• 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.

parallel single-ended 12W6

I have not built this yet.

The grid leak resistor for the 6N1P should be OK since my preamp output impedance is low, < 600 ohms.

I'm not sure about the shared grid resistor for the 12W6. The data sheet says 500K. Is it correct to halve that? Will 220K be OK?

Any other critique is more than welcome. Thanks.


I just realized I forgot to label the CCS, it is a 10M45S.


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I think that your cathode bypass capacitor is quite small unless you are using it to attenuate low freq. In addition, IIRC, the cap should bypass both the fixed and variable. I would also use the variable in parallel with the fixed (recalculated values of course) to reduce the power it needs to dissipate.

I can't see why the common grid leak will cause a problem. That will depend on output impedance of the driver tube.
Yes, with current flowing through a fraction of it would would need to dissipate less wattage. In this case the resistor will need to be set for about 40R.


Wattage of variable resistor is given for nominal resistance. If cathode current flows thru a fraction of it, then you have to take it into account.
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Updated drawing to show the cathode bypass capacitor for the power tubes across the entire resistor chain.

Although not shown on the drawing, each diode in the full-wave bridge is bypassed with a 0.01/2kV ceramic capacitor and 1M/1.5kV resistor.

Also, the 120uf capacitor following the bridge rectifier circuit is bypassed by a 10uF metallized polypropylene capacitor. The 56uF capacitor for the driver stage is bypassed by a 4.7uF metallized polypropylene capacitor.



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I built the circuit. All of the voltages measure as calculated.

The 100R pot in series with the 12W6 cathode resistor doesn't seem to have as much effect on adjust the bias voltage as I though it would. I've got 12 of the 12W6 and the bias range varies from 29V to 32V. The pot only allows about 1V of adjustment.

The paralleled 6N1P has plenty of drive for the 12W6s.

The amp sounds rather nice. I haven't done any extensive measurements yet, but I would guess I am getting about 5 - 6 watts.



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I've been listening to this amp every day for the past 2 months. I can't explain scientifically why it sounds as good as it does. It rivals the KT88SE kit that I offered based on the Mikael Abdellah design.

I did although use standard principals when I calculated the circuit parameters and values used.

I really wish someone here would build this thing and tell me that I'm not...well I know I'm crazy...but seriously, it sounds very good.

I'm currently using it with my Leach 2-way speakers that are 89dB sensitivity. My studio apartment is only about 18' x 22' and this amp is more than enough to get me in trouble if I crank it up. Great low, mid, and high end response.

Not that expensive. The 12W6GT are only $3.



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Scott I have other 2 questions:
Do I need of an 15W Output transformer? didn't it make just 5-6 Watt? if that is the power rating I could just buy a 10W OT.
and what is the load in mA of the B+ in this amp?
Sorry if they are newbie questions but I don't know much about Parallel Single Ended amps..