• 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.

Russian 6R2P for small amp.

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Well thats a good suggestion sir wavebourn...i will take note on that and maybe a 33 to 100 ohm will be suitable enough for the anode and screen grid and planning an opt of 3.8Kohm primary...will this be good enough sir?

using the 16ohm tap of your opt instead of 8 ohms to connect your 8ohms speaker lowers the reflected impedance to half of 5.6k aa load.....

anode stoppers are needed only when you encounter oscillations otherwise screen grid stoppers are fine.....
 
hi sir sir tony nice to have you dropping by....yes i had tried using 5 volts dc power supply from PS2 to supply the filament of small tubes and i cant hear any difference in sound. In these case the 6R2P are using 6.3 volts ac but i put a series 0.5 ohm resistor to reduce to about 6v per tube and even the 6N16B's...

just waiting for the OPTs to finish and evaluate the sound...
 
Noted sir...i dont put yet anode resistors but on grid i put 82 ohms 2 watt metal film resistors which i have...

all resistors used closely matched using DMM and other are perfectly matched


not really required to match resistors, the tube are not matched anyway, if you want you can put trimmers to get to the operating point you like....

i use carbon composition resistors on anything grid.....
 
Amp tested, no smoke, it sound but not loud enough even for 5w amp. I indicate red measurement voltage of the actual schematics. can anybody help me what is the cause of the lacking gain maybe...i tried to use my aikido preamp with gain of around 30..with it get a little louder and distort at max gain...one thing more is when i connect the passive tone control associated with the aikido preamp the sound output is whisper loud. i still want to test it with higher efficiency speaker...

Phase splitter supply and grid is regulated only the anode is separated.amp is dead quiet but lacking gain...
 

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Everything looks fine, except if you drive one half of symmetrical input you need twice higher voltage.

hi sir thanks, by the way i have parallel ouput, one tube paralleled that's why the current at anode is 70ma...

"except if you drive one half of symmetrical input you need twice higher voltage." what do you mean by this sir?...i have grounded one of the phase splitter input as suggested. so i have to increase the plate supply of the splitter?
 
No, not plate supply. The author specified voltages to drive the amp, 0.81V peak to peak each in respect to ground, on each symmetrical input. That means twice higher driving voltage between grids. If you ground one grid that means you need 1.62V peak to peak on an opposite grid.

Got it, thanks....but I tried to drive it with a aikido preamp with a gain of 30 but still seems very weak....Im expecting at around 10 w of ouput the by hearing alone but for me, it's not even 5w... maybe i should have a good speaker and have to borrow oscilloscope to see.

is there any possibility to increase the gain or modify the input circuit for standard single input?
 
Yes, it is a good idea to borrow oscilloscope, as well as to have more sensitive speaker.
To increase sensitivity you can use one more 6N16B tube. One half with resistor in anode, another half as a Conertina phase splitter. Excess gain you may reduce by negative feedback.

okay thanks that what im thinking to provide prestage circuitry with another 6N16B...do you have reference concertina PS schema sir?
 
what speakers are you trying to drive?

This one sir, a self made box with selectable impedance from 4 to 16, i use 8 ohms with box rated 100w 8 Inches woofer. 2 outside 2 inside the box...assume to have at least 80 % efficient. used for testing my other tube amp and provide good results but with this thing it can hardly drive.
 

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To increase sensitivity you can use one more 6N16B tube. One half with resistor in anode, another half as a Conertina phase splitter. Excess gain you may reduce by negative feedback.

Is it like this one ? dunno how much gain in it but I think this will be sufficient enough to provide extra gain. will I still need to have negative feedback to dictate or control the overall gain?
 

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