Well silence is golden... I have received the AR FU29 and run it up. This amp definitely sounds much better than any of the solid state gear I have, including a high end MOSFET power amp the manufacturer of which I will not name. The build quality of the AR FU29 seems quite high with metal film resistors and ceramic tube sockets. Just my impression on initial run up using a Cambridge Audio Azur 640C as input, but time will tell.
I have one of these i bought used for a cheap price. It has some issues, so I'm gutting it and rebuilding the power supply and circuit. I will rebuild so i can bias each section of the tube independently and will be adding bias pots and test points to the chassis so i can bias from outside the unit. Here is the circuit showing the changes i propose. Please let me know if you see any errors. Has anyone seen a schematic of the power supply online?
I read the attached and decided against using the lm317 regulator and I'm not crazy about the balance adjustment so that is why i have decided to go this route.
Here is the pdf discussing the lm317 bias regulator mod.
I read the attached and decided against using the lm317 regulator and I'm not crazy about the balance adjustment so that is why i have decided to go this route.
Here is the pdf discussing the lm317 bias regulator mod.
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OK i have gutted the amp and plan on building the new circuit board with eyelets. The preamp tube socket will chassis mount nicely so thats a bonus and i will likely drill hole in the circuit board for accessing the tube connections. This may take a while, but i will post as i go and post the power supply schematic when I figure it out.
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i converted on such amp from fixed bias to cathode resistor bias and the amp still works till today...that was about 5 years or so ago..
with the 829b, red plating in one section is a problem with such tube types, you have to have several on hand, the 5894 otoh, being a single cathode construction is a better tube to use imho, i used the amperex 5894 tube in place of the 829b...
with the 829b, red plating in one section is a problem with such tube types, you have to have several on hand, the 5894 otoh, being a single cathode construction is a better tube to use imho, i used the amperex 5894 tube in place of the 829b...
the circuit is a mullard 5-20 derivative, i use that topology a lot,
the last time i made one is using a 5814 voltage amp and 6SL7 ltp, i like the combo..
yes, you have to put a 10 ohm resistor in series with each plate to monitor current...
but i think the biasing arrangement has both voltage and balance controls, the plate resistor monitoring will be most accurate..
200 volts on G2, might even go lower a bit say 180v.....
i am using a full wave voltage doubler so screen supply is easy...
the irons are very decent in this amp....
try the 5894's they are very nice tubes and a drop in replacement to the 829b...
the OPT in this audioromy does not have ultralinear taps...
so if you go EL34, then you are constrained to go pentode mode...
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