• 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.

Small Tube/SS hybrid amplifier design 9V

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#21
Soro,

Nice project!

Dovla,
Interesting link. I used this because I wanted to run the ECC82 from 12V DC. To see what happened!

Bigun,

" Photo's of the inside"

It was done in a few hours so it's a bit of a birds nest!

Because it was in a wooden box I had to screen cables. I used PTFE silver plated cable as a twisted pair covered in foil with a drain wire twisted around the foil, covered with heat shrink!🙂

Regards
M. Gregg
 

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#23
Have you considered abusing an op-amp or emitter follower
as a unity gain buffer to drive the grid in continuous A2?

Bootstrap plate load to increase both voltage and impedance.

Seriously look into capacitive charge pump doubler or tripler.
Also investigate boost switcher ICs for driving a string of LEDs.
 
#24
M Gregg said:
Bigun,
Because it was in a wooden box I had to screen cables. I used PTFE silver plated cable as a twisted pair covered in foil with a drain wire twisted around the foil, covered with heat shrink!🙂
M. Gregg
Click to expand...

It looks pretty dapper to me, nicely done !

p.s. my amp is also a bit of a birds nest, I'm the process of trying to tidy it up but I'm not sure its worth the trouble.
 
#26
kenpeter said:
Have you considered abusing an op-amp or emitter follower
as a unity gain buffer to drive the grid in continuous A2?

Bootstrap plate load to increase both voltage and impedance.

Seriously look into capacitive charge pump doubler or tripler.
Also investigate boost switcher ICs for driving a string of LEDs.
Click to expand...

Post a few circuits! LOL

A bit off topic:

I am building an Aikido pre using recom DC to DC for the heaters and inverter for the HT 450V with 350 V 60mA regulation at the moment. Also EM81 Vu meters. Run from 12V power supply. I will post this in another thread when complete! 🙂

Its an on going project!

Regards
M. Gregg
 
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#30
If you don't mind building a power supply, get a 12VAC transformer, stack a six stage voltage doubler on it, smooth it with a couple pi filters, and run your tube off that. This will get you a quiet, high enough voltage to make a high quality amp. Use a lm7812 for both your heater and the output stage. I did a lot with the lm386 in my beginnings, and honestly think their gain is too high to use a tube in front of them for hi-fi. I'd just build a Szekeres mosfet follower, and drive that with the tube, that's my favorite low-watt hybrid amplifier setup.
 
#33
M Gregg said:
Soro,

Did you have any problems with vibration microphonics?

Where did you put it in the circuit " Car stereo"?🙂
Click to expand...

No it is not has any vibration microphonics.
sound is good and sweet.
you shall try it.
this is prototype.
it can use 6DJ8 6922 12AU7
(also 12AX7 but must change some thing)
more choose more fun
 

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#36
Well, my build is coming along. I just completed the 12.6VDC linear power supply last night.
I've got the Vero board layout complete, and all the parts, so I'll start building this weekend. If any one wants the Vero board layout, I can post the link here.

Stay tuned for pictures. Thanks again everyone for the suggestions.
Glenn

Again, here's the circuit I'm building:NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier

Here's the Vero board layout: http://webpages.charter.net/porkchop/tubeamp/12AU7%20Headphone%20amp-%20Vero%20board%20layout.jpg
 
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#37
Okay, I've got it built and now we move into the troubleshooting phase 😀
I'm using the 10k trim pot to try and set the voltage to 1/2 the power supply
voltage of 12.6vdc. I can only get down to 9.5v using the full 10k of the pot.
Now I can add a resistor in front of the pot to get me there, but it seems like
something isn't working correctly. The schematic says that you can use a 4.7k
resistor instead of the pot, but I set the pot to the 4.7k value before testing, and I was still getting around 12v. Seems like something isn't drawing enough current? Maybe the MOSFET?
Any ideas? Both channels are working the same, so I don't think it's a wiring issue.

Thanks
Glenn

Edit: Does this circuit need to be loaded on the output to work??
maybe that's the problem?
 
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#38
This may be of help from the forum;

1) In: Photograph 14: Setting the Bias "Adjust the two trim potentiometers to one-half of your supply voltage, 6 volts since we are using a 12v supply. "

Where should the 6v be tested for - at the junction of the FET Source and the LM317's 'IN'?
Heh - I've been testing AT the plate - only can get that down to about 9.2 volts or so... I'm guessing I'm testing in the wrong spot...

Yes, or at the postiive lead of your output electrolytic.

Link

NP-100v12 - 12AU7 / IRF510 HeadAmp Support Thread • DIY Audio Projects Forum

Regards
M. Gregg
 
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