OPERATION MANUAL MODEL : ZMA - ZEN MYSTERY AMP
REV 1 MAR 2014
NOTE:
The OA3 tubes are different in that they will often flash a few times during
start up and during shut down. This is a normal characteristic of the tube. OA3
tubes (also known as VR75’s) do not get hot. Therefor it is safe to hide the bias
level controls behind these tubes and safe to put the power switch in front of these
tubes.
!
Tube Matching
The default factory tube compliment on each channel consists of a pair of 6N23P’s
driving a matched pair of KT66 output tubes complimented by an OA3 voltage
regulator tube. To keep the volume of both channels exactly matched we
recommend only using matched QUADs of output tubes. Simply split the quad into
two pairs and install the matched pairs from the quad into each channel.
Due to the direct coupling between the two smaller tubes we recommend they be of
the same type and be matched from side to side. 6N23P is a dual triode, so
actually two tubes in a single bottle, which is why it’s desirable to have both halves
of the tubes match.
If you can’t find 4 matched tubes like this, you can get by with two matched pairs.
Simply make tube location A11 and location B11 match. Then do the same for A12
and B12.
!
Tube Substitutions
STOCK
Alternates
KT66
KT77, KT88, 7027, 5881, EL34
6N23P
7DJ8, 6N1P, 6922, 6DJ8
OA3
None
!
Tube substitutions are many times part of the reason why people own tube amps
since changing from one brand to another of even the same tube type will change
the sound of the amplifier.
Your Zen Mystery Amp has been carefully tested with hand selected and matched
tubes that we feel represent the best possible voicing for the amplifier. We match
the tubes so carefully that we are able to match channel for channel output to
within a couple milliwatts throughout the range of the volume control. You can
always obtain replacements from Decware.
That said, if you were going to tube roll, as it’s called, we would recommend trying
different brands of KT66 both in current production and new old stock (NOS). To
compliment that you can also explore 7DJ8’s as a new old stock replacement for the
original Russian 6N23P’s supplied with your amp. If you desire a warmer smoother
presentation you can use Russian 6N1P’s.
!
!
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