Little Sweetie Forum amplifier project

[henry4841]

One should expect the labor cost to more inline for what it is worth. It takes me approximately 10 hours of my time to build one of these. You should expect the labor rate to more realistically to be in the $20 to $30 an hour range.  I am just trying to bring out just how swell this amplifier sounds and my hope is more members will see if they are impressed as I am with the sound. I probably will not build another one to sell being this is just a hobby for me. 

[The Dude]

56 minutes ago, henry4841 said:

You should expect the labor rate to more realistically to be in the $20 to $30 an hour range. 

Even if someone works for themselves out of the home, this is still a pretty low rate in my opinion.  

 

How do the Edcor's compare price and quality wise?  If someone is planning on building later down the road, maybe a 2 month wait is worth it? 

[Curious_George]

On 8/7/2022 at 9:55 AM, Edgar said:

I don't know if anyone here has tried any of these. I have a pair to use in a PP EL84 amp that I haven't built, yet, so I cannot comment about sound quality.

I contacted Matt at Musical Power Supplies and he has a new line of output transformers that are "HiFi". The ones on eBay are more suitable for guitar amps, which is what he is specializing in until recently. He said the OT10SE HF 5k/4 & 8 ohm / 10 watt would be about $38 a piece, 3 week lead time. The HiFi outputs are speced at 40Hz~20kHz. I'm getting more info and will post when I get it. 

 

These seem like a real competitor for the Edcors that are almost double the price. 

 

I'm ordering 4 to see how they perform. 

[henry4841]

1 hour ago, Curious_George said:

I contacted Matt at Musical Power Supplies and he has a new line of output transformers that are "HiFi". The ones on eBay are more suitable for guitar amps, which is what he is specializing in until recently. He said the OT10SE HF 5k/4 & 8 ohm / 10 watt would be about $38 a piece, 3 week lead time. The HiFi outputs are speced at 40Hz~20kHz. I'm getting more info and will post when I get it. 

 

These seem like a real competitor for the Edcors that are almost double the price. 

 

I'm ordering 4 to see how they perform. 

I am glad you posted this because I could not find the SE OPT's on ebay you described for $38. Look forward to your test and opinion.

[henry4841]

2 hours ago, The Dude said:

How do the Edcor's compare price and quality wise?  If someone is planning on building later down the road, maybe a 2 month wait is worth it? 

I have used Edcor's exclusive for all my tube builds except one so I cannot compare them to others but Edcor makes excellent transformers IMHO. Years ago they shipped in approximately 3 weeks except for my last two orders. It took 2 months and an email to them before they shipped.  

[capo72]

My last order from Edcor was in June and took 2 weeks. Maybe I just got lucky.

[Curious_George]

I ordered twice this year from Edcor and the lead time was less than what they initially said, though I can't remember the exact time frame I had to wait. 

[henry4841]

I still get excited when I get a package from Tubedepot. Got my tubes for this build today. Two Westinghouse 6y6's and two from a brand I have never heard of. CEI electron tubes 6SJ7's with the markings of Made in England. With a little googling it appears that CEI was a distributor that bought from others and put their stamp on them. Made in England, Mullard perhaps is what I found out. Common practice for manufactures to buy from a competitor way back when and put their stamp on. When a company made a run they made a lot of them with no marking for this reason. 

[Curious_George]

21 hours ago, henry4841 said:

I am glad you posted this because I could not find the SE OPT's on ebay you described for $38. Look forward to your test and opinion.

Below is more info from Matt at MPS (Musical Power Supplies):

 

1. The OT10SE+5K-HiFi SE output Xfmr is designed for 10W

2. Max Bias Current is 50mADC (at 60mADC inductance would roll-off another 10 to 15% w/o saturating the core)

3. Frequency Response - 40Hz to 20KHz (at 10W)

4. This transformer weighs in at 2.2LB  (EI7/8 x 1.25 in core stack)

5. Inductance - typically 20H at 1V/100Hz  (as you increase bias current it will roll off)

 

The OT10SE+5k-HiFi is a pretty solid transformer for 6V6 circuits, it'll be pushed a bit for 6L6 with higher currents.

If I go up a size to the OT20SE on 1 x 1.25 bobbin a solid 60-70mADC is doable for larger tubes.

 

Overall looks like a great transformer for tubes that will be running around 50mA of output current. I'm going to test it at 60mA in a 2A3 circuit and see how it performs. 

[tube fanatic]

Hey folks!  It has been a while so Henry twisted my arm to say hello.

 

The plate curves of the 6Y6 are very similar to those of the 2A3.  The former have the distinct advantage of being inexpensive and abundant, and don’t have the DHT filament issues to deal with.  It is a wonderful tube all around.

 

I have taken a break from amp design and building for now due to a number of old radio restoration projects which have accumulated due to the move 6 months ago.

 

Hope everyone is well.

 

Maynard

[Curious_George]

Here is the Little Sweetie amp schematic. The amp was originally designed as a mono unit, but you can use the alternate power supply to make a stereo unit. 

Little Sweetie Mono Amp Schematic.pdf Little Sweetie Stereo Power Supply Schematic.pdf

[henry4841]

R11 in the alternate PS is 3K2W. Wonderful to see 11 downloads already. You will want to adjust the value of R10 where you have 200V's between the cathode and plate of the 6Y6. If my calculation is correct you will be running the plate dissipation at 10 watts. The 6Y6 is rated for 12.5 plate dissipation. This is at 50ma. This is from Maynard. My experience is making a tube or transistor work gives better sound. That is as much as can be safely run. Nelson Pass runs a lot of bias in his transistor circuits for this reason. 

 

There once was a reviewer for a noted publication that was an active member on this forum that said the best sounding amplifier he ever heard was a 1 watt one. Not this one so as not to get the wrong idea I am saying this is the one he was talking about. Just for those that turn their nose up at just one watt. Maynard's stereo power supply has two sections. Two PS sections with one transformers. My builds, this will be the third, just use one PS section of the schematic. Two would be better but one has always been good enough for me. Keeps the build simple and less expensive. Plenty of imaging with big soundstage with one PS section. 

 

Just for comparison below is the power tube for this amplifier vs the one for the Decware Zen. 

 

[Curious_George]

Are you implying "bigger is better" Henry?  Sorry, had to throw that in there. 

 

There are so many tubes based on a few great tubes developed in the late 30's and 40's. You can obviously see the difference in manufacturing costs in the photo of these two tubes; smaller glass envelope, Noval 9-pin base, small(er) pins and reduced size Mica wafers inside the tube for support. 

 

 

[Curious_George]

13 hours ago, Curious_George said:

Here is the Little Sweetie amp schematic. The amp was originally designed as a mono unit, but you can use the alternate power supply to make a stereo unit. 

Little Sweetie Mono Amp Schematic.pdf 141 kB · 13 downloads Little Sweetie Stereo Power Supply Schematic.pdf 58.26 kB · 13 downloads

When I get around to building one of these, I'm going to redo the driver circuit and use a 12AV7. I don't need the gain of the 6SJ7 pentode since I always use a preamp. 

[henry4841]

1 hour ago, Curious_George said:

Are you implying "bigger is better" Henry?  Sorry, had to throw that in there. 

😃   

 

Better looking for sure. Many say look good sound good. 

[henry4841]

1 hour ago, Curious_George said:

When I get around to building one of these, I'm going to redo the driver circuit and use a 12AV7. I don't need the gain of the 6SJ7 pentode since I always use a preamp. 

Please share the schematic when you decide to build. 

[henry4841]

I have one potential buyer and we have discussed spending a little more for a solid cherry wood stand for the amplifier to sit in with hand cut dovetails. Let's face it a Bud chassis is very plain looking. I want whoever owns it to point with pride at this amplifier. Pictures coming of stand when finished. Little rusty, been two or more years since I cut any dovetails, but they turned out pretty good to my old eyes. 

[Curious_George]

On 8/6/2022 at 8:23 AM, Curious_George said:

The 6Y6G was designed as an "Beam Tetrode". This would indicate that it was designed for audio service, but could also be used in TV sets as well for video. The 6Y6G was used in a lot of table top radios or where only a few watts were needed for audio. The 6V6 was the successor which is also a great tube for a low power SET amp.

“The 6Y6G was designed to operate on a somewhat lower G2 voltage, but drew a higher plate current. Also had considerably higher heater current than other tubes of the era. The combination of those two characteristics required use of larger power transformers and in many cases two rectifier tubes were used. 

GE and a few others used them in some radios for a while. Other beam power tubes are more efficient, so they were never very popular in consumer radios. Some were used in TV's, but the main usage appears to have been in commercial/industrial equipment. They make a decent series pass tube in voltage regulator applications.”

 

Info from a Google search… 

[tube fanatic]

22 hours ago, Curious_George said:

When I get around to building one of these, I'm going to redo the driver circuit and use a 12AV7. I don't need the gain of the 6SJ7 pentode since I always use a preamp. 

Nick, how are you planning on configuring the 12AV7?  Getting around 21V rms from one section to fully drive the 6Y6 as used in the Sweetie will bring the distortion of the 12AV7 into the 5% range.  This is not a bad thing in my opinion.  You could set up the 6SJ7 for minimum gain to allow use of your preamp and minimize driver distortion if desired.

 

Maynard

[Curious_George]

3 minutes ago, tube fanatic said:

Nick, how are you planning on configuring the 12AV7?  Getting around 21V rms from one section to fully drive the 6Y6 as used in the Sweetie will bring the distortion of the 12AV7 into the 5% range.  This is not a bad thing in my opinion.  You could set up the 6SJ7 for minimum gain to allow use of your preamp and minimize driver distortion if desired.

 

Maynard

I have not decided on the 12AV7 input configuration yet. I'll probably do an SRPP/Totem Pole running at 300V on the plate. This way I'll get a 150V bias point which looks pretty good for a decent voltage swing (drive). 21VRMS (60-PP) is not that much. I usually bias my input tubes between 1.75V and 2V for some headroom depending on the tube and other factors.