Re: Tweed Princeton question 5/21/99 03:08 in reply to MKB Bruce missionamp@aol.com IMO the 5F2-A is a better sounding tone circuit. There is very little attentuation with the tone control in the middle of this and preamp can still rock the 6V6GT just fine. There will be no tone boost anyhwere anyhow because the 500pF cap is a glorified variable bright cap over the volume control when set for max treble and the .005uF cap is like high freq short ground when set for all bass. When the volume control is set for full volume, there is no resistance to shunt highs around and it sounds great that way. Use a 10uF on V1a the 1K5 Rk instead of the 25uF and if you need a little more boost use a 1uF across the V1b 1K5 Rk. When you are done with this, replace the 220K grid load resistor on V1b with a 250K audio pot for a master volume control...works cool. Bruce Mission Amps Re: Tweed Princeton question 5/22/99 02:41 in reply to Bruce MKB markbrid@hickory.net Thanks for the reply, Bruce. I sort of suspected that the 5F2-A was the better one. I have wired up the amp with the 5F2-A tone circuit and it does sound pretty good. I had a single ended PT that was from a PA amp using one SE 6L6, and I used a PT that could handle the 6L6. Just for kicks, I installed a Mullard EL34 and adjusted the cathode resistor for Ip=50mA at ~300V B+. So, the amp is basically a 5F2-A without feedback with an EL34. This is so far the best sounding amp I have made. Plenty of gain and tone, with the primary design feature realized: I can play the thing on 12 without my wife complaining or waking the baby up!!!! I plan to put it in a pine cab with an alnico 12" spkr out of my dad's old stereo. Thanks again for the help! Re: Tweed Princeton question 5/23/99 08:29 in reply to Bruce Steve A. steveahola@worldnet.att.net http://www.techaccessinc.com/blueguitar/ Bruce: When you are done with this, replace the 220K grid load resistor on V1b with a 250K audio pot for a master volume control... I believe you meant to say "V2" (the 6V6 output tube)... So is the pot wired up as a variable resistor (using 2 terminals), or as a pot (all 3 terminals)? And if as a pot, is the wiper going to the 6V6 grid or back towards the coupling cap? Thanks! Steve Ahola P.S. I'm looking for a PT for a project such as this (or your SoulKicker Jr.)? Preferably with the 5V heater tap. Got anything like that for sale? I picked up that AX84 OT from Randall Aiken a few months ago and just got some tube sockets and pots. They are going to go into the chassis and cabinet from my 1978 Peavey 20w ss Studio Pro for that "stealth" effect! Glad you mentioned the MV because there are 7 pots on the chassis and it'd be weird if all but two of them were just dummies. Or maybe I could go crazy and add in a tube buffered FX loop with FX send and return levels. Would you put the loop between the preamp volume control and the grid for V1B? I'm thinking of using the loop from Kurt's Amps that has a DPDT switch to remove the loop from the audio path when it is not being used: http://www.techaccessinc.com/blueguitar/fx_loop.gif So whaddaya think of that loop? Re: Tweed Princeton question 5/23/99 22:02 in reply to Steve A. Bruce missionamp@aol.com CRAP! I hate it when I do that. You are correct sir! If you wanted to make it a master volume pot, where it adds a little resistance in front of the wiper you certainly can wire it with the wiper going to the grid as you said. Doing that however, seems to roll bass off a little too. These little amps need some clean bass response. I've found that it works fine as a variable resistor or like you mentioned in reality. **** P.S. I'm looking for a PT for a project such as this (or your SoulKicker Jr.)? Preferably with the 5V heater tap. Got anything like that for sale? I picked up that AX84 OT from Randall Aiken a few months ago... Oh my GOSH!!! I'm stunned. Heck yes, I have tons of PTs for little amps like this! I'll send you SoulKicker Jr. circuit board, layout and schem (W/FX loop and line out). Would you put the loop between the preamp volume control and the grid for V1B? Yeah, that works. With a master volume on this amp you'll need four pots total. Volume, Master Volume, Tone, and Variable NFB. You can use one more of the pots and make your power tube line out sampler into a slave amp drive control. Bruce Mission Amps Re: Tweed Princeton question 5/25/99 12:34 in reply to Bruce jason jbone@mail.hcc.cc.nc.us Bruce, I think this is the amp I'm going to be building and have a few questions. 1. I noticed that the 5F2 uses a choke where as the 5F2-A uses a resistor. Is the one with the choke going to have a little higher B+ or what? Soniclly is there a difference? Any opinions on which way to go? 2. Power transformer...any recommendations (do you have any for sale)? 3. The 5F2 has three filter caps, all 8µF's where as the 5F2-A has four filter caps,two 16µF's in parallel and two 8µF's. Any suggestions on which way to go here (I have a lot of 20µF/450v caps already, can these be used with out making a big difference in tone/performance)? 4. I'd like to make the NFB variable. Any suggestions on a pot value and should I leave the 22K resistor in the circuit and just wire the pot in series as a variable resistor? I think that's all the questions for now any way. Thanks, jason Re: Tweed Princeton question 5/25/99 16:04 in reply to jason Bruce missionamp@aol.com Hi Jason, 1. I noticed that the 5F2 uses a choke where as the 5F2-A uses a resistor. Is the one with the choke going to have a little higher B+ or what? Soniclly is there a difference? Any opinions on which way to go? Yes it will have slightly higher screen voltage but in a small wattage amp like this, where the final PA is running class A, a single resistor in place of the choke is OK. Personaly, in little amps, I like the screen voltage about 5vdc to 15vdc lower then the plate voltage. Of course a choke makes for a better power supply but considering all things, a 50 cent 2 to 5 watt resistor works pretty darn good. I don't hear any difference in a class A SE amp if the supply is well filtered and there are no ground loops. 2. Power transformer...any recommendations (do you have any for sale)? If you want to go for a hollow state rectifer, you'll want a PT with around 320vac@50ma-70ma, if you want a solid state rectifier you can figure a smaller PT with about 275vac@50ma-70ma. My SoulKicker Jr. use <350vac@50ma and runs a 5Y3 rectifier... but rips with a solid state plug and a 6L6GC. Yes, I do have some iron, but I'm always a little uncomfortable hawking my products or parts here. 3. The 5F2 has three filter caps, all 8µF's where as the 5F2-A has four filter caps,two 16µF's in parallel and two 8µF's. Any suggestions on which way to go here (I have a lot of 20µF/450v caps already, can these be used with out making a big difference in tone/performance)? You can use a 33uf on the first cap position with a SS rectifier or HS rectifier. With the SS rectifier, connect the OT right to the 33uF cap, then follow with a small resistance like 120ohm 5watter to a 22uF followed by a 2K-5K 2W screen dropping resistor, then another 22uf cap, followed by a 15K to 20K 1 watter to the last cap which can be anything from 10uF to 22uF. 450v is OK. If you use a rectifier tube, you don't have to use the 120 ohm resistor. Just go with 33uF@450v cap on the rectifier tube and connect the OT there. Two more 22uFs laid out like the 5F2 is usually OK. But a 10uF-16uF is also OK for the last cap. Follow the normal grounding rules and connect the center tap of the PT right to the negative lead on the FIRST filter cap and run a wire from there to the star ground. 4. I'd like to make the NFB variable. Any suggestions on a pot value and should I leave the 22K resistor in the circuit and just wire the pot in series as a variable resistor? Pull the 22K off your design and use a 1K5 to 4K7 instead but feed the new valued feedback resistor with NFB voltage from a 100K pot wired in series as a variable resistor connected to the speaker jack. Bruce Mission Amps