Hello there,
I've been reading here a lot but until now I was mainly drawn to guitar tube amps, of which I built and repaired several. Now I'm planning to build my first "Hifi" tube amp.
I do have an old Technics V65A which I restored but I just love to tinker with tubes and have really enjoyed all the stuff I learned (and still learn) when building guitar amps. That's why I decided to build a small tube amp for use in our livingroom. It's a relatively large livingroom but I won't need really loud music, more like low to medium volume, mostly low. I usually listen to a lot of Folk, Jazz, Blues and also Electronic, Ambient or Post Rock music. I'm not particularly looking for the audiophile side of things, but of course, if it's going to sound nice, that's a great plus!
I'm looking for some advice on what to build. I really like the design of the old Mullard 3-3.( Mullard 3-3. Three Watt Amplifier ) It's clever but simple, that's cool. Besides it's been published in the year my dad was born. After he died surprisingly two years ago I always wanted to build something from this year.
My idea was to build a stereo version of the 3-3 using a shared PT, EZ81 or GZ34 and a CLC-supply for B+.
My concerns with the Mullard 3-3 are about the output power. I have an old pair of Heco PCX-2 3-way loudspeakers of which I don't know the sensitivity. Back in the day I think these were some decent speakers but nothing to special. I'm wondering if I can expect "enough" volume from this setup...?
Do you think it's worth building the 3-3 for this setup or will i be disappointed by not enough volume or something? I could still get some higher sensitivity speakers later on but I would prefer if the setup would be usable as is.
I was also thinking about adapting the 3-3 design for another type of output tube. Adapting for a 6V6 should be fairly easy, but would a higher power bottle like a EL34 also be possible? It would of course involve changing the anode and cathode resistors of the EF86 to ensure a proper grid-voltage for the EL34 and also other modifications would be necessary (transformers of course). But would it be a theoretical option or is the EF86 alone not able to drive the EL34 to full output?
Well, you see I'm not really convinced yet. However, I would really like to build something like the 3-3, it seems to be a simple and clever and (from what I've read) nice sounding little amplifier.
I would appreciate some thoughts of you more experienced tube hifi people around here. I'm still in the planning phase and have not bought specific parts yet, apart from the parts I have on hand anyway.
Thanks a lot!
I've been reading here a lot but until now I was mainly drawn to guitar tube amps, of which I built and repaired several. Now I'm planning to build my first "Hifi" tube amp.
I do have an old Technics V65A which I restored but I just love to tinker with tubes and have really enjoyed all the stuff I learned (and still learn) when building guitar amps. That's why I decided to build a small tube amp for use in our livingroom. It's a relatively large livingroom but I won't need really loud music, more like low to medium volume, mostly low. I usually listen to a lot of Folk, Jazz, Blues and also Electronic, Ambient or Post Rock music. I'm not particularly looking for the audiophile side of things, but of course, if it's going to sound nice, that's a great plus!
I'm looking for some advice on what to build. I really like the design of the old Mullard 3-3.( Mullard 3-3. Three Watt Amplifier ) It's clever but simple, that's cool. Besides it's been published in the year my dad was born. After he died surprisingly two years ago I always wanted to build something from this year.
My idea was to build a stereo version of the 3-3 using a shared PT, EZ81 or GZ34 and a CLC-supply for B+.
My concerns with the Mullard 3-3 are about the output power. I have an old pair of Heco PCX-2 3-way loudspeakers of which I don't know the sensitivity. Back in the day I think these were some decent speakers but nothing to special. I'm wondering if I can expect "enough" volume from this setup...?
Do you think it's worth building the 3-3 for this setup or will i be disappointed by not enough volume or something? I could still get some higher sensitivity speakers later on but I would prefer if the setup would be usable as is.
I was also thinking about adapting the 3-3 design for another type of output tube. Adapting for a 6V6 should be fairly easy, but would a higher power bottle like a EL34 also be possible? It would of course involve changing the anode and cathode resistors of the EF86 to ensure a proper grid-voltage for the EL34 and also other modifications would be necessary (transformers of course). But would it be a theoretical option or is the EF86 alone not able to drive the EL34 to full output?
Well, you see I'm not really convinced yet. However, I would really like to build something like the 3-3, it seems to be a simple and clever and (from what I've read) nice sounding little amplifier.
I would appreciate some thoughts of you more experienced tube hifi people around here. I'm still in the planning phase and have not bought specific parts yet, apart from the parts I have on hand anyway.
Thanks a lot!
Definitely eliminate the tone controls. Phase compensation in the NFB loop is O/P transformer specific.
If you use this O/P "iron", ultra-linear (UL), instead of full pentode mode, operation of the EL84/6BQ5 "final" can be considered.
Think about saving some $, while keeping performance up, in the B+ PSU. "Full wave" voltage double the O/P of a Triad N-68X isolation transformer. "Snubbed" UF4007 diodes will do quite nicely, here.
If you use this O/P "iron", ultra-linear (UL), instead of full pentode mode, operation of the EL84/6BQ5 "final" can be considered.
Think about saving some $, while keeping performance up, in the B+ PSU. "Full wave" voltage double the O/P of a Triad N-68X isolation transformer. "Snubbed" UF4007 diodes will do quite nicely, here.
Attachments
Thanks Eli for your thoughts!
I was actually considering an Edcor OP for this build, as they are good to come by here in Germany, but I was planning to use the 10W version. Any advantages of the 15W version for this build with 3W output power?
Also, wouldn't the UL mode bring the power further down? What do you mean by "final"? Sorry, I just didn't understand you correctly I guess.
I'm still considering to build this with a EL34. It needs about 12-14Vpp on the grid for full output if I'm not mistaken. This should be possible with the EF86 front-end, no? Some adjustments of the EF86 periphery and it should be possible to bring the bias of the output tube in the right ballpark. I'm thinking that this approach could give me a hair more output power to better suit my current setup.
I will have to check this in Spice when I have time, at the moment I'm only brainstorming.
But still, I would also be happy to build the normal version with EL84 if you think it'll be loud enough.
Thanks also for the Power-Supply advice. Using Diodes for rectification is definitely an option as well.
I was actually considering an Edcor OP for this build, as they are good to come by here in Germany, but I was planning to use the 10W version. Any advantages of the 15W version for this build with 3W output power?
Also, wouldn't the UL mode bring the power further down? What do you mean by "final"? Sorry, I just didn't understand you correctly I guess.
I'm still considering to build this with a EL34. It needs about 12-14Vpp on the grid for full output if I'm not mistaken. This should be possible with the EF86 front-end, no? Some adjustments of the EF86 periphery and it should be possible to bring the bias of the output tube in the right ballpark. I'm thinking that this approach could give me a hair more output power to better suit my current setup.
I will have to check this in Spice when I have time, at the moment I'm only brainstorming.
But still, I would also be happy to build the normal version with EL84 if you think it'll be loud enough.
Thanks also for the Power-Supply advice. Using Diodes for rectification is definitely an option as well.
Just a note on the Mullard design. It is directly coupled (there is no capacitor between the EF86 and EL84) and gets the EF86 screen grid voltage from the cathode of the EL84, about 28 volts.
Altering the design will end in problems, even getting some EF86s to perform correctly can be a problem with some valves...
The BBC used this design in their AM8/2 in the UK, but had to make changes in their later versions of this amplifier the AM8/2A. http://www.bbceng.info/ti/eqpt/AM8_2.pdf
The 3-3 is a sweet amp when working. But personally I would build the BBC AM8/2A version.
If you want more power or a different output valve look for another circuit.
Alan
Altering the design will end in problems, even getting some EF86s to perform correctly can be a problem with some valves...
The BBC used this design in their AM8/2 in the UK, but had to make changes in their later versions of this amplifier the AM8/2A. http://www.bbceng.info/ti/eqpt/AM8_2.pdf
The 3-3 is a sweet amp when working. But personally I would build the BBC AM8/2A version.
If you want more power or a different output valve look for another circuit.
Alan
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I suggested the 15 W. model, as that (with NFB) will surely get you full bass extension. Edcor's GXyy models are rated to 40 Hz. More mass is needed to get down to 20 Hz. and a GNFB loop requires yet more magnetic headroom. "Better safe than sorry."
"Final" is nomenclature for O/P devices, both tube and SS. Alan4411 makes an excellent point about the tricky nature of DC coupled circuitry. 2 stage amps are quite straight forward. Less finicky would be a 12AX7/ECC83 section voltage amplifier RC coupled into the multi-grid O/P tube. Lots of console amps to model for that sort of thing.
BTW, the difference in power O/P between full pentode and UL is (IMO) negligible. A SE EL84 operating in a multi-grid mode will yield approx. 5 W.
Thanks Alan and Eli for your suggestions.
Actually, I find the DC coupling in the Mullard 3-3 quite appealing, mainly because it's a little uncommon. I know it might be more difficult to set up but I'm willing to tinker with the values if necessary.
Thanks also for the clarification regarding UL vs pentode. I will definitely try UL then, especially since the Edcor transformers have the Screen taps anyway.
However, my main questionmark is still if this kind of amp (SE EL84) will deliver enough power to the speakers for low to medium listening levels. But that's hard to tell without knowing the efficiency of my speakers, haha. What would you suggest as a minimum speaker efficiency with an amp like this?
Actually, I find the DC coupling in the Mullard 3-3 quite appealing, mainly because it's a little uncommon. I know it might be more difficult to set up but I'm willing to tinker with the values if necessary.
Thanks also for the clarification regarding UL vs pentode. I will definitely try UL then, especially since the Edcor transformers have the Screen taps anyway.
However, my main questionmark is still if this kind of amp (SE EL84) will deliver enough power to the speakers for low to medium listening levels. But that's hard to tell without knowing the efficiency of my speakers, haha. What would you suggest as a minimum speaker efficiency with an amp like this?
Paul Joppa has provided us with a rule of thumb. Joppa's Rule states that, for "typical" listening spaces, an amp/speaker combo should be capable of 102 dB. SPL peaks, at a 1 M. distance. So, 95 dB. or better sensitive speakers are in order.
Thank you again Eli! This makes me think I might need a larger amplifier to suit my setup. Maybe a Mullard 5-10, Dynaco ST-35 or something like this. Well, I'll wrap my head around the options.
I'm still really tempted to build the Mullard 3-3, as it's a really simple circuit and I've read so much positive about it. However, I'll bear in mind that I'll probably have to tinker with the resistor values to adjust the EF86 Anode voltage to suit the grid-voltage of the EL84. And I might need other loudspeakers als well, haha.
You've definitely helped me getting a better idea of the things to bear in mind.
I'm still really tempted to build the Mullard 3-3, as it's a really simple circuit and I've read so much positive about it. However, I'll bear in mind that I'll probably have to tinker with the resistor values to adjust the EF86 Anode voltage to suit the grid-voltage of the EL84. And I might need other loudspeakers als well, haha.
You've definitely helped me getting a better idea of the things to bear in mind.
From what I've read the 3-3 is supposed to be the best sounding of Mullard's three amp designs, IE, 3-3, 5-10 & 5-20. Most average listening is done at about 1w, measure your amplifier OP going into your speakers sometime, the AC voltage will jump about with music so it's a bit of guesswork but it gives you a rough idea.
All valve amps that use an OPT will need some jiggling of component values etc, but I wouldn't advise trying to cobble different OP stages onto the front end of the 3-3, all valve amps are designed around the OPT and OP stage,that dictates everything else.
To find out if the 3-3 will be loud enough find a half decent OPT and knock it up using wood or whatever to get a quick amp, if it's not to your liking sell the OPT.
Lastly the 3-3 etc is a good amp to build for a "beginner" as it has good plans with the layout given, layout is very important.
Andy.
All valve amps that use an OPT will need some jiggling of component values etc, but I wouldn't advise trying to cobble different OP stages onto the front end of the 3-3, all valve amps are designed around the OPT and OP stage,that dictates everything else.
To find out if the 3-3 will be loud enough find a half decent OPT and knock it up using wood or whatever to get a quick amp, if it's not to your liking sell the OPT.
Lastly the 3-3 etc is a good amp to build for a "beginner" as it has good plans with the layout given, layout is very important.
Andy.
Hey Andy, thanks for your thoughts. This motivates me to give it a go. I might put it together with a pair of Hammond 125BSE OPTs and can still upgrade for a pair of higher quality Edcors or Hammonds later if needed.
I might try and measure the output voltage of my Amp at normal listening levels to calculate the power I'm actually using. I can also feed the amp with a sine wave to check that but its hard to set the volume of a sine wave to a level comparable to music. Well, let's see.
I will definitely study the layout given by mullard but will have to come up with my own design, as I want to build a stereo version. However, I'm confident I'll be able to work out a good layout, I have done this for all my guitar amps so far and never had issues with hum or oscillations. I put a lot of time in planning the layout.
Thanks heaps guys!
I might try and measure the output voltage of my Amp at normal listening levels to calculate the power I'm actually using. I can also feed the amp with a sine wave to check that but its hard to set the volume of a sine wave to a level comparable to music. Well, let's see.
I will definitely study the layout given by mullard but will have to come up with my own design, as I want to build a stereo version. However, I'm confident I'll be able to work out a good layout, I have done this for all my guitar amps so far and never had issues with hum or oscillations. I put a lot of time in planning the layout.
Thanks heaps guys!
