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The "$250" Amp? - 6LU8 Compactron SE, UL

Here's the Wiring Diagram with scale Components..I just have 3 Items that I'm not sure with...One being how to deal with the 6.3VCT Lead from the Hammond 270FX. I've read that it can be Cut, or it should go to Ground. Which is best? The second is the AC Ground, which I've read should go thru a Cap, or not. All of the Grounds will be going to a Single Point Ground under the Choke's Mount. The last Item would be whether the Common Connection at Pin 8 of the Rectifier is Proper, as I haven't seen it shown that way before. Any thoughts on this will be Greatly Appreciated, and maybe help keep some of Us from a Shocking Experience.....
 

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The BOM will go to Keg and Squid tomorrow for review then I will post it here this week. I just have to finish it up. I was going to do that Sunday, but I had tooooo much fun and the SMAC meeting and paid for it on Sunday. Also had to clean the house before Annie got home from work.....that was the deal and I had to honnor my agreement. She was happy when she got home. Cheers.
 
Will this be a single output mono amp or a stereo amp ? If it is mono we will have to build 2 , one for each channel ?
 
This will be a 2 channel, or Stereo, amplifier. It will provide over 5 single ended tube watts to each channel. It's a great match for efficient speakers. If you're using inefficient speakers, it would be good for near field listening, but it might not "rock the house".

You could, with a little bit of modification (not a lot), turn this amp from a stereo single ended amp in to a mono push pull amp. Then it would output probably somewhere between an EL84 and EL34 in terms of power. Say, around 20-25WPC. It might be slightly cheaper to build as a mono, too.

The Antek power transformer is a real beast. If you wanted to go really power crazy, and still keep it cheap, you could use the same iron in the power supply that is currently there (the Antek PT and the 2 Radiodaze chokes), and make it a dual rectifier job with 2 6ca4 rectifiers, 1 per channel. Or go solid state diodes at that point. The Antek would provide enough high voltage and heater to comfortably run stereo amp like that. You'd need more chassis, tho.
 
Before Keg or Dave beats me to it, yes, it could also work as a mono Parallel Single Ended amp, too. Lot's of options here, folks.
 
I would think that for "rock out" levels, one would want a 93dB or higher speaker. Running on Cornwalls with a real-world dB rating of 98dB or so, we were able to drive them outside at any level we desired, limited only by the host's willingness to piss off the neighbors. I would guess that 91-92 dB speaks would be good for moderate listening, 93-94dB could start to rock out, and anything 95 and higher would be really safe at levels starting to be less than sane.
 
To go along with ED's recomendations, 89-90 would be the low side of what you would
"want" to run on this amp in it's standard configuration, lower then that on some small
6.5" woofer or less bookshelves should be fine as well.
 
The Pinoneer HPM series, most JBL and KLIPSCH series of speakers would generally
be fine candidates here to.
 
I was planning on building a high end MT bookshelf ( .75 cf enclosure ) to go along with this amp . It would be 8ohms but only have a sensitivity of 87db . I would think an MTM wouldn't work because it would drop it down to 4ohms .

Speakers are going to get pricey with a sensitivity rating in the 90's ...... I will have to look around and see what I can come up with . :scratch2:
 
If you're building your own you can go anywhere you want with them.

Kegger or Squidward, will this support a 4ohm load? Squid, the MTM TL's I had at the fest were a nominal 4 ohm and they sounded pretty good on your 5W monster amp. How does the output compare to the compactron?

Ray
 
The outputs come in, 4ohm, 8ohm or 16ohm. (single taps, pick yours)

I originally had the 16ohm outputs in the test amp an ran on Jeffs speakers that dip to
3.5 ohm but are normaly around a 5ohm load and we were both surprised plus satisfied.
 
RayW said:
If you're building your own you can go anywhere you want with them.

Kegger or Squidward, will this support a 4ohm load? Squid, the MTM TL's I had at the fest were a nominal 4 ohm and they sounded pretty good on your 5W monster amp. How does the output compare to the compactron?

Ray
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I'd say they are pretty darn close. Similar power levels, I believe a similar schematic, and if I'm not mistaken, the small signal triode in the 6LU8 isn't far off from the driver that Ed used. I wouldn't be surprised if they performed about the same.
 
I am building mine with 4ohm OT. I am using it to drive my Heil tweeters only and they are 4ohms. They are 105db spl so this amp should drive them just fine. Cheers.
 
Tube newbie speaking here...so we have to pick the output transfomer based on our speaker impedance beforehand and that's what we get, right? No multi-tap capability? I'm just asking here, not complaining. I just need to figure out what I'm going to design for. Being in my line of work coming up with a new set of speakers to match the amp isn't too big of a problem. :D

Ray
 
Edcors, which are going to be the standard choice here, are only available with one secondary impedance. You could contact them about making one with multiple secondary taps. Expect a 20.00 engineering charge and maybe a bit of a premium on the iron. However, if the group of potential builders decided to all go in together, with enough volume, i suspect Edcor might give us more competitive pricing.

Other output transformers with multiple taps are certainly options here, as well. You just need the primary impedance and power handling to be similar.
 
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