Baby Tube Subwoofer Amp help wanted

[rotaspec]

Anyone have a schematic for a lowpass filter/channel summing circuit to suit a little SE pentode sub amp. I have a few 6AQ5s and el84s along with some 12AT7's. I also have the odd ECL86 which might prove simpler. Needs to be SE as that is all that I have transformers for
I'm a fairly newbie to designing with tubes, but I can probably deal with the power amp and supply part.
Here's the background that got me thinking:
I just scored an old mono console with a little ECL86 tuner/amp and a Rola 12K speaker which has the matching transformer attached. Anyone have specs on that driver? It doesn't appear in the Rola PDF I have.
I also picked up a couple of awful cabinets from the rubbish with pristine Plessey C8MX 3.5 ohm drivers in them. 8" with whizzer cone.
Maybe the basis for a tube sub to go with the C8MX and a KSN1038 piezo tweeter on my little ECL86 stereo amp?

Happy New Year all
Gary

[killerfishes]

You may want to look at parallel single ended, the EL84s are a good pick for this. you can get about 5w out of the EL84 SE and about 8w out of the parallel single ended. KT88 would be a better choice with about 20-25w parallel SE. I also would not use the k12 as a sub. If I where you I would find a high sensitivity subwoofer and build an amp to fit with it.
some links that may help you along the way
XO
Tube Active Crossover
Steve's Tube Pages
Tube Crossover (Page 1): January's Circuit of the Month
Gorillia
summing
http://www.forsselltech.com/download...mming_buss.pdf
Simple Mixer Schematics
Three Channel Audio Mixer

[aardvarkash10]

hey gary - specs on the 12K are the 12M speaker and the K model transformer. See attached...

Dang - won't attach cos its too big. PM me for the sheet and I'll e-mail it to you.

The 8MX is a great unit in an open baffle design - they have as close to zero excursion as you can get and still make noise! Get a half sheet of 19mm MDF (1220 x 1200) cut it in half so you have two pieces 1220 x 600, mount the drivers around 2/3 of the way up and you have a set of hi-kudos speakers. You can stop them falling over by buying some cheap shelf brackets and mounting them as feet. Bunnings or Mitre10 are your friends!

I have two of the 12MX units. Again, they have 3/5 of 5/8 of feck-all excursion. They ain't no woofer! I've tried all sorts of enclosures and just can't get'em to huff. Again, a candidate for OBs if you can get them past your SO.

Cheers

[rotaspec]

Thanks for your help guys. I'll look at those xover pages for future reference.

Ash, I have the Rola PDF that covers the 12M, so that answers that one.
I don't think 1/2 sheet OBs would work in my smallish lounge, there would be little room to sit down (it's bad enough as it is).
Fortunately, I have a Wharfedale active home theatre sub that I can unplug from rest of the system and use if I decide to get brave enough to try the OBs.

Gary

[coldcathode]

rota,

I have been down this route before. The power expected from a small SE EL84 amp and one sub is practically useless if the sensitivity of the woofer is not in line with the F/R drivers.

I am not sure of what components you have at hand but a simple "bi-amped" stereo system would probably be best.

Assuming you have the iron you could build an SE EL84 stereo amp and drive the C8MX's with that and the ECL86 amp driving the tweeters.

As far as an Xover is concerned. Pete Millets and Steve Bench's are two nice examples. Bench's is a little easier to build Point to Point. I have a Millet PCB for a future project and looking it over it would be difficult for a newbie to wire up Point to Point construction.

You might want to look at this thread

here

and this thread

here

for a "subwoofer amp". I have joined the group buy for the Bpa300 boards. I will run them as a "Push Pull" type sub amplifier. Using a 6SN7 (or any dual triode) as a Split Load Phase inverter. PM me if you're interested in a schematic of the amp.

"Mono" subwoofers are great for home theatre where most low bass signals are already "summed" in the mastering process (hence the "point one" in 5.1). In most stereo music recordings the bass is not "mono" and strange colorations can be heard when summing them. I have tested this using a pair of identical powered subs (Cerwin Vega) and found stereo bass to be more pleasant.

Overall my recommendation is to use a "biamped" setup with the crossover point a good compromise between the responses of the drivers and their impedance curves.

Solid State unfortunately can deliver a lot more power per dollar and seems to have its place.

[coldcathode]

here is a sketch of the "sub amp"