SET Suggestions

[nogoodboyo]

Hi all

I'm fishing for some suggestions / links to specs etc.

I want to build from scratch an SET to drive a Pair of Klipsch LA Scalas.

requirements:

-- About 5w per ch

-- No expensive power tubes

-- Tube rectified with a choke or 2


-- I already have this power transformer:

http://www.triodeelectronics.com/pa7dynst35sc.html

and wish to use it


-- Will get an extra transformer for rectifier.

-- wish to use the Hammond 125ESE output xformers or similar.


I already have a nice chassis and I am a competant/experienced Audio DIYer. (got stop electrocuting myself tho' [ouch!!]).

I intend to upgrade in the future but want something nice/simple/inexpensive to start off.

I guess there posts similar to this in the past, but a quick browse yielded little. But hope this post starts of some discussions -- I'm sure you folks like this kind of thing anyhow


Thanks in advance

[rcavictim]

You will not be satisfied with the poor F response of this output xfmer. It is only rated from 100 Hz to 15 KHz. The quality of the ouptut xfmmer sets the sound quality of the entire amp after you have done your best everywhere else. A poor xfmer will kill the best design. Here are much better xfmers.

http://www.hammondmfg.com/1627.htm

Check for recent posts by Tubelab or use search term "edcor". He has been testing economical new offerings from a company called Edcor that appear to be good value.

[SHiFTY]

I intend to upgrade in the future but want something nice/simple/inexpensive to start off.

OK, here's a tip- buy the best output transformers you can to start with, they make the biggest difference in the sound. The 125ESE are not the greatest, they have a slight harshness to them and roll off at 100Hz or so. Do yourself a favour and buy some decent ones at the start.

Apart from that, consider using triode-wired pentodes such as KT88 or EL34 instead of triodes proper; or even parallel KT66 / 6L6GC tubes. For a driver stage, you need to have something with some grunt, like 6SN7 or even an EL84. Have a read of the 2A3 driver thread.

For a tube rectifier, use a GZ34 for slow turnon and low voltage drop.

[Geek]

Hi Nogoodboyo,

Try the Edcor's. I'm 100% sold on their sound

If you want 5W of great sound without the cost, try trioded EL/PL36. Think of it as a 5 watt 2A3

Bias at 60mA with 260 to 300V on the plate with a 5K load. Your tranny with a tube rect. and L-C filter, will give just about that.

Yeah, we're pushing her at 18W total at 300+60, but it will take it!

[protos]

I would get two of those txs and use 6c33 which have the following advantages:
1.You can get them at around 15-20 usd each this is cheaper than any other power triode/tetrode .
2.They are twice as powerful as anything close i.e. 300b,kt88 etc.
3.They will work a dream with about 300-370 volts cathode biased.

Transformers should be in the 600 to 1000k range which are not extremely common but are available from most big tx manufacturers.If you really want to do it really cheap look at the 6c33 diy otx thread.I think a pair of otx cost the guy something like 50 usd in wire and laminations!

[rcavictim]

Originally posted by protos
I would get two of those txs and use 6c33 which have the following advantages:
1.You can get them at around 15-20 usd each this is cheaper than any other power triode/tetrode .
2.They are twice as powerful as anything close i.e. 300b,kt88 etc.
3.They will work a dream with about 300-370 volts cathode biased.

Transformers should be in the 600 to 1000k range which are not extremely common but are available from most big tx manufacturers.If you really want to do it really cheap look at the 6c33 diy otx thread.I think a pair of otx cost the guy something like 50 usd in wire and laminations!

You have specified a factor of 1000 times too high a transformer load Z for the 6C33 tube.

What purpose would the two transmitters serve?

[Sherman]

Nogoodboyo,

Search this forum for Mikael's KT88 SE amp schematic. While not a real triode it can be connected as a triode or use it per the schematic in UL mode. I have built this amp and it sounds good (provided you use a good output transformer).

My amps (I built monoblocks rather than an integrated amp) have an output of about 7W just before clipping so an output of 5W should be reasonable. I haven't done any distortion measurements yet, my distortion meter needs work. (Maybe that should be my next project!)

I'm with the others who are advising getting the best OPT you can. If budget constraints are an issue (and really, they always are unfortunately) I would go with the Edcor transformers over the Hammonds. Recent threads indicate they perform far beyond their price and they have a UL tap (which the 125ESE doesn't).

[protos]

Originally posted by rcavictim



You have specified a factor of 1000 times too high a transformer load Z for the 6C33 tube.

What purpose would the two transmitters serve?

Sorry , 600 to 1000R is what I meant and I think you probably understood as well.
The original thread proposed a power trafo (not a transmitter as you mistakenly wrote)that would be a little underrated for a 6c33.
There is however a more expensive and bigger tx on the same site that would also serve.The 6c33 needs about 140-160ma at those voltages and about 6A filament each.

[protos]

Other ingredients for success
1.to save on heavy expensive chokes use a capacitor multiplier- ripple filter
2. use ccs on driver stage to maximize efficiency.The simplest ixys 10m45 or a more complex gary pimm clone.

[tubelab.com]

Any time you ask a question like this you are bound to get several differing opinions. OK here is mine.

You already have a power transformer, so find a way to use it. It can be used to create a power supply in the 300 to 400 volt range. This is about right for a 5 watt SE amp.

Many advise to buy the best transformers that you can afford. This is good advice, but you must also work within your budget. If you have $100 plus per transformer, then buy some One Electron's or Electra-Prints, but since you specified "no expensive tubes". I am going to take this as "no expensive trasnformers either" This means the Hammond 125 series or the Edcors. There are those who claim that the larger Hammonds (125ESE) don't sound as good as the 125CSE. I have not tried the larger ones, so I don't know. The small Edcor XSE25-8-5K sounds as good as the Hammond 125 CSE, and it costs $18. See the following thread for further info:

Cheap SE output transformers

"No expensive tubes". This rules out most true triodes. What we have left is a triode connected pentode, or a UL connected pentode. If you use the Edcor transformer, then you can try it both ways.

There are lots of tubes that will work with the Edcor or the Hammond output transformers, and the power transformer that you currently have. The suggested 6L6, KT-88, EL-34 types come to mind. Another possibility is a tube made for TV sweep use. There are some of these that never caguht on with the CB linear amplifier crowd, so they are still cheap. I recently got several 6AV5's for $3 each. They work well with the Edcor transformers.

The Edcor meets the 6AV5


There have been several amplifier designs mentioned that use vertical output tubes. These tend to only deliver 2 to 3 watts, but are very simple and work very well. Search for 6DN7, 6EM7.

Baby SET w/6FD7 and ilk, for Bas and others....