[Drake] TR-4 and TR-3

[Garey Barrell]

The main difference is the sideband filter.  The TR-3 had the "soupcan" 
filter which has both filters, with discrete crystals soldered together 
inside a single "tin" can.  They are four pole filters at 9 MHz.  The 
same filter was used in the early TR-4's, later changed to a pair of 
filters.  At first the separates were probably also four pole filters, 
as were the 5.645 MHz filters used in the T-4X.  They switched to eight 
pole 5.645 MHz filters in the T-4XB and may have also changed to eight 
pole 9 MHz filters in the TR-4 at around the same time.

The four pole filters are marginal with poorer carrier and unwanted 
sideband suppression than the eight pole units.

The TR-3 was made in 1963-64.

The TR-4 started in 1965 as did the T-4X.  I don't know how many of the 
soupcan TR-4's were made, but I have seen three or four.

The T-4XB came out in early 1968 so TR-4's probably started using the 
eight pole filters at around the same time.

The TR-4C came out in 1973.

You can look down in the top cover right behind the Sideband switch.  
The soupcan is a square, tin-can silver box mounted through a hole in 
the chassis.   The later units have two blue or silver colored 
rectangular filters mounted vertically, side-by-side to a plate parallel 
to the front panel. 

There are other minor changes, such as changing from a tube type PTO to 
a bipolar transistor one, but the TR-3 and early TR-4 circuits were very 
similar.

73, Garey - K4OAH
Atlanta

Drake C-Line Service Manual
<http://hr99.home.mindspring.com/R-4C_Servicez/>



Eric wrote:

>
> What are the main differences between the Drake TR-3 and TR-4?
>
> Rick WA1RKT
>