. Thank you Ron! Good info!

Pepper

[morzh]

the answer to your #1 question is:

Your det-osc. is an Autodyne type. The coil in the cathode is the Osc. positive feedback coil. You're simply varying Cathode relative to the Control grid, which is the same as varying Control grid relative to the Cathode.
Due to the negligibly small value of the active resistance of the coil relative to the 10K resistor, the DC bias is determined by that resistor, and the coil only impresses the AC voltage on the Cathode.

When designing this circuit, engineers realized that the operation was not very reliable with various tubes, and it was also found that the 10K resistor provided the compromise between the most uniform oscillation, ability to handle very powerful signal and the most detector sensitivity.

This is why you will find that value of around 10K in many Philco det.-oscillators. (it is there in 80 jr). In your case it is 15K.

[Pepperoni]

Thanks morzh! So I take from what you're saying that my new winding will do the job. I'm already replacing the 15K resistor with a 10K.

Pepper

[morzh]

well, I would not touch the resistor, if it is what is specified. As for the winding, same gauge at same turns and same coil diameter shoud've given you the same resistance. There's something amiss. But , if it is indeed lower resistance and you are sure the number of turns is correct, the possibly larger gauge reponsible for it won't do anything bad, as your inductance will stay the same, your skin losses will become smaller, and yor DC resistance does not really matter.

Again, don't change the 15K resistor.
And, make sure you DID count the turns right.

[Pepperoni]

In the link I provided earlier there is a note on one of the 89 schematics that says to change that 15K to a 10K to improve oscillator performance. What's your take on that?

Pepper

[morzh]

Oh, I did not know they actually recommended the change across the board.
As I wrote earlier, it is indeed the optimal value for this type detector, I missed that in the manual; so they did discover it after all.

Then, sure, go change it. It is 10K in my 80 jr.

[Pepperoni]

I believe Ron Ramirez built this site and there's some great info on there if you're working on a Philco. I think we're actually on the site now but just the forum section of it. You probably know all this. I think he's the original founder of the Philco Co. reborn. He sure knows his Philcos.
http://www.philcoradio.com/

Pepper

[morzh]

Yes of course I use the info from this site, and Ron has indeed buit one of the greates resources on the web. It's just when it comes to schematics, I like a little challenge of figuring stuff out myself, being an EE and all that, so I have a proclivity towards "re-inventing a wheel" when it comes to troubleshooting of circuits. But I do know that most info anyone would ever need is here.

[Pepperoni]

I kind of figured you had an advanced education in some form of electronics. You've helped me out a lot. I've only been doing this for 6 years or so but have been around electronics all my life. My father was an EE and his hobby was televisions from the, well I guess the first ones. I believe I could solder by the age of 5 and he had me using a slide rule by the age of 10. He passed in '68 from the cancer but I'll never forget his words... "Son if you don't know how to use a slide rule you'll never amount to anything". Not long after he passed I was carrying a pocket calculator around. I took electronics for 4 years in high school and two years of college focusing on electronics and mathmatics for electronics but it became evident that I had to make a living so I never earned my degree in electronics. Electronics was my career but I don't think I stopped going to school until I retired. It was advancing so quickly I had to just to keep up. I remember when logic circuits hit the market. Back to school to learn how to troubleshoot them and take a refresher course in boolean math. I actually caught on quite fast and it was fun and easy. I could troubleshoot a logic circuit faster then a dead battery in my car. And of course the computer world. Had exposure to it but was never allowed to do anything that wasn't printed in the manual. Government missile & aircraft projects. Then I came to the NW and was thrown into the computer world and didn't really know how to do anything. Back to school taking computer science classes. This was when Windows 3.1 hit the market.

Always appreciate your help morzh!

Pepper

[morzh]

Sure, any time, although compared to you I'm an uneducated boor (no offense meant to boors ).

I do have an education in physics, but believe it or not, department of physics in my former country taught only half-year course of very basic "electronics for physicists" (so we do not electrocute ourselves when working with experimental equipment).

I am largely self-taught as an EE, starting from a radio kit my dad gave me for my 8th birthday and then having fun doing all kind of stuff. But it allows me so far to be gainfully employed as an EE for 22 years of being here in the US.
I grew up in the era of the tubes going away and transistors being the mainstay of electronics, the ICs just appearing (60-s-70-s). Especially in my country where we lagged behind some 15 years.

Most of my career in the old country I spent as a troubleshooter, hence my love for it. Here I am in the development, which has always been my ambition, but I still enjoy troubleshooting and I was always known across the companies where I used to work as a go-to person when something weird needed to be figured out. This is why I always try to figure out stuff all by myself first, and only then, if I feel I am punching above my weight, I go for help.
Keeps me young