Federal FA-5238 (Dept of Commerce Limiter)

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Switch to the high input (600) and put a 30 dB U pad in front of that.  Should get some top back; not much there ITFP.  With the low mods, you can get kick and bass a tiny bit better before it all falls apart.  
 
This is an awesome forum!

I have in my possession a Federal Aviation Agency VOR Regulated Output Amplifier very similar to the one referenced in this thread, but with significant differences (different tube types, for one). Unfortunately, I have not been able to find a schematic. Also, someone cannablized the oil caps and fuse holders. I would really like to restore this gem but really am over my head without a schematic. Any help would be appreciated. Hopefully the .jpg will attach...
 

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I found some interesting trivia on a VOR Tube Avalability Study on the web. VOR Regulated Output Amplifiers (Limiters) were produced in the following models and quantities:

CA-1486 - 38
CA-1589 - 2295
CA-1609 - 155
CA-1782 - 1575
FA-5238 - 618 (Tri Tronics)
FA-5424 - 114 (Doughboy Industries)

http://www.tc.faa.gov/its/worldpac/techrpt/rd76183.pdf

It seems that my 1963 vintage FA-5424 is fairly rare. That makes restoring it even more attractive...

Cheers...

Mike Lonas
 
the schematic will mostly match what's out there already on the other models. 

before you go into restoration mode, make sure the iron is all good. 
 
Hey Guys,

Not to bring this thread back from the dead.... but I'm 99% done with a restoration I did on a CA-1782, and am missing one small bit of information. emrr could you kindly let me know what the values were for the attack and release pots on your mod?  You are an absolute gentleman for taking the time to draw up that scheme, it's been instrumental to be completing this project (which came out of the dumpster!)  Also MLonas... It might interest you that I have another model in my possession which didn't make your list and which closely resembles the one you are looking for info on internally and cosmetically. It's a CA-1763 Limiter and uses that same 5y3 rectifier and 5915 tubes. I have it here in original working order... let me know if I can be of any help. If I have time at some point I might be able to draw something up.

Thanks all. I'll post pictures when I finish up!

EB

MLonas said:
This is an awesome forum!

I have in my possession a Federal Aviation Agency VOR Regulated Output Amplifier very similar to the one referenced in this thread, but with significant differences (different tube types, for one). Unfortunately, I have not been able to find a schematic. Also, someone cannablized the oil caps and fuse holders. I would really like to restore this gem but really am over my head without a schematic. Any help would be appreciated. Hopefully the .jpg will attach...
 
TubeMonkey,
That is exciting! Perhaps I should send you some close up pictures of my unit in order for you to determine how closely their design is. I can try to do it within the forum or if you want to use email just send me a message at [email protected] with "Limiter" in the subject line and I'll send you some pictures.

Thanks so much!

Mike
 
MLonas said:
Thanks so much!

Mike

Hey Mike,

Here's a few images of my U.S. Science Corp (Topp Industries) Regulated output amplifier.  This one is bone stock...  it has a much more robust power section than the other Dept of commerce limiters i've seen. This one uses a 5y3 , an OA2 regulator and a 50y choke thats larger than the power transformer!  Looks extremely similar to yours, including the hum balance and meter calibrate pots on the right side. as Emrr stated this thing is pretty band limited and kind of a one trick pony. I really enjoy it on electric guitars.... sounds like Mussel Shoals or Motown...  but not much else.

The other unit you can see in the first pic is in the process of extensive mods. I pulled it out of a dumpster and was missing input transformer, most oil caps, and meters.  Had to replace the power transformer as I found it had a short on the filament winding, which was likely the original reason for it's cannibalization.  I re-assembled mostly from parts I had laying around (HA-101x input transformer) and it works great... Still not full bandwidth (Starts to slope off at about 160, -4db at 100) ... but it's very pleasing on vocals... surprisingly transparent.  I think in the near future I will be continuing to mod this to get around the specialized output transformer.... which will result in the unit ending up somewhere between the original and a UA175. I don't think the unit would be worth buying just to mod...  like everyone said it's best left as an effects unit... unless you happen to come across one extremely cheap, then may be worth swapping trafos and playing with the vari-mu circuit.

http://imgur.com/2FRACLP
http://imgur.com/8VIWcjU
http://imgur.com/N42enQN
http://imgur.com/y0iXOGe
http://imgur.com/Kv8A5QV
 
Here's a Maxson CA-1589 I worked on recently:

full size here

35040243321_58ea93db81_b.jpg
 
Hey Doug, I know you have particular thoughts on letting these things be or selling them off... but I had a quick question which you may be able to help with...

I recently dug back in the Tri Tronics unit I mentioned earlier in this thread. As mentioned I had revived this unit from the dumpster and added a HA100 on the input... still was pretty band limited.  Now after digging back in I discovered the second output transformer ( the 1:1 right before the XLR's)  Was causing a large part of the rolloff. Now I have a pretty wide bandwith unit but now i'm encountering another problem...

The more the unit compresses the more 60hz hum it imparts on the signal. I think this has something to do with the ground potential between the plate and either the grid or the cathode.  I think that the low end rolloff disguised this design flaw, and now that it's opened back up i need to consider solutions.

I should also mention that I have 6BD6's in the input pentode position but the 60hz problem persists with either pair. If I can't figure this out I may opt to just mod the input section to that of the BA6A (conveniently the 6BD6 is a 6sk7 equivalent). 

Not sure yet if I can get away with any of this without an interstage... but I thought I might pick your brain in hopes of some insight.

Thanks in advance!

EB

 
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