Kenwood TS 830S

[Nemo1956]

Im not having a good month.
Now my much beloved TS830S has gone tits up on my.
It started to fail two weeks ago when i switched it on no RF output. So I left it running for about 1 hr and then 60 watts. OK that will do. But this weekend nothing at all. so I took some measurements only to find that the 12AY7 valve base had problems. So I pulled the RF board out and I found cracks around the solder joints. The pins where in a mess so I had to remove the base and clean up all the pins. Put it back and re-soldered it in. But as the board was out I took some other measurements and found the 12AY7 grid leak resistor was open circuit and the one of the two cathode resistors had gone a bit high. Both replaced. So i put it all back together. Switched it on and still on RF output but then I could see the HT volts dropping to 350 volt and not 850 volts.
I think I may have a short in one of the PA valve now ?
Has any one had anything like this???

[CJay]

I'd be checking capacitors and rectifiers first before I panicked about shorts in valves but as you've worked on it, recheck everything and any HV capacitors in the filters.

[Nemo1956]

Hi. Many thanks for your help.
I have had a good look at this now and found that the one of the HV caps has gone open circuit and many resistors in the power supply have also gone high or open circuit.
But after doing all this work replacing capacitors and resistors I find the main problem is the mains transformer has died and it has a some shorted turns in the HV winding. It gets very hot after running a for 30 seconds. Even when disconnecting all the winding's so its running open circuit.
So sadly my much loved TS 830S is now scrap.
Thanks for all help.

Paul

[CJay]

That's a shame, second hand transformers do appear from time to time but they would of course be just as old as the one that failed and who knows how they've been treated, perhaps you could install a solid state amplifier instead?

It'd take a little experimentation as V1 would also need to be replaced as well as the final assembly but if the alternative is to scrap the radio...

[Armadillo]

Hi. Many thanks for your help.
I have had a good look at this now and found that the one of the HV caps has gone open circuit and many resistors in the power supply have also gone high or open circuit.
But after doing all this work replacing capacitors and resistors I find the main problem is the mains transformer has died and it has a some shorted turns in the HV winding. It gets very hot after running a for 30 seconds. Even when disconnecting all the winding's so its running open circuit.
So sadly my much loved TS 830S is now scrap.
Thanks for all help.

Paul

It should be possible to rewind the transformer isn't it? Such a typical EI laminated core.

[Radio Tech]

This is a reason why I stress to the audience so much about replacing old capacitors.  When they start going bad it is too late to notice the load on the transformer. 

Options now is sale the radio as is,
Re-wind the transformer.
Or hope that one will show up on ebay.

Ohm out the secondary and see if you can find which one is shorting.  I have repaired these in the past and only found shorted turns a couple of layers deep.

[Armadillo]

I have repaired these in the past and only found shorted turns a couple of layers deep.

After going through such trouble to disassemble the EI core, if possible, change the enamelled windings completely as chances that the insulation has been eroded due to PDIV voltage discharge and temperature deterioration is highly possible. No point going through the trouble again. 

[Nemo1956]

Now that's interesting. I will remove the transformer over the weekend and see if there is anything I can do with it.
I have never had or heard of one of these transformers going bad but I guess there has to be one somewhere. lol