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Cheap project SE 6BQ5 : SUCCESS!

Redboy

Redboy

a few good watts
A while back I pulled apart an old console that had an Olson tuner and a little SE 6BQ5 amp in it. I wasn't too jazzed about the tuner, and the thing has sat in my little workshop for awhile.

Today I figured I'd take a stab at making it a little more user friendly. The tuner / preamp fed into the amplifier via one of those octal plugs (what do you call those?). I picked up a 100K volume pot and some input jacks from the RatShack, and wrecked two drill bits trying to get through the THICK steel chassis (!). I didn't have any shielded wire around, so I just used some single strands of CAT5... bad idea?

Anyway, it worked! :banana: Made music, anyway, and the volume pot seems to function properly. I'll hook it up to the Forte's later to see how noisy it is. None of the caps have been replaced yet.

I'm really thrilled, seeing as I had no schematic for this thing, and had to figure it out on my own.

Eventually, I might recap this thing and add a switch, fuse. I also want to put the little pilot light back in - I've got a jewel lens from another amp. Need new drill bits, first... :sigh:

BEFORE:

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Here it is now...

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"Anyway, it worked! Made music, anyway, and the volume pot seems to function properly. I'll hook it up to the Forte's later to see how noisy it is. None of the caps have been replaced yet."

I've had good luck using SE 6BQ5 amplifiers with my Cornwalls.
 
Shielded wire can help you reduce/elimanate one source of hum. If you have no hum, and no shielded wire, you're doing great and don't need it!

Neat project, BTW!
 
Mike Stehr said:
I've had good luck using SE 6BQ5 amplifiers with my Cornwalls.
Click to expand...
Funny... I've gotten it into my head lately that I need some Cornwalls. The Forte's are really great speakers, but something makes me think I'd like some Corns.

I like that the tubes are "up front" now (thought they were never meant to be seen at all, originally). I think I'll look for a simple strip of nice wood to run along the frontside, and put it up on some little feet of sorts. Keep it fairly zen looking.
 
"I like that the tubes are "up front" now (thought they were never meant to be seen at all, originally). I think I'll look for a simple strip of nice wood to run along the frontside, and put it up on some little feet of sorts. Keep it fairly zen looking."

Yep. That will make it look nice. Olson made some rather decent output transformers in the day. I wouldn't doubt those little OPT's are pretty good as far as linearity.

The only bummer is the PEC's they used to couple the 12AX7 driver to the output 6BQ5 stage. Swapping those out would probably help.
I had a Motorola console amp that used PEC's for coupling stages.

I didn't mean for you to want Cornwalls, I guess was trying to point out that the little SE 6BQ5 can sound good with high efficiency speakers. I would think the Fortes should sound fine with the SE amp.
 
Wasn't your fault that I want Cornwalls, Mike. That's been brewing for awhile. I do think the Forte's (98db, IIRC)will be great for this.
 
Wow, it's really quiet!

Pleasant surprise - this thing's not any noisier than my Eico! And it sounds really nice, to boot. :thmbsp: More bass output than I imagined it could have. This makes me even more excited to finish the 2A3 project I've got in the works!

Kucing the cat approves... :yes:

See if you can find the little Olson in the system...

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Hint: I'm not spinning vinyl right now.
 
I'm happy to hear that the Rat Shack volume pot worked. I've got one setting in the bag waiting to be put into an old RCA 6BQ5 PP amp. I was suprised to see that the pot was made by ALPS.
A good drill bit for drilling into medium weight sheet metal is one of the stepped bits-they used to call them uni-bits. A small pilot hole helps too.
 

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The RS pot works great. It feels smooth, and you don't hear it at all. Nice cheap alternative to some of the spendier ones on the market. In this case, I didn't even know if I had the right value so I wasn't willing to spend much. I think you'll like it.

Thanks for the tip about step bits. I'm actually trying to psych myself up to shell out the cash for a big one - up to 1.25" - for my other project. I think I'll end up buying it online.
 
Cool !

I really like the bang for the buck of the little console amps :music:

whatcha got in the tube rolling box to play with ?
 
Everything I've got is old stock, mostly American but I do have some British tubes too. They're all scrounged from console amps, and fortunately for me just about everything I've picked up has had EL84 power tubes.

This little amp came with a Bugle Boy rectifier, but I don't recall what the power tubes were. I've got Raytheon tubes in there now. Gonna play around with 12AX7 tubes to see what comes out.

I listened to a little Dire Straits on it tonight. :music:
 
Redboy said:
None of the caps have been replaced yet.
Click to expand...

I don't see any caps to replace! The filter can would be the only candidate if you have hum, but there are no paper or wax caps on the underside.

--Bob
 
"Pleasant surprise - this thing's not any noisier than my Eico! And it sounds really nice, to boot. More bass output than I imagined it could have. This makes me even more excited to finish the 2A3 project I've got in the works!"

Cool. Old man Klipsch said what america needs is a good 5 watt amp. It's always interesting how those little amps can boogie with the right speakers....

Line and filament noise is going to be a little more of a challenge to tame than a single ended indirectly heated 6BQ5 amp. But if I can do it, you can too.

I have a little Magnavox 6BQ5 SEP console amp. I rebuilt the Magnavox amp, then built a 2A3 amp about a year later.

The 2A3 amp sounds bigger and more open, has a larger soundstage and can get louder with more bass.
But tonewise, the little Magnavox is pretty much the same to me....

The 2A3 amp sounds great through the Cornwalls. The Magnavox sounds great as well, it just doesn't get as loud. A pre-amp helps.....

I better go buy some more RS 100K pots......
 
I too have a SEP Magnavox 6BQ5 amp. It amazes me what that thing can do at only 6 WPC. has ploenty of bass too.
 
Today I added a switch, fuse assembly and jewel light. Everything seems to work except the light, which was recycled from the same console. I know the thing was fine when I pulled it from the console, but didn't test it before wiring it in... oops, maybe. Something for later.

Oh yeah, I replaced the power cord, too.

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Bob E. said:
I don't see any caps to replace! The filter can would be the only candidate if you have hum, but there are no paper or wax caps on the underside.
Click to expand...
About that filter can... it seems dead quiet, but that isn't necessarily an indicator of good health, is it? Shouldn't I replace this thing if I intend to use the amp much, just to be on the safe side?

Values are:
60 uf @ 400
40 uf @ 350
40 uf @ 300
50 uf @ 25

I looked around a bit and can't find anything exactly like that. The 60uf value seems to be a little unusual in the cans. I was thinking something like 40/40/40/20 would be good, and to tie a 40 and 20 together to make 60uf. The little 50uf cap should be easy to sneak underdecks. Does such a can exist (the 40/40/40/20)?
 
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