• 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.

Tube amplifier

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Hi everyone, just wondering as I am about to build my first tube amplifier is the attached design o.k. and also does anyone know a suitable replacement tube for a 6AU6 driver tube and a 5Y3G rectifier.
Here is the amplifier schematic...
FUNZIKGFWEGK7VT.jpg

...and the power supply schematic.
FGQTZT4FWEGK7Q6.jpg
 
I need a replacement for the two tubes as I live in the UK and cannot find a UK supplier that stocks them. I don't want to order form the US because of the high postage costs. Also, if a suitable replacement can not be found could someone possibly give me a website address of a UK supplier that stocks the 5Y3G and the 6AU6.
 
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Yes, you must be right, I didn't notice the label in the schematic. I was going by the credits at the foot of the page -

Composed by J. B. Calvert
Created 30 October 2001
Last revised 2 November 2001


Looking at the circuit, the operating points are strange, don't you think? Whoever runs a 12AU7 with a 220k plate load? 330k for a 6AU6 plate load is also odd, because it suggests a very low plate current for a tube that, as far as I know, runs best with about 3 to 5 mA plate current.
 
Thanks for all of the replies and the help. Yes, the schematic was originally from the RCA manual as explained here. I just have a few more questions:

>Is the power amplifier circuit in the image that I posted just a redrawn version of the RCA circuit or does is it different (the RCA circuit diagram seems to be drawn a bit more clearer to me)?

>Will the amount of feedback and the plate load affect the amplifier in any way?
 
The schematic is a redraw but I made no changes to my knowledge. I found that schematic hard to read and drew it to my liking.

If you wish step 14 has a better resolution and more detail: http://www.instructables.com/id/6V6-Pushpull-Calss-AB-Tube-Mono-Amp/

This is the article that inspired me to try the circuit from the RCA receiving tub manual:

Composed by J. B. Calvert
Created 30 October 2001
Last revised 2 November 2001

He did a great article on the function of the amp. I took his word about the performance and he was rite.

This amp suits me just fine. There are probably beater amps out there. My goal was to see what 10 watts will sound like with a speaker with an spl of 100 dB or better. I am officially now a low watt high efficiency fan.

Cheers to all.
 
The resistor which is bootstrapped is not normally present, as the normal cathode bias arrangement does not need a resistor from cathode to grid. They needed this resistor to establish the correct bias, as the cathode resistor was too large to do this in the simple way. This extra k-g resistor is bootstrapped but I don't think it would matter if it were not, hence my suggestion that the bootstrap is accidental. I don't mean they don't realise it is bootstrapped; I mean that the boostrap is unnecessary but happens to arise from a circuit arrangement which they need for other reasons. I have no idea at all what this will do to 'timbre'.
 
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