Finally Completed!!!!

2nd harmonics for the masses

Finally Completed!!!!

Postby EWBrown » Sat Dec 27, 2008 2:59 pm

I finally completed my second G*S*G amp, I had started it earlier in the year, and had all the machanical assembly done, and the PC boared "stuffed" leaving only the final wiring to be completed.
It is built on a Hammond 12X10X2 Steel, black powder-coated chassis.

I finally got around to doing that yesterday, and everything came up running perfectly!

The OPTs are a set of "custom" MQ RH-60s, and I replaced the paralleled 180 ohm WW resistors with a second 1.5H choke. Other than that, it is more or less "stock". The "custom" part of the MQ OPTs is that they have end bells and no UL tap on the primary, as opposed to the stock RH-60s which have a UL tap on teh primary, and brass shannel frame mounting.
They look very good mounted on the black PC chassis.

The output tubes are 1958 vintage Russian 6C4C (6S4S) which are the old fashioned twin plate version. These run with 46.5V across the three paralleled 2.74K resistors, or about 50 mA per side, with 305V on the plates. The rectifier is GE 6AX5 and the driver tubem Tung-Sol 6SL7, both NOS / NIB. Interstaeg coupling caps are the green Russian K42y-2 PIO 0.1 uF / 500V "kommie kaps", as they are often called over at Bottlehead.

Sound quality is great, and is improving with more and more runtime.


The tube data sheets enclosed with the 50 year old Russian tubes indicate that they were manufactured at the Leningrad "K-18" tube works, in 1958.

Interestingly enough, these tubes have the "winged C" Svetlana logo, as does the data sheet.

The data sheets also have a form on the back, to be filled in with the date of installation, the date of removal, the number of hours of operation, and the reason for removal.

One thought occured to me - I am sure that the folks who were making these tubes five decades ago had no idea that they would end up in the USA half a century later... From Cold War to "cool sounds"... Yellow_Light_Colorz_PDT_06

/ed B
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Postby MashBill » Sat Dec 27, 2008 5:06 pm

Nice! Please post some pics for us to drool over.

Also, did you use LEDs for the biasing?
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Re: Finally Completed!!!!

Postby Shannon Parks » Sun Dec 28, 2008 8:11 am

EWBrown wrote:One thought occured to me - I am sure that the folks who were making these tubes five decades ago had no idea that they would end up in the USA half a century later... From Cold War to "cool sounds"...


I also think this quite often, Ed. WWII JAN tubes - 60+ years old and did their part to save the world.
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Postby EWBrown » Sun Dec 28, 2008 2:00 pm

This one is pretty much "stock", maybe on the next one, which will be set up to run with 6CK4s, I'll try the LED biasing for the 6SL7.

Sometime I also have to try out the "floating paraphase" 6B4G PP version.

The "numbers" according to SET CAD are 2.5W @ 3.5% 2HD and 0.1% 3HD.

The 5K OPT primary results in somewhat lower power output, but also lower THD, which is a pretty good trade off.

/ed B
Last edited by EWBrown on Fri Mar 27, 2009 12:32 pm, edited 1 time in total.
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pix o' da beast

Postby EWBrown » Fri Mar 27, 2009 8:56 am

Image

Image

Image

I know I posted these elsewhere, but danged if I can find them... :? :P ;)

/ed B
Last edited by EWBrown on Mon Feb 14, 2011 7:10 pm, edited 3 times in total.
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Re: Finally Completed!!!!

Postby Ty_Bower » Sun Apr 19, 2009 5:07 pm

EWBrown wrote:I replaced the paralleled 180 ohm WW resistors with a second 1.5H choke. Other than that, it is more or less "stock".


Nice looking amp. Ed. Has the substitution with the second choke affected the B+? Why are your two 120 uF caps different looking?
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Postby EWBrown » Mon Apr 20, 2009 8:30 am

The B+ voltage stayed fairly close (within 5-6VDC) to the original design. A few volts' worth of extra B+ voltage doesn't hurt (unless you stick a finger in there...) :'( ;) (lol)

The electrolytic caps were what I had on hand, the larger (light blue) one is 180 uF, 500V, and the smaller one is the "standard" 120 uF 450V cap.

I had gotten the 180 uF 500V from a local "antique" shop which also sold electronic parts, which came from a local "green technology" (solar and alternative energy) business which went out of business a couple years ago. Alas, the antique shop has changed ownership, and no longer serves as a parts store.

The blue caps were the right size, just short enough to fit on the board under a 2 inch deep chassis, and the pin spacing was also correct.

I figure that a little extra PSU capacitance is always a good thing.

Overall, the GSG circuit isn't all that "critical" as to parts values precision.

I have a coupke more modified GSG designs, using 6AV5GAs and 6CK4s, in the works (once I complete the move to NC).

As these are both indirectly heated tubes, I'll dispense with the DC power for the filaments. I can always add the 6.3VDC circuitry later if it is needed.

/ed B
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Postby Ty_Bower » Tue Apr 21, 2009 7:58 pm

Ed, you wouldn't happen to have the mounting dimensions for those bell ended RH-60, would you?
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Postby EWBrown » Wed Apr 22, 2009 10:34 am

For once, something that isn't a thousand miles away from me.
;)


IIRC, they are the same as a Z565, but before I declare that to be 100% bona fide, I'll measure the unit, and then post the dimensions here...

FWIW, the bell end RH60 isn't an MQ "standard" item.


My normal transformer mounting measuring method is to place the trannies where I want them, and then trace out the trannies' mounting holes, then locate the lead feed through holes (usually half inch diameter) halfway between them.

For the black steel chassis, I cover the whole thing with the blue painter's tape, and that serves to protect the surface from scratches and makes marking the drilling and punching locations a lot easier.


stay tuned....




/ed B
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two by two inches

Postby EWBrown » Wed Apr 22, 2009 4:45 pm

I just measured the RH-60s, the mounting holes are on a 2 inch X 2 inch square. The two "wire" holes are 3/8 inch diameter with a rubber grommet to protect the wire leads. These are one inch between the bell end mounting holes. These can be clearly seen in the "under the hood" view of my GSG.

The 5K primary is the red (B+) and blue (plate) leads. Secondary is black (0), orange (4 ohm) and yellow (8 ohm).

HTH

/ed B
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