Tavish Design MC series Owner's Manual - page 8
7
3.2O
PERATION
If you removed the cover to adjust to set the cartridge loading and gain switches, you must replace it
before operating the unit. To avoid a risk of electric shock, never operate the unit with the cover
removed.
When the unit is switched on, it goes through a 40 second warmup sequence before the blue “ready”
LED turns on. The phono stage will not pass signal until the blue “ready” LED is on. Before playing an LP,
turn down the volume control on your amplifier until you are familiar with the required gain setting.
3.3T
UBE
R
EPLACEMENT AND
S
UBSTITUTION
Vacuum tubes last much longer than most people realize, and although the lifetime of any particular
tube is impossible to predict, hopefully it should be many years before any tube replacement is
necessary. Replace tubes with the same type. That is, replace the 12AU7A/ECC82 only with another
12AU7A/ECC82, not with another type. The only exception is the 5751, which can be replaced with a
12AX7A/ECC83 if you can’t find a 5751, or if you prefer the 12AX7.
The JJ 5751 tube usually supplied with the kit appears to have the same 300 mA heater current rating as
a 12AX7 tube, but some 5751 tubes have a 350 mA heater. SW2 provides some adjustment range to
accommodate this variability, as shown in Fig. 3.3 below.
Fig. 3.3: Position of switch SW2. Left for 12AX7 (factory setting), right for some types of 5751.
The unit is supplied with JJ Electronics tubes, but tubes of other manufacturers are also OK. It is very
unlikely that you will find a tube with lower noise than the JJ 5751 (if you do, please let us know). New,
old-stock (NOS) tubes tend to be noisier. The noise levels in the electronics are well below the surface
noise on vinyl LPs, so you may wish to choose the input tube by other criteria as well.