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ANY 100W Monoblock Schematics???

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Posted on October 30, 2009 at 22:03:27
Audiodyssey
Dealer

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Contributor
  Since: July 18, 2006
 I have a pair of monster OPTX's rated for over 100 watts with 5K primarys. These are Woodward-Schumacher and they were tested and found very usable for Hi-Fi. Each one weighs about 15-20 pounds. I was looking for a schematic that might work with these and have strongly considered using the Russian 6N3c-e (6P3C-e)6L6GC equivalent, since I now have about 30 of them. I am looking for an all tube circuit. Anyone, have or seen anything that might fit the bill?
Thanks!
"I KNOW you can hear it, but are you REALLY listening?"
RE: ANY 100W Monoblock Schematics???, posted on November 1, 2009 at 21:33:53
casouza
Audiophile

Posts: 486
Joined: March 18, 2008
 One basic rule of DIY is to never stretch the OPTs.
Since they are rated at 100W, why not make a nice and simple 60-70W KT-88 based push-pull amp?. The difference in maximum volume as compared to 100W is about 1.5db.
Bass and dynamics will sound much better than a 100W amp, due to less core saturation.

There is a mis-conception that one can use a transformer at maximum allowable dissipation by carefully biasing each tube individually and matching the idle bias current, however, tube transcoductance and current draw vary dynamically (with signal and over time), so there is no such thing as a zero net current PP transformer.

RE: ANY 100W Monoblock Schematics???, posted on November 1, 2009 at 09:24:20
Michael Koster
Industry Professional

Posts: 585
Location: Bridgeville, CA
Joined: October 24, 2007
 The best match I can come up with is parallel 807s, 600V in class AB1 with 5K plate-plate will give you a little over 100W. I guess KT88 or GU50, etc. will work as well (TT21...) anything with a 600V or better rating.

Some smaller 6L6 types can take 550V, which would get you pretty close.

You can also go to class A2 with a single pair of 807s to get about 75W.

Also bigger transmitting tubes like 813s would work in AB2 but somewhat overkill with 100W plate dissipation and 50W filaments.

RE: ANY 100W Monoblock Schematics???, posted on November 1, 2009 at 09:33:05
PakProtector
Audiophile

Posts: 9953
Joined: May 14, 2002
 hey-Hey!!!,
-----Also bigger transmitting tubes like 813s would work in AB2 but somewhat overkill with 100W plate dissipation and 50W filaments.

They also work well in A1, and the 100W plate rating would allow a near 100W Class A amp. It would be done with a single pair of finals too. I have not had any issues with my 813 amps...though I'm closer to 50W due to a 600V limit on B+ and a 10k a-a output TX build that was originally designed for 40W.
cheers,
Douglas


Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
1955 100W Monoblocks by Chicago Transformer Co., posted on November 1, 2009 at 06:48:13
Interstage Tranny
Audiophile

Posts: 1408
Location: Eastern
Joined: October 4, 2006
 Using the rare Chicago BO-14 opt, these are similar to the Williamson front end, using a 5687 and a 6SN7 to drive 6550s. 4 6L6 types do the same thing. That amp used a choke input filter for 40W triode 6550s, or 60W Ultralinear; or 100W Pentode output with cap input filter. They ran 600 Volts on plates, 300 V on screens for 100W. 6550s and 807s can handle that, but 6L6s seem wimpy with 600V Ep.

The front end of this Chicago amp is very similar to the Talbot Wright upgraded Williamson circuit, legendary magazine stuff...

When I get my new printer/scanner, I'll dig out the schemes.

Another nice circuit is the Grommes 260 amp;not an easy to locate cascode scheme, IIRC...

RE: 1955 100W Monoblocks by Chicago Transformer Co., posted on November 1, 2009 at 14:17:26
PakProtector
Audiophile

Posts: 9953
Joined: May 14, 2002
 hey-Hey!!!,
I am looking forward to building with those BO14 outputs. It's a 6k a-a load if you include the cathode winding. I'm thing the big TV sweeps can deliver me a Class A amp with a bit more than 40W. I hope to have one of them re-built so that subsequent construction can have a modified U-L tap location v. the original's 37%( and get rid of the 70V secondary ).
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
RE: ANY 100W Monoblock Schematics???, posted on October 31, 2009 at 07:25:12
Tom Bavis
Audiophile

Posts: 397
Location: Upstate NY
Joined: May 25, 2007
 To get 100W into 5K Ohms, you need 707 V, or 1000V peak. You'd need to run a DC supply of about 600V to reach that... I don't think ANY variety of 6L6 will be happy at that voltage. 70W may be a more reasonable goal.

AUDIO magazine build project, posted on October 31, 2009 at 05:40:04
grhughes
Audiophile

Posts: 1872
Location: Central US
Joined: February 17, 2004
 The audio article was titled; A KING SIZE QUARTER HORSE POWER STEREO AMPLIFIER by Robert M. Voss and Robert Ellis, October 1966, AUDIO

This used 6550/KT88 but the transformer primary secondary impedance was around 5k. It used Triad transformers and chokes. This was built on two chassis and was rather heavy.

Another good article by Herbert Keroes; ULTRALINEAR WILLIAMSON which used an Acrosound TO-330, which also used 6550 and all 6sn7gtb input/driver. But I only have one page and can't tell you what magazine it was published in.

A pair of 6l6s will not give you 100 watts. Why do you need such power? Push pull parallel 6l6 may but then your reflected impedance to the primary of the output transformer drops significantly. Ray




"I think the journey should be just as enjoyable as the destination." GRH
RE: AUDIO magazine build project, posted on November 1, 2009 at 10:54:07
Audiodyssey
Dealer

Posts: 512
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Contributor
  Since: July 18, 2006
 Ray,

This is perfect, I found the AX article. Thanks a lot!
Actually, I don't need the power, I just want to use what I have to it's potential and see what happens. I will probably not get around to this for some time, but it looks doable.
Anthony
"I KNOW you can hear it, but are you REALLY listening?"
Good! Hope it works out. nt, posted on November 2, 2009 at 04:23:49
grhughes
Audiophile

Posts: 1872
Location: Central US
Joined: February 17, 2004
 nt
"I think the journey should be just as enjoyable as the destination." GRH
RE: ANY 100W Monoblock Schematics???, posted on October 30, 2009 at 23:14:59
FenderLover
Audiophile

Posts: 3313
Joined: July 31, 2007
Contributor
  Since: May 17, 2009
 You wouldn't happened to have impedance spec's? My Twin Reverb runs around 2100 ohms on primary impedance of the output transformer. I'm running a quad of 7191A's. Very powerful tone. Great bass.

RE: ANY 100W Monoblock Schematics???, posted on October 30, 2009 at 23:38:51
Audiodyssey
Dealer

Posts: 512
Joined: November 7, 2004
Contributor
  Since: July 18, 2006
 I just updated it, they are 5k. Actually I'm looking at HI-FI. Really more for kicks than anything else.
"I KNOW you can hear it, but are you REALLY listening?"
RE: ANY 100W Monoblock Schematics???, posted on October 31, 2009 at 02:08:30
FenderLover
Audiophile

Posts: 3313
Joined: July 31, 2007
Contributor
  Since: May 17, 2009
 Of course if I actually read your initial post, I would have seen that (5K)... o.O Sounds like OPT more in range of two 6L6GC-types in parallel.

I think that quad 6L6GC or Russian 6pi3C-E would be quite an awesome hi-fi amp. My Twin is one of the cleanest sounding amps. The 7581A are great tubes. Maybe not the midrange of the Tung-Sol 6550. But, great bass and nice high frequency. I've had pretty good luck with the quad power tubes. Pretty stable. I did up the power supply to 1N5408 diode in the rectifier and up'ed the voltage rating of the filter caps (running pair in series). Anyhow, post how the experiment turns out.

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