All posts by Mike

I keep an electronics test bench and I love repairing old radios or building other electronic or amateur radio projects, usually late at night listening to shortwave or talking with other hams. My Amateur call sign is KM5Z.

A $10 Scope

My B+K 1435 Oscilloscope went down over Thanksgiving weekend. Really, it went down – it fell against my chair (I shouldn’t keep it propped up like that, I guess). However – the “A” channel input went bad. I took it all apart – screws everywhere on the carpet.

I was so close to parting it out then W5AAN (Ginger) urged me to keep trying on fixing it. Turns out these old scopes are old-school. The traces are nice & wide and the parts aren’t surface mount (SMT). I wound up fixing a total of three problems with it.

The pot for the “A” channel vertical positioning had two broken traces right near the pot. I was able to easily scrape and short ’em with a bit of component lead wire. Soldered those on and it worked just great.

Got it all back together and found that now the “B” channel didn’t work. Well by this time, I know where everything is – opened it back up and the lead to the center conductor on the BNC connector had broken. Soldered THAT back into place and now the scope works great.

It works so well I’m considering buying some new Gel batteries for it – it’s a portable model and while it was all apart, I tested the charge circuit to be working.

Perseverance. My $10 scope soldiers on…

Heathkit IG-102, Solid State Edition

I’d recently heard about a conversion of a tube Signal Generator to Solid State. I found the original article in a great old book called ’99 Test Equipment Projects You Can Build’, by 73 Magazine. I snagged the book from eBay for only $2.00 (plus shipping). My copy is a small hardback, red cover. Print’s kinda small.

Same article mentions adding a three-range (10khz, 1mhz, 10mhz) crystal calibrator on-board (since you now have boatloads of room inside without the tubes and the transformer).

Each ‘half’ of both tubes is replaced with a FET Pin numbers are mentioned, so you go underneath (unfortunately sticking the leads in the tube socket holes won’t work…) and solder a FET lead to a Socket Hole. I think there’s one socket hole (besides the filaments) that remains unconnected.

I’ve written on the schematic which FETs appear to work. I settled on MPF-102s, although I tested a couple of versions. The book project specifies four 2N5951’s.

An IG-102 FET Conversion Schematic

There are two resistor changes (actually mods) due to the lowered voltages:
Solder a 75 ohm resistor across the existing 33k (see left of ‘BF Front View’ switch.
Solder a 90 ohm resistor across the existing 4.7k (see above V2A 1/2 6AN8). On some models the existing resistor may be a 10k.

There are no other changes other than what’s marked at bottom of the schematic (removing the cord and power supply. Replace w/9V battery. I also did the fancy LED thing. Nice to know if it’s ON so you don’t run down the battery.

I also added a ‘wall wart’ plug for outside power. Fancy.

IG-102 FET Version – Tinkering with Tubes

I’d recently heard about a conversion of a tube Signal Generator to Solid State. I found the original article in a great old book called ’99 Test Equipment Projects You Can Build’, by 73 Magazine. I snagged the book from eBay for only $2.00 (plus shipping). My copy is a small hardback, red cover. Print’s kinda small.

Same article mentions adding a three-range (10khz, 1mhz, 10mhz) crystal calibrator on-board (since you now have boatloads of room inside without the tubes and the transformer).

Each ‘half’ of both tubes is replaced with a FET Pin numbers are mentioned, so you go underneath (unfortunately sticking the leads in the tube socket holes won’t work…) and solder a FET lead to a Socket Hole. I think there’s one socket hole (besides the filaments) that remains unconnected.

I’ve written on the schematic which FETs appear to work. I settled on MPF-102s, although I tested a couple of versions. The book project specifies four 2N5951’s.

IG-102 - FET
Schematic for the FET version of the Heathkit IG-102

There are two resistor changes (actually mods) due to the lowered voltages:
Solder a 75 ohm resistor across the existing 33k (see left of ‘BF Front View’ switch.
Solder a 90 ohm resistor across the existing 4.7k (see above V2A 1/2 6AN8). On some models the existing resistor may be a 10k.

There are no other changes other than what’s marked at bottom of the schematic (removing the cord and power supply. Replace w/9V battery. I also did the fancy LED thing. Nice to know if it’s ON so you don’t run down the battery.

I also added a ‘wall wart’ plug for outside power. Fancy.