Moondog 300Bs!

[Erik Mandaville]

This is what I can do instead of the Moth modification (which needs holes drilled in the chassis for extra filament transformers -- won't do that on this amp).

I looked for MagneQuest parafeed OPTs with a 3K primary and can't seem to find one, so I probably won't go that route, otherwise this would be very easy to do with the Horus amps using a 5 volt filament replacement.

Actually I have a copy of the Welborne Labs Laurel 300B schematic, and the Moondog chassis came into existence using that particular design -- and the Moondog uses a suitable OPT for the 300B. It should work well.

Several have asked about how this is going, so I'm mentioning the latest.

Erik

[Daddy Dee]

The Moondog conversion to 300B sounds workable indeed.

Looking forward to hearing more updates and how you like the sound when it's done.

[jt1stcav]

I like the fact that you won't be modifying a perfectly good Moth 2A3 for 300B duty, especially since you're completely satisfied with the 2A3s overall sonics as it is (why mess with a good thing, even if it is restorable to its original condition).

[Erik Mandaville]

Jim/Dee:

The Moth should have been fine if I used AC on the filaments, and would thus not have needed to drill holes for additional transformers. One of the reasons the amp is as quiet as it is has to do with the fact that it has three regulator boards for all the DC heater supplies -- one for input/driver, and two each for the 2.5VDC used by the 2A3s. I know the AC heater route would have worked just fine for a 300B, but there is often a little residual hum despite a hum-null potentiometer that would be used in the cathode bias resistor circuit. Since the primary use of the Moth is for headphones, any filament supply noise generated by AC current would be bothersome -- particularly with the more laid-back music types I listen to on weeknights. I suppose with Eno's Ambient Music, I could just pretend that low-level but persistent background hum was an intentional drone and part of the recording[], but with other things it would be a distraction I think.....

The 300B alteration on the Moondogs will be much easier because I can simply use wood screws to attach the 5 volt transformers to the inside walls of the chassis.

I have to thank Marie for helping with this. She happily and willingly carried that Moth for me when I needed it moved. My back hasn't been itself recently, but I'll hopefully start feeling the benefits from the surgery in a couple of weeks.

[jt1stcav]

Plus I think the monoblock chassis from Welborne Labs are aesthetically pleasing and well suited for 300B useage...looking forward to seeing the finished products in the near future.

You are truely blessed with a wonderful wife like Marie who doesn't mind helping you out (plus lending an ear from time to time). Every audiophile should have a wife who also appreciates this hobby.[ip]

[Erik Mandaville]

Jim:

Thanks! You are very right about that. I appreciate your kind words, as I'm sure she will when I tell her![]

Erik

[Painful Reality]

For the several interested in this, those that have the MQ DS-025 in their Moondogs will be glad to know that this OPT will be perfect with the 300B providing you choose an operating point that don't exceed 60 mA.