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

GOYA said:
An update on this transformer. I ordered one from John at Antek and he told me that it changed again. It now has a 12.6v secondary again. But John said he could give me a center tap on the 12.6v winding. So it should still work for this amp project. I've forgotten exactly how many amps are on the 12.6v but there are 4 amps available on the 6.3v winding. If I use half of the 12.6v for the rectifier heater, do I need to do anything with the other half? Would it make more sense to use the two halves of the 12.6v winding to heat the 6LU8s?
Click to expand...

I ordered this Antek transformer on June 7. After 4 phone calls, each one promising that it would be shipped in a day or two, I finally got it yesterday. In two of those calls, John reiterated the different 12v secondary. Well, it doesn't have a 12v secondary. It has two 6V secondaries. That in itself isn't a problem for this amp but overall the service from Antek was poor at best. The kicker is that he told me he had it in stock the whole time my order was sitting there collecting dust.

Hopefully, the iron is a lot better than the service.

I hope to have the amp up and running by this weekend.
 
I just picked up (in a trade), a NIB Hammond 270DX power transformer.
275v-0-275v, 90ma.
6.3v/2A
5.0v/2A
Will this Hammond tranny work properly in the 6LU8 amp without any modification?
If not, what componants do I have to change out, and to what value?

ANY help would be GREATLY appreciated!!

THANKS!!!
Steve
 
I don't think 90mA current is going to be enough. One of the guys who really know should confirm.

But I do know this: You need at least 3 amps of 6.3V heater current for the 6LU8s.
 
Sorry....my mistake.
The Hammond 270DX tranny is rated for 3 amps at 6.3 volts. NOT 2 amps like I previously posted.


Steve
 
Then you'll need to use a 5V rectifier or go with a SS rectifier. (or use a small transformer for more 6.3V current for the rectifier)
 
gearhound said:
I just picked up (in a trade), a NIB Hammond 270DX power transformer.
275v-0-275v, 90ma.
6.3v/3A
5.0v/2A
Will this Hammond tranny work properly in the 6LU8 amp without any modification?
If not, what componants do I have to change out, and to what value?

ANY help would be GREATLY appreciated!!

THANKS!!!
Steve
Click to expand...

To be honest that tranny really isn't going to cut it, you'll be taxing every winding on it.

The amp it'self runs roughly 106ma on the B+ (could be lowered) the 6.3v will take your
full 3a for 6LU8's and using say a 5V4G rectifier will take your full 5V 2a here as well also.

I wouldn't advise using it, if your dead set on it we can revise the supply and cathode res
on the outputs to get the right voltage an drop the current, but it won't be the same amp.
 
Thanks Kegger!

Since it appears the tranny isn't gonna cut it with THIS amp.
I found a DIY 6au6/12b4a SE amp build that WILL cut it.....since the amps designer used a Hammond 270DX power transformer.
About a whopping 1.5 wpc!!
I have a pair of 98db Coral's that will probably work, although at a moderate volume.....at best?

Steve
 
vinylkid58 said:
Looking forward to pics and sonic impressions.

Jeff
Click to expand...

Well, I didn't quite get there over the weekend. I'm about 75% done. I've run into a snag with one of my caps. The 33uF polars that I chose are cans with a plastic threaded base and a nut to tighten from the underside. One of them got the plastic threads stripped all to hell. I've got some mounting rings but they are too small. I'm thinking I'll just glue the sucker on there.

I chose to go with an all wood enclosure. I don't think I'll do that again. The ground wires are a bit more than I envisioned.

The power supply is done and one channel is done and everything on the other channel is mounted except for the stripped cap. I'm going back in tonight to fill in the remaining guts.

Should I do some tests on the power supply before running it through the circuits?
 
I got distracted. But I'm happy to report my Maggie 8802 and tuner/pre are now working like a charm. I just had to bypass the power switch.

I'll get back to the compactron soon.
 
I finally got everything done and fired it up late last night. I immediately blew the fuse without so much as a noise or lights dimming or anything. It was too late to troubleshoot last night but this morning I took a look at the fuse. It looks like I may have been sent .1A fuses instead of 1A.

Edit: I just looked and Parts Express doesn't list any .1A fuses. The fuse is marked F.1A which I assume would mean fast-blow 100mA. Is it that I should have gone with a slow-blow?
 
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I don't know but it seems a slow blow fuse of the same value would still blow. .1A does seem strange though.
 
Parts Express does sell 100ma fast blow fuses, it looks like that is what they sent you. :(
(you got those rather short 5x20mm fuses correct?)

And yes any 100ma fuse is going to light up pretty quick, fast or slow blo.

------

With it being tube rectified and the heater current there, I'd go more for the 1.5A fuse.
 
Well I'm not sure what to tell you.

Anything could happen in packaging, and wrong fuses sent, or you could have a wiring
error in the amp, try a new fuse and no tube rectifier installed, if it still blows you have
a 100ma fuse and or wiring on the heaters is more then likely messed up.

(might want to try it with no tubes installed an see if those fuses still blow in the amp)

Other then that you got some troubleshooting to do that I'd bet we from here couldn't
help out all that much, but ask anything you want and we'll try an help. :D
 
Never let it be said that the Tandy corporation has become completely useless. I stopped into Radio Shack on the way home from work and picked up some 1.5A slo-blo fuses, stuck one in there and it works like a charm.

I had some cheap little throw away speakers attached so I'll get it hooked up to my DCMs and give it a good listen. But I can say this, those little cheap speakers sounded MUCH better with this amp than they did with my Maggie 8802.

As far as pics, I don't have a camera but I'll try to get my hands on one. Don't expect much. It's a bit of a rat's nest with all the ground wiring.
 
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