[belle harbor]

Many of the amps I design are requested by DIYers looking for something specific to build, or audiophiles who want a particular type of amp for a particular application. 

The "Little Bruisers" are mono SEPs (nothing compares with mono amps for preventing crosstalk issues which can greatly affect the sound stage size) which put out approx. 1.3 wpc at the onset of clipping.  While this seems like a ridiculously low amount of power, it is actually more than enough when powering very high efficiency speakers (especially when the latter are in smaller size rooms, or are used for near-field listening).  The design goals were a potent bottom end and a very smooth midrange and high frequency characteristic.  The former was achieved with a frequency dependent voltage feedback network, and the latter with a variable low pass filter at the input which allows the user to set the high frequency response to individual need.  The driver is grid-leak biased which allows the tube to self adjust over its entire operating life.  Power supply regulation isn't the best by any means; however, the dc current draw difference between the quiescent operating condition and the onset of clipping is so minimal that it is not an issue.  Ripple is extremely low resulting in no hum even with an ear against the speaker grille.  Only a trace amount of hiss is evident with an ear against the grille overlying the tweeter.  Another goal was the use of inexpensive, readily available, tubes (although life expectancy is so great due to conservative operating conditions that replacement may never be needed).  The driver can be a 6AT6, 6AQ6, 6T8 and the output tube a 6W6 or 6DG6.  The power transformer runs only slightly warm even after a few hours of use.  Lastly, parts cost needed to be fairly low and came in at approx. $400 US. 

I've attached some pics which show the construction techniques used as well as the 320 Hz square wave.  My schematic is a PDF and I couldn't figure out how to get that on here for those who may want to build their own (my computer literacy stopped when Fortran became unpopular!)

[randytsuch]

Cool looking project.

Think you would need to convert the PDF to a jpg file to be able to post it here.
A parts list would be nice too.

Looks like hammond iron?

Randy

[FullRangeMan]

Wow nice amp, what rectifier are you using?
Hard to see a so perfect square wave.

[belle harbor]

OK, let's see if this works.  I printed and photographed the schematic to get it into jpg.  It contains the full parts list.

[belle harbor]

It isn't too bad.  Can anyone copy, enlarge, and post a clarified version?

[roscoe65]

It isn't too bad.  Can anyone copy, enlarge, and post a clarified version?

Your posted schematic is perfectly legible.

[JohnR]

Larger is here: http://www.audiocircle.com/index.php?action=gallery;area=browse;image=170805;size=huge

[poseidonsvoice]

Wow nice amp, what rectifier are you using?
Hard to see a so perfect square wave.

Oy vey.

It’s a solid state full wave cap input rectification as shown in the schematic. Also on the pics on the left side you will see 2 diodes.

Reproducing square waves at 320Hz is not challenging. I’m glad the OP is happy with his subjective goals. Nice clean build as well. Enjoy.

Thank you so much for sharing.

Best,
Anand.

[belle harbor]

Larger is here: http://www.audiocircle.com/index.php?action=gallery;area=browse;image=170805;size=huge

Thanks for posting the enlargement.  Much easier on my old eyes!

Actually, getting a decent 320 Hz square wave in a budget design isn't all that easy, particularly when using limited bandwidth output xfmrs.  Had the person who requested this design wanted to spend more the amp would have been done in a very different way.  But, for what these cost, their performance is very remarkable and will provide a wonderful intro to "tube sound" for someone who is curious.  But, my mind is always open to suggestions about how to improve things, although in this case it would have to keep the budget the same.

[poseidonsvoice]

Thanks for posting the enlargement.  Much easier on my old eyes!

Actually, getting a decent 320 Hz square wave in a budget design isn't all that easy, particularly when using limited bandwidth output xfmrs.  Had the person who requested this design wanted to spend more the amp would have been done in a very different way.  But, for what these cost, their performance is very remarkable and will provide a wonderful intro to "tube sound" for someone who is curious.  But, my mind is always open to suggestions about how to improve things, although in this case it would have to keep the budget the same.

I’ll hand you that. Especially with low budget being an issue. My lowest I go is with Edcor CXSE.

Try running the square wave at <50 Hz, things look bad awfully quick! That’s one of the limitations of tube designs. Trade offs.

My favorite flea power design I’m looking at is a spud amp that revolves around the 6LR8 in Triode.

Best,
Anand.

[FullRangeMan]

I suspect 6LR8 may be a great tube to driver position.

Interesting tube, how much power do can get in SEP?
Any reason you choose this tube?

[poseidonsvoice]

I suspect 6LR8 may be a great tube to driver position.

Interesting tube, how much power do can get in SEP?
Any reason you choose this tube?

With a plate dissipation of ~ 15 watts, the 6LR8 9 pin Novar sweep tube (a triode and pentode combo in one tube) will pump out 4.5 watts triode and closer to 5.5 watts pentode (3% THD at clipping). The advantage is that all that performance conveniently comes from one tube envelope. Only one heater supply.

Apologies to the OP for the off topic ramble.

Best,
Anand.

[Speedskater]

Two small comments on the schematic:
1] The AC power Safety Ground/Protective Earth should use a different ground symbol and be connected to the chassis at one point near where the power cord enters the chassis.
2] The circuit and DC supply grounds should be connected together at one point near the input jacks.

[belle harbor]

Two small comments on the schematic:
1] The AC power Safety Ground/Protective Earth should use a different ground symbol and be connected to the chassis at one point near where the power cord enters the chassis.
2] The circuit and DC supply grounds should be connected together at one point near the input jacks.

A well taken point which warrants an explanation. 

These amps use a star ground bus which connects to the chassis at the ground end of the output tube cathode resistor.  The power cord safety ground, dc supply ground, and signal ground is tied into this as well since I don't like to separate grounds in equipment.  Given that the power cord safety ground is earthed through the ground rod attached to the service panel I use the earth ground symbol to denote that all amplifier grounds are at earth potential.  I find that doing this avoids any ground loop issues with associated equipment, and also results in amps which are dead silent with no hum issues at all. 

I'm well aware that others take a different point of view on this issue and I don't know that one is more valid than another as long as the chassis remains protected so the user can't be electrocuted.   

[Speedskater]

You should check some expert's viewpoint.
The experts like:
Neil Muncy (RIP)
Henry Ott
Jim Brown
Keith Armstrong

[belle harbor]

You should check some expert's viewpoint.
The experts like:
Neil Muncy (RIP)
Henry Ott
Jim Brown
Keith Armstrong

You may as well throw Whitlock into the discussion as well since I'm familiar with his work also.  So, are you objecting to the method of grounding which I employed, my use of an earth ground symbol in the schematic, the fact that the amps are dead silent, or something else?  Are you suggesting that owners of modest home audio systems set up their electrical service as if they were building a recording studio?  Do you consider it necessary for a budget amp to be totally immune to RFI from wireless networks, etc.? 

Obviously we can go on with this until the cows come home.  I invite you to construct a pair of these using both my methodology and your own, compare the results, and form your own conclusion.  And remember that even Whitlock clearly stated something to the effect that a system having no hum or buzz should be the goal of any audio installation.  What else matters if this is accomplished in a safe manner?

[FullRangeMan]

I would like to ask a question on this subject, in my building there is no grounding of the electrical wiring, what kind of ground should I have in a tube amp?

[john61ct]

A wire soldered to a copper water pipe might do if the building's plumbing is that old.

Otherwise live with the float, not going to kill you. probably.

My apologies if resurrecting zombie threads is verboten here, mod may delete.

[FullRangeMan]

Thanks, unfortunately the water pipes are PVC.
Someday when I got a vacancy I will connect the strip ground to a alu window for testing.

[Speedskater]

For old building with 2 wire AC power (no Safety Ground) use GFCI receptacles.  There are some with low form factor to fit in old, small outlet boxes.

I will connect the strip ground to a aluminum window for testing
That would serve zero purpose. The Safety Ground/Protective Earth needs to connect to the Neutral in the main breaker box.

What does this have to do with a flea-power SEP?