Circuit Questions - Gretch 6160 "Chet Atkins" Amp

[W5FH]

Hello-
    I have been studying the Gretch 6160 amp with great interest. If anyone else interested in this amp has opinions/info I have two questions:
#1. I see that all four of the input triode stages have the same B+ feed arrangement of a 100K series resistor from B+ rail, 0.05 uFd bypass and 270K plate load resistor to triode plate. In my understanding this represents a split plate load resistor 270K/100K with approx 1/3 of signal voltage swing being present at resistor junction and being bypassed to ground by 0.05 uFd cap. If this is correct then is this arrangement used to reduce signal level or is there other benefits?
#2. I see differences between channel 1 and channel 2 in regards to cathode biasing components, namely presence or lack of presense of cathode bypass caps,  for the 4 input triodes. Appears bass and treble "flipped" in regards to the cathode bypass cap. I am studying a build using this concept of separate treble and bass triodes at amp input but want to do a single channel. I wanted to ask anyone who is knowledgeable about this amp which input channel is the preferred one for a fairly clean bluesy type playing?
Thanks, Byron W5FH

[passaloutre]

Regarding #1, I don't think you can call it a "split load" on the plate, as you are pulling the output signal from the plate directly. A split load uses the node between two resistors for the output signal. Furthermore that .05 cap between the resistors is bypassing everything above 30Hz to ground, which makes it essentially a filtered power supply node. I think it's just the way that it's drawn makes it look like a split load, but really it is a 100k dropping resistor, filter cap, and then a 270k plate load.

As far as #2, I think the bass and treble controls have just been labelled backwards on the second channel, as the circuits are otherwise identical.

[bmccowan]

I was watching to see if anybody was going to jump in. Rift amps has an interesting 7 part Youtube series on this amp https://www.youtube.com/playlist?list=PL6WtOUEy2VmM3k7zO2DS2QsS0FJkgIDaR
I have not run across this particular amp. I have rewired 2 2x10 6V6 Valcos (one labelled Gretsch, the other National.) The preamps were similar but without the split load and the funky input grid stopper set up. Great sounding amps. If you build one, you could wire the pots so that controls work intuitively. You will see what I mean when you get to video #7.
 Edit - I posted just as Passaloutre did. Agree on the plate load thing. I recall that I rewired a Valco Harmony 420 that had that same arrangement.

[SEL49]

I agree with passaloutre's assessment. Many Valco amps from that time period used that same preamp design. My Supro S-6624 preamp is identical to your Gretsch.

If that .05 filter cap bothers you, then replace with a 10µF or 20µF. But you won't hear any difference.

The tone circuit is very interesting on paper. A friend of mine had this same amp back in the late 60s. He played Chet Atkin's style with a Country Gentleman. A very clean sound. I thought the built-in single note tuner was cool, even if it was not accurate. That's all I remember about that amp.

[passaloutre]

I've always wanted to try that tuner circuit