The AM Forum

I want to make parasitic chokes per the old handbook with 47 ohm 2 watt carbon resistors with 6 turns of #18 on the outside... Does anyone have a source for 47 ohm 2 or 5 watt carbons..? will carbon FILM resistors work the same?  Can I use 2 ea 100 ohm 1 watts in parallel?  Is there an acceptable substitute for the old handbook parasitic choke...?  I'm building push pull 100th's and the PC's are for the grids...I've got it working but I have some parasitics on 20 meters.....which is where I really want to run this rig.... Thanks...Steve

Metal Film or Metal Oxide resistors are good to use, and handle heat better than carbon resistors. Look at Rich Measures AG6K's website, he used to have available some nice Panasonic resistors and nichrome wire (along with solder and flux) that made great suppressors. I have used them and they work out FB. I found him after my 4x1000 experienced a DRAMATIC explosion when the 3 carbon resistors in the parasitic suppressor cooked. The 6000 volt/50 ufd B+ supply survived.

http://www.somis.org/

I know they are harder to find these days, but I use glow bars for suppressor resistors. They commonly come in 30-90 ohm values.  They are big, but I've never blown one out. Even on 10M and QRO.

For the smaller rigs, I just parallel up a few carbon 1 watters and expect to replace them every so often... ;D.

Good luck with your new p-p 100TH project OM!  Post some shots.

T

Tom... I've got some glowbars but they are just too damn big( for the grid circuit) and don't fit in with the old buzzard look I'm after,  I would like to find some Allen Bradley 2 watt carbons...I usually don't have to  put PC's on the plates of a push pull rig..But they are important in the grid circuit with 100th's on 20 meters.. .I haven't tried carbon films in this application before but it sounds  like they will work.(Thanks Fred I'm glad the Power supply survived)....I can't find anything in carbon film larger than 1 watt.......I would like to post pictures but I don't have a web page.....How do I put pictures directly on my post?. Thanks...Steve

OK, Steve -

To upload a picture from your computer hardrive, do the normal reply to topic and then hit "additional options" down below. It will give the opportunity to browse and find the pic to upload. Follow the instructions.

The size of the pic is limited using this way compared to a web page.

BTW, doesn't Mouiser carry lots of resistor values, including power stuff?

T

A while ago I bought some nice 47 ohm 2 watt resistors from Digi key. They also had 3 watt parts. Metal film type. Carbon parts drift up over time. I have jars of carbon resistors that have drifted up one value.