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The Story
My 8th Darling ... yes, I like them.
This one designed from scratch to be quiet enough for headphone usage,
or the most sensitive of speakers.
This amp runs both the 1626 "Darling" tube and the 12V6GT.
This one is a bit wider and heavier than my previous Darlings.
That is mostly due the the larger output trannys and the heavy duty
DC power supply for the heaters.
I did a lot of listening to get the heater supply just right. As you know, DC heating is different
from AC heating and tubes respond to DC heating differently according to their type.
In this case, a final value about 5% below rated seemed sonically the best.
The amp supports the 12V6 in triode connected mode.
A switch changes the cathode bias to accomodate each tubes operating point.
In both cases, the tubes operate with the same effective plate voltage and current.
In that regard then, the 12V6 sounds more like the 1626. In fact, it is quite amazing
how good it can sound, and I am going to put up a page on how to convert a Darling to 12V6
operation as the 1626 is getting scarce.
The front end tube is the 5965, which is my favorite match for the 1626 and works quite well
with the 12V6. Options are the 12AV7, 12AY7, 12AT7 and any other of these families where the 12.6V
heater current does not exceed .225A. The 12AV7 worked nicely with the more sensitve 12V6.
Showing NOS 12V6GT and black plate 12AY7.
The amp uses a 5Y3 rectifier, and any 5Y3 type may be used, but not other types.
The power supply is set up to provide the correct operating voltages and currents,
and changing the rectifier to another type may result in exceeding the 1626's power rating.
The amp delivers about 700mW/channel from the 12V6 or 1626. Output speaker impedance is 8 ohms.
Small power amps like this won't appreciate a lower load, but 16 ohm loads are fine.
As you can see above I use carefully selected high quality parts.
The output stage cathode biasing is bypassed with a low-loss Nichicon and further
bypassed with a high value MKP (polypropylene). PIO caps were chosen for coupling after
sampling many others. The final high voltage B+ is also film bypassed. The power supply is
the CLC type for lowest noise. Quality metal film resistors used throughout.
Even the DC for the heaters is filtered CLC for maximum quietness.
Except for the 5965 which is near new condition, all the tubes are NOS.
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