Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Esquirefreak on April 11, 2025, 10:30:53 am
-
So, long time no build...
I'm in the early phase of putting together a new amp, based on the 6G8 preamp and the 6G12 power amp. I'm reusing most of the parts from other builds and parts I have laying around.
Biggest difference is that I have swapped out the LFO CF triode for a mosfet. So 5 tubes instead of 6 (or 5½ really).
I'm gonna be using a Deluxe Reverb chassis and build a head cab for it. I know that there are nice replica brownface chassis on eBay, but shipping to Sweden is more expensive than the chassis itself.
I'll draw a schematic once I have proof of concept and I'm statisfied with the amp.
/Max
-
Main board drilled.
-
And populated.
-
Pots wired up
-
Cap board borrowed from the left-over-bin.
-
Heaters ✔️
-
Starting to look like an amp
-
Almost there
-
Done.
Fired right up without weird noises or mishaps. Dead quiet at idle and very loud when played.
Only changes I've made, so far, was to decrease the 10M R from the LFO output to 4M7. And then I increased the NFB R from 22k to 100k, which gave me a softer response.
This is my first build using a James TS, so I have yet to figure out if these TS component values are what I want.
I might experiment with the bias and plate load Rs in the first 2 gain stages. But for now I'm very pleased with how this came out. Gonna take a break from amps for a week or two before making the head cabinet.
/Max
-
This is my first build using a James TS, so I have yet to figure out if these TS component values are what I want.
Well done on getting it right first time!
Re the James TS, I've guilt a few amps with these and the attached schematic is what I find produces an ideal combination for me (when driven by a 12AX7 triode). With both pots at mid-rotation, the output is dead flat. With both pots cut, there is a mid-hump. With both pots at full rotation there is a mid-scoop. The slope switch enables a decent growl with P90s. The raw switch is completely unnecessary and optional. YMMV
-
Thanks!
I may temp in a TS outside the amp to try different values, atleast for the normal ch which I think has a little overwhelming mids. Will use your values as a starting point!
I think the vibrato ch sounds good, and the hi/lo filters is another variable that affects the sound. The taper of these tapped pots are weird, though. They feel a little binary, like on/off. Very narrow window between too little or too much treble.
/Max
-
Is the slope resistor replaced by the 70k tap here? I couldn't figure out why that resistor (which is part of all other James TS schematics I've seen) is missing.
-
Yes its a slightly different way of getting the result