Hi Everybody
After two amps delivering less than 8W and a nice headphone tube amp I am looking for a new tube amp project.
Outline:
- Monoblocks to have an "optically" less heavy chassis layout
- around 20W output power to power my new speakers
Unfortunately I am not having the competences to design that thing, so I am looking for some schematics.
I found this one which looks quiet nice to me, being simple. Don't know though if the design is good or not.
I would appreciate some comments, or a schematics for a working design.
Thanks a lot and best regards
Christoph
After two amps delivering less than 8W and a nice headphone tube amp I am looking for a new tube amp project.
Outline:
- Monoblocks to have an "optically" less heavy chassis layout
- around 20W output power to power my new speakers
Unfortunately I am not having the competences to design that thing, so I am looking for some schematics.
I found this one which looks quiet nice to me, being simple. Don't know though if the design is good or not.
I would appreciate some comments, or a schematics for a working design.
Thanks a lot and best regards
Christoph
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Go for a push pull amp. Everybody will advise you to try the "engineers amp" designed bij Pete Millett. google his website and look for the thread on this forum. You cannot go wrong with this one. Best price/performance ratio, no risks.
The Mullard 5-20 is nice for its time, but not very compatible with modern standards. A little too sensitive , and who wants to use a wasteful vacuum rectifier?
I like the simplicity (I don;t like transistors in my tube amp). I would probably replace the EF86 with a triode too.
Still a good stating point for modifying. Would make a nice point-to point construction. Are you up for experimenting?
I like the simplicity (I don;t like transistors in my tube amp). I would probably replace the EF86 with a triode too.
Still a good stating point for modifying. Would make a nice point-to point construction. Are you up for experimenting?
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Too sensitive? Increase R5 to increase the negative feedback and reduce the gain. Replacing the EF86 with a triode will spoil the whole system. Vacuum rectifier ... If you want solid state, go for it but remember the voltage differences!
What is "the system" and how is it spoiled? 😕
But, true, will need tinkering to work, including tuning the feedback parts with a scope. You and me could do it, but the OP hs to confirm he's up to it.
Referring to the schematic in the original post, a single EL34 cannot produce 20W at 300V of plate voltage, it´s rubbish. Apart from that the EL34 symbol in the schematic is wrong, G1 and G2 should be inverted (although pin numbers of the connections are correct).
Apart from that it is a really conventional amp, but the other amps posted are much better options.
Apart from that it is a really conventional amp, but the other amps posted are much better options.
The schematic in the original post shows some kind of 'screen drive,' not a normal EL34 circuit configuration. Funny that the circuit description makes no mention of this. I'd be wary...
@costis_n - I think the 'system' is the whole circuit taken together. The reason the Mullard 5-20 works is that the pentode has lots of gain (making the amp very sensitive) which can be used to add negative feedback, which reduces the gain/sensitivity and also reduces noise and distortion. Of course the gotcha is that it also reduces stability, but the Mullard 5-20 is less problematic vis-a-vis stability than the Williamson, for instance.
@cgraf - Did you mean 20 watts per channel, or 20 watts total?
If 20W total (10W per channel), there are lots and lots of those. Most any push-pull triode EL34 amp will do that, and push-pull EL84 ultralinear or pentode will do that too. Poinz' Musical Machine and gingertube's Baby Huey spring to mind. There's also SY's Red Light District and Morgan Jones' Beavois Valley Amplifier in Valve Amplifiers 3rd edition.
If you meant 20 watts per channel, then there are quite a few of those to choose from as well. Pete Millett's DCPP looks great, but it is kind of a complex build since it has so many parts. However, it is the 'Engineer's Amplifier.' Any push-pull 'ultralinear' EL34 or 7591 amp you find will deliver that kind of power. There's a thread here where Eli Duttman is collaborating with a member on a build called 'El Cheapo Grande.'
Maybe talk to member Tubelab, he sells circuit boards for a few different designs -- Tubelab | Dedicated to advancing the state of the art in affordable high end audio.
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@costis_n - I think the 'system' is the whole circuit taken together. The reason the Mullard 5-20 works is that the pentode has lots of gain (making the amp very sensitive) which can be used to add negative feedback, which reduces the gain/sensitivity and also reduces noise and distortion. Of course the gotcha is that it also reduces stability, but the Mullard 5-20 is less problematic vis-a-vis stability than the Williamson, for instance.
@cgraf - Did you mean 20 watts per channel, or 20 watts total?
If 20W total (10W per channel), there are lots and lots of those. Most any push-pull triode EL34 amp will do that, and push-pull EL84 ultralinear or pentode will do that too. Poinz' Musical Machine and gingertube's Baby Huey spring to mind. There's also SY's Red Light District and Morgan Jones' Beavois Valley Amplifier in Valve Amplifiers 3rd edition.
If you meant 20 watts per channel, then there are quite a few of those to choose from as well. Pete Millett's DCPP looks great, but it is kind of a complex build since it has so many parts. However, it is the 'Engineer's Amplifier.' Any push-pull 'ultralinear' EL34 or 7591 amp you find will deliver that kind of power. There's a thread here where Eli Duttman is collaborating with a member on a build called 'El Cheapo Grande.'
Maybe talk to member Tubelab, he sells circuit boards for a few different designs -- Tubelab | Dedicated to advancing the state of the art in affordable high end audio.
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Screen and control grid are swapped as noted above, more importantly the bias supply polarity is incorrect, should be negative. This is not a screen driver design. Such a glaring error and the claims of 20W of power makes me believe this is an intellectual exercise or a poorly vetted build.
The Engineer's amp, the red light district or something else would be better candidate.
Piling on, there is no way that 20W is going to come out of an EL34 SE design.
FWIW, the Engineer's Amp is good for 35 watts/channel, the Red Light in its most recent version is about 25 watts/channel. I have both and would have trouble choosing between them. The Engineer's has the advantage of an available circuit board, the RLD is strictly point to point.
FWIW, the Engineer's Amp is good for 35 watts/channel, the Red Light in its most recent version is about 25 watts/channel. I have both and would have trouble choosing between them. The Engineer's has the advantage of an available circuit board, the RLD is strictly point to point.
Oops, sorry SY. I stand corrected. I didn't know the RLD could make that much power.
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...and looking at the schematic...
Yowza! 47k grid stoppers on the EL84's.
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...and looking at the schematic...
Yowza! 47k grid stoppers on the EL84's.
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Hi guys
I appreciate your answers 🙂
@rongon: 20W per channel would be optimal for the speakers, but I tried a 10W class A solid state amp this afternoon and the power was sufficient as well... so the choice is open.
I will stick on my idea to build two monoblocks for design reasons although more expensive. So I will start looking at the Baby Huey, but also at the red light district (have been in Amsterdam 2 weeks ago but no time to visit the RLD)...
Thanks Stuart for the schematics. Do you also have the power supply schematics and the specs for the trannys ?
Regards Christoph
I appreciate your answers 🙂
@rongon: 20W per channel would be optimal for the speakers, but I tried a 10W class A solid state amp this afternoon and the power was sufficient as well... so the choice is open.
I will stick on my idea to build two monoblocks for design reasons although more expensive. So I will start looking at the Baby Huey, but also at the red light district (have been in Amsterdam 2 weeks ago but no time to visit the RLD)...
Thanks Stuart for the schematics. Do you also have the power supply schematics and the specs for the trannys ?
Regards Christoph
There's a reason for that, and you can actually go higher.
Originally, it was about 15 watts, but I took a hint from Roger Modjeski and went much higher on B+ and lower on idle current, and lo and behold, 25 watts out! He does a few other things and claims 40W out of a pair of EL84, and I believe it.
if ss 10w is ok you can go with a single ended 300B 7w, tube as have soft clipping sound like have more power
You should look for Single ended El34, KT88 or better FU13.
SE EL34 and KT88 ar cheap to build and can sound very good.
SE EL34 and KT88 ar cheap to build and can sound very good.
300B or KT88 sounds not bad either, nice big tubes.For single ended I would even have two new james-6123 HS left from a recent visit to taiwan...
@nicoch58 and @koifarm: do you have any working schematics for your ideas?
regards Christoph
@nicoch58 and @koifarm: do you have any working schematics for your ideas?
regards Christoph
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