how to calculate cutoff frequency for Low pass (grid stop)

[mikepukmel]

It can be anything from LF motorboating to Megahertz.

I know that you have Merlin's books. They have an excellent chapter on stabilizing an amp with NFB. IMO it's worth carefully studying that chapter.

Do you have scope? And a frequency counter? Or are you flying totally blind?

Thanks for the tip on the book, I got part way through and didn't finish, will go back and re-read it again. Unfortunately, still haven't picked up a cheap scope yet. Here in Eastern MA, used stuff is fairly rare and expensive. A 50.00 junky scope goes for 150. if you can find it. I looked at a box full of very old, ancient, pre-historic Weller solder guns a few months ago for 25.00 each, *firm*, that would NOT melt solder.

Anyway, flying blind for now, really dying to get a scope, maybe old Tenma, something like that, and look at what is going on in these amps.

When I lived in New York, on the Hudson river, there was a surplus store across the river, can't remember quite where, maybe towards Kingston. Title was something like Army Surplus but good God they had tons of cool old stuff, not necessarily military surplus. Lots of used electronic equipment. Wish there was some place around here like that. Tons of junky Bed Bath And Beyond type stores with overpriced dishes and pottery around here.

[SoulFetish]

You Do It Electronics
40 Franklin Street
Needham, MA 02494

[mikepukmel]

You Do It Electronics
40 Franklin Street
Needham, MA 02494

Cool, thanks for the tip! You know, the many trips down 95 to my sons soccer games over the past 10 years, I think Ive seen a big sign, visible from the highway. Never knew what it was. From the vantage point I thought it might be like a self storage or something. Will get there this weekend!

[Leo_Gnardo]

When I lived in New York, on the Hudson river, there was a surplus store across the river, can't remember quite where, maybe towards Kingston. Title was something like Army Surplus but good God they had tons of cool old stuff, not necessarily military surplus. Lots of used electronic equipment. Wish there was some place around here like that.

You're thinking of P&D Surplus, Abeel St. Kingston, on the Rondout Creek. About 20 years ago they were bought out by an employee, he teamed up with his son, changed name to PT Surplus. I've been there a couple times but not recently. Besides having allsorts of odd n ends, they also have a bizarre sense of humor. It's the kind of place you have to go to, I don't see any indication of a catalog or inventory. Here's a website & a Farcebook page.

http://site.ptsurplus.com/Home.html

https://www.facebook.com/PT-Surplus-272491392795397/

Also, for a scope I'd keep eyes on your local Craigslist. Every now & then one is offered in this area. I'd expect more would turn up in the "inside 128" Boston suburbs.

[bob p]

If you live in any Metro area, eBay is also a good option. There are likely to be decent scopes at decent prices that are within pick-up distance. I bought one of the 1970s Hitachi 60 MHz dual channel scopes for $40, just to have a scope that has a JUMBO CRT display. Don't underestimate the value of a *BIG* display... especially if your eyes are getting older. I find that I preferentially use this scope because the images are so big.