• 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.

6N3 Tube Preamp with DC-DC converter

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#6
I found the schematic that it came with...I'll post it up after I get back from the library...It claims to only boost the voltage up to 30volts which seems really weak to me...

Anyways, I built one and it sounds ok for the price...I think that it is better suited to instruments than to HiFi...Guitar sounds amazing...
 
#12
Twin voltage multipliers followed by discrete regulators to produce +/-30V.

Weird, but you can get more current (at the same ripple voltage) from two voltage doublers than you can from one voltage quadrupler with the same capacitor values. So it makes sense, in a strange way.
 
#13
lazzer408 said:
Yup.

Too bad it's from China or I'd grab one to try it. I'd hate to post my opinion 2 months later when I receive it.
Click to expand...

I buy fairly small stuff (<5lbs or less) from eBay sellers based in China regularly, and the shipping time by air is usually a week or less all the way to Boston. The product quality is of course variable, but you usually know that going in. Can't say I have had any significant problems either.. (I won't however buy anything that could be regarded as a knock-off of someone else's product.)
 
#14
TheGimp said:
Twin voltage multipliers followed by discrete regulators to produce +/-30V.

Weird, but you can get more current (at the same ripple voltage) from two voltage doublers than you can from one voltage quadrupler with the same capacitor values. So it makes sense, in a strange way.
Click to expand...

I don't think that the power supply puts out + and - 30 volts.
More like + and - 15 volts. 30 (absolutely max) total volts.
 
#15
Why not? 12.6 * 1.414 * 2 = 35.6V

Given that the regulator can work with less than 5.6V drop, it should be capable of +/-30V with two voltage doublers.

Simulation shows 28.57V after 10 seconds (6K8 * 220uF is a long rc time constant).
 
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#16
TheGimp,

You're absolutely correct. So this little buffer operates on 60 or so volts rather than the 30 volts as stated by nige838. Might actually sound pretty good with 60 volts across the tube. I'd still like to see a bit more voltage. Perhaps if you used a 15 volt transformer. You'd probably need a voltage dropping resistor on the input of the 78L05 regulator to keep the input voltage in the safe area.

Looking at the 78L05 regulator with a 1N4001 from the GND pin to the common side of the 12V supply. Wouldn't you need a pair of 1N4001 diodes to bring the output of the regulator to something near 6.3 volts?
 
#17
I agree that two diode drops would be much better.

In addition, I doubt a 78L05 will be able to dissipate the power necessary to drive the heater given that the spec for the 6N3P is 350mA at 6.3V.

I expect regulator dissipation to be above 2 Watts so a 78M05 might work (rated at 0.5A) but a 7805 would be even better.

I just went and looked at the sale site and they are using a L7805 with a heat sink. So the schematic is slightly out of date / incorrect.
 
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#18
Hi all, i'm reading this debate with interest as i have the exact kit and 15volt transformer. I've built the kit, but as my mains are quite strong, i'm getting nearer 18volts unloaded from the transformer. What do people think, should i try it or put a couple of resisters to drop the voltage slightly first?

Cheers
 
#19
DIYNick said:
Hi all, i'm reading this debate with interest as i have the exact kit and 15volt transformer. I've built the kit, but as my mains are quite strong, i'm getting nearer 18volts unloaded from the transformer. What do people think, should i try it or put a couple of resisters to drop the voltage slightly first?

Cheers
Click to expand...

Find a 12vac transformer and let us know what the voltages really are. 😀
 
#20
Thanks for entertaining the idea...

TheGimp said:
I agree that two diode drops would be much better.

In addition, I doubt a 78L05 will be able to dissipate the power necessary to drive the heater given that the spec for the 6N3P is 350mA at 6.3V.

I expect regulator dissipation to be above 2 Watts so a 78M05 might work (rated at 0.5A) but a 7805 would be even better.

I just went and looked at the sale site and they are using a L7805 with a heat sink. So the schematic is slightly out of date / incorrect.
Click to expand...

This doesn't use a 6n3P, it's a CHINESE 6N3, totally different tube. Your right about the IC, they do use the L7805CV on the two that I bought...One sounds great with little hiss/buzz, but the other has a horrible hiss that appears and disappears...

I was wondering if I can feed the output of one channel into the input of the other to bridge the amp.? I can't see any reason why I can't, except for the volume control...it's definitely not matched...I use the one with the hiss as a guitar preamp...

oh yhea, and I run this with a 12v 2amp wall wart...don't know if that matters or not...

Then I run it into Mr. Helder's TA2024 amp, then into a TK2050. I wish I knew more about what causes hiss and hums..

I don't know, for $20 it's hard to go wrong...I would like to know if anybody can find a schematic on this tube, I haven't been able to...I've thought about using a 12ax7 or something instead.

Also, if I used a 12ax7, I could just chunk half of the power supply and power the plate with this, what do you think?

http://cgi.ebay.com/Car-Auto-Charge...ltDomain_0&hash=item230a643e33#ht_4374wt_1071

I could safely make the 110v, right? I've just been playing with low voltages so far...
 
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