"Jim Pruitt" <[EMAIL PROTECTED]> made an utterance to the drakelist gang
--
Hello Ron.
Here is a link to Scott's comments about the article:
http://www.dproducts.be/Drake_Museum/tr-7mods.htm
I will paste them below then comment some more after the Prather comments
that are copied from JM Cherry's great Drake web page:
"Improving the Drake TR-7 by Scott D. Prather, N7NB (ex-KB9Y)
Reversible Modifications Enhance Performance
Please Note: The mailing address included on the first page of this article
is no longer current. Please address all correspondence to Scott Prather at:
[EMAIL PROTECTED]
Abstract.
The Drake TR-7 is an outstanding all-band, solid-state transceiver that was
a trendsetter when it was unveiled to the amateur radio market in 1978.
However, the TR-7 was not without its problems, some of which included:
Poor receive performance below 1.5 MHz
No full break-in (QSK) CW operation
Compromised signal/noise ratio when using narrow CW filters
High cooling fan noise, and the stock fan operates only when the radio is
powered from an AC source
My article, which originally appeared in the Summer, 1992, issue of
Communications Quarterly, addresses these four problems with modifications
that require no drilled holes, making them 100% reversible.
Notes
Improving the TR-7 is reprinted here in its entirety, and it appears on the
Web with the permission of Communications Quarterly. I scanned the original
19-page paper and converted it into an Adobe ® PDF file. The size of this
file is approximately 1.9 MB, so it will take a while to download if you are
using dial-up Internet access. For example, at 28.8 kbps it took me about 14
minutes to download the file.
Component Availability
At the time that this article was written, all of the components required
for these modifications were readily available. However, there are a few
components that are currently difficult to obtain. The most difficult
component to locate is D2005 (MA4P4002D), a stud-mount, high-power PIN diode
manufactured by M/A COM. It's my understanding that this diode is no longer
available from the manufacturer, and I've been unable to locate a diode that
I'm convinced will function as a substitute. The MA4P4002D has the following
specifications at 25 degrees Celsius:
Series Resistance @ 100 mA forward current: 0.5 ohms
Carrier Lifetime: 6 microseconds @ 100 mA forward current
Voltage Rating: 200 Volts
Power Dissipation: 15 watts
Initially, my decision to use M/A COM's stud-mounted PIN diode was driven by
the requirement to support 100% duty cycle operation, such as RTTY or SSTV.
However, for low duty-cycle modes such as SSB and CW, I have successfully
used the MA4P4002B axial-lead PIN diode with a small heat sink on the diode
body. Unfortunately, this diode is not readily available either. Generally,
any axial-lead PIN diode capable of dissipating about 5 watts and meeting
the series resistance, voltage rating, and carrier lifetime specifications
listed above should function in a low duty cycle application at the 150W
power level of the TR-7. I will continue my search for a substitute, and
I'll post my findings here. If anyone has a suggestion for a substitute,
please send the information to me at the e-mail address listed above.
The second component that's difficult to obtain is reed-relay K2001,
manufactured by Magnecraft. I've been unable to locate a source for this
part, however, it appears that an EAC P/N 20-1121-30 reed relay should work
in its place. The primary difference between the original Magnecraft part
and the EAC substitute is the lead pinout. The EAC relay has short in-line
pins, while the Magnecraft part had longer leads which would permit a
"triangular" PC pad configuration at each end. Also, the NC contact on the
EAC part is on the opposite side of the relay from the Magnecraft part.
However, minor redrilling of the PC board along with a jumper to the NC
contact will solve these minor compatibility problems.
Miscellaneous:
A minor change in operation is required if a TR-7 is modified with my QSK
card and subsequently used to transceive with a Drake R-7 receiver using the
Drake 1548 cable. Because the QSK card RX Mute line only functions when the
TR-7 is turned on, the R-7 will be muted if the "Mute" button is depressed
and the TR-7 is turned off. To use the R-7 when the TR-7 is off, just
release the R-7 "Mute" button.
Errata:
Although I carefully reviewed this article prior to its publication, in a
project of this scope some errors are bound to occur. The known errors are:
Page 22, Figure 3: Two minor labeling errors exist in this schematic. There
are two capacitors labeled C2002, one connected to point "C" and the other
to the drain of Q2002. The capacitor connected to point C should be C2006.
Also, there are two capacitors labeled C2005, one connected to point "I" and
one from L2002 to ground. The capacitor from L2002 to ground should be
C2007.
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