- Old 'Scope inductor and cap help please - 9 Updates
- Water heater relay moot - 1 Update
| etpm@whidbey.com: Oct 04 10:53AM -0700 Down with water heaters and up with old tube oscilloscopes, that's what I say. Well, I picked up a couple of old scopes. One is a Dumont 241 and the other is a DeVRY. No model number on the DeVRY. It's not a Bell and Howell model 34, but it is similar, and older. As near as I can tell it is also a B&H, but I can't tell much. It came with construction manual as it was a kit. The manual is # 9027A. It has some sections of the schematic for the scope but not the whole schematic. Though the scope sorta works it ignores all signals fed into it. I can get a dot, a line, and a small waveform but those just come from switching the dials. By small I mean it is not very tall or long on the CRT. It is not a pure sine wave but instead looks like a jagged triangle wave. Sort of. On the front of the manual someone wrote that an inductor is bad. It is a 35uH coil wound on a 10 meg resistor. It is called a peaking coil and is in the signal path of the vertical amplifier. I have not been able to find this style of inductor online. Maybe I'm not using the correct search terms. Can anyone point me in the correct direction? Maybe I could just wind my own. Anybody know what the permeability of a carbon comp resistor is? I also would like some advice on where to buy caps for tube gear. Digikey or Mouser? Someplace better? Finally, it looks like I need to get me a cap tester. One that can check caps in circuit would be ideal. But since this is a hobby I need to keep the costs down. So suggestions would be great. Thanks for reading. Cheers, Eric |
| Fox's Mercantile <jdangus@att.net>: Oct 04 02:04PM -0500 > I'm not using the correct search terms. Can anyone point me in the > correct direction? Maybe I could just wind my own. Anybody know what > the permeability of a carbon comp resistor is? 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. -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Oct 04 12:11PM -0700 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 simplicity, 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) being next. Note that Mouser will answer the phone, typically by/with a knowledgeable person, typically also patient with amateurs. d) LR networks are common enough and there is nothing magical about them. Winding 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, that would not have been necessary, but with such an old device, pretty much 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 and 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 is far more practical and immediate than much offered here. I make it to Kutztown twice a year, which serves very nearly all of my needs. Peter Wieck Melrose Park, PA |
| Ralph Mowery <rmowery28146@earthlink.net>: Oct 04 06:03PM -0400 In article <wOidnSPBTuJZCgrAnZ2dnUU7-W2dnZ2d@giganews.com>, jdangus@att.net says... > Unwind the old one, count the number of turns, measure the wire > size. Wind new turns and replace. > -- 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. |
| Fox's Mercantile <jdangus@att.net>: Oct 04 05:29PM -0500 On 10/4/19 5:03 PM, Ralph Mowery wrote: >> size. Wind new turns and replace. >> -- > Would it not be 1 instead of zero ? The same as air. You're right. It's 1. -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com |
| etpm@whidbey.com: Oct 04 04:13PM -0700 On Fri, 4 Oct 2019 14:04:36 -0500, Fox's Mercantile <jdangus@att.net> wrote: >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. 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 |
| Fox's Mercantile <jdangus@att.net>: Oct 04 06:31PM -0500 >>> correct direction? Maybe I could just wind my own. Anybody know what >>> the permeability of a carbon comp resistor is? >> The permeability is zero. Correction, it's 1. It's "just a coil form" > 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 You don't need the 10 meg ohm resistor. This will be fine. <https://www.mouser.com/ProductDetail/API-Delevan/1025-56J?qs=sGAEpiMZZMsg%252By3WlYCkU%2Fuy0w9T3GDQ2AQE7IS6yJE%3D> -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com |
| tabbypurr@gmail.com: Oct 04 04:53PM -0700 > 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 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 |
| legg <legg@nospam.magma.ca>: Oct 05 09:40AM -0400 On Fri, 4 Oct 2019 17:29:31 -0500, Fox's Mercantile <jdangus@att.net> wrote: >>> -- >> Would it not be 1 instead of zero ? The same as air. >You're right. It's 1. Permeability of free space is 4 x pi x 10^-7. ... but yeah, it's just a coil former. RL |
| etpm@whidbey.com: Oct 04 10:33AM -0700 Thanks everyone for your replies about the water heater relay. My brother has decided it's all too much trouble because they are going to move in a few years. Still, I appreciate all the replies. Cheers, Eric |
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