The AM Forum

I do not know Collins ampliiers very well at all. A friend of mine is showing me one but he is not a ham and basically I have to go by the book, and ask for others' experiences.

It says 1000 watts SSB PEP output, and 1000 input/600W output on CW input at 50% duty. Is this thing any good for AM or would it cook?

The book says mode: any emission, but not to run an (average) output of 600W or more for long periods of them because the power supply is not designed for it. It also indicates 2KW peak power input (in the ALC section). Also it uses a 4CX1000, which may be hard to get.

I see it runs 3000V on SSB mode and 2000V on CW mode. By the book, it looks like it is intended to be a cathode-driven amplifier with 200V on the screen, -50V bias (referenced to cathode), but has the DC ground at the screen grid rather than the cathode. The Eimac care and feeding book describes this kind of use.

Is this amp under best circumstances a 200W carrier/800W PEP amp for AM? More like 150W carrier to avoid overheating?

I put a 4CX1500 in one once for a friend to get more plate dissipation. I think we got about 1200 pep out of it. You have to be careful with grid dissipation.
I would solid state the 3B28s. You can't see them from the outside.

I wanna shop at Particks' sto .... beefus

If you can get it for a good price, get it and flip it to a Collins nut. Ya the grid current is teh weakest link and the tube for that thing is hard as hell to get an expensive if you do. the 1500 is a good idea but Collins was in full "SSB UBER ALLES" mode when the S-line was made - last thing they were thinking was how it would work on AM.

I have 2 of these which work great on AM. I believe someone did some kind of screen voltage modification because they both make 1500 watts P.E.P. with 4CX1500Bs installed. No grid current. Both were in mothballs for at least 20 years.

They overheated on AM over 150 watts carrier and the temperature sensor kicked them off the air.

Solution was a large cabinet fan sucking air out of the final compartment. I mounted the fan to what was the bottom of a cardboard box whose top flaps are duct taped to the back of the amp cabinet, side and top. Fits airtight. The paint was shot on this unit anyway. I did this in dedication to some Collins collectors I've met over the years.

The tube in getters with filament operation so let it run for a full day without B+ if it's been some time. Anything more than an occasional tickle of grid current means distortion and shortly a bad tube. Keep a close eye on screen current for a very sensitive indication of proper loading.

Ebay prices on these are soft right now. Use it for 20 years and sell it when you retire.

Funny you should mention collins collectors. It's almost a stereotype. They are a particular and eccentric lot but most are OK, except the ones that snub/snob my 618S-1's.

Thanks for the opinions and experience on it. If it does come my way I will know not to abuse it. If it is somehow trashed unseen, at least there are options for changing the tube to something better. I have the sticks for the rectifiers already here, as long as no one sees it that's OK.

the collins snobs will turn up their nose at it if you make any changes. After all, Art Collins was a god.

Absolutely not! Operation on AM will put the tube into class J mode, and cause parasitic re-radiated harmonics that will turn you into a girl!

By the way, since I already have an S-Line, I'll take it off your hands ...

73,

Bill W1AC

I ended up passing on it today. After looking all through the lab, he wanted only my RCA BA-6A limiter in trade. I need that, to have fun repairing it and then use it with the AM transmitter I'm working on elsewhere. I looked at the Collins and it is pristine, hardly a bit of dust on or in it, but I didn't want to trade for the ancient and venerable BA-6A, no matter how nasty it looks. If it's my mistake later, so be it. I'm happy with it. One look at the schematic should explain.

I already have a working linear amplifier that I hardly use and also the "Jaws II" amplifier which is under repair. And I'd hate to ruin the 30S-1 by changing anything - which would probably happen, or get turned into a girl by using it on AM. So I'll kindly leave the Collins to someone that will cherish it more. If only he'd have settled for something else or a whole pile of stuff. That's the 2nd time he's wanted that RCA, can't blame him there.

Bill if you really are interested in it I can talk to the guy and see if he would talk with you about it, I would have no interest in any dealings and he likes to trade as well.