Drake Mods - Early/Late TR4
Authored by VE3EFJ
9.1 EARLY AND LATE MODEL TR4
I copied this from the Drake list server in early April. Consider the
following quoted text. I left Tom's name in here simply because he
should get credit for it and the message was sent publicly.
I have two different TR-4's. These are plain TR-4's; not TR-4C's or
later models. I was surprised to find a number of differences in these
two radios. The early TR-4 has many characteristics of the TR-3, while
the later TR-4 shares features with the TR-4C.
By comparing your TR-4's serial number with mine and your radio's features
with the list below, we might be able to figure out when each feature
was introduced in the TR-4.
The serial number of my early TR-4 is 1965. I noticed that the rear view
picture of the radio in the TR-4 manual (Fig. 7, p. 17), shows a TR-4
with a serial number of 16050. My early TR-4 has these characteristics
that differentiate it from the later TR-4:
- Has a TR-3 style main tuning knob
- The 9 mc sideband filters are sealed inside a soldered box. Bill
Frost of Drake calls this the "soup can" model and says that the
filters inside are four pole filters.
- The tubular capacitors in the radio are white, larger, and made by
- The "Plate" and "Load" markings on the front panel are printed in
silver letters on a gray background.
- The red dial indicator is the full vertical height of the frequency
- There is no noise blanker knob on the lower right front panel.
- There is no receptacle for a 34PNB noise blanker on the chassis
The serial number of my later TR-4 is 31985. It has these differentiating
characteristics from its younger sibling:
- Has a TR-4C (or R-4C) style main tuning knob.
- Has a VFO "in use" light above the main tuning knob. The indicator
is driven by a two transistor board mounted behind the noise blanker
- Has an open sideband switch (versus the sealed "soup can") and two
blue Tyco filters. Bill Frost says these are eight pole filters.
- The tubular capacitors are yellow, smaller, and made by CDE.
- There's a little circuit board behind V17, the 6AQ5 audio output
tube. The circuit board is labeled, "TR-4 audio" and it is an audio
- "Plate" and "Load" markings on the front panel are printed in black
letters on a gray background.
- The red dial indicator is the one third the vertical height of the
frequency plastic window.
- There is a noise blanker switch on the lower right front panel.
- There is a receptacle for a 34PNB noise blanker on the chassis
I'm sure there are other differences.
Layout and Design Copyright © 1997 by Thom LaCosta-K3HRN
All Rights Reserved