This kit was released under several names. Boulevard and National are two of the marketers. No two seem to have the same power transformer. I have one labeled National that sounds quite good considering the little output transformers. I was very surprised. I eliminated the 12AX7 and the bass, treble and loudness controls and brought the input to a 100k stereo pot with the wipers going to each channel's 12AT7 grid. For the power supply, I installed a 50uF cap as the input cap (under the chassis) to a nice low DCR choke and then a 100uF cap and then to the output tube's plate supply. This amp sounded really nice on my high efficiency Zu Dirty Weekend speakers. Note the amp was also available as a mono unit for which I have supplied the schematic.
Wow, what's the plate current for V2, the 12AT7?
Rp on the voltage amp is 270k (R18?) with Rk (R13) of 2.2k ohms. Rp (R17) and Rk (R14) for the split-load inverter are 100k. Quite large values for 12AT7.
Does 12AT7 work pretty well with such low Ip?
Rp on the voltage amp is 270k (R18?) with Rk (R13) of 2.2k ohms. Rp (R17) and Rk (R14) for the split-load inverter are 100k. Quite large values for 12AT7.
Does 12AT7 work pretty well with such low Ip?
It has been quite a few years since I got this amp from eBay and rebuilt it. I don't remember if I actually used this circuit or if I re-biased the first two stages with different value resistors. As I said above, I rebuilt the unit the way I thought would sound best, but never drew up a schematic.
It is now down in the basement along with a pile of other equipment waiting for a new home.
It is now down in the basement along with a pile of other equipment waiting for a new home.
