Tube Amp Archive

I am about to build a D amp #124 with CLEAN ONLY preamp (only one ECC83 valve), low plate classic with 100k slope and 100k anode resistors etc. Per the 124 schematic and layout, Rf is 4k7 and Rt is 390. So my 2x EL34 approx. 30W clean-only preamp #124 variation amp shall have Rt of 390 and Rf of 4k...

Also, this amplifier has 2x EL34 output valves, supposed to be used so that they give about 25-30 W output (not more than 30 W anyway). Output impedance is for an 8 Ohm speaker. So, what would my Rt and Rf be for a standard guitar NFB? You didn't mention that before. Combined with an 8-ohm output y...

Here is why I asked what stack you are using and why I asked Martin about the tail resistor. All of the Low Plate Classics I have seen use a 3k3 or 2k7 for a NFB resistor with a 270 ohm tail on a Twin OT 4 ohm tap. So for a Low Plate Classic, a 4k7 NFB/ 270 ohm tail on the 8 ohm tap would be equiva...

For the voltage division, Rf can be changed as required. In this 124 example Rf is 4k7 and Rt is 390, making the divider ratio 390/(4k7+390) = 0.077. Do I understand this correctly, as it looks like it is stated above at quoted sentence: VERSION A: 4 Ohm tap on OT connection requires Rf 4k7 resisto...

Thank you, gentlemen, for your kind participation/advice. Perhaps a small detail scheme should be drawn (as it is on Accent switch - since I think this solution of Presence is really very useful in general... there is no need for subtle changes in this domain, it is ON or OFF... one could hardly tel...

Charlie Wilson wrote: ↑Wed Jun 08, 2022 9:41 pm Are you using a classic tone stack or skyline?
CW

After consultation with people on this thread, their advice, I think the tone stack is the following (already pots are installed, not yet wired): Bass 250kA (log), Mid 250kA, Treble 250kB (linear).

Greetings, I am building a clean preamp only version of #124. I am not about to have Presence pot (2k linear), but instead it would suit me fine to have a switch that changes between two settings: 1. no resistance at all (like if pot would be at minimum) 2. full resistance of 2k Ohma (like pot would...

Thank you, M.M.! Or would it be ¨m&m¨ ha, ha, ha... I thought so, but it is nice to read this generous, clever confirmation and advice. That's exactly what I shall do: test both 150k and 150k with 270k in parallel and try it out. Nice to know that it is about 150 Hz move on the frequency scale, I di...

Greetings, For this CLEAN-ONLY amp (#124 variation) I have in mind (already being built, actually!), what would be better for clean ROCK guitar sound (never distorted), a 100k or 150k slope resistor? Does anyone know what is the (approx.) center frequency of mid dip for each of these two options? Th...

Thank you, M.M.! That is exaclty what I shall use: Treble 250kB (linear); Mid 250kA (don't know if I shall get exactly 10% taper, but I shall try); Bass 500kA. THANK YOU, AGAIN!

Greetings, Here I come again, after many years... I am about to build a D amp #124 with CLEAN ONLY preamp (only one ECC83 valve), low plate classic with 100k slope and 100k anode resistors etc. My goal is to make CLEAN sound only, with just a touch of ¨crunch¨ on higher gain - think sound of Peter G...

Greetings, Here I come again, after many years... I am about to build a D amp #124 with CLEAN ONLY preamp (only one ECC83 valve), low plate classic with 100k slope and 100k anode resistors etc. My goal is to make CLEAN sound only, with just a touch of ¨crunch¨ on higher gain - think sound of Peter G...