Hey guys- another question in relation to this amp, my plan is to run an ef86 and a 12ax7 for the preamp and as you know a 6v6 and el84 in the power amp. so how do I go about determining the proper high and low voltage fuses for this amp? for the HV should i just add all the plate currents of the tubes up? (by my math i think a 250mA fuse would be a good choice?) Would a 1A LV fuse be fine for the mains side? Sorry if this seems like a terribly uneducated question, I do know my way around a tube amp and am an experienced electronics guy i swear! I've just never done anything where I have to spec. fuses and I just want to make sure I'm as safe as possible! Thank you all for your help in advance!
I'm not using an ef86, I forgot to say that. EF184/6EJ7 is cheaper and better sounding that current production EF86s. It also has a lot more gain so I might get away using only this tube to overdrive the 6V6/EL84 combo.
We'll see.
About microphonics: it can be a problem with these tubes as with the ef86.
A 250mA slow-blow fuse is fine.
We'll see.
About microphonics: it can be a problem with these tubes as with the ef86.
A 250mA slow-blow fuse is fine.
Stalker thanks for the reply - Do you think that a 1A fast blow fuse for the 120v mains would be okay as well?
I like the sound of 1 gain stage in the preamp slamming the output valves into creamy OD! Wouldn't mind bragging to my friends about that at all
I'm not very familiar with the EF184, is it still in current production?
I like the sound of 1 gain stage in the preamp slamming the output valves into creamy OD! Wouldn't mind bragging to my friends about that at all
I'm not very familiar with the EF184, is it still in current production?
Hi,
Yes, that fuse would be OK.
It's not easy to find a good ef86... I would just use another pentode with no microphonic problems, maybe the 6SJ7. A tube with a triode and a pentode would be a great idea too. I used the ef184 because that's what I had at hand.
Yesterday I tested the pentode preamp... not enough gain with single coils pickups and no space for another socket so I rewired for a 12AX7 which is a good idea anyway since I want to compare this amp against the Champ.
Today I will test the output stage with both tubes (yesterday I only tested the amp with a 6v6).
Yes, that fuse would be OK.
It's not easy to find a good ef86... I would just use another pentode with no microphonic problems, maybe the 6SJ7. A tube with a triode and a pentode would be a great idea too. I used the ef184 because that's what I had at hand.
Yesterday I tested the pentode preamp... not enough gain with single coils pickups and no space for another socket so I rewired for a 12AX7 which is a good idea anyway since I want to compare this amp against the Champ.
Today I will test the output stage with both tubes (yesterday I only tested the amp with a 6v6).
OK, this amp sounds great but:
1. Don't bypass the el84/6v6 cathode resistors--it oscillates at all volume levels.
2. Get an OT with different impedance taps, with 2.5k I got farting distortion, I'm using the 7.5k tap for best sound.
Classic Champ preamp with no current feedback and no Gnfb loop. I would suggest to use a more sophisticated preamp if you do want to get more than one type of sound out of this amp. EL84/6V6 currents are matched with 470 and 220 ohm resistors.
Tone is 10,...feeling lazy for audio adjectives today.
* With a different OT your results may be different, mine is a vintage unit.
1. Don't bypass the el84/6v6 cathode resistors--it oscillates at all volume levels.
2. Get an OT with different impedance taps, with 2.5k I got farting distortion, I'm using the 7.5k tap for best sound.
Classic Champ preamp with no current feedback and no Gnfb loop. I would suggest to use a more sophisticated preamp if you do want to get more than one type of sound out of this amp. EL84/6V6 currents are matched with 470 and 220 ohm resistors.
Tone is 10,...feeling lazy for audio adjectives today.
* With a different OT your results may be different, mine is a vintage unit.
Awesome! I'm glad you got around to testing it! I'm actually working on some preamp designs right now and was getting ready to post about it! Just curious, what do you think the power output is, 10W maybe?? Because that would be perfect for me
Just a couple questions first- for the 470 and 220 ohm resistors, your talking about the cathode resistors right? and did you use a 470 for the 6v6 and a 220 for the el84 as per my original schematic or did you do it the other way around? Also what values did you find work well for the grid resistors, I was just going to use a 1.5k for the el84 and possibly a 470 ohm for the 6v6- just educated guesses from schematics floating around the net! Man this is really making me want to start building the amp- not too much longer now! Thanks for the tips about the OT (very interesting!) and the cathode caps- you probably saved me a lot of trouble and frustration!
Now I just have a quick question about my preamp design (open to any who can give input please!) I'm thinking about running both halves of V1 - which will be a 12ax7 - in parallel, I've never owned an amp that does this, but I've heard some Matchless models do it with quite good results. Can anyone guide me as to what the plate resistor should be? Since the plates are in parallel, should I just divide the plate resistor in half? So i was thinking about using a 100k for each of the V1 cascaded stages originally, but now should I do something along the lines of 50K-68K maybe? Also, would it matter if I kept the cathode resistor a 1.5K still and used a 20-25uf bypass cap?
Thanks in advance!
Just a couple questions first- for the 470 and 220 ohm resistors, your talking about the cathode resistors right? and did you use a 470 for the 6v6 and a 220 for the el84 as per my original schematic or did you do it the other way around? Also what values did you find work well for the grid resistors, I was just going to use a 1.5k for the el84 and possibly a 470 ohm for the 6v6- just educated guesses from schematics floating around the net! Man this is really making me want to start building the amp- not too much longer now! Thanks for the tips about the OT (very interesting!) and the cathode caps- you probably saved me a lot of trouble and frustration!
Now I just have a quick question about my preamp design (open to any who can give input please!) I'm thinking about running both halves of V1 - which will be a 12ax7 - in parallel, I've never owned an amp that does this, but I've heard some Matchless models do it with quite good results. Can anyone guide me as to what the plate resistor should be? Since the plates are in parallel, should I just divide the plate resistor in half? So i was thinking about using a 100k for each of the V1 cascaded stages originally, but now should I do something along the lines of 50K-68K maybe? Also, would it matter if I kept the cathode resistor a 1.5K still and used a 20-25uf bypass cap?
Thanks in advance!
10 Watts? I really doubt it due to the OT high impedance (7.5k). Can't measure the power out, no oscilloscope but louder than 5W it is.
Grid resistor values are not critical, anything between 1K-10K is OK.
470 ohms for the 6v6.
Copy the Machtless schematics:
Post 70's Amp Heaven Schematics - Acoustic Bogner Kettner HiWatt Matchless Orange Peavey Rickenbacker Rivera Soldano
Grid resistor values are not critical, anything between 1K-10K is OK.
470 ohms for the 6v6.
Copy the Machtless schematics:
Post 70's Amp Heaven Schematics - Acoustic Bogner Kettner HiWatt Matchless Orange Peavey Rickenbacker Rivera Soldano
OK, this amp sounds great but:
1. Don't bypass the el84/6v6 cathode resistors--it oscillates at all volume levels.
2. Get an OT with different impedance taps, with 2.5k I got farting distortion, I'm using the 7.5k tap for best sound.
Tone is 10,...feeling lazy for audio adjectives today.
Good to hear you are making such rapid progress and that it already sounds good. In the schematic I've seen, which is the amp for recorded music reproduction and not a guitar amp, it definitely does have 220 uf capacitors bypassing cathode resistors. However it isn't on the schematic for some reason. Don't know why your amp oscillates with the caps. I understand guitar amps generally don't use as big capacitors for cathode bypass anyway.
BTW, I don't see any reason for us not putting up our own modified schematics from Mesa Boogie's. While I don't feel comfortable putting a schematic up publicly that I got directly from Mesa for the reasons I've stated I don't think our own would be a problem. That being said, I'll restate that even modified versions we put up uses Mesa's intellectual property and should not be used for profit. Nobody here would go after them but they might.
Eric
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I have no idea... anyone? It is a loud motorboating sound.
I unbypassed the preamp stage thinking too much gain might be the cause but it didn't change a thing.
It didn't bother me much because I like the sound without them and this was done in guitar amps before with good results -Valco comes to mind.
You lose power though but it's loud enough for my needs.
Well, this a SE guitar amp...nothing to do with the Tigris except the triode/pentode switch. I will post the schematic once I am done with the experimentation part.
Interesting. I thought maybe it couldn't be done but it can. Not in my amp...again, any ideas?
Maybe 100uf for each tube was too much, I am going to try lower values.
OK with 22uf caps it doesn't do motorboating just some obscene noises everytime I hit a string. I mute the string and the amp remains quiet.
Youngb4 here's an idea to get full power; as I said before 2.5k wasn't good with the output tubes cathodes unbypassed but with a feedback loop from the cathode of the preamp's 2nd stage (Fender Champ 5F1) you can use the 2.5k tap with no distorted bass ugly sounds. More power if you need it.
Youngb4 here's an idea to get full power; as I said before 2.5k wasn't good with the output tubes cathodes unbypassed but with a feedback loop from the cathode of the preamp's 2nd stage (Fender Champ 5F1) you can use the 2.5k tap with no distorted bass ugly sounds. More power if you need it.
Thanks for the tip stalker, once I start testing I'll make sure to experiment and see what I find out - plus I'm designing this amp for use in an apartment so running with less power might be just the ticket! Did you notice any differences in tone when using the 7.5k tap opposed to the 2.5 with NFB?
Thanks
Thanks
Man, this amp sounds wonderful, we played 'til 4 a.m... I didn't want to stop. lol
10W is only 3dB louder than 5W. I need a 99 dB/m speaker to play clean with this amp, breaks up early. Heavy distortion sounds mushy without feedback...but I don't care, I don't play hard rock that much and I liked it best without Gnfb. Experiment with your preamp ( I'm using a 5965 and 1/2 12ax7) and for the output stage this is what I found out:
1. You don't need to match the currents...I have tried different tubes and no problems.
2. No bypass caps. You won't miss them.
3. A 220K grid resistor for both tubes. Two 1.5K grid stopper resistors.
4. I'm using 2.5k but experiment here...different sounds with 5k and 7.5k.
Good luck but you won't need much to find great tone.
10W is only 3dB louder than 5W. I need a 99 dB/m speaker to play clean with this amp, breaks up early. Heavy distortion sounds mushy without feedback...but I don't care, I don't play hard rock that much and I liked it best without Gnfb. Experiment with your preamp ( I'm using a 5965 and 1/2 12ax7) and for the output stage this is what I found out:
1. You don't need to match the currents...I have tried different tubes and no problems.
2. No bypass caps. You won't miss them.
3. A 220K grid resistor for both tubes. Two 1.5K grid stopper resistors.
4. I'm using 2.5k but experiment here...different sounds with 5k and 7.5k.
Good luck but you won't need much to find great tone.
Stalker this might be kind of a newbie question but I just wanted to clarify- the 1.5k resistor (in which the signal travels through) goes on the grids of the el84 and the 6v6, and the 220k is for the screen grid of each tube, am I correct or am I just completely mixed up!!?? Did you stick with the same values for the cathode resistors btw?
I'm glad the amp is sounding so good, but I'm sure it wouldn't have without your tinkering! It's much appreciated! About the distortion characteristics, I tend to play at higher gain levels, not metal or anything like that but alternative-semi hard rock levels, and I def. want the distortion to be fairly tight. Where's the best place to apply negative feedback in the preamp? I'm prob. going to run the first 12ax7 in parallel and the second in cascode operation (never heard an amp that does this method, but I've read good things!) with a 1meg pot in between for gain, the tone stack and MV will follow the cascode gain stage. Like you said, I'm sure I will have to experiment to find what sounds best with my preamp configuration first before I get into negative feedback, but I'm just tryin to tie up as many loose ends as I can so I can finally order some parts! Thanks for your help (and anyone elses) in advance!
I'm glad the amp is sounding so good, but I'm sure it wouldn't have without your tinkering! It's much appreciated! About the distortion characteristics, I tend to play at higher gain levels, not metal or anything like that but alternative-semi hard rock levels, and I def. want the distortion to be fairly tight. Where's the best place to apply negative feedback in the preamp? I'm prob. going to run the first 12ax7 in parallel and the second in cascode operation (never heard an amp that does this method, but I've read good things!) with a 1meg pot in between for gain, the tone stack and MV will follow the cascode gain stage. Like you said, I'm sure I will have to experiment to find what sounds best with my preamp configuration first before I get into negative feedback, but I'm just tryin to tie up as many loose ends as I can so I can finally order some parts!
Thanks for your help (and anyone elses) in advance!
Hi,
The 220k resistor goes to ground. Screen resistors are 470 ohms. Yes, same cathode resistors.
My problem with tight distortion may have to do with my OT, I suspect it can't do 10W without saturating the core. I recommend you a Hammond 125ESE.
Your preamp stage has a lot of gain, it will need some kind of feedback. Mine is switchable. Just build it, listen to it and then make changes. That's the fun part about DIY.
The 220k resistor goes to ground. Screen resistors are 470 ohms. Yes, same cathode resistors.
My problem with tight distortion may have to do with my OT, I suspect it can't do 10W without saturating the core. I recommend you a Hammond 125ESE.
Your preamp stage has a lot of gain, it will need some kind of feedback. Mine is switchable. Just build it, listen to it and then make changes. That's the fun part about DIY.
I know its not SE or 6V6 and EL84 but hey take a look at this:
Servicing of a Majuscule Hi-Fi Amplifier
Check out Johns site as well it is good
Servicing of a Majuscule Hi-Fi Amplifier
Check out Johns site as well it is good
okay new question in regards to my amp- I'm in the process of designing the power supply and am heavily referencing the P1 builds over at ax84.com. I was thinking about using the hammond 269ex power transformer which has a 380v CT secondary with 71ma of current. Unfortunately I don't think it will be powerful enough to supply the el84 and 6v6 along with the 2 12ax7s. Looking at some previous builds around the web, typical plate current for an el84 SE is around 43ma and 50-60ma for the 6v6 SE. So since I'll be using both the el84 and 6v6 in parallel in my amp, this already exceeds the hammond transformer current rating for the secondary winding correct?? Can anyone recommend a way for me to estimate my plate currents for each of the power tubes? I'll be using a 250 ohm cathode resistor for the el84 and a 470 ohm resistor for the 6v6 and was planning on supplying around 250 volts as my B+1. alot of sites I've been looking at assume my amp is already built and I can stick a multimeter around to pull values (well I cant because nothings built yet ) also, does anyone have any recommendations on the voltages I should be sending to the el84 and 6v6, is 250v too cold? I know this is just a giant group of questions, but I'm trying to learn as much as I can so I can order everything I need on the first go!
) also, does anyone have any recommendations on the voltages I should be sending to the el84 and 6v6, is 250v too cold? I know this is just a giant group of questions, but I'm trying to learn as much as I can so I can order everything I need on the first go!- Status
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