[R-390] R-392 help

[Mark Huss]

Change 1;  Just got my hands on an old LS-166/U speaker.  I repeated my 
experiment with the low frequency cutoff of the 600 ohm to 8 ohm 
transformer.  Either I mis-remembered, or they changed the transformer 
design.  It swept 3dB down at 4 Hz to 0dB down from 10 Hz to greater 
than 200kHz!  Noted a few peaks and troughs less then 3 dB from the 
speaker load. as I swept it.  I did note that it sounds quite as tinny 
as I remembered.  But the speaker itself is entirely different from what 
I remembered.  So changing the transformer won't work on the LS-166/U 
for bettter lows.  At least not without changing the speaker itself.  
Cabinet size probibily has something to do with it, but the sound does 
not change with the back off.  Can't do an audio sweep because the Sound 
Level Meter brought the farm many moons ago.  Sorry about the bum steer.

Mark Huss wrote:

> That was my first thought, too.  That is why I tried Stand-By.  I 
> think Barry is right.  Sounds like an AGC problem. I also own an 
> R-390A from 1955, Origional Collins #2792.  And if anybody has a spare 
> PTO they want to part with, I am buying. (the origional one has about 
> a khz of 'slip' from wear).
> As for the LS-166.  I actually need the UG-77 connector on it.  As a 
> point of note about the tinny sound.  Researched this while stationed 
> in Korea for the RATT Rig operators, who liked to tune in shortwave on 
> the secondary receiver.  They couldn't use stereo speakers because 2nd 
> LT 'Crash' Rothman objected to the 'Unauthorized Equipment'.  The 
> little 600 to 8 ohm transformer is the main culpret.  Manually swept 
> it using an audio oscillator and there is a nice rolloff below 300 
> hz.  Cured the problem by replacing the transformer with a 70.7 volt 
> one, and stuffing the metal cabinet with fiberglass.  The ops were 
> appreciative.  Said it sounded a lot better.  And 2nd LT 'Crash' 
> Rothman was none the wiser.
> R-392/URR, Stewart-Warner, Sn# 2681R, Order nr. 11653-PH-52.  And from 
> the paint on the case, belonged last to the Radio PLT, Co B, 198 Sig.