Federal AM447

[tardishead]

Federal AM447

Anyone heard what these sound like? Class A single ended with no feedback. Must have some sort of a cool sound even though it would thump on big gain reduction.
I am intrigued what these sound like.

There was an RCA limiter which was on Ebay a couple of weeks ago that had a identical tube line up. Probably the same design.

 

[emrr]

Never seen an RCA with same; do you still have a link? This Federal was discussed here within the last month.

 

[Ciardhubhan]

Looking to resurrect this thread, putting out some feelers if anybody has worked on one of these recently?

I've got a couple lying around here that hum like crazy right of the bat and are looking for a restoration... those gigantic stone-age "amphenol" style connectors in the back are a bitch to find!

Emrr - I couldn't find the thread you were referring to that was discussed shortly before this one, do you happen to have a link to it by any chance?

It looks intriguing, like a Federal AM-864 that got chopped in half...

 

[strangeandbouncy]

    ....




  http://www.groupdiy.com/index.php?topic=21158.0

 

[Ciardhubhan]

Yeah, I saw that post too... unfortunately, not too much discussion there! I've searched but I can't find any real discussion on this amp.. maybe it's referred to differently that I can't pull it up on the search query..

 

[emrr]

Hum may be a part of the package, since these were designed for voice work.  I've seen at least one person go to the trouble of replacing all the oil caps (I wouldn't; they virtually never go bad) and didn't change a bit of noise.  A friend got a pair up and running and then immediately sold them on ebay; don't have any real reliable report there.

Experiment with all the possible ground connections.  Limiters can be funny in that regard and shriek or hum if not exactly right.  I have one that either shrieks, hums, or motorboats if the audio input ground is not connected in an exact way. 

Consider DC filament connection.  Bang in a bench supply temporarily to see.  Should be no harder than disconnecting AC filament taps at power trans.    Gates SA-39's tend to be hum monsters without DC filament at the 1st stage. 

 

[MatthewleBlom]

I just bought one of these babies.
Haven't received it by mail yet so I can't tell anything about it at the moment.
But in the future I hope I will.

I also have two Federal AM864 limiters running (which I like a LOT).
As soon as the AM447 is up and running I'll make an A-B comparision between AM447 and AM864.
Wavs will be posted here.
but be patient..I'm not a fast worker with this kind of projects.

 

[MatthewleBlom]

Today the unit arrived.
The next problem will be (like Ciardhubhan told so) the connector.

 

[MatthewleBlom]

Did the first testrun.
It's not completely humfree but I have to experiment with that a little more.
The first time I fired the unit up the was LOT OF hum.
But after soldering the signal leads directly to the in- and output trannies with connecting the signal ground to the centre tap hum was almost gone.
I replaced the original power lead with a 3 prone lead for proper chassis-grounding.
Chassis ground and signal ground aren't connected to each-other.

The sound:
It's boxy. Trannies have a frequency scope between 250hz and 3500hz.
So all low end and top end disappears.
This makes it more like a nice-to-have-unit then a multi purpose high end vari-mu limiter.

I'll take some more time to make it less hummy and to find out for which sound-sources it's usefull.
After that I'll post some files.

 

[emrr]

Keep us posted, thanks.

 

[videojunkies]

Today the unit arrived.
The next problem will be (like Ciardhubhan told so) the connector.

I too am looking for one of those connectors. Not sure the brand. Part # just says "16824-15", which doesn't bring up any online or forum results. Looks like a dual 12-pin. We may just replace ours with something else that fits close enough.

 

[emrr]

I too am looking for one of those connectors. Not sure the brand. Part # just says "16824-15", which doesn't bring up any online or forum results. Looks like a dual 12-pin. We may just replace ours with something else that fits close enough.

Might be Winchester. You'll need to scour surplus parts sources. Apex, Nebraska, etc.

 

[Brian Roth]

That connector may be an Amphenol Blue Ribbon. That line of parts was bought by WPI which was bought by someone else. I've seen a similar looking connector on some European gear as well, but they were red in color.

Bri