Texas Star 667V help

[Turbo T]

I have one of these that only does 300 watts into a Bird 43 with a pep board installed and a 1000H with the end ran into a dummy load. The volts are 14.1 VDC. Drive in is 2 watts swinging to 14.

I'm wondering if this is a sign that one of the Toshiba 2879's has failed? As I understand this amp should be doing an honest 500 watts if not more.

Someone before me did switch out the driver from a 60 watt Toshiba 2290 to an 80 watt MRF454. So that has me wondering if one or more of the 2879's failed?

Where should I check?

Thanks.

 

[nomadradio]

Have a look at the output combiner. It's a toroid (doughnut) coil positioned to the rear of the relay, just to the rear of the gap between the front and rear circuit boards.

A 2-Watt resistor may be mounted inside the combiner's hole, or alongside it. If this resistor is toasted, a failed 2SC2879 is possible.

Problem is, you won't usually get 300 Watts PEP with this problem. Should be less if you have a blown 2879.

Are you sure the power supply is up to the task? The 667 is a power hog. If the supply voltage is dropping under load this will limit your power.

The 667 is a bad idea, IMHO. The driver is just a little too big, and the drive power it can accept is a lot less than most radios deliver. The resistors they used to reduce the drive power to that driver transistor can overheat, fail and cut the drive power too much. People want to see a bigger number on the wattmeter, and the 667 appeals to them that way.

When one of these comes in the door I recommend converting it back to a DX500, bypassing the driver. The reduction in power is less than the S-meter at the other end can tell if you are using a dual-final radio. Tends to improve the audio, since the four transistors are not being overdriven this way.

But have a look at that combiner. If it looks overheated, this tells you that the front pair and the rear pair of 2879 are not delivering the same power into the combiner. More than one possible cause of this, but the resistor on that combiner is the canary in the coal mine. If anything is a little out of balance between the two pairs of 2879 it will roast.

73

 

[Turbo T]

Thanks for the advice. I looked at the combiner and I can't tell if the resistor is burnt or not. It has dark browninsh crusty deposits on the ends where the leads go in that can scrape off. My first thought was solder flux. The center doesn't show any discoloration.

The supply voltage doesn't drop hardly any. I used my truck to power it with the engine running. Usually when I key my DX500 I can hear the engine bog down 100 rpms. But not the 667. The engine doesn't bog at all. It's as if it's not drawing much current. I have the power wire mod on both boards.
There's 10 gauge wire both positive and negative off of both.boards, ran together, and fed with 8 gauge wire straight off the battery.

I have considered converting this box to a straight 2879 4 pill. But I can't find anything online that shows what all must be removed. I would imagine it's more than removing the driver pill, the two transformers, and whatever else is required.

 

[9C1Driver]

How far of a run is it? A 667 can draw 55-60 amps, if it's a long run #8 wire will not be enough.

 

[Turbo T]

Maybe 6 feet, tops