I tried one, but to my ears, there's too much hiss with some high-end
headphones with the AF control at low settings and even full CCW. I've tried
the LM383, LM380, and TDA2002. The hiss can be reduced with an in-line
attenuator, then running the AF control at a higher level to compensate. I
would rather just deal with the root issue and solve it.
Paul, W9AC
----- Original Message -----
From: kc9...@aol.com
To: w...@arrl.net ; drakelist@zerobeat.net
Sent: Wednesday, October 31, 2012 2:39 PM
Subject: Re: [Drakelist] R4C Hum and audio transistor
Why not install a Sherwood audio kit ...I have one in mine..works FB
73,
Lee
-----Original Message-----
From: Paul Christensen <w...@arrl.net>
To: drakelist <drakelist@zerobeat.net>
Sent: Wed, Oct 31, 2012 2:37 pm
Subject: Re: [Drakelist] R4C Hum and audio transistor
Max,
I'll get crucified for saying this, but that class A transistor stage was
poorly designed -- and I think we can dispense with the "but they didn't have
cost-effective transistor technology back thirty years ago" as an excuse. A
two-transistor complementary-symmetry PP pair running class AB and a moderate
amount of negative feedback would have sounded substantially better, and
produced much less heat.
As an example, look at the Marantz, Sansui, Kenwood, and other mid-fi
Japanese audio amplifiers being produced during the same period. Those
designs, or a variant, could easily have been leveraged into the R-4C.
Eliminate the audio output transformer and tap the symmetry pair mid-point,
then couple with 500+ uF of series coupling C. I don't know what Drake's cost
was for the audio output transformer, but I have to believe the production cost
difference between the transformer and an extra audio output transistor, and
surrounding passive parts would have been reasonably minimal.
I jettisoned the R-4C AF stage after the volume control and won't be going
back.
Paul, W9AC
----- Original Message -----
From: Max Cotton
To: drakelist@zerobeat.net
Sent: Wednesday, October 31, 2012 2:10 PM
Subject: [Drakelist] R4C Hum and audio transistor
I have a very nice R4C it had a hum with bad audio distortion so I decided
to investigate, whilst taking it apart I noticed that if I touched the noise
blanker the hum would alter, I removed the NB board and the hum was still
there, I found eventually that the audio transistor had desoldered itself, do
they really run that hot? so I resolded the wires, now the radio does not work
anything like as well and has a high amount of white noise, has that audio
transistor died and if so where do I get a new one, is there an equivalent for
that power transistor?
73, Max M0GHQ
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