Developing the DIY "Champ" for first time builders

[RJ Guitars]

Hey guys,

As the last of the Eagle Premium parts packages go out, I am thinking about building their Big Brother, the Eagle Supre amp.

Looking at output transformers there are a few options, some of them a little bit expensive and some of them entirely reasonable. I looked outside of Edcor and found a couple possibilities but nothing that inspired me as similar or equivalent for the $$.

A 15 Watt output tranny seems right for either a 6L6GC - KT-66 - or EL-34 and a 3.2K primary seems appropriate. A 25 Watt output tranny seems best for a single KT-88 and also considering a 3.2K primary impedance.

Any thoughts?

rj

[Zippy]

A 15 Watt output tranny seems right for either a 6L6GC - KT-66 - or EL-34 and a 3.2K primary seems appropriate...

Any thoughts?

The 15W OT fills my needs.

[angelodp]

Upon reflection the 6L6 platform and 15 watt will be good for me.

Ange

[RJ Guitars]

OK Guys - 15 watts should satisfy all but the most sinister of Single Ended beasts... but for some is 25 enough? For those that thought the end was in sight, we have not even talked about the KT-90 and KT-120 tubes! Single Ended doesn't mean we have to build lightweight amps!

rj

[RJ Guitars]

Speaking of output transformers...

I want to go to the other extreme of the spectrum and mention the 5 watt generic output tranny that is in the Eagle Basic amp. I bought these as a quantity buy of generic output transformers. I know squat about them except they are claimed to be rated at 5K input and 8 ohms output impedance.

I found that on my first prototype build that the wire they use on these is very hard to tin and solder to if you cut the leads off. It has some sort of cruddy oxide or coating on it. I had to scrape the wire and work at it to tin them. If you don't do this you'll have a terrible time soldering them and this could cause significant disappointment for you sooner or later.

thanks,

rj

[angelodp]

Tell us more. Are you thinking in terms of punch and great throw. Damn pricey tubes. But if its a quest for the ultimate single ended amp, all bets are off. What would that look like, any big changes, I guess not, aside from B+ requirements.

[RJ Guitars]

Tell us more. Are you thinking in terms of punch and great throw. Damn pricey tubes. But if its a quest for the ultimate single ended amp, all best are off. What would that look like, any big changes, I guess not, aside from B+ requirements.

Ange, part of the tongue in cheek humor is in the phrase "lightweight amps". Single ended output transformers are big beefy units that get heavy and expensive real fast.

Single ended amps are cool and for a great big one there doesn't need to be any more parts than in the 5 watt version. So all that has it's merit.

However, folks sorted out long ago that sonically the sound of push pull tubes in combination with the efficiency of the circuits really made them the preferred choice when you want to create a loud amp... maybe even a not so loud amp. Also, look at the spec sheets on those tubes and see how absurdly high you can run the voltages up if you want the really big wattage output. That will get expensive and kinda makes me a little queasy when it comes to working at 600 or even 700 volts DC.

So I expect at some point (I'll guess and say 10 watts), it's just for the coolness of the idea but not necessarily a better way to build an amp.

YMMV,

rj

[angelodp]

Queasy as in, 400vdc is enough to kill you and 700vdc? Kill you you even more. Or is it purely expense related.

[RJ Guitars]

Queasy as in, 400vdc is enough to kill you and 700vdc? Kill you you even more. Or is it purely expense related.

...It's the high voltage first. After that it's knowing that for the same weight and dollars there are a lot of other options. To really max out a KT-90 or KT-120 would require some crazy power and output transformers plus the power supply filtering would need to be beefed up. I would love to hear what that all sounds like but not bad enough to make it my own project.

I plan to build one for myself with a KT-88, but in all my builds I am applying a few principles that I took from Ken Fischer.
1- Over-rated iron
2- Slightly higher primary impedance on the output tranny
3- Reduced B+ voltages

I like the way that these things work together sonically, again YMMV.

rj

[Zippy]

I found that on my first prototype build that the wire they use on these is very hard to tin and solder to if you cut the leads off. It has some sort of cruddy oxide or coating on it. I had to scrape the wire and work at it to tin them. If you don't do this you'll have a terrible time soldering them and this could cause significant disappointment for you sooner or later.

Back in olden times, when soldering irons were still made of wood and stone, I used to keep a jar of flux just for such occasions. That's what the stuff is for - taking out the "cruddy oxide" as you have astutely characterized it.

[xtian]

I used to keep a jar of flux just for such occasions.

Right. And for us modern kids, we have flux pens! (Ha! I'm 43.) Thanks for the heads up, RJ.

[surfsup]

RJ, what have you decided on for a PT for the supre?

[xtian]

RJ, my two packages arrived today. You have already doubled the value of the components by your careful organization and packaging! Wonderful!

I love the blue Edcor iron. That chassis is going to get spray painted and sit atop a walnut and maple base, like a trophy.

Thanks! Can't wait to build!

[RJ Guitars]

RJ, what have you decided on for a PT for the supre?

Narrowed down to three colors at this point and all of them will be available. I am going to use orange for my own build.

Blue - 245-0-245 @ 150 mA
Orange - 275-0-275 @ 175mA
Red - 300-0-300 @ 150mA

I received the quote from Edcor today and I am expecting another from Heyboer tomorrow.

I was also looking for a custom output tranny with mulitple secondary taps. Edcor said they don't make SE trannies with mulitple secondaries. I am not sure if I can get Heyboer to quote since I can't guarantee them the quantities that they need for a custom wind like this. So it could very well be that 8 ohms is the standard.

Keep in mind that the specs I have above are for Loaded voltages. The actual will be higher than the label indicates if it is an Edcor tranny. I've adjusted the quote specs to Heyboer so that they are ~equivalent since they use an unloaded rating on their power trannies.

rj

[surfsup]

I saw edcor has some dual tapped PTs:

XPWR145-120
Power transformer for a 120V, 60Hz. line to 600V and 480V (300-240-0-240-300) at 120mA center tapped, 6.3V (3.15-0-3.15) at 3A center tapped and 5V at 2A.

This would kinda fit the lower and higher voltage preferences, and maybe a dropping resistor can put it similar to the 275, and with one PT, satifsy all the builders? (maybe quantity puts it at a more attractive price, too, and you can get it with a higher mA output)