I'm looking at the 6B5 output section of this Silvertone 4463 model. http://www.nostalgiaair.org/PagesByModel/051/M0017051.pdf
I have not seen this arrangement before.
The triode on the left has it's cathode wired directly to the grid of the trio on the right.
Looks like the left triode is driving the right triode with what seems to be a "cathode follower" arrangement... is that right?
Can Norm or one of you other more knowledgeable guys enlighten me a little on why this arrangement was used and what the particular benefits may be?

Peter

That's exactly what it is. A cathode follower driving a pentode output stage. This was done to save a cathode resistor and bypass cap. A 6B5 can be replaced by 42 tube if a 470 ohm resistor is added in series with pin 5. Resistor should be bypassed with an electrolytic cap.

Basing is 6AS. You will notice there is a resistor built in connected to the cathode of follower stage. It's not shown on the Silvertone schematic. If this resistor opens and there is internal leakage the tube runs away with current. You can't replace the resistor.

http://www.mif.pg.gda.pl/homepages/frank/sheets/121/6/6B5.pdf

Another tube like this is 6N6. It also can be replaced by 6F6 or similar with bias added.

Norm

:I'm looking at the 6B5 output section of this Silvertone 4463 model. http://www.nostalgiaair.org/PagesByModel/051/M0017051.pdf
:I have not seen this arrangement before.
:The triode on the left has it's cathode wired directly to the grid of the trio on the right.
:Looks like the left triode is driving the right triode with what seems to be a "cathode follower" arrangement... is that right?
:Can Norm or one of you other more knowledgeable guys enlighten me a little on why this arrangement was used and what the particular benefits may be?

Peter

It's a triode cathode follower driving a triode output tube (not pentode). That's the way it's shown in most books. Noticed Sylvania added another grid in their spec. Most books show it as a dual triode.

Norm

:Peter
:
: That's exactly what it is. A cathode follower driving a pentode output stage. This was done to save a cathode resistor and bypass cap. A 6B5 can be replaced by 42 tube if a 470 ohm resistor is added in series with pin 5. Resistor should be bypassed with an electrolytic cap.
:
: Basing is 6AS. You will notice there is a resistor built in connected to the cathode of follower stage. It's not shown on the Silvertone schematic. If this resistor opens and there is internal leakage the tube runs away with current. You can't replace the resistor.
:
: http://www.mif.pg.gda.pl/homepages/frank/sheets/121/6/6B5.pdf
:
: Another tube like this is 6N6. It also can be replaced by 6F6 or similar with bias added.
:
:Norm
:
:
:
::I'm looking at the 6B5 output section of this Silvertone 4463 model. http://www.nostalgiaair.org/PagesByModel/051/M0017051.pdf
::I have not seen this arrangement before.
::The triode on the left has it's cathode wired directly to the grid of the trio on the right.
::Looks like the left triode is driving the right triode with what seems to be a "cathode follower" arrangement... is that right?
::Can Norm or one of you other more knowledgeable guys enlighten me a little on why this arrangement was used and what the particular benefits may be?

Thanks very much Norm
... but I was wondering why cathode follower is not otherwise used often/ever...in Radio audio amps.... and what the salient features were that were enough to incorporate them here.

Peter

A cathode follower gives current gain but not voltage. Not needed in most radio circuits. It's used when current is needed to drive a circuit. The second triode is operated with zero bias, grid can go positive. Under this condition grid current will be drawn by the tube.

Norm

:Thanks very much Norm
:... but I was wondering why cathode follower is not otherwise used often/ever...in Radio audio amps.... and what the salient features were that were enough to incorporate them here.
:

Peter,

A cathode follower circuit was used sometimes to drive a low impedance line between two pieces of equipment that are separated by some distance. A cathode follower uses 100 percent feedback so it has very low distortion and a very good bandwidth. It also has a higher input impedance than other standard amplifier circuits so there is almost no loading of the circuit preceding it.

Radiodoc
************

:Thanks very much Norm
:... but I was wondering why cathode follower is not otherwise used often/ever...in Radio audio amps.... and what the salient features were that were enough to incorporate them here.
:

I have the exact chassis you are looking at. It is from a consol radio that someone was throwing away. I actually have the entire cabinet. It's going to need a lot of work. Then I'm going to give it to my brother, since he was the one who insisted that I pull it out of the garbage. The chassis was also used in at least one table model radio that I've seen on-line.

I re-coned the speaker, but I haven't re-capped the chassis. The audio has a lot of distortion. I really want to hear what it will sound like. Since I obtained the radio, I've bought a couple of 6B5s and 6N6s. I've used the 6N6s in some radios I own that use 6K6s or 6F6s. They sound pretty nice, though you must short out the cathode bias normally used by the 6F6 or 6K6, or else you won't get much power (6B5 and 6N6 don't need cathode biasing).

T.

Thanks Guys...
So... the effective qualities are wider bandwidth and lower distortion...?
Seems nice... I'd like to listen to one now... and see if it's particularly noticeable to me.
..and Just because I don't often see this design in typical radios of or after this period.. I wonder why?
Was this a short lived design idea that was improved upon some other way?.. or maybe just simply replaced by lower cost designs that weren't at all as good in audio quality?

I put a 6N6 in my Airline 62-306. I connected the grid resistor so that it is at the same potential as the cathode (not more negative....and the resistor that biases the cathode also biases some other circuits, so I can't short across it--negative filtering). I am pleased with the audio. It is very deep and rich. It is much better than the 6F6 that the radio originally used. Though this change makes the radio unoriginal, I think I'm going to leave it this way. It is a simple change that can be changed back at any time (the radio even has its original dogbone resistors). It sounds wonderful with a 6N6. I should try 6N6s in my Crosley 1117. I tried them once before, but without shorting the cathode bias resistor. It would be interesting to hear 6N6s in push-push.

T.