Bottlehead "hand me downs"

[Alonzo]

Growing up poor in Alabama, I've learned to make do with what I have and "find a way" to make what I have work.  I have a ton of "not used since upgrade" BH parts and I was wondering how to make something of it.  I hate to see it just sit in the garage.  I've got BH gear or BH design through out my gear but my sub amp and speaker are a generic Monoprice sale item.
Is there any way to make a 2A3 sub amp?  I have a 2A3 mesh NI output tweeter amp, a soon to be 45 Litz NI main amp, 2 other extra 2A3 amps for garage and backup but my sub isn't tube based and I wondered if I could modify something to a push-pull to get the power and response needed for a sub amp.
Does anyone have suggestions of schematics I could modify?
Thanks,
Alonzo

 

[Paul Joppa]

RCA says you can get up to 15 watts from a P-P 2A3 in fixed bias. Is that enough for a sub? Most subs have 100W or more.

 

[Tim G.]

I have headed down that path myself.  I have used some calculators based on a generic 15" parts express woofer I have lying around and 15 watts to show that it would output about 94db at 3 meters distance...would that be viable?  Curious where this might lead,  there is just something alluring about an entire 2A3/DHT system.

Tim

 

[Paul Birkeland]

Viability is a tough question!  I have a pair of ~98dB efficient 18's in my system that are down about -7dB at 25Hz.  Paramounts really do well with this system, but the SR-45 amps I have run out of gas with the music cranked.

Essentially, YMMV... a lot.

 

[Paul Joppa]

I have headed down that path myself.  I have used some calculators based on a generic 15" parts express woofer I have lying around and 15 watts to show that it would output about 94db at 3 meters distance...would that be viable?  Curious where this might lead,  there is just something alluring about an entire 2A3/DHT system.

Tim

Unless you are doing this outdoors (big party?) it's the 1-meter equivalent that is most relevant. That would be about 104dB at 1 meter, or in the reverberant field throughout a typical listening room. Compare with PB's 98dB speakers and 8-watt Paramount = 107dB. PB is way younger than me; if you like me like your music a hair less loud then the 15 watts might just be adequate. If needed, make two subs and stack them!

Stereomour could be modified to a push-pull which would do close to 15 watts on momentary (musical) transients. This would however require a push-pull output transformer capable of 15 watts and with a 3000 ohm CT primary. Those are few and far between; you may have to go for a 50-watt transformer or greater to get there. Selecting one with good deep bass performance means a lot of iron and copper (5 to 10 pounds I'd guess).  There's no way to fit it on the Stereomour chassis.

Hmmm.... what might work would be to use the Paramount iron with the two output transformers in parallel as a parafeed output, keeping the Paramount plate chokes. At this point, the total deviation from designs that have been tried is substantial, which makes the engineer in me nervous.

I'm pretty sure I would not like it for fullrange use. The crossover distortion in this nearly-class-B operation would be significant, and I don't really like the even-harmonic cancellation of push-pull either. But it might be acceptable as a sub amp, in a frequency region where the ear is less critical.

You may have noticed that this scenario is not exactly dumpster-diver cheap!

 

[Tim G.]

 

[Tim G.]

But seriously, that might have to get put on the project list.  I go to the Parts Express tent sale over the summer and they have scratch and dent hammond iron sometimes (never in pairs)...I will have to keep my eye out for some suitable output iron to give it a try.

I love threads that get the project gears turning....

Tim

 

[Paul Birkeland]

Which PE woofer do you have? And how many?

 

[Alonzo]

Would the power requirements be less if it was into a woofer line array instead of a large single sub or pair?

 

[Tim G.]

http://www.parts-express.com/dayton-audio-dc380-8-15-classic-woofer--295-325

I have two of these collecting dust at the moment, the line array is an interesting thought too...  that configuration is why the straight 8 is so efficient right?

Tim