Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on September 24, 2019, 02:03:51 pm
-
I converted an Ampeg J20 to a 6G3, almost identical circuits except the Ampeg had only one vol and tone for each channel (bright, normal). Fender Brown Deluxe 6G3 has vol and tone for each channel. The pictures below show the layout of the circuit, you see the two 220k (1) watt plates resistors, I used two 470K ohm off the coupling caps as seen in picture, the bright channel is missing the 250p paralleled across the bright side 470k (still working on that value for brightness, 500p too bright. I have two inputs on the Ampeg faceplate, Normal and Bright, I used the Normal for input and a mini toggle switch, on,on,on in the bright input hole, up for normal down for bright, middle for both, worked out great.
My question is the two 470k divider R's to the switch, one is just hanging as I disconnected the bright cap, still searching for best valve, this amp is very bright. "Should I use 250k dividers or keep with the 470k?" Does the size of these R's have anything to do with the brightness? Both channels are basically identical, except I didn't share the same values for the 1st stage cathodes, Normal channel is 820 and 10uf, bright is 1k5 and 10uf.
Just trying to cut down on the brightness of the bright channel, a did add a snubber 47p across the, 82k and 100k to 6V6s. I guess besides the best value for volume dividers (?), all I can do is lower the bright cap on the bright side of divider R or the 500p on the vol? The vol pot cuts treble nicely, just that the change is fast, a hair movement at 5 and very bright, no middle ground.
The wire under the two 470k's dividers is just a ground wire, of course the two 470k's go to the channel switch.
-
using this schematic;
https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_6g3_schem.pdf
I don't see much overly bright, V1 is fully bypassed, couplers are .02uF
you can try and replace the .0005 with a .001 on the TS, but I suspect if your set the TS full bass AND you're still bright, something else is amiss :dontknow:
-
I flowed the 6G3 exactly, except I have a single TS and the bright channel was very bright, the normal was too muddy. Took the .003uf paralleled off the normal plate R and normal channel was much better, maybe a hair too bright, probably just use .001uf.
The "only" difference in the original 6G3 volumes are one has coupling cap of .01uf the other .02uf and that paralleled .003 plate resistor. Since I have only one vol and tone pot to share, I just used a paralleled cap across the bright divider (250p).
So you suggest lowering the tone pot bright cap from 500p to 100p? Or maybe something in between. But with the 500p, the normal tone pot works great. Just that when I flip the switch to the bright channel not much transition from dark to super bright. Seems I need to work the brightness on that channel either with a lower coupling cap, or lower the "paralleled cap" on that side divider R...?
Anyway, does it make any difference what value R's I use to split the channels to the switch? I have 470k now, would 250k make any difference?
-
You should really post a schematic of your actual build; and use the Duncan TS Calculator to model your TS as-is, and with different values.
-
how "original" do you want it?, IF that's nbd, make the V1a and V1b get their own cathode stuff, pick ONE n tune to your liking Rk and Ck are good starts, then TS, Then coupling caps, then it gets kinda complicated :icon_biggrin:
-
Yes, l need to show a schematic of what l have now, and l’ll check out the Duncan TS calculator.
I put a 200p on the bright side to vol. down from the 250p l had, getting better. Plus, a GH1230 spk is way less bright than the Weber/Jensen PQ12 l was using. Think l’m learning you can’t have your cake and eat it too :icon_biggrin: . I’ll work on posting a schematic, thanks all.
I’m probably not aware of what a true 6G3 sounds like. They say Marshall crunch to Fender clean, with the values on the schematic that’s what this amp sounds like, l might be looking for something else, learning every day.