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Now Complete- the Model 10-5 Integrated Amplifier

GordonW

GordonW

Speakerfixer
Subscriber
I'm finally pretty much finished with this project.

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If you were following THIS thread:

http://www.audiokarma.org/forums/showthread.php?t=209894

... then the name of the project makes perfect sense to you. :D

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Based on a chassis from a very distressed Pilot 232 amp... which was stripped to the bare metal... the amp has very oversized transformers (power transformer specified for a large Motorola console, and output transformers specified for a Seeburg 24w/ch jukebox) and a circuit design loosely taken from the Stromberg-Carlson ASR-333 integrated amp.

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Tubes are a 6CG7 (RCA cleartop) for the preamp stage, two 6GH8 driver/phase inverter tubes (Amperex), two pairs of 6BQ5 output tubes (RCA), and a GZ34 rectifier (Philips). Power is around 15w/ch... a STRONG 15w/ch., at that.

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I've just started listening to it in earnest... after the first session, I made a few changes to the gain structure (added a bit more feedback to the amp section, reduced the anode resistor values on the preamp stage to drop gain and increase current, and added a 220K RF-stop/gain-drop resistor to the volume control, as well as going back to the original 100K grid resistors on the output stage, instead of the 220K resistors I had first experimented with), which helped to make the volume control more "usable" (originally, it was "wide-open" at around 11:00 on the volume... now it takes about 2:00 to get it near wide open on a standard line-input), and seemed to both smooth out the sound and increase the dynamic contrast a bit.

For a collection of parts from the "four winds", this thing really came together very well. The transformers run almost COLD, even though I'm running the 6BQ5s about as hard as is prudent (nearly 365V B+!). The nice thing about the amp, is that if someone wanted to "ease up" a bit, I determined that it will also work just fine with a 5U4 rectifier... which drops B+ to around 340V. With the cathode bias setup, it seems to run quite fine... no excess heat from the output tubes, even with the "hotter" GZ34 rectifier tube.

I'm gonna hook it up to some killer speakers, and listen for a while now...

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Regards,
Gordon.
 

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Well, this thing just gave the Tannoy Glenair 10s a real kick in the pants!

HOLY COW... THAT's some BASS from an EL84 amp!!

Dynamics are a KILLER, too. Drums just sound REAL.

Great balance top-to-bottom... just sounds natural...

Still need to drop the preamp gain a little more... hooked it up to a Theta CD transport/DAC, and I'm still banging away below half-way on the volume control. No worries... just a couple of resistors to swap out...

WOO HOO!! :banana: :banana:

Regards,
Gordon.
 
Very nice! I confess I haven't followed the thread, but that looks/sounds like a lot of mojo in a compact package. Kudos!
 
That turned out real nice, Gordon.

You might be able to find those chrome caps that cover unused holes in kitchen sinks, to cover that hole in the back of the chassis. Along with the smaller one next to the PS xformer.

Those Motorola PS xformers are monsters.
 
Mike Stehr said:
You might be able to find those chrome caps that cover unused holes in kitchen sinks, to cover that hole in the back of the chassis. Along with the smaller one next to the PS xformer.
Click to expand...

That's what I'm thinking. A quick trip to a hardware store should take care of that. :thmbsp:

Though, I'm inclined to leave the one next to the transformer open... it's not large enough for anyone to stick fingers into, and it's pretty near the cathode resistor for the output tubes...

Regards,
Gordon.
 
Very nice. :thmbsp: Looks a little like a mono amp I picked up awhile back, in a mystery amp thread.
 
Man, that didn't last long here.

A friend of mine came in... and wound up taking the amp home with him last night. Now he won't bring it back. Says it kicked his Audio Research CA-50 amp in the butt. Almost as loud, bass just as good if not better than the ARC, and the tonal balance of my amp was better (he found the ARC to be a bit bright on the highs, where mine was "dead on")...

He has acceded to actually giving me money in return, though... can't complain, I guess :D :D

Man, I guess I sort of exceeded expectations? Now, where can I find another pair of those output transformers?!?!?

BTW: We will be making one upgrade- BrassTeacher volunteered that he had a new Alps Blue 250K volume pot. I'm gonna snag that, and put that in the amp, in place of the run-of-the-mill CTS pot that's in there now. Could make it even better???

Regards,
Gordon.
 
I can testify that integrated amp does rock. I was in Audio Atlanta Thursday night and got the pleasure of hearing this guy driving the Tannoy Glenair 10s.


Corey
 
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