General Discussions => The Lab => Topic started by: squib on May 14, 2009, 08:24:34 PM

Title: Harman Kardon AM-413/G info required
Post by: squib on May 14, 2009, 08:24:34 PM
I have on the bench a AM-413/G. This is an old tube compressor / amplifier made for the US Navy

having a devil of time finding any schematics. The unit uses 5 x 12AT7 and one 6AQ5 and just probing around it is clear that the circuit falls outside the box for a typical vari-mu compressor.

any thoughts ( or circuits ) much appreciated

Title: Re: Harman Kardon AM-413/G info required
Post by: snafu on November 18, 2013, 01:09:40 PM
FWIW, I am looking for the same information. There is a Technical Manual for this which I'm sure has a schematic, title is NAVSHIP or NAVSHIPS 91905, published in 1952. Also, the AM-413 came in several revisions so there is an AM-413, AM-413A/G, AM-413B/G...AM-413F/G.

This compressor was also supplied as part of a radio beacon set designated AN/FRN-24, whose associated tech man is NAVSHIPS 93291, might be a schemo in there too.

In I found this:,d.Yms

bottom of pg.5 starts a discussion of the AM-413 compressor with some helpful tidbits... no schemo though.
It mentions that the 413 "has a fixed compression circuit which provides constant level output for signals -30dbm or less. The 413-A (AM-413A/G) has a variable compression circuit which will provide a threshold of compression which may be varied from -30dbm to around -8dbm of signal input." "...the level control knob setting determines the maximum output."

My tech has been working on one of these units but has been having a difficult time figuring it out as this is not a usual circuit.
If anyone has a source for more info or even better a schemo, please let me know! Thanks!