Still Having RCA 8TS30 Issues

[old_coot88]

I feel your frustration bro. I might've missed it, but have you checked voltages on:

V118 (6SK7) 1st sync amp ----- pertinent voltages are pins 4, 6, 8 (that's G1,G2, plate)

V119 (6SH7) sync separator --- pertinent voltages are pins 4, 6, 8 (that's G1,G2, plate)

V120 (6SN7a) 2nd sync amp -- pertinent voltages are pins 1 & 2 (that's G1 and plate)

Are those tubes lighting up good? If any are metal, they should be getting warm after a few minutes running.

[Chris K]

Originally Posted by old_coot88

I feel your frustration bro. I might've missed it, but have you checked voltages on:

V118 (6SK7) 1st sync amp ----- pertinent voltages are pins 4, 6, 8 (that's G1,G2, plate)

V119 (6SH7) sync separator --- pertinent voltages are pins 4, 6, 8 (that's G1,G2, plate)

V120 (6SN7a) 2nd sync amp -- pertinent voltages are pins 1 & 2 (that's G1 and plate)

Are those tubes lighting up good? If any are metal, they should be getting warm after a few minutes running.

I'll check those tonight. Yes they are warm and NOS but I've tried several tubes from my stash and from the parts chassis with no change.

[jr_tech]

It might be worthwhile to check all power supply voltages cold vs hot.

jr

[old_coot88]

Originally Posted by Chris K

I'll check those tonight.

Cathode is ground on all 3 tubes, so wasn't included in voltage chart.

[Chris K]

Originally Posted by old_coot88

I feel your frustration bro. I might've missed it, but have you checked voltages on:

V118 (6SK7) 1st sync amp ----- pertinent voltages are pins 4, 6, 8 (that's G1,G2, plate)

V119 (6SH7) sync separator --- pertinent voltages are pins 4, 6, 8 (that's G1,G2, plate)

V120 (6SN7a) 2nd sync amp -- pertinent voltages are pins 1 & 2 (that's G1 and plate)

Are those tubes lighting up good? If any are metal, they should be getting warm after a few minutes running.

I really don't see a smoking gun here except for the lower voltages associated with the reduced 135V line being bled off to another voltage line source.

6SK7 #4 -3.6V #6 96V #8 187V
6SH7 #4 -4.3V #6 104V #8 103V
6SN7a #1 -1.3V #2 68V

[old_coot88]

A suggestion - from a dead-cold start, with your voltmeter on the 135V source (jct. of R185/R186), turn the set on. Since the 5U4s give full B+ almost instantly, is the 135V still low? Or is there a signifigant drop as the rest of the tubes begin conducting? This would tell you if it's tubes lugging the 135V down, or something else circuit-wise.

[Chris K]

Originally Posted by old_coot88

A suggestion - from a dead-cold start, with your voltmeter on the 135V source (jct. of R185/R186), turn the set on. Since the 5U4s give full B+ almost instantly, is the 135V still low? Or is there a signifigant drop as the rest of the tubes begin conducting? This would tell you if it's tubes lugging the 135V down, or something else circuit-wise.

Great suggestion. The diagnostic skills available here are an invaluable instruction. I don't know why trying that didn't occur to me...it should be a pretty revealing exercise but I guess that's part of the learning curve! I will take a look at that this evening and thank you so much for hanging in there with me.

[Chris K]

Originally Posted by old_coot88

A suggestion - from a dead-cold start, with your voltmeter on the 135V source (jct. of R185/R186), turn the set on. Since the 5U4s give full B+ almost instantly, is the 135V still low? Or is there a signifigant drop as the rest of the tubes begin conducting? This would tell you if it's tubes lugging the 135V down, or something else circuit-wise.

295V DC when first turned on and it held for 4-5 seconds and then took a steady dive down to 104V in the next minute.

[Username1]

Originally Posted by Chris K

I really don't see a smoking gun here except for the lower voltages associated with the reduced 135V line being bled off to another voltage line source.

6SK7 #4 -3.6V #6 96V #8 187V
6SH7 #4 -4.3V #6 104V #8 103V
6SN7a #1 -1.3V #2 68V

.

These voltages are I think pretty far off.... How are the resistors R160, 161, 157, 228, 153, 156, 157....
I'm wondering about the -18, -2, and -100 v sources, as it looks like they are providing bias for all
the little tubies that are also using the 135V & other sources... Higher G1 voltages will
mean all the tubies conduct just a little bit more for each one.... and you know
what that means.... More Ampies being used.... and if the 3 tubies you
provided G1 voltages for, they are each a little higher..... More
ampies means B+'s all go down..... Good suggestion about
monitoring the 135V as the set warms up, I suspect it will
go down as the set gets going, no surprise there...

.

[Chris K]

Originally Posted by Username1

.

These voltages are I think pretty far off.... How are the resistors R160, 161, 157, 228, 153, 156, 157....
I'm wondering about the -18, -2, and -100 v sources, as it looks like they are providing bias for all
the little tubies that are also using the 135V & other sources... Higher G1 voltages will
mean all the tubies conduct just a little bit more for each one.... and you know
what that means.... More Ampies being used.... and if the 3 tubies you
provided G1 voltages for, they are each a little higher..... More
ampies means B+'s all go down..... Good suggestion about
monitoring the 135V as the set warms up, I suspect it will
go down as the set gets going, no surprise there...

.

Hello there...from my read of the schematic the volts on these should be:

6SK7 #4 -4.3V #6 129V #8 165V
6SH7 #4 -5.2V #6 135V #8 134V
6SN7a #1 I don't know! #2 88V

As for resistors, 228, 153, 159, 157, 158, 160 all test dead on. I replaced 154 and 155 because they were a smidge high.

[old_coot88]

Originally Posted by Username1

... Higher G1 voltages will
mean all the tubies conduct just a little bit more for each one.... and you know
what that means.... More Ampies being used.

Higher negative G1 voltage with respect to cathode reduces plate current. Plate voltage is in reverse phase to the grid.

[Username1]

Originally Posted by old_coot88

Higher negative G1 voltage with respect to cathode reduces plate current. Plate voltage is in reverse phase to the grid.

.

Look at the voltages, Readings Vs. Schematic the readings are closer
to 0, not closer to -7V cutoff. They are increasing with respect
to cathode 0. -3v is higher than -4v.

.