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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Good to see some love and development of this amplifier. I've had mine for quite a few years now and it suffered from intermittent popping, so since then it has languished at the bottom of my audio to-do list.
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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It appears you do have the earlier version built to the schematic shown. I have a slightly later one that reverted to a Williamson topology.
I have been debating for a while whether I wanted to do a gut job. Mine seems to work reliably, but I hardly ever use it.
I have been debating for a while whether I wanted to do a gut job. Mine seems to work reliably, but I hardly ever use it.
Yeah I figured I'd rebuild it. One channel had a crackle and I did'nt want to fix it. I got the amp for a very good price and should be fun.
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...
this amp surprisingly sounds very good...i see that the irons used were Z11, an M6 equivalent in our part of the world..
the one i repaired had a defective power switch and was red plating, the plate caps were crap nylon crimp type end terminators, there are better alternatives...
the one i repaired had a defective power switch and was red plating, the plate caps were crap nylon crimp type end terminators, there are better alternatives...
Hey Tony, I figured if i biased each section separately with its own bias pot it should make the amp a little more reliable in fixed bias.
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..
Looks like a cool amp Tony!
I'm tempted to build the altec 345 in this amp. I built it before and really like it. It runs el34's and a 6au6 with 6c4's in the pre/PI. However it might be nice to build the original circuit too....
I'm tempted to build the altec 345 in this amp. I built it before and really like it. It runs el34's and a 6au6 with 6c4's in the pre/PI. However it might be nice to build the original circuit too....
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...
Oh no I would still keep the power tubes the same for sure. I received 6 tubes with this amp. I also like the individual biasing because matching is not necessary. I'm going to look into that mullard circuit too!
I would probably add screen regulation using some combination of OA2 (150V), OB2 (108V), or OC2 (72V).
Based on Tony's recommendation possibly on 0B2 and 0C2 for 180V would be good.
Combination should not exceed 225V according to the data sheet for the 829B.
Based on Tony's recommendation possibly on 0B2 and 0C2 for 180V would be good.
Combination should not exceed 225V according to the data sheet for the 829B.