Why do you want to replace the 6AU6? Looks like it's a pretty cheap tube. Found them here: http://www.esrcvacuumtubes.com/vacuumtubes_tubelist_tubes_6A3-6CZ5.html
as well as the 5Y3G.
The only comment that I have is that there is a lot of feedback in that design...
as well as the 5Y3G.
The only comment that I have is that there is a lot of feedback in that design...
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.
Hi,
A good source for valves in the UK is Langrex. They stock all the valves you need for your build.
http://www.langrex.co.uk/
Cheers
Colin.
A good source for valves in the UK is Langrex. They stock all the valves you need for your build.
http://www.langrex.co.uk/
Cheers
Colin.
I don't know who Michael Holden is, but that design bears a more than passing resemblance to
this design from J.E. Calvert in 2001
this design from J.E. Calvert in 2001
ray_moth said:I don't know who Michael Holden is, but that design bears a more than passing resemblance to
this design from J.E. Calvert in 2001
On the link you refer to, the schematic is credited to the RCA Receiving Manual, so perhaps it is from there...
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.
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.
If Langrex run out, and if you can't source them in the UK, then Antique Electronic Supply has both tubes in stock. (Don't get hung-up on the price of postage. The last time I ordered from them it was only about £25. Instead think about the overall cost of getting the job done quickly and effectively).
Their site: http://www.tubesandmore.com/
Their site: http://www.tubesandmore.com/
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?
>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.
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 EF94 grid sits at 3/4 of the cathode voltage, which is unusual. I assume they did it in order to have a higher cathode resistor so the feedback resistor could be higher too so it doesn't load the output too much. There is a bootstrap, true, but I suspect that is accidental as it is not really necessary in a stage driven by an ECC82.
I don't know about "accidental".
To much arrangements for a accidental bootstrap.
I think (IMHO) that they stablish a timbre compromise greater than a performance compromise. we may simply open the plate resistors of the output valves and try it without. Timbre matters always (IMHO). Kind regards. Nafy
To much arrangements for a accidental bootstrap.
I think (IMHO) that they stablish a timbre compromise greater than a performance compromise. we may simply open the plate resistors of the output valves and try it without. Timbre matters always (IMHO). Kind regards. Nafy
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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