Kenwood TS-450/TS-690

I like this radio but wow the TS-690 I got has shot finals. This is all TBD as I turn my notes into a doc.


There are a lot of weird things to fix in this radio. The mods I’ve done are pretty extensive:


I’ve been slowly rebuilding the finals on this unit.

Inductor rewinding

Here are some notes about the inductors.





Thermistor / fan control

The thermistor is mounted very far from the finals transistor making it take a long time to turn on. I’d rather it turn out sooner rather than later, so I did a couple things:

The fan now kicks in much sooner and keeps things much, much cooler.

Replacement transistors

I used replacement 2SC2509s from Eleflow which have higher HFE than the low-ish HFE parts used by Kenwood. So, I did the finals modifications appropriate for the 2SC3133 - I have a feeling the eleflow parts more resemble the 2SC3133 anyway. It seems to work OK.

Finals oscillating issue

As noticed in the TS-450_HELP link below, the finals have a habit of oscillating when operating on at least the 20m band.

I’ve done the following finals mods, based on both the service manual and an eham post about this.

The post is here:

.. and a backup PDF:

So far so good? The 20m oscillation seems to have gone away.

IF gain above 12m

This is from WB4KDI:

(TS-690 - 6 Meters) There is a pad to decrease the IF gain when AIP is turned off for frequencies above 22 MHz. The service manual claims that the pad is to reduce IF gain so the signal strength meter reading will remain the same as below 20 MHz. Who cares is the signal meter reading increases? That’s the purpose of the preamplifier! Note that this change will worsen the strong signal handling capability of the receiver on 12 and 10 meters. Make this change only if you need to increase the IF gain to hear weak signals on 22 - 50 MHz.

To disable this pad remove R68 and/or Q14 (R69 and Q17 for 6 meters). If for some reason the signal meter ever needs to be recalibrated at 28 or 50 MHz remember that the signal strength reading has been increased by about 15 db.

Reduce the RF Gain to limit band noise above 22 MHz.