Old 'Scope inductor and cap help please

The permeability is zero. It's "just a coil form" Unwind the old one, count the number of turns, measure the wire size. Wind new turns and replace.

A few things:

a) I keep the Peak/Atlas ESR & Cap tester. There are much cheaper Chinese devices that test more things than it does, but for reliability and simplic ity, I find it a better choice. Note that if all you want is capacity, any decent DVM/VOM will have that function these days. But having reliable ESR readings is very helpful.

b) I also keep a fairly vintage (maybe 20 years old) B&K LCR Meter, useful for measuring inductors. I see them on-line in the $$$ range, with Chinese LCR meters along side in the $$ range. I got mine from a retired Tech at a garage sale. Recently calibrated (then) and works fine.

c) Mouser and DigiKey are my first two choices, with Newark (Element 14) be ing next. Note that Mouser will answer the phone, typically by/with a knowl edgeable person, typically also patient with amateurs.

d) LR networks are common enough and there is nothing magical about them. W inding one yourself is no trick either. The trick is to wind on a few more turns, then back off until it is where you want it to be. In the factory, t hat would not have been necessary, but with such an old device, pretty muc h nothing is as it was then, so you may need a bit of range. Nor does that coil have to be around the resistor if space permits. But, if you are lucky enough to be able to find a 10-meg film resistor of the correct diameter a nd wire of the correct gauge, just count the turns and rewind.

Not knowing where you are, I would suggest you look for vintage radio clubs and/or hamfests in your region. Oftentimes, you can find parts, pieces and all sorts of vintage stuff at such events, and advice through clubs that i s far more practical and immediate than much offered here. I make it to Kut ztown twice a year, which serves very nearly all of my needs.

Peter Wieck Melrose Park, PA

Would it not be 1 instead of zero ? The same as air.

I do agree that resistors that have over 100 times the resistance (reactance) of the wire will appear to almost not be there and just a coil form.

You're right. It's 1.

The schematic just shows the inductor in the circuit. It does not show the inductor as being in parallel with a resistor. And it is described as 35 uH "ON 10 M". So I'm thinking I either can just replace the inductor with an off the shelf 35 uH coil and not worry about the resistor or connect the coil and a 10 meg resistor in parallel. Eric

Correction, it's 1. It's "just a coil form"

You don't need the 10 meg ohm resistor. This will be fine.

As said the resistor is nothing but mechanical support. If you buy inductors they're often cored, but you want air cored. Those kind of wound on a resistor Ls were always a case of wind your own.

NT

Permeability of free space is 4 x pi x 10^-7.

... but yeah, it's just a coil former.

RL

Thanks, I thought so. Today I order caps and an inductor. I'm excited to see this old scope work. Eric

Given the age of the scope, you might want to consider replacing the electrolytic in the power supply section. Everything starts with solid, clean and correct power J

I will be replacing practucally every cap. Besides all the electrolytics there are some others that, from what I've read about and seen on YouTube, are also suspect. Eric

Caps are cheap. Collateral damages from bad caps are not cheap. Replace ALL the electrolytics. Replace ALL the paper caps.

Leave the silver dipped micas, tubular ceramics, and any "postage stamp" micas alone for the time being.

Replace them one at a time. Take pictures, make notes.

I have tried to identify what types of caps are in this scope but have been unable to find a site that shows the caps I'm wondering about. I think some are tubular ceramic caps because they are white ceramic tubes that are filled with some sort of hard potting compound. The other type of cap is also tubular but is molded brown hard plastic. These caps are 5/8" diameter x 1 5/8" long. They are .1 MFD at 400 WVDC. Anybody know? Thanks, Eric

The wax paper caps come in several varieties. (Usually) Brown cardboard with a wax coating. Molded plastic, and ceramic tube. All of those need to be replaced.

What kind of cap should I replace them with? Thanks, Eric

These: Yellow mylar film 630 vdc.

Thanks. I'm ordering all the caps right now on my tablet. With the little inductor its way I''l be set to repair the scope. BTW, as I was looking for all the caps I found a broken wire in the vertical stage. After figuring out where it was supposed to go and re-soldering it I tried the scope again and now it works! Still, the waveform is messed up so the new caps are needed. Eric

You will of course encounter restorers who don't agree with this approach. Foxy is not known for seeing both sides of this picture.

Ceramic tube caps are often paper. A chinese component tester picks up most

NT

Tabby is dangerous - much as unvaccinated stray cats are dangerous. He loves pissing on the fire.

Peter Wieck Melrose Park, PA