807s, a couple of transformers, New Year's Day build
I had a rather quiet New Years' holiday, and I decided to clean out my shelves in the shop. While looking for a power transformer for another project, I found an output transformer whose lineage I traced to a Sears PA amplifier. I had a power transformer, some chokes, a reused chassis, three 807s and plenty of capacitors. So I thought: "why not build an amplifier?" So I got out my Greenlee chassis punch and went to work.
Here's a closeup of my 807 amplifier:
Here's the spectral output of the 807 amplifier:
At moderate signal levels, THD is below 0.05%. At full power, it remains under 0.2%. Power bandwidth improved with the addition of negative feedback. Initially, the low end only extended to 60Hz due to the speech grade output transformer. With NFB, full power extends to 35Hz and half power, an octave below that. HF is limited at high power levels, again, due to the transformer, but at moderate levels, it extends well past 20KHz.
Here is the waveform showing the symmetry of clipping and stability when overdriven:
Part of the good performance despite mediocre transformer is due to this servo balanced cathode coupled phase inverter. A transistor looks at a voltage divider between the phase inverter plates and balances the cathode current until the differential approaches zero. The result is a self-balancing differential drive for the output tubes. The amplifier comes up to full performance within 11 seconds of turn on.
Listening test with the 807 amplifier:
Despite the lack of good iron, the amplifier sounds quite good for its diminutive 50 watt output and will give many expensive 'boutique' amplifiers a run for their money.
I had a rather quiet New Years' holiday, and I decided to clean out my shelves in the shop. While looking for a power transformer for another project, I found an output transformer whose lineage I traced to a Sears PA amplifier. I had a power transformer, some chokes, a reused chassis, three 807s and plenty of capacitors. So I thought: "why not build an amplifier?" So I got out my Greenlee chassis punch and went to work.
Here's a closeup of my 807 amplifier:
Here's the spectral output of the 807 amplifier:
At moderate signal levels, THD is below 0.05%. At full power, it remains under 0.2%. Power bandwidth improved with the addition of negative feedback. Initially, the low end only extended to 60Hz due to the speech grade output transformer. With NFB, full power extends to 35Hz and half power, an octave below that. HF is limited at high power levels, again, due to the transformer, but at moderate levels, it extends well past 20KHz.
Here is the waveform showing the symmetry of clipping and stability when overdriven:
Part of the good performance despite mediocre transformer is due to this servo balanced cathode coupled phase inverter. A transistor looks at a voltage divider between the phase inverter plates and balances the cathode current until the differential approaches zero. The result is a self-balancing differential drive for the output tubes. The amplifier comes up to full performance within 11 seconds of turn on.
Listening test with the 807 amplifier:
Despite the lack of good iron, the amplifier sounds quite good for its diminutive 50 watt output and will give many expensive 'boutique' amplifiers a run for their money.
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Push pull mono. However, I do have a sinister idea that I'm working on in my spare time, which is to time division multiplex the input, using analog switch, and the outputs, using solid state relays, to synthesize stereo from one amplifier. It's a rather ambitious undertaking and I don't expect hi-fi results. But it will be an interesting and novel experiment for fun.
Schematic is in my head. That's how I've always worked. Too lazy to sketch things on paper anymore!!
Schematic is in my head. That's how I've always worked. Too lazy to sketch things on paper anymore!!
Woah there is some serious tube work in this thread!
I just posted those pictures in the new member section but a mod suggested I copied them here. That is a modest - I'm almost ashamed to post here when I see the expert work being done by you guys - hybrid headphone amplifier called the NP-100V12 by Rogers Gomez. That was my first point to point build and I really loved the process. The amp sounds great too.
Comments and critics are welcome!
I just posted those pictures in the new member section but a mod suggested I copied them here. That is a modest - I'm almost ashamed to post here when I see the expert work being done by you guys - hybrid headphone amplifier called the NP-100V12 by Rogers Gomez. That was my first point to point build and I really loved the process. The amp sounds great too.
Comments and critics are welcome!
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Comfortably -- Yes! A wonderful build, very, very good work. You should be proud.
Sincerely looking forward to seeing more of your constructions.
EDIT - I need to add, you made very good use of tabs, legs and terminals to secure the other bits. Bravo!
Thanks much 6L6. I'm happy to read the positive comments. That's encouraging for my future builds. Next in line : Millett Starving, a bench regulated PS (somewhat boring) and the AX84 P1 guitar amp.
Happy to read I made good use of those terminals. I looked at many pictures of the Bottlehead Crack (would you have guessed) and tried to replicate things that I saw in this amp.
I agree with these comment!
Nice preamp can you share the schematic with us.
Greetings
I agree with these comment!
Nice preamp can you share the schematic with us.
Greetings
Thanks Gabor. It's a headphone amp
Schematic is here NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier
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My first tube project.
It's and Aikido 6SN7 based preamp with balance controls (tube rectified) and can accept 3 inputs.
I'm in the process of building a Aikido based Head Phone Amp and perhaps even build it as a dual purpose Pre and HP Amp. The board has been completed (it uses 6SN7 tubes as well!) although I haven't started the PS yet.
Best Regards,
TerryO
Woah there is some serious tube work in this thread!
I just posted those pictures in the new member section but a mod suggested I copied them here. That is a modest - I'm almost ashamed to post here when I see the expert work being done by you guys - hybrid headphone amplifier called the NP-100V12 by Rogers Gomez. That was my first point to point build and I really loved the process. The amp sounds great too.
Comments and critics are welcome!
Bon jour to the neighbours in La Belle Province from Ontario (like the rest of the 98% in Ontario, here my French is somewhere between bad to poor). Other than the Habs and having the most hottest women in Canada, I welcome you and your tube amp.
Though there are some expert level builders here, I don't think that you ought to be ashamed of what you put together. In fact, pretty sweet if you ask me. How long did it take you?
Is this your first tube amp or have there been others? And what headphones are you using with this amp?
Howdy. I have to agree our women are the bestest
Thanks for the kind comments. That was my first tube project and first point to point project. Purists will say it's not really a tube project since it's a hybrid and it runs on 12V but what the heck. I like it and I enjoyed the build.
As for the time spent :
- 4 hours reading everything about the project
- 2 hours stealing ideas on forums
- 2 hours discovering how the Digikey website works and ordering the parts
- 2 hours trying to get an acceptable finish on that &*$%#? industrial aluminum sheet
- 1 hour drilling
- 3 hours soldering all together
I first built the base out of MDF but it was so ugly. So I had another base made by a local woodworker.
That's a lot of time. I'm slow!
I have a pair of Sennheisers HD580. Lovely headphones.
10Wsin PL502
PL 502 amplifier tubes and 6N2P ev config . SE
An externally hosted image should be here but it was not working when we last tested it.
PL 502 amplifier tubes and 6N2P ev config . SE
Next my experiment PSE 815 RCA. I like this great tube. Incredible, detail, deep, clear sound....IMO, maybe close to 300B. This tube needs Hi Quality OT.
Pretube 6Н8С, left tube not used.
U plate about 290 - 300 V. /I haven't 400 v, that is need/. I plates 100-110 ma from both parts in balloon. Very comfortable driving -U bias -9-10 V.
Price of tube 12$. You can try with more +U and more current for better sound and more power in PSE.
https://picasaweb.google.com/109570777566485968551/Amplifiers#6108235820775591122
815 - double pentode for PSE or PP /something like 6L6, EL34.../.
Thanks Chris from San Diego for advise.
Pretube 6Н8С, left tube not used.
U plate about 290 - 300 V. /I haven't 400 v, that is need/. I plates 100-110 ma from both parts in balloon. Very comfortable driving -U bias -9-10 V.
Price of tube 12$. You can try with more +U and more current for better sound and more power in PSE.
https://picasaweb.google.com/109570777566485968551/Amplifiers#6108235820775591122
815 - double pentode for PSE or PP /something like 6L6, EL34.../.
Thanks Chris from San Diego for advise.
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The only difficult part of building an Aikido amp is getting rid of the hum which always seems to be grounding scheme related, but the sound is great coming from these.