• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

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Hi GlossMaster,

What input impedance did you order for the Tortuga board? The default 20K or a different value?

Do you notice any heating effects, using the LDR module?

Regards, Gerrit

Hello Gerrit
Yes, default 20K impedance. No I have not noticed any heating effects but also did not pay attention specifically to it. However, i might have noticed something was off if that would have been the case.

Stephan
 
Got a pair of red tubes. Looks cool. Sounds the same.

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a colorful line preamp...

..full of magic eyes :)

two 1629 as voltage amplifiers and one dual EM83 to dance to the music (switchable)
OK, there is also an ECC82 as CF hidden inside ;)
 

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So, could we look inside?

it's a bit of a mess currently and I plan to rearrange and tidy up.

with regard to pcb's, the one on the left is a proximity sensor on/off switch, right is the EM83 driven by a NE5532 and top is the HV capacitance multiplier together with a slow turn on filament supply based on LT1086 and 2N4036
 

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Pandemic project #2

Got my second pandemic work-from-home project finished. It started from meddling with PCB layout software just to not forget how to do it. First I laid out the PCB and saw that it may be a base for a decent amplifier so I built one. My daughter named it and will get it as a gift.

It runs a cathodyne phase splitter on 6N23P and Svetlana black anode 6P31S in a push-pull no feedback configuration. All large transformers are Hammond: 370JX for power and 1620 as OT. Input signal transformer is from LEHLE and this is the first time I tried these products and they do sound impressive.

Cathodyne has direct coupling between gain stage and split load stage.

Max output power is app 12W. Hum at the output is at 0.1-0.2mV rms.

Quite happy with the sound quality!
 

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:cheers: Nice work!

Got my second pandemic work-from-home project finished. It started from meddling with PCB layout software just to not forget how to do it. First I laid out the PCB and saw that it may be a base for a decent amplifier so I built one. My daughter named it and will get it as a gift.

It runs a cathodyne phase splitter on 6N23P and Svetlana black anode 6P31S in a push-pull no feedback configuration. All large transformers are Hammond: 370JX for power and 1620 as OT. Input signal transformer is from LEHLE and this is the first time I tried these products and they do sound impressive.

Cathodyne has direct coupling between gain stage and split load stage.

Max output power is app 12W. Hum at the output is at 0.1-0.2mV rms.

Quite happy with the sound quality!
 
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Where did the chassis come from and how did you do the artwork and lettering? Silk-screen?

Thank you!

Case came from ebay, from a Chinese seller. They come in native aluminum, needs to be drilled and painted afterwards.

I use multiple coats of spray primer with sanding in-between, and one finish coat of spray paint.

They are white for a reason :) as labels are laser printed waterslide decals so for highest contrast it is black letters on white background.

After a day or so of drying, a thin spray coat of transparent polyurethane to protect the surface is finishing the process.
 
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Got my second pandemic work-from-home project finished. It started from meddling with PCB layout software just to not forget how to do it. First I laid out the PCB and saw that it may be a base for a decent amplifier so I built one. My daughter named it and will get it as a gift.

It runs a cathodyne phase splitter on 6N23P and Svetlana black anode 6P31S in a push-pull no feedback configuration. All large transformers are Hammond: 370JX for power and 1620 as OT. Input signal transformer is from LEHLE and this is the first time I tried these products and they do sound impressive.

Cathodyne has direct coupling between gain stage and split load stage.

Max output power is app 12W. Hum at the output is at 0.1-0.2mV rms.

Quite happy with the sound quality!


That THD plot is that at 12W output power?
 
Here is the circuit diagram for the PCB which was used for layout. It is not that easy to read because of that but the signal chain is an input transformer, volume control (Noble 10K stepped), gain stage and the split load stage. Output stage is external and wired point to point.

Plate current of both halves of 6N23P is about 3mA.

370JX is technically capable of delivering all of the voltages required for the operation of the amplifier but I used a separate small transformer for bias generation. 370JX is designed to support almost all of the AC line options, but not mine :) so the bias tap is at the edge.

Typical 6P31S operating point is 290V/40mA/-50V.
 

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There is one thing I particularly happy with in this design. Tubes with a nipple on the top for plate connection are always a challenge as those 'standard' plate caps are not really sitting tight and firm on the top. For an unexperienced user it is a safety concern if the plate cap could easily go off.

I used a solid core thick copper wire which was bent as a spring to push the cap onto the tube. It worked surprisingly well and produced a very sturdy assembly.

Another interesting thing is I listened to a number of sweep tubes in triode without a top nipple (GE and Westinghouse 6AV5) before ending up with the one which got this additional challenge. Distortion profiles did not look that much different from 6P31S but the sound of 6P31S was clearly at a different level.

Sorry, I forgot to mention that 6P31S is in triode!!
 
Re: distortions.

I used 96/24 WAVs for generating the test signal for distortion measurements running them on Yamaha network player. The project was actually to build a cathodyne driver so I measured that one separately. Here are the distortion plots for 1kHz and standard bi-tone IMD test signals for cathodyne output which produces 1W into 7.5R active load at the output. The last one is a 1kHz from Yamaha.
 

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