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 Post subject: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Fri 08, 2012 1:49 am 
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Joined: Jan Sun 24, 2010 10:52 pm
Posts: 4307
Location: Phila Pa
As some of you know I have been laid up a bit due to a Hiatal Hernia operation,.
I have been coming along real well and had the time to work on this Beast,
It's a Stromberg Carlson AU-35 which the wife had to carry in and put on the bench since I have weight limitations at this time,
Here is the Schematic if you are interested,
http://www.audiophool.cjb.net/Schem_A/S ... _schem.gif
It has 14 tubes,
2, 5U4s
2, 6N7s
3, 6SC7s
3, 6SJ7s
and 4, 6L6s
13 Lytics and 19 Paper caps which were the wonderful plastic ones,
I installed 3, 1/4" mono plugs instead of the old Mic input plugs and 2 more for the speakers at 8 Ohms and left the octal speaker sockets as stock.
There was not too much room since this Amp is a bit odd, Two channels, 2, speaker outputs each with it's own output transformer and MONO at that.
I may modify to Stereo if I get real bored,,,,,,
Anyway, Not too much room so the Lytics needed to be restuffed and I was just able to squeeze a Radio Shack 3A transformer on the deck to act as a bucking transformer,
Someone before I got it installed a Decibel meter and a three way switch so I can monitor each of the two channels. Kinda neat so I left it, (Plus the 2,1/8" hole would be hard to cover" :lol:
This is a beast, The main transformer is HUGE and it eats 240 Watts, So a real solid Amp that seems to be built like a tank.
Now that the mechanicles are done, I may repaint the top, But that is all that remains to do except to install a new set of rubber feet.
I just wanted to share some pics with your guys,
It is supposed to be 30 Watts per side,,, ? I can't vouch for that,
All I know is that it is stinkin' powerful through the small pair of speakers I have. Sounds great too!
It has been a fun project keeping me busy for the past few days,
Thanks for looking,
Peter B.


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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Fri 08, 2012 1:54 am 
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Location: Raleigh NC USA
A good-looking and solid job, Pete, and a fine-looking amp. What does the meter on the front panel read?

PS: Still wondering just how all these old PA amps happen to find their way to your door... :wink:

30 watts per channel sounds appropriate; that could easily be achieved with original 6L6-series tubes even in class AB1.

Keep up the good work and best wishes for a speedy recovery post-op,

Larry

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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Fri 08, 2012 2:08 am 
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I really like that, great job.
I reckon 30watts is quite possible with that bad boy.

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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Fri 08, 2012 2:38 am 
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Joined: Jan Sun 24, 2010 10:52 pm
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Location: Phila Pa
I will say this,
Getting all the new caps under the down of resistors was time consuming as well as restuffing the cap cans but I feel it was well worth the detailed work.
Peter.


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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Fri 08, 2012 5:24 am 
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Joined: Nov Sat 27, 2010 6:15 pm
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Great restoration. FYI some of these sets were really made for fail safe Mono, with dual power suppies and strapped output strips. Have a couple of Schumerlich Organ tower amps like this. Knock down a barn with these. Seriously, 30 serious tube watts per channel.


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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Mon 11, 2012 10:11 pm 
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Joined: Apr Mon 24, 2006 1:05 am
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Location: Ellington CT
WOW!! :shock: Never saw one of those guys, and I was in commercial sound for a while. Do you have any documentation on it? Love to get a look at the driver stages using the 6N7's. Enjoy that beast!! :D

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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Tue 12, 2012 1:49 am 
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http://www.audiophool.cjb.net/Schem_A/S ... _schem.gif

:wink: Larry

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Last edited by BigBandsMan on Jun Wed 13, 2012 1:25 am, edited 1 time in total.

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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Wed 13, 2012 1:17 am 
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Location: Phila Pa
Larry, The link above does not work,
I too would like to see the link,
Thank you
Peter


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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Wed 13, 2012 1:27 am 
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Fixed. Sorry about that. Try it now.

:wink: Larry

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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Wed 13, 2012 2:44 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Rochester NY USA
If you're trying to open it in Internet Explorer 7 or lower, it won't show up, as image is too large (though you COULD download it to view in another program). I was more interested in providing a full-resolution image than having it work in every browser. It WILL open in Firefox, Opera, Chrome, even Netscape...


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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Wed 13, 2012 12:18 pm 
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OK, I see. Having Firefox, I wouldn't have noticed incompatibility with other browsers...

C'est la guerre.

Larry

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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Wed 13, 2012 1:40 pm 
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Location: Marietta/Moultrie GA
That's the second one I've seen, where someone cut the front panel and put in a VU meter.

I have the OTHER one here- it came to me with bad output transformers and needing a LOT of cosmetic work besides.

I'm going to convert it to a nice hi-fi integrated amp. 6L6GCs, Edcor 60w output transformers, probably either 5AR4 or 5V3A rectifier tubes, 6SN7GTA amp drivers, Loktal preamp tubes (7F7/7F8/7N7). I'm thinking of using it with one of the Hegaman style circuits (like maybe the HK A250 output stage), but with fixed bias. Sims show it should be capable of 40w/ch, pretty easily. Maybe even 50w/ch, if I get lucky.

I'm still considering options for the cosmetics. That's what's keeping me from going full-bore on it yet...

Regards,
Gordon.

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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Wed 13, 2012 1:50 pm 
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GordonW wrote:
That's the second one I've seen, where someone cut the front panel and put in a VU meter.

I have the OTHER one here- it came to me with bad output transformers and needing a LOT of cosmetic work besides.

I'm going to convert it to a nice hi-fi integrated amp. 6L6GCs, Edcor 60w output transformers, probably either 5AR4 or 5V3A rectifier tubes, 6SN7GTA amp drivers, Loktal preamp tubes (7F7/7F8/7N7). I'm thinking of using it with one of the Hegaman style circuits (like maybe the HK A250 output stage), but with fixed bias. Sims show it should be capable of 40w/ch, pretty easily. Maybe even 50w/ch, if I get lucky.

I'm still considering options for the cosmetics. That's what's keeping me from going full-bore on it yet...

Regards,
Gordon.


Hi, Gordon, I take it that you're planning to replace the power transformer as well as the output transformers...

And why bother with a 6SN7 for a driver? The 6N7 will run rings around it.

:wink: Larry

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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Wed 13, 2012 7:49 pm 
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Curious, but if you are sure ypu have to replace both output transformers and the power transformers, and most of the rest of the innerds, just what purpose do you have in mind?


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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Wed 13, 2012 9:29 pm 
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Whoever installed that meter knew what he was doing. I had figured the amp was bought that way.


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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Thu 14, 2012 1:02 am 
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I thought so too, but the meter certainly doesn't show on the schematic.

Easy to set one up. Installing it is the hard part. Been there, done that.

:wink: Larry

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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Thu 14, 2012 2:31 am 
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Joined: Jan Sun 24, 2010 10:52 pm
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Location: Phila Pa
The Meter was aftermarket and was in the Amp when I bought it,
If you look above the meter there is a 3 way toggle and it is hooked up in such a way that going from left to right you can see the output on the L and R channels,,,,
Don't know why it was installed, But I felt leaving it was the only thing to do,
Otherwise I would have a big hole there,
Amp sounds great and have been using it quite a bit,
Now if I can only get it to be stereo instead of dual mono,
Looking at the wiring diagram it should not be too hard.
WIll see when I have some time.
Peter


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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Thu 14, 2012 12:11 pm 
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The easiest way would likely involve "un-mixing" the two mike channels, separating the two output chains at their splitting point, and routing one mike channel straight into each chain.

I'll download the schematic when I have a chance, mark the best places to make (and un-make) the necessary connections, and post it. I should be able to do it this evening after I get home from work.

:wink: Larry

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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Thu 14, 2012 1:14 pm 
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For me, at least, those handles on the top of the cabinet tell the story of that piece of equipment.<VBG>

RJ

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 Post subject: Re: Stromberg Carlson AU-35, BIG Amp, Finished with pics
PostPosted: Jun Thu 14, 2012 2:55 pm 
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Looks like you have four input channels. If each goes to its own tube then you could modify the amp to make two channels have an RIAA EQ if you have a record player with magnetic cartridge and the other two can be line inputs. Could add a switch to the front panel to select between the two inputs.


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