Simple Octal SET help.

[forsakenrider]

Ok, Im not a complete n00b, but new to many things. I have built a plentiful amount of headphone amplifiers, a submini tube 1w guitar amp, a gain clone, and random other things over the last few years. I am 25, so fairly new to all this (3-4 years?). I have recently built some open baffle speakers based on this driver. Now I want to build a simple SET to drive it. I have never used Octal tubes so this is one of the requirements. I don't need MUCH power because I live in a small apartment all by myself.

This is was I want

1.5-3w power
octal tubes
simple
~$200 usb not including case.

This is what I've found:

This 6EM7 amp
with these output transformers
Now the power supply is the part I really need help with. with the power transformer and 2 chokes I get a over what I feel reasonable to spend on iron. I know it is VERY important but I want to start lowish and hearthe differences as I build other things throughout the years. Also, the Edcor output transformers "look" decent to me. I like the blue and the label, ha!

heres the schematic for easy viewing.

[mwiebe]

What is your budget? What power transformer are you planning on using? Hammond 158Q ($22) or 159P ($28), around $50 a pair for a choke input supply. If you are just playing around you could always do an RC smoothed supply and save the choke costs. Remember those resistors sitting under the power triode are at least 10W units which adds a bit of cost. You might as well knock out a bill of materials to see what you are looking at money wise.
Matt

[Eli Duttman]

Once again, the Greinacher (full wave) voltage doubler "rides to the rescue". I know of no better way to build a highly competent PSU, while spending comparatively little money. You can use the B+ supply from "El Cheapo" (schematic) attached, with little change.

Buy the B+ power "iron" from Allied Electronics. Stock # 967-2343 is the Triad N-77U isolation trafo. Stock # 967-1004 is a highly suitable Triad C-24X filter choke.

As shown, you will not get to 325 VDC, but you will come close. If you are determined to have 325 V., we will discuss boosting techniques.

[forsakenrider]

Well It doesn't have to be THAT cheap, and it would be interesting to use a tube rectifier (I haven't tried that either yet). I used a step-up transformer on my guitar amp which worked but it was tricky with wiring and hum.

I was thinking something like this from Edcor again for power, and that already puts me just over 100$ for transformers. another 50 for chokes and I only have 50 left for everything else! Max MAX budget would be $300, but that's really pushing it.

Eli, that is interesting for sure, but as I understand it, I need at least the 325v to get enough "clean" watts on my output.

[chrish]

If you are looking to save cost, the tube rectifier can be replaced by solid state.

Have you considered the Tubelab Simple SE? It can be made cheaply, adding options later to improve the power supply. It is a great amp with plenty of support. My first tube amp. Simple SE schematic

These power tubes are cheap and work very well RARE !!! 5881 = 6L6GC = 6P3S-E tubes. Lot of 2 NOS - eBay (item 190513706521 end time Apr-17-11 11:45:03 PDT)

[forsakenrider]

I have looked at the Simple SE, Im sure it a great amp but it just doesn't quite "grab" me. I'm picky the way I pick my projects I guess. I think I am pretty stuck on this design, its just the power supply is really adding up quickly.

Do I really need one choke per channel? is there a better rectifier to use? or what about a solid state rectifier, what would I gain/lose by going that route and how would it play in my "cost".

[Eli Duttman]

Eli, that is interesting for sure, but as I understand it, I need at least the 325v to get enough "clean" watts on my output.

OK, boosting technique time it is. Add Allied stock # 967-8020 to the mix. That trafo has 2X 3.3 A./"12" V. secondaries. You will use 1 of the secondaries to power the 6EM7 heaters. Wire the heaters in series, for "12" V. operation. The junction of the heaters will be the point to which bias off B+ will be applied. You have to phase up the remaining "12" V. secondary and the secondary of the N-77U. The windings are wired in series. One arrangement will yield approx. 133 VAC, while the 2nd yields approx. 107 VAC. You will Greinacher double the larger voltage. That gets you past the "magic" 325 VDC.

Gary Kaufman set things up as pseudo dual mono, for improved channel separation. The "El Cheapo" PSU is pseudo dual mono, only for small signal. So, things get tweaked a bit. The 820 μF. doubler stack caps. and single filter choke stay as is. Follow the filter choke with a 47 μF. 'lytic. The UF4007s at split point are fine, as they can tolerate up 1 A. of forward current. You will have to experiment with the value of the following resistors to bring the B+ rail voltage in where desired. The final reservoir caps. are as Gary showed.

[MrCurwen]

I'm always rooting for the Darling amp as a first DIY SET! 1626's are very cheap and very easy to work with. The sound to my ears is much better than any of the common pentodes or beam tetrodes triode strapped.

[Ty_Bower]

Originally Posted by forsakenrider

This is what I've found:

This 6EM7 amp

If you've decided on the 6EM7 tube, take a look at Pete Millett's "Jonokuchi" amplifier for inspiration. His amp uses the 13EM7, which is the same tube but with a different heater voltage. Edcor sells a transformer kit for his amp. It is available at a small discount. (EDCOR Electronics Corporation. PM-101)

You can build the Jonokuchi point to point, and skip the cost of the circuit board. You might even take his power supply design and build the Kaufman amp around it. Pete's power supply should make about 340 volts.

another 50 for chokes

You can get a lot of Henries for your dollar if you buy the Triad filter chokes. The C-14X is popular. At the low currents you will draw, the C-7X should work fine too. Otherwise, just use a lot of capacitance. If you've got 400uF~800uF, you could probably skip the filter choke entirely and still not be bothered by excessive hum.

[ratbagp]

About a year ago, our group from the MD / VA / DC / PA area had a competition for an amp based on 6V6's for under $200. The chassis had to come from Ikea. The winning entry cost less than $150.

6V6 Entries

We all agreed that a 6V6 wired as a triode was really good.

ray