The long awaited "Little Sweetie" mono SETs

[CECAA850 29071]

On 1/31/2020 at 12:28 PM, Jeffrey D. Medwin said:

I am busy with the stock market ( see my thread I started this week in LOUNGE section

Yet another boner of a thread.  I have to admit though, I always get a chuckle out of your posts.

[richieb 7217]

1 hour ago, CECAA850 said:

Yet another boner of a thread.  

Yep, this thread is Hard to take —

[CECAA850 29071]

36 minutes ago, richieb said:

Yep, this thread is Hard to take —

I see what you did there. 

[Marvel 5429]

There's always the synergy thing that goes on with equipment. Some speakers simply sound bad with certain amps.

 

Bruce

[henry4841 301]

The little sweetie schematic was posted on diyaudio forum and I have built it. Sounds as good if not better than my SET 45 tube amplifier. Wonderful sounding little amplifier. 

[CECAA850 29071]

On 8/10/2020 at 6:03 AM, henry4841 said:

The little sweetie schematic was posted on diyaudio forum and I have built it. Sounds as good if not better than my SET 45 tube amplifier. Wonderful sounding little amplifier. 

Congrats.  Maynard is da man.

[John N. Lumley 6]

Hello, I just completed a pair of "Little Sweetie" mini-mono-blocks, based on Maynard's great design.

I  basically used the same Hammond iron, but added a choke to replace R10; the 180-2W resistor.

I also added a damper-diode tube in series with the red/yellow C/T wire, in the ground rail to provide a slow-turn-on.

I put a stopper-diode in the B+ rail to the blue wire of the output transformer.

It took me a very long 3 days to machine the chassis and wire the amps!

And upon first start-up, they sounded really nice, and are improving every day.

Thanks again to Maynard for sharing his wonderful designs and providing help to builders.

(I will try to upload photos when I figure out how to resize them below the 2MB limit.)

rgds, John N. Lumley

 

 

[tube fanatic 1150]

Definitely post pictures and a schematic showing your changes.  I’m glad you took the time to build them and I hope you get lots of pleasure from listening to them.  
 

Maynard

[John N. Lumley 6]

On 11/20/2020 at 6:08 AM, tube fanatic said:

Definitely post pictures and a schematic showing your changes.  I’m glad you took the time to build them and I hope you get lots of pleasure from listening to them.  
 

Maynard

Hello again, here's a few external pix to start with.

Front view first.

rgds, JNL.

[John N. Lumley 6]

On 11/20/2020 at 6:08 AM, tube fanatic said:

Definitely post pictures and a schematic showing your changes.  I’m glad you took the time to build them and I hope you get lots of pleasure from listening to them.  
 

Maynard

[John Warren 233]

Are you isolating the power supply transformer from chassis ground?  

[tube fanatic 1150]

Your build looks very nice John!  Can you post pics of the underside?  If you have time, please add the pics to Henry’s picture thread in this section.

 

It would be informative for those following this thread to discuss your power supply mods and why you chose to implement them.

 

 

Maynard

[John N. Lumley 6]

On 11/22/2020 at 7:39 AM, tube fanatic said:

Your build looks very nice John!  Can you post pics of the underside?  If you have time, please add the pics to Henry’s picture thread in this section.

 

It would be informative for those following this thread to discuss your power supply mods and why you chose to implement them.

 

 

Maynard

 

Hello, I did not isolate the transformers from the chassis.

I use star washers to bite thru the varnish used in manufacturing, thereby grounding them.

I employed a 6W6GT 1/2 wave damper diode, right after the MUR4100E diodes.

This provides a nice and slow ramp-up of the B+, and helps filter out diode hash.

I also use UF4007 "stopper" diodes in series with both the B+ and the B++ rails.

These prevent interaction between the two stages, and improve the bass.

I used 47uF-470uF-47uF caps in the power supply, based on PSUD2 simulations.

I measure under 1mV-AC at the speaker terminals.

Overall, a very worthwhile project, proving again that the circuit design is paramount!

Expensive "audiophile" parts can't fix a bad design sound.

A schematic will follow; still having to reset my password every time I try to log-on again...

rgds, JNL.

 

[John N. Lumley 6]

Ok, here's the 2) schematics in jpeg format.

I'm still very impressed with the sound of these little and affordable mini-mono-blocks!

It's all I really need to power my Tang-Band W8-1808 full-range drivers (93dB),

that are in a 2-way system, with a Tang-Band 25-1166SJ tweeter (93dB).

Hat's off to Maynard, again.

rgds, JNL.

 

[mike stehr 974]

The art deco flair in the schematic you've drawn is awesome.

 

I use a pair of 6AU4GTA half-wave damper diodes in full-wave for a 2A3 SET amp of mine.

[tube fanatic 1150]

You are quite the artist John.  Looking at the schematic made me feel good!

 

For the benefit of those following, can you explain why you chose to add the diodes in series with the opt and plate/screen supply of the driver?  
 

Maynard

 

 

[John N. Lumley 6]

23 hours ago, mike stehr said:

The art deco flair in the schematic you've drawn is awesome.

 

I use a pair of 6AU4GTA half-wave damper diodes in full-wave for a 2A3 SET amp of mine.

 

Hi Mike,  great idea!

The TV damper-diodes give you a slow turn-on, and a low voltage drop.

The oil cap gives you low DCR, and a very long lifetime.   (if not forever)

As you know, that first cap right after the rectifier is the most stressed cap in the whole amplifier!

The Marantz model 2 amps used 2) 6AU4 then a 8uF motor-run oil cap.

rgds, JNL.

[John N. Lumley 6]

22 hours ago, tube fanatic said:

You are quite the artist John.  Looking at the schematic made me feel good!

 

For the benefit of those following, can you explain why you chose to add the diodes in series with the opt and plate/screen supply of the driver?  
 

Maynard

 

 

 

Well, in a nutshell, the diodes prevent the driver tube voltage sagging, when the power tube draws heavy current.

 

If you Google "stopper diode", you find better explanations.

rgds, JNL.

Edited November 28, 2020 by John N. Lumley
wrong description

[mike stehr 974]

3 hours ago, John N. Lumley said:

Hi Mike,  great idea!

 

Actually, the idea was from a friend of mine who designed the circuit and coached the build for me.

The PS transformer is a Gramer television transformer, with a 10-12 Awg heater winding for the 6AU4.

A 36uf Mallory oil is the first capacitor in the supply, with a 4 Henrie choke, a 100uF Sprague Atom with another Mallory 36uF oil cap in parallel with the Sprague.

 

And I thought this audio amp power supply using 6AU4 for full-wave was just a bizzaro one-off...and it turns out Marantz did it with a commercial amplifier.