Motorola ts907 low hv

[timmy]

Originally Posted by Yamamaya42

Before doing anything to L4, you should try what others have suggested, V1 removed, and feed in the tuner subber into pin 7 the same as you did before, through a isolation capacitor, to see if you can get any signal through, you may have to adjust the gain on the subber a bit.

I had taken v1 pin2 off L3 and fed the subber in got the same as befor and with that wire off L3 I tried pin 7 but the tube was in and I got less of a response. When I fed v2 I used pin 2

[Yamamaya42]

It would most likely work better for you to put the original K1 couplet back in, as the 24meg section was not really that far off to matter that much to start with, and replacing it did not really do much.

[timmy]

Originally Posted by Yamamaya42

It would most likely work better for you to put the original K1 couplet back in, as the 24meg section was not really that far off to matter that much to start with, and replacing it did not really do much.

I already put the original k1 back in problem with it is the 2.2meg measured 2.4meg and the 2meg measured 2.4meg the 24meg measured 30meg and the 680k measured 740k this is why I made it up so I’ll leave it in for now and it may not be needed at all.

[Yamamaya42]

Originally Posted by timmy

I already put the original k1 back in problem with it is the 2.2meg measured 2.4meg and the 2meg measured 2.4meg the 24meg measured 30meg and the 680k measured 740k this is why I made it up so I’ll leave it in for now and it may not be needed at all.

https://www.allaboutcircuits.com/too...de-calculator/

that's all pretty much within 20% save for the 24 meg, which is just a hair.

most people say it's safe to let it go to 30%, then worry about it.
tube stuff is very forgiving with this!

[timmy]

I do have a 1000pf mica from the 1940s for test purposes it tests like new exactly 1.00

[Yamamaya42]

I would never trust it in a 60s type set, especially in the RF area, no idea what the voltage rating is, but it is a neat souvenir however!

[timmy]

Rather then use that old mica can modern micas be put in parallel to make the right capacitance. I know it’s the IF so it can be touchy.

[Yamamaya42]

Originally Posted by timmy

Rather then use that old mica can modern micas be put in parallel to make the right capacitance. I know it’s the IF so it can be touchy.

Doing that in an IF is not recommended...

the cap I pointed out IS the right capacitance, .001 @ 500v

598-CD19FD102JO3F mouser part #

[timmy]

So if the red cap that’s in L4 if it’s not a mica but rather a special type ceramic disc then replacing it with a mica should be better for the circuit.

[timmy]

Going to try 2 disc caps in v1 see what results I get if it works then when I get the mica cap then I’ll put it in. Regular disc cap should work in place of a mica if that’s infact what’s in there hopefully I get a good result.

[Yamamaya42]

If you are thinking of trying 2 capacitors in parallel, then that would not be advisable on a IF circuit, as it would drastically change the rc constant of it, and make it worse than when you started.

[timmy]

Originally Posted by Yamamaya42

If you are thinking of trying 2 capacitors in parallel, then that would not be advisable on a IF circuit, as it would drastically change the rc constant of it, and make it worse than when you started.

No I’m going to try the 2 .001 ceramics in L4 to see what the result is hopefully video. Ordered the micas if it’s good then I will put the mica in.

[timmy]

Ok tried the 2 .001 caps in L4 made no difference but v1 pin 8 is 100v but pin 7 is only 200v should be 210v after a couple of minutes and the 275v buss is only at 260v I cannot figure out why this b+ is low something here still seems to be pulling it down. The voltages are the same on v2.

[Electronic M]

Look in the parts list in Sam's and see if there's temperature constants listed for the original caps. When permanently replacing caps in tuned circuits especially original ceramic in the IF you want to use the same temperature coefficient. Sometimes a coil changes inductance a meaningful amount when it heats up and a cap is chosen with a temperature coefficient such that the cap changes value in step with the coil such that the tuned frequency of the pair remains constant despite the R and C values shifting with temperature.
Temp codes are typically 2 letters and a number like C0G, NP0 which are no change temp constants.

[Yamamaya42]

Originally Posted by timmy

Ok tried the 2 .001 caps in L4 made no difference but v1 pin 8 is 100v but pin 7 is only 200v should be 210v after a couple of minutes and the 275v buss is only at 260v I cannot figure out why this b+ is low something here still seems to be pulling it down. The voltages are the same on v2.

you are putting too much emphasis on the voltages posted in the SAMS, it's not unusual for there to be variances of 10-15% or even more and it being perfectly fine, no two sets are alike, even more so as they age.