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 Post subject: Homebrew 6L6 stereo tube amplifier
PostPosted: Oct Sat 21, 2006 7:40 pm 
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Sorry if this is OT a little bit but I am in the process of building a 2 channel 6L6 tube amp. Here is the mock up with the parts just sitting on top of the chassis. I used relay sockets to hold the 6L6 tubes. Output will be somewhere between 20-25 watts per channel. Chassis will be painted black or hammertone gray after the holes are drilled and punched out.

I have so many different things I want to do and build, I need to clone 3 or 4 of me to do them all... :)

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Sal Brisindi

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 Post subject:
PostPosted: Oct Sat 21, 2006 9:13 pm 
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Hi, Sal. Sounds like a great idea, but, I'm a little concerned about the safety of the relay sockets. First, cant they handle the heat, current, voltage these tubes will produce? Second, either you can get heavy phonelic tube sockets, or , perhaps ceramic. These sockets are still readily availlable at many dealers.

If you do decide these sockets are your best choice, why not mount them under the chassis on studs, and make the holes larger for the tubes to be sunk in slightly, say maybe 1"?


I think it's a noble idea, and with the correct design, it should perform very well. I love power amps like this.

Will you be putting on bass and treble controls? How about a good scratch filter as well, and if you ever intend to play old mono records, you might want to cnosider a good stereo-mon switch.

Best wishes to you.
Bill Cahill

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 Post subject:
PostPosted: Oct Sat 21, 2006 10:08 pm 
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Hi Bill,
I used the relay sockets just to hold the 6L6 tubes from falling, I will be using regular or ceramic octal sockets in this amp.

This amp will have treble and bass controls, and your idea of a mono/stereo switch is a good one, thanks for the idea.

Not sure about the scratch filter, I need some ideas about building that. I will also have a rotary switch for multiple inputs. It will be a fun project, not that I really need another tube amp :D .

Thanks,
Sal Brisindi

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 Post subject:
PostPosted: Oct Sun 22, 2006 12:35 am 
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Glad to see you won't be using the relay sockets 8) So what schematic will you be working from? I have thought an easy way to building an amp would be to buy one of the empty driver boards for a Dyna 70 from eBay and all you need then is a power supply and hardware. The lazy guys way out :roll:


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 Post subject:
PostPosted: Oct Sun 22, 2006 1:01 am 
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Lou, Sal, Bill,

I will be following this thread. I have too many amps but I want to build another one. I may use 6BG6G tubes for the outputs just to be different.

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 Post subject:
PostPosted: Oct Sun 22, 2006 1:09 am 
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Lou deGonzague wrote:
Glad to see you won't be using the relay sockets 8) So what schematic will you be working from? I have thought an easy way to building an amp would be to buy one of the empty driver boards for a Dyna 70 from eBay and all you need then is a power supply and hardware. The lazy guys way out :roll:


Lou,
I won't working from any one schematic, but bits and pieces from multiple schematics, then some tweaking to make it sound right... :o, thats the reason why I bought the relay sockets, to breadboard the amp before the final constrction. I will be making two 9 pin breadboard sockets also. This amp won't be built over night, but maybe a week or 2.... I wish.

About the ST-70 driver board, there is no bass/treble controls plus I don't think there is enough gain to connect from a portable cd or mp3 player, thats why the 4 12AX7's, I might get away with 3, thats why I want to breadboard it first.

Sal Brisindi

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 Post subject:
PostPosted: Oct Sun 22, 2006 1:43 am 
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Sal, if built correctly, you shouldn't need all that gain for a cd player. :shock:

I would reccommend using a schematic for one of the high end , like Fisher 50"s hi fi sets to get schematic idea for scratch filter.

Best of luck. :) Bill Cahill

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 Post subject:
PostPosted: Oct Sun 22, 2006 1:53 am 
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The output from the CD player that I used as input for the amp I built was two volts peak to peak. I had more gain than needed using two 6SL7s.

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 Post subject:
PostPosted: Oct Sun 22, 2006 2:17 am 
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Terry Judkins wrote:
The output from the CD player that I used as input for the amp I built was two volts peak to peak. I had more gain than needed using two 6SL7s.


Geez Terry,
With 2 volts peak to peak why would you need a amplfier... :wink:

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Sal

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 Post subject:
PostPosted: Oct Sun 22, 2006 2:27 am 
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Ok, so you are building what is called an integrated amp which contains both preamp,tone controls and power amp in one. I have a pair of Eico HF-20 amps which are just that. A portable CD player will drive a Dyna 70 to full power from the headphone out. True you won't have any tone tone controls but some like that full spectrum with any coloration from a preamp.


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 Post subject:
PostPosted: Oct Sun 22, 2006 2:42 am 
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How about a tone control section from an HH Scott 299? They have great control over the signal. The 12AX7 AF amplifiers have DC on the filaments. Check out this link...

http://hhscott.com/pdf/sd/299A_3_4s.JPG

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 Post subject:
PostPosted: Oct Sun 22, 2006 2:44 am 
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Lou,
You are right, what I am building is a integrated amp. I have 3 stereo tube integrated amps in my basement, a Scott 299B, Knight 724A and Lafatette LA-250A (Was my daily driver for a few years). I also have a Heathkit W4-AM Williamson amp with its WA-P2 preamp.

I have 2 other tube PA amps and other assorted amps from consoles.

Whenever I sell my parents house, I have a Motorola console stereo in the basement with a 15" woffer in the center and midrange/tweeters on the left and right to it. I hate to rip it a part but I am sure no one will want it intact. I remember when my father bought it around 1965-1966.

I really don't need another tube amp but I've always wanted to build one. Its a sickness we all have......

Don, Thanks for the Scott 299 Schematic, great for ideas.

Sal Brisindi

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 Post subject:
PostPosted: Oct Mon 23, 2006 2:15 am 
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I have noticed that a lot of commercial amps have the power transformer laminations situated at 90 degrees to the output transformer laminations. My assumption was that it is to minimize stray field interaction. Is it a good idea to follow this practice when building an amp?

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 Post subject:
PostPosted: Oct Mon 23, 2006 2:36 am 
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I noticed that too but when I situated the power transformer that way the transformers were a little to close. Now you got me thinking, which is good. I have to research that.

Thanks,
Sal Brisindi

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 Post subject:
PostPosted: Oct Mon 23, 2006 2:39 am 
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Yes, it is. Otherwise, you may have the transformer field causing trouble. That is unless they aren't going to be near it. Then, it's not so crittical. But, that depends entirely on the distance.
Bill Cahill

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 Post subject:
PostPosted: Oct Mon 23, 2006 1:31 pm 
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Sal, I had that same console. It was a Mediterranean type cabinet. It had reverb, 15" center spk and 5 small speakers on each side. It used 6- 6V6 tubes in the power amp! Sad to say I moved and didn't have room for it so I gutted it. I still have all the parts. I wish now I could have kept it, the cabinet was real nice. I bet someday these giant consoles will be rare. I still have the factory service manual for it.


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 Post subject:
PostPosted: Oct Tue 24, 2006 12:01 am 
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Sal Brisindi wrote:
Terry Judkins wrote:
The output from the CD player that I used as input for the amp I built was two volts peak to peak. I had more gain than needed using two 6SL7s.


Geez Terry,
With 2 volts peak to peak why would you need a amplfier... :wink:

Regards,
Sal


Just pointing out that if you are feeding the amp with a CD player you do not need a preamp. Two volts peak to peak is normal line out from players, tuners, etc. I had to put 100K resistors in series with the inputs and the volume control to reduce the signal. I used lots of local and global feedback so a 6SL7 feeding a 6SL7 phase inverter worked well

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 Post subject:
PostPosted: Oct Wed 25, 2006 9:27 pm 
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Sal,

I'm curious. What would the parts cost for an amp like this. I keep looking around for a stereo tube amp that I'd like to use with a set of Mission bookshelf speaker in a spare bedroom set up as an office/reading room. Any kit I've ever seen has been way out of my range. But, I'd really like to get a clean sounding tube amp.

Thanks for any info.

Michael


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 Post subject:
PostPosted: Oct Thu 26, 2006 12:33 am 
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Micheal,
I don't have a total tally but so far the transformers cost me $117.00 shipped, chassis $16.00 (I might purchase a black Hammond 12"x10"x2" for $20.00) Octal tube sockets $1.00 each, 9 pin I already had and the quad 6L6WXT (Sovtek) for $20.00 shipped.

I have the speaker and rca jacks plus many resistors/capacitors. I have to figure another $25-$40 for other items like potentiometers (I am pretty sure I have them) and parts not in my parts bin.

It should be under $200.00. I could have added a $100 more and bought a Dynaco 70 but this will be a fun project for me.

But.... sooner or later I will buy a Dynaco 70... just because!

Antique Electronic Supply (AES) has a 8 watt stereo push-pull tube amp kit for $137.00 which I read pretty good reviews.

Regards,
Sal Brisindi

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 Post subject:
PostPosted: Oct Thu 26, 2006 1:49 am 
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Building amps is fun. Unfortunately(?) the one I built around 1965 turned out so well I've been using it ever since, with no need to build another. I put the power transformer smack in the middle, on a very compact chassis, and have no hum problems at all. All the transformers are potted, though, which probably helped. As I recall, I did have to add a small metal shield between the volume control and power switch wiring. Breadboarding will disclose most any problem in time to fix it.


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