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henry4841

Pictures of your Tube Amplifiers

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My clone of the Scott LK-72A amplifier section with the cage removed.   Needs a nice wooden plinth.  I have a pair of the Scott LK72A/299C output transformer replacements from Transcendar and will swap those in after spending time with the Hammonds.  The Hammonds are a wee bit oversized for the power levels but I had them lying around so why not.  Compensation needed some tweaking with the Hammonds.  Also, the original design used silver mica in the FDBK return which I had a bit of a time with.  For some reason, which I'm still noodling, MLCC provided much better stability based on the analyzer response. 

 

 

The amp is insanely quiet.  Spectrum analyzer shows flat well out past 50kHz.  

 

If there's ever another Pilgrimage I might be tempted to drive this thing and a modified version that's almost complete down to Hope so we can all listen, compare, contrast.

 

  

chassis_15.jpg

chassis_16.jpg

chassis_17.jpg

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On 9/6/2020 at 8:22 AM, Backfire said:

 

Regretfully, my constructions tend to be rather utilitarian in comparison to some of the beautiful ones built by others!

There are historically renowned artists, architects, designers, and engineers whose works focus strongly on exactly of what you speak!!!  I have taught art and art history for 30 years (now retired), and the fascinating relationship between form and function was always a very important topic of discussion.

 

An amplifier, regardless of how well-dressed-up, machined and polished its chassis may be, is worthless without the circuit inside.   The 6C33C is one tank of a triode.   Very interested in your OTL.

 

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9 hours ago, dwilawyer said:

Interesting,  what is it?

 

A bread-board of this circuit, created by an retired EE audio friend of mine. Frustrated with the price of interstage transformers along with lousy bandwidth and goofy ratios, he experimented using a cheap Allied SE to PP interstage transformer connected as SE to SE.

 

Square waves ring like crazy, until one bridges the interstage with the 0.1uF capacitor.

The cap more or less brute forces the interstage to give better bandwidth, or gives the best of both worlds. (advantages of cap coupling and interstage coupling)

 

It's a circuit that makes SET luddites cringe. But it will output a decent square wave at 30kHz, with strong bass at 30Hz.

The 6EA7/bridged Allied IT front end circuit can run upwards of 120 volts peak to peak if I recall...I could be wrong. It's rather difficult to clip this amplifier for what it is.

 

post-6643-13819853605856_thumb.jpg

 

6EA7 Allied IT 2A3 amp circuit.JPG

 

Personally, I think John Warren won this thread...

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On 9/6/2020 at 11:22 AM, Backfire said:

The first is my everyday amplifier, a conventional type of OTL amplifier using 6C33C output tubes.  I quite like the second one too; again OTL, using 6082 output tubes.  The novelty with this one is that there are no transformer

 

very impressive ,four   6C33C   could deliver125 watts/8 ohms  ,  I 'm thinking this is  a 25 -30 watts amp  x 2  -/  question for you ,  you  are only using 1 power supply in this setup , any advantages versus 2

 

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5 minutes ago, RandyH000 said:

very impressive ,four   6C33C   could deliver125 watts/8 ohms  ,  I 'm thinking this is  a 25 -30 watts amp  x 2  -/  question for you ,  you  are only using 1 power supply in this setup , any advantages versus 2

 

 

Yes, the 6C33C OTL is about 25W into 8 ohms.  I'm just using the single power supply for the two channels, if that's what you mean.  The big toroid on top is 117-0-117 secondary, for the main positive and negative HT supplies for the output tubes, and also, with voltage doubling, for the input and stages driver.  There are a couple of smaller toroids under the chassis, for the heaters.  The main HT transformer is a bit of an overkill in terms of power handling, I think.  I don't have any problems with it.  The design of the OTL is based on one by Tim Mellow; it appeared in Audio Express, February 2010.

 

The power transformer for that other OTL is a bit bigger, and sits in my front garden...power-transformer-s2.thumb.jpg.a7c86ebc15e457e52f07f54deb741916.jpg

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2 hours ago, mike stehr said:

Personally, I think John Warren won this thread

 

As Dave would say: TRUTH!

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8 hours ago, pallpoul said:

One of many tube amps in my collection,...addictive stuff.

inspire.png.5d9d1b19e5445e424298c012f41fded2.thumb.png.25e906598b39a5731cdbb44f79d3fc42.png

What model are your amps

 

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I'd love to try that ^ amp out JW...

 

 

 

 

44072666292_e90f76ddb1_k.jpg

39816794270_f23182cdba_k.jpg

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5 hours ago, bkwa1959 said:

What model are your amps

 

mono blocks firebottle, by dennis had. 

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On 9/7/2020 at 1:09 PM, Marvel said:

Personally, I think John Warren won this thread

I know I needn't apologize, and I'm really not....but sorry, John.  I will say what you did is cleanly soldered, with nicely dressed leads.   In my view and experience, the P-to-P folks have it quite easily.  As if this were a race or a competition; which sure, in good fun why not...

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My former 45 amp, built on a mounting bracket from a used shipboard keyboard in 1997, schematic was from an article in Glass Audio. The power transformer burned out once, I replaced it, then stripped it when Maynard came out with the Lil Sweetie schematic. Not the best layout here, the parts had to fit the available space.

IMG_5358.JPG

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1 hour ago, erik2A3 said:
On 9/7/2020 at 4:09 PM, Marvel said:

Personally, I think John Warren won this thread

 

I know I needn't apologize, and I'm really not....but sorry, John.  I will say what you did is cleanly soldered, with nicely dressed leads.   In my view and experience, the P-to-P folks have it quite easily.  As if this were a race or a competition; which sure, in good fun why not...

 

Not my quote, but I agree with it. John designed the boards and layout and worked out more of the circuit.

 

I appreciate the nice/ beautiful work by those who do the PtP builds, too. Maynard's be at the top of that class. 😉

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