Need help understanding the difference in two versions of a tube stereo circuit

[jake.unruh]

Hi there.
I've been cleaning up wiring on a Silvertone Model 1029 tube stereo. Excellent little unit and it sounds great. The information for these units are pretty scarce, but in the schematics i've found there's one spot that's kind of given me pause for understanding and was reaching out to see if the audio hive mind could help.

To the point: There is a Silvertone 1029 and a Silvertone 2029 version. They seem to be identical save one coupling (i think) cap that comes off pin 3 of the 7199 driver tube for each channel. On the 1029 version, it goes from pin 3 around to pin 6. Not directly to ground. On the 2029 version the caps go from pin 3 directly to ground.

The only other thing to note is that the B+ feeding that tube in the "directly grounded version" is 25 volts higher off the filter capacitor, thus making the voltage off pin 3 35v instead of 30 volts in the "not directly grounded" version. That's really the only main difference I could even dream that would be cause for change...other than one of the schematics just straight up having a mistake.

I mainly want to know what the effect of the difference would be.

In my unit, the caps were grounded...but my unit is also a 1029 which that schematic is the version that isn't directly grounded. But I've also seen pictures of 2029's that go from pin 3 to pin 6, contrary to it's schematic but in accordance to the 1029.

I also found that someone before me had mismatched the output coupling caps .022uF / 0.05uF instead of both being .022uF...so I just kind of wanted to have a bit more understanding of this part before just slapping it all back together.

I've attached links to two schematics I've been looking at. I put red boxes around the section of the circuit with the cap in question, as well as the voltage differences.

1029 (not directly grounded) version - https://imgur.com/brUU0qX
2029 (direct to ground) version - https://imgur.com/LeNHuro

I totally can put this unit back together the way it was and it will work "just fine" meaning it seems fine. I'm just seeking to grow my understanding of uses of these caps in the circuit and figured it's a great example to understand a little more. Maybe even find a mistake in my unit as well!

Thanks for the help in advance!

 

[zackthedog]

Unless I'm mistaken, that's a screen bypass cap and there are two ways to connect it--to the cathode (in this case, pin 6) or to ground, depending on the design. I would restore it to follow the schematic of the unit you're working on.

 

[AmadeusMozart]

It's a screen bypass cap when it goes to ground and when it goes to the cathode it acts as a sub sonic feedback - it helps preventing "motor boating".

 

[Tom Bavis]

The screen should be bypassed to the cathode, which should give lower distortion. But there are a lot of components around that tube - it's not easy to connect 3 components to one pin - it may have been easier to connect to ground. Won't affect any of the DC voltages in the slightest. You'll notice that even on the Sams schematic, voltages are different on right and left channels - swap the tubes and the voltages would swap too - tubes probably vary more than any other component.

 

[jake.unruh]

That makes sense. I had looked at the 7199 data sheet / pinout and saw that it was the screen going to either ground or the cathode, but I guess I just didn't know what to call it or what it did. Upward and onward!
Thanks @zackthedog and @AmadeusMozart for the quick response!
Edit: @Tom Bavis ! I missed your reply when I was writing this. Thanks for even more clarification. It helps me understand that either way nothing was being wrecked and what the better way to go seems to be! Thanks again.

 

[zackthedog]

It's a screen bypass cap when it goes to ground and when it goes to the cathode it acts as a sub sonic feedback - it helps preventing "motor boating".

That's informative, thanks!