• 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.

Anyone try DHT 33 or 1Q5 Pentodes wired as Triode?


Paid Member
2010-11-07 3:46 am
1Q5 measurements

Hello all,

I'm working on a 1Q5 triode strapped driving a 45 SE. The original idea came from an article in Glass Audio regarding harmonic cancelation. The author was Larry Lisle (sp). The coupling is RC rather than IT in the original design. Not sure I'll have the drive needed.

Batteries for the 45 and 1Q5 heat and fixed bias). All without the help of 1Q5 triode curves. The 1Q5 bias is adjustable to cancel distortion in the 45.

I picked up some W8-1808's for an open baffle that should be able to work with the flea power, assuming the amp works.

My last (second) build was a pair of 6A3 A2 monoblocks that used to be on the ElectraPrint site. Lots of power, very nice. Best Regards, Heybill
How are you measuring harmonics?

My experience with harmonic cancellation was: (1) that odd harmonics were more difficult to cancel ( Iiirc math can be used to show this), (2) cancellation was very bias dependant, especially on the bias of the output tube, (3)Amps sound better with a nice watterfall of harmonics rather than disjoint decaying amplitudes (supported by psychoaccoustics).

I was using a 6P41S SE in triode mode as well as UL mode.

I'll be interested to see how your results compare to mine.


2010-12-02 5:06 pm
I tried the 1Q5 in triode mode recently...
Very nice sound... clean, clear and "sounds" natural. All this after you get them to stop ringing like a Hollywood haunted house recording... Now I know how they did those sound effects in the movies :)
According to the data sheets... 5-6.5% THD in pentode mode.


2010-12-02 5:06 pm

Just about to finish up on the 1Q5 breadboard. I recently ordered a used Keithly analyzer (Parts Connexion) so that I can see how the harmonic cancellation works. Thank you for the feedback on the ringing. Can't be much worse than my ears. :D


Well, they went from ringing a fine crystal glass to a siren singing from the depths of an abyss. Smooth as silk all the while.

I will have to check the Plate voltage... I fear they may have been crying from too many V's on their plates and screens :eek: