AX84 Moonlight Amp Build Project

[Marcel]

Cool build plans.

On the face of it your tube substitutions all seem good. The 12SL7 and 6SL7 are the same except for the heater voltage (so nice when the ID numbers actually mean something and have relevance to what's inside the thing). From memory my Radiotron book refers searches on the 12AX7 to the 12SL7 page for operating specs so you should be right there. Have to have a look in the book on the EF184 to EF86 swap but I presume you have done your research.

I did have a cheeky 'a little heater for when in the dog house' comment floating in my head but I'll let out only the nice civil ones... Looking forward to see how your build turns out.... ;-) ...

[DrNomis_44]

Cool build plans.

On the face of it your tube substitutions all seem good. The 12SL7 and 6SL7 are the same except for the heater voltage (so nice when the ID numbers actually mean something and have relevance to what's inside the thing). From memory my Radiotron book refers searches on the 12AX7 to the 12SL7 page for operating specs so you should be right there. Have to have a look in the book on the EF184 to EF86 swap but I presume you have done your research.

I did have a cheeky 'a little heater for when in the dog house' comment floating in my head but I'll let out only the nice civil ones... Looking forward to see how your build turns out.... ;-) ...

As far as I can understand, both the EF184 and EF86 are small signal Pentodes that have 6.3V AC heaters and indirectly heated cathodes, although the pin connections may be different, I seem to remember reading somewhere that the EF184 had a mu of about 150, or thereabouts, the EF86 might have a higher mu spec, I do remember building the Moonlight amp circuit before moving to Darwin, and substituting a 12AX7 for the 12SL7, and a 6SN7GT for a 12SN7 actually did work and I got pretty good results, even with the home made output transformer that I made for the amp.

I'm having a debate with myself on whether to use tagstrips to mount the resistors and caps point-to-point style, or mount them on a piece of perfboard or pad-per-hole board, or even make a custom turret board for the amp.



Note: For those of you unfamiliar with the term "mu", in this case it refers to the theoretical voltage-gain of a valve, a 12AX7 is a high mu twin triode (there are two triodes within the glass envelope) with a mu of 100, the 6SN7 is a medium mu twin triode with a mu of 70.


Incidentally, the EF86 was one of the valve types used in the Vox AC30 preamp circuit.