Identifying The Drake TR-7 Differences and Versions
by: Ronald Baker / WB4HFN
The Identity Question
Over the last few months there has been discussion around the Drake TR-7, what are the actual differences and how can you determine which version you really have. In recent months we have seen TR-7's for sale described as the later TR-7A version or upgraded to the TR-7A version. In some cases a front view photo of the radio appeared to actually be the "A" version, but to be revealed in other photo's that it wasn't truly the case. Need we be concerned about the possibility of counterfeit TR-7 transceivers on the market? That question I'm not going to address here, but I will give you what information I have discovered through a lot of research to help you determine for yourself that answer. Since Drake manufactured several versions of the same model, for example the Drake R-4 receiver, here we have four versions, R-4, R-4A, R-4B, R-4C, each externally looking very similar if not identical. The same is true for the solid state transceiver, the TR-7 and TR-7A. To make sure the equipment model and versions stayed the same Drake implemented a simple procedure. When you wanted to replace a damaged front panel you shipped your old front panel to the company before they would ship out the replacement panel, ensuring the radio model and version identity remained the same. Today with the advent of after-market products and the availability of new and used parts including front panels being sold over the Internet accurate product identification now becomes a gray area of concern. In this article I will discuss the Drake TR-7 transceiver, identify the best I can the differences between the models and versions within the same model. In my research I have identified three significantly different versions of the TR-7 transceiver. First there are two versions of the original TR-7, which I will classify as the early and late version, and then the last version the TR-7A model. Also, the last three pages of this article discuss the various circuit changes the TR-7 went through is its life time, these include the power amplifier, noise blanker and 2nd IF/Audio board.
The Rear Panel Configuration
First lets identify the external differences in the original TR-7 transceiver. From the front both the early and late versions look identical, the real differences was on the back panel. The early version had a one piece back panel from one side to the other. The late version incorporated a three piece sub-panel construction where a center sub-panel with all the connectors screwed to end panels on either side of the radio. Take a look at the following two pictures identifying both versions.
( click to enlarge pictures )
( click to enlarge pictures )
The change to the late version three piece panel made it much easier to gain access to the wiring side of the connectors over the earlier version. This production change to the three piece rear sub-panel happened somewhere between July 1978 to February 1980, the best I can determine. By serial number, the best I can tell this production change occurred somewhere between 4800 and 6000. The later TR-7A transceiver used the same rear panel configurations as the TR-7 late version. On the rear panel the only difference between the TR-7 and the TR-7A was a wiring change to one of the connectors which is discussed in detail later in this article.
The Front Panel
|
|
 |
( click to enlarge pictures )
The next area we'll look into the the transceiver front panel. The TR-7 early and late version front panels were identical. Even with the TR-7A the front panel was left unchanged except for the model number designation in the top right corner of the radio. See the pictures showing that difference.
The TR-7 front panel was divided into two sections. The lower front panel section was identical across all both models and variations. The upper front panel section was also identical with both the TR-7 early and late version, and the only change to the TR-7A was the model number designation on the panel.
In this area you need to be careful when making a purchase. There has been a quantity of the upper front panels with the TR-7A designation available over the Internet and other sources. It is a simple task to remove the TR-7 panel and install the TR-7A panel. Doing so from the front it would now be hard to tell the difference between the TR-7 and the later TR-7A model. Since the value between the TR-7 and the TR-7A is a few hundred dollars, not thoroughly checking out the radio could be a costly mistake. Don't let the front panel model designation be the only factor in determining which model it is exactly. Use this along with the rear panel configuration and the serial number.
Regarding the serial number, the transition from the TR-7 to the TR-7A occurred somewhere between the high 10,000's and low 11,000's range. In my research the highest TR-7 serial number I seen is 10889, and the lowest TR-7A serial number is 11289, so the model transition is somewhere in the range. The TR-7 to TR-7A model change-over occurred in late 1981.
The serial number is stamped on the rear panel just below the antenna connector. If you suspect this has been tampered with, Drake also stamped the serial number on the front aluminum sub-panel. The serial number is on the front side of the sub-panel just behind the lower front panel, left of center towards the microphone connector. By removing the lower front panel section the serial is visible from the front. With that said, be aware removing the front panel is no easy task and does require a lot of disassembly. You will need to remove the case top, the black side panels, all the knobs, remove the VFO dial assembly and disconnect and remove the microphone connector.
TR-7A Production Changes
What are the production differences between the original Drake TR-7 Transceiver and the later production of the TR-7A? Between the TR-7 and the TR-7A there were basically five circuit changes. Along with the circuit changes the only physical differences were the front panel (see page two for details) and the labeling of a rear panel connector. The circuit changes include:
-
A noise blanker (NB-7) has been installed.
-
A 500Hz filter (SL-500) has been installed in selectivity position "A"
-
Selectivity "B" has been adapted to provide a bandwidth of 9kHz for AM reception.
-
A surge protection device has been added to the receive antenna input to provide additional protection from static discharges from lightning.
-
The unused phono style tip-jack on the rear panel has been labeled "TX", and now provides an alternate audio input to the transmitter for sources other than microphone. This jack is connected in parallel with pin 1 on the front panel microphone jack. See below the pictures showing the connector labeling on the TR-7A rear panel.
( click to enlarge pictures )
( click to enlarge pictures )
Here again you need to be cautious if you suspect a TR-7 identity issue. Someone could easily use black rub-on lettering for the transmit audio connector creating a look-alike TR-7A rear panel.
Other Noteworthy Items:
Here are a few other tid-bits of information I uncovered during my research. Drake does not exact record of how many TR-7 transceivers were manufactured. The best we can determine Drake built around 10,500 TR-7's and around 2500 TR-7A's. We know the TR-7A production started with a serial numbering in the low 11,000's range, and the highest TR-7A serial number I've seen or heard about is serial number 12269.
Some of you may have seen the TR-7 transceiver cabinets in black. Drake never built a TR-7 or TR-7A using a black cabinet. The Drake cabinets were either the early version gray sometimes referred to as the "sticky paint" cabinet, or the later version dark gray hard vinyl clad aluminum cabinet. So where did the black case come from? As I understand the story, the black case was available from Drake after they stopped manufacturing amateur radio equipment. After the stopped building amateur radio equipment they were still receiving many orders for replacement cases, so Drake had a quantity of them reproduced as replacement parts and sold them as such for several years until they ceased providing spare parts a couple of years ago. But why a black case? During that time Drake's cabinet manufacturer was producing black cases for other Drake products including the TR-270 and several of their short wave radios, so Drake decided to use the same material because it was readily available.
Did Drake perform TR-7 to the TR-7A upgrades? Yes, for a fee Drake did offer to upgrade the TR-7 to the later TR-7A version. What Drake did was to upgrade the circuitry and internal wiring but did not change the outward appearance of the radio. Specifically, Drake did not change the front panel top strip.
The Transmit Power Amplifier
The Drake TR-7 power amplifier has two versions of the pre-driver board, both shown in the picture below along with the power amplifier module. The version #1 board consisted of a transistorized three stage amplifier with an on-board +8VDC regulator supplying power. The version #2 board has a two stage amplifier and is powered directly from the 13.6VDC power supply through a set of relay contacts. Both boards have signal limiting and impedance matching on the input and variable gain output to set the proper level to the power amplifier module. The advantage of the version #2 board was a simpler design with less components, and has a design change to better control and increase stability of the output level driving the power amplifier.
In the TR-7 the change-over from the version #1 to the version #2 board came very early in the production of the TR-7. The TR-7A version used the version #2 board exclusively.
( click to enlarge pictures )
The NB-7 Noise Blanker
|
The NB-7 series noise blanker came in three versions. There was the original version which is used in the early TR-7 transceiver production, referred to the picture as the early version. The NB-7 later version has a totally redesigned circuit board layout, but uses basically the same circuit design, with two exceptions. First, the later version incorporated an additional stage of amplification, transistor Q816, at the input to the noise blanker to make up for some signal loss needed over the earlier version. Second, the circuit board layout was redesigned to incorporate a crystal filter, assumedly for better noise selectivity. However, the later version of the NB-7 installed in the TR-7 transceiver never used the filter, a jumper wire was installed in place of the crystal filter. Notice on the NB-7 later version the open circuit board area on the lower left side of the circuit board. In the picture you will notice the NB-7 later version and the NB-7A circuit board layout are the same. The 2nd generation noise blanker, the NB-7A, did incorporated the crystal filter. Notice in the NB-7A picture the previously discussed open circuit board area, lower left side now has the crystal filter installed. The best I can tell is the NB-7A was used in the companion R-7 and R-7A receivers. The noise blanker, NB-7A, with the crystal filter was standard equipment in the R-7A receiver and available as an installable option in the R-7 receiver. All three versions of the NB-7 noise blanker are interchangeable between all models of the TR-7(A) transceivers and the R-7(A) receivers. However, I have noticed when using the NB-7A with the crystal filter, when the noise blanker is switched into the circuit you will notice on the "S" meter a small drop in signal strength. |
|
The 2nd IF/Audio Board
At some point during the production of the TR-7 transceiver, not sure exactly when, Drake redesigned the 2ndIF/Audio Board to allow for a product detector improvement. The early version used discrete components for the product detector, which is used for the modes of SSB, CW, and RTTY. This early version used signal diodes and transistors to detect the audio signal. In the later version that entire circuit was replace with a single integrated circuit, specifically the Motorola MC1496. This circuit change gave the radio better dynamic audio range which is a definite improvement in the transceiver's receive audio over the earlier version. Other that this one change the rest of the board is approximately the same on both versions.
In the photos below, you can see both versions and I've marked the product detector IC on the later version board.
( click to enlarge pictures )
[ Top of the page ]