[R-390] triple mica tubes

[Flowertime01 at wmconnect.com]

Scott,

Some believe the triple mica tubes are better.
If your receiver is just setting on the bench and not mobile or subject
to more than normal vibration, the mechanical benefits of the extra mica are
lost in your application. The Navy and mobile Signal Corp. ask for the extra 
mica.
 
Tube noise does make a difference. Try all of your 5814's into the first FR 
section of the audio deck. Use a signal generator and power meter (AC volt 
meter an 600 ohm resistor on the local output.

Compare Modulation on and modulation off meter readings. At modulation off 
the lower meter reading is less tube noise. As tubes are used, the noise goes up 
and the power goes down. With the signal generator modulation on the output 
will be lower. With the signal generator modulation off the noise level will be 
higher.

Run the 6C4 in the second mixer and use some Rf above 8Mhz.

Rank all the tubes you have as spare.

Put the low noise tubes to the front end, starting with the best 6C4 in the 
first mixer.

With your pulls and spares run all of these tubes again in you receiver that 
now has better tubes in it than you had in the first pass. (assume some of the 
spares were better than what was in the receiver and you now have the best 
tubes forward in the circuit.

Now you know which of the tubes are really better from a signal to noise 
prespective.

You can do this with all the tube in the receiver. 
Do the 6AK6 in the last IF
Do the 5749's in the First IF.

Put the best 5814's in the audio chain you use (local line). Then put good 
ones in the AGC. The IF follower is not used by most of us so put a poor tube in 
that socket. If you do not use the limiter, then a noisy tube can go in 
there. If you use your limiter, then put your best 5814 into that circuit.

Hope this provides you some insight to getting the most use out of the tubes 
you have in hand.

Roger L. Ruszkowski AI4NI



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