http://www.westernelectric.com/spec_sheets/429A.pdf
Somewhat like a 6V6, although rated for less voltage. I just finished building a PP amp with 429As. Heres what a member from another forum suggested in regards to operating points.
"In push pull 20-25 watts or so in ultra linear mode. Plate load 5k 30%
screen tap 250VDC on the plate. Bias is adjustable 1-10 volts adjust for zero signal of 41ma plate current."
However if mine are biased at 41ma the grid voltage would be like -1.5 volts. Hardly enough to swing any voltage. At 30ma they range from -4.2 to -5.5
Somewhat like a 6V6, although rated for less voltage. I just finished building a PP amp with 429As. Heres what a member from another forum suggested in regards to operating points.
"In push pull 20-25 watts or so in ultra linear mode. Plate load 5k 30%
screen tap 250VDC on the plate. Bias is adjustable 1-10 volts adjust for zero signal of 41ma plate current."
However if mine are biased at 41ma the grid voltage would be like -1.5 volts. Hardly enough to swing any voltage. At 30ma they range from -4.2 to -5.5
astouffer said:http://www.westernelectric.com/spec_sheets/429A.pdf
Somewhat like a 6V6, although rated for less voltage. I just finished building a PP amp with 429As. Heres what a member from another forum suggested in regards to operating points.
"In push pull 20-25 watts or so in ultra linear mode. Plate load 5k 30%
screen tap 250VDC on the plate. Bias is adjustable 1-10 volts adjust for zero signal of 41ma plate current."
However if mine are biased at 41ma the grid voltage would be like -1.5 volts. Hardly enough to swing any voltage. At 30ma they range from -4.2 to -5.5
The data sheet reports 150V max on the screen grid....
Heres the details for my 429A amp. 250 volts on the plates, 130 on the screens from a regulated supply. Output transformers are japanese and are supposedly meant for 6BM8s and don't have UL taps. I got good results using the 4 ohm tap with 8 ohm loads. RMS power is pretty low, around 5 watts before it gets noticeable on the scope. However it sounds much louder than my 10 watt 845 SE.
First gain stage is half of a 407A with a 15k plate load and 330 ohms on the cathode unbypassed. A 0.1uF cap couples it to the other half of a 407A phase splitter. 10k resistors on the plate and cathode with 1k for grid bias. 0.1uf caps then couple to each 429A. The datasheet says 100k max for fixed bias so thats what I used. After the initial bias adjustment the tubes are pretty stable and haven't drifted any.
To get the 20 volts I used a switching supply from an old lcd monitor that put out 24 volts at 1 amp. An LD1085 regulator drops that to 20 volts. The b+ is a choke input into a 330uf cap, then a 100 ohm resistor and another 330uf cap. Hum is inaudible and it sounds good so far
First gain stage is half of a 407A with a 15k plate load and 330 ohms on the cathode unbypassed. A 0.1uF cap couples it to the other half of a 407A phase splitter. 10k resistors on the plate and cathode with 1k for grid bias. 0.1uf caps then couple to each 429A. The datasheet says 100k max for fixed bias so thats what I used. After the initial bias adjustment the tubes are pretty stable and haven't drifted any.
To get the 20 volts I used a switching supply from an old lcd monitor that put out 24 volts at 1 amp. An LD1085 regulator drops that to 20 volts. The b+ is a choke input into a 330uf cap, then a 100 ohm resistor and another 330uf cap. Hum is inaudible and it sounds good so far
45 said:I'd like to see what this tube is capable of when used in triode connection in a single stage preamp.
130V anode voltage and -3V bias.
Ask and you shall receive:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
http://www2u.biglobe.ne.jp/~tossie/KM-429A.CDB.html
http://www2u.biglobe.ne.jp/~tossie/KY-CDB.html
Merry Christmas and happy new 2009.
-- josé k.
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Joined 2006
Can someone explain why the circuit above works? Apparently the specs from it's measurements are respectable...but...
WE429A has a plate resistance of 37k, while the A20 transformer is something like 600 ohm:600 ohm.......all because of using parafeed topology such that the impedance matching is not important? Thanks!
WE429A has a plate resistance of 37k, while the A20 transformer is something like 600 ohm:600 ohm.......all because of using parafeed topology such that the impedance matching is not important? Thanks!
In triode connection the rp is much lower, probably on the order of a few K ohms or so.
I'm not sure the A-20 is the optimum choice, but it does have quite a lot of primary inductance which is how it achieves relatively decent performance down to 10Hz in 600 ohm applications. I think around 30Hz it is probably able to provide a primary Z on the order of a couple of K ohms which is probably why it works well here. I use a lot of A-20 in my system, but the primary inductance is higher than my meter can measure so these remarks are something of a conjecture on my part.
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Joined 2006
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