Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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The TR-3 is very similar in this area.
There are several components involved in modifying the frequency
response of the received audio. The TR-3 had a 470 pF cap from plate
to ground of the 6GX6 Product Detector to roll off the high frequency
response, (and reduce bfo feedthrough,) and a 0.0015 pF coupling
capacitor to limit the low frequency response.
The early TR-4 was the same, then around s/n 32000 added a 1.5 k
resistor in series with the 0.0015 coupling capacitor to further limit
the low frequency response.
Around s/n 35000 a second 470 pF cap was added from the plate to ground
to further roll off the HIGH end audio, for a little "warmer" sound.
The "sound" of a receiver can be modified by adjusting the frequency
response of the AF amplifier stages. Reducing the high "tones"
emphasizes the low ones, and vice versa. The majority of "articulation"
in speech is carried between roughly 500 to 2700 Hz. Frequencies below
500 Hz contribute very little to the "understandability" of speech,
while requiring much more audio power to reproduce, so are usually
suppressed in the interest of efficiency. You can demonstrate this
effect with any receiver with Passband tuning. You can vary the
response of the receiver by adjusting the Passband tuning to favor the
low frequencies. The further you go in that direction, the less
intelligible the speech becomes. Conversely, if you adjust it to favor
the high frequencies the speech becomes clearer and clearer.
So... If you want maximum intelligibility, the Drake engineers probably
made the right decision. If you are willing to give up intelligibility
for a more "pleasant" sound, then just increase the value of the 0.0015
uF coupling capacitor in the TR-3 or TR-4/C until you get the "sound"
you want.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Hunter Ellington wrote:
I have a TR3 that could use some cajones adjustment to get some base
sounds. Any similar information for that older rig?
R. Hunter Ellington, Esq.
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*From:* [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] *On Behalf Of *Ken Bessler
*Sent:* Thursday, October 04, 2007 3:32 AM
*To:* [EMAIL PROTECTED]
*Subject:* [drakelist] TR4 adding a touch of bass
I just performed the minor mod I spoke of in my
earlier posting, IE: adding capacitance to V16's
#5 lead.
I hooked up a 1.5k resisitor and a .01 microfarad
cap between the #5 pin and the center conductor
of the coax cable next to it. It's tight work but
the results are most satisfying.
I measured the passband with Spectrogram and
it appears I've added about 200hz to the bottom
of the rig.
I have the .pdf file showing the mod. If anyone
want's a copy please contact me off list....
Ken
73's de Ken KG0WX - Kadiddlehopper #11808,
Flying Pigs #-1055, Grid EM17io
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