Output Transformers? Power? Amp design? Caps?

VintInfinity

VintInfinity

Tactophonic
I am going to be building a simple preamp/headphone amp circuit soon, using either 12au7 with 6cg7, 6sn7 and 6cg7 or all 6sn7.

I have almost all the parts on the way except for the sockets, caps and resistors, etc.

I want to build an integrated or separate power amp after this, using possibly el34, el84, 6L6 or others... can you suggest which power tubes would be a good match for what I have on hand and plan to do already?

So far I have:

7 pairs of 12AU7
11 6SN7
5 6CG7


I have seen Antek toroids listed before, they look to be good for the money. Any others? For both power and output for preamps, amps, integrateds.

Any amp designs, tube suggestions, etc are welcome.


Which caps are a good value for high sound quality? Sources? Resistors?
 
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For output transformers I first look at Edcor, well priced and perform nicely.

As far as power transformers go I'm not much help there as I usually scrounge what I use.
But I have used the triode Electronics ST-70 replacement power tranny in a couple projects.
(It's a nice tranny for push pull EL34, 6L6, KT88 and such with all the needed taps)
 
With that many 6SN7s, I'd look at building a Williamson type amp. Some good ones out there, using 6L6s. Bricktop's modded Heafhkit W4 design (spec'd for 5881s, which are equivalent to 6L6GB) would be an obvious choice:

attachment.php


The Antek AN-3T235 would make a perfectly good power transformer... it's got enough capacity to run a stereo 6L6 amp. I'd use a solid-state power supply (diodes instead of the 5V4 in the original design), with a filter choke. For output transformers, I'd recommend the Edcor CXPP60-MS-6.6K... plenty of oomph, and the right connection terminals available.

As for caps- the Dayton film-and-foil caps, the Sprague Orange Drops and the Illinois poly caps are good choices for coupling caps. For power supply, something like the JJ double-section caps can be a good deal, at least in the first stages (where 500v capacity is needed).

For resistors- I prefer going with carbon film... decent stability, and "middle-of-the-road" sonic behavior. Not bright, not dull, not boomy, not thin... they tend to work well almost anywhere... and you can frequently find them quite inexpensively.





Regards,
Gordon.
 
VintInfinity said:
Excellent! Thanks for the info.

Do these really bottom out at 70Hz response though?
Click to expand...

Presumably you're looking at the open frame XPP series OPTs at 70~18,000 Hz; the CXPP are stated as 20~20,000 Hz.
 
GordonW said:
With that many 6SN7s, I'd look at building a Williamson type amp. Some good ones out there, using 6L6s. Bricktop's modded Heafhkit W4 design (spec'd for 5881s, which are equivalent to 6L6GB) would be an obvious choice:

The Antek AN-3T235 would make a perfectly good power transformer... it's got enough capacity to run a stereo 6L6 amp. I'd use a solid-state power supply (diodes instead of the 5V4 in the original design), with a filter choke. For output transformers, I'd recommend the Edcor CXPP60-MS-6.6K... plenty of oomph, and the right connection terminals available.

As for caps- the Dayton film-and-foil caps, the Sprague Orange Drops and the Illinois poly caps are good choices for coupling caps. For power supply, something like the JJ double-section caps can be a good deal, at least in the first stages (where 500v capacity is needed).

For resistors- I prefer going with carbon film... decent stability, and "middle-of-the-road" sonic behavior. Not bright, not dull, not boomy, not thin... they tend to work well almost anywhere... and you can frequently find them quite inexpensively.
Click to expand...

Thanks for the tips, seems like I was thinking on the right track as far as caps and resistors as well.

What kind of power output does that circuit give?


Is it possible (advisable) to run an integrated off one power transformer?

Tinkerbelle said:
Presumably you're looking at the open frame XPP series OPTs at 70~18,000 Hz; the CXPP are stated as 20~20,000 Hz.
Click to expand...

:thmbsp:
 
Why would I go with SE vs push pull? I want to start simple, build a few preamps and headphone amps, then add a small simple power amp to those.

I will be using ~89db/w 2 way speakers. Eventually it would be nice to have a big tube amp that can power the high pass on the Kappas.
 
VintInfinity said:
Why would I go with SE vs push pull? I want to start simple, build a few preamps and headphone amps, then add a small simple power amp to those.

I will be using ~89db/w 2 way speakers. Eventually it would be nice to have a big tube amp that can power the high pass on the Kappas.
Click to expand...

There's lots of articles online about the pros & cons. For example:
http://homepage.mac.com/tlinespeakers/vaughn/downloads/SE-v-PP-Part1.pdf
http://homepage.mac.com/tlinespeakers/vaughn/downloads/SE-v-PP-Part2.pdf
 
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VintInfinity said:
Thanks for the tips, seems like I was thinking on the right track as far as caps and resistors as well.

What kind of power output does that circuit give?


Is it possible (advisable) to run an integrated off one power transformer?


:thmbsp:
Click to expand...

Probably around 25 watts per channel. Maybe a little more (30-35w?) with the Edcor output transformers and a SS power supply.

If the power transformer has enough "oomph", there's no problem running an integrated off of it. I'd think, with 300VA capacity (that's about one AMP of current capacity, to rough numbers), the Antek should be loafing...

Regards.
Gordon.
 
I have a 100K Alps attenuator on the way... would a 250k be useful as well?

Some tubes showed up, they aren't all the same plates as I had hoped, but we will see what they can do. Pics in a bit.

I just need sockets, caps, resistors, and transformers now. I ordered some Cardas Quad Eutectic solder. We have a nice DMM, soldering iron, tools, o-scope, tube tester, and a retired tech at hand. :)


Is it best to mount on a copper plate, or other metal? I want to use aluminum and wood for the chassis eventually. Right now I just need a test board with good noise protection.
 
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Mostly RCA, a couple GE, a 3 sylvania. A few black plates that look like 12au7 but bigger and more complex, some staggered plates, some odd ones.

There is one that has a flaky looking scum in it.. Is this oxidation from a leaky tube?
 

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The Edcor outputs are under rated, they spec them very conservative, expect a nice
at least 20hz to 20K performance possible with a fine tuned circuit. :)

(In other words don't let the specs make you think they are under performers)
 
Kegger said:
The Edcor outputs are under rated, they spec them very conservative, expect a nice
at least 20hz to 20K performance possible with a fine tuned circuit. :)

(In other words don't let the specs make you think they are under performers)
Click to expand...

I don't, they look nice.

How are the Antek toroidal outputs?
 
Toroidal outputs are a little more hard to tame. They saturate a lot easier than EI-core (like the Edcor) type transformers. Makes it REALLY important to match output bias current between the two PP tubes.

For a first project, I'd recommend a "standard" type output transformer, like the Edcors. It's a little more money, but you'd pretty much be guaranteed success.

Regards,
Gordon.
 
I have a pair of monoblocks 6L6 designed by Kegger. It is a simple schematic and they sound great. Might want to ask Kegger for a pic of the schem. Cheers.
 
The epay seller that shipped me 9 of those 6sn7 said he would send me replacements for any that broke in shipping... what a good seller. I think one got developed a leak, but will have to test all of them to be sure.

Would a SET amp using any number of tubes be an easy task? The power amp stage of these builds will be after I have built a few working preamps and headphone amps or combos thereof.

I want the most delicate sound from a pair of Indignias or similar speakers. Imaging and soundstage with sound quality, and ease of listening over time valued over sheer volume. I heard a Glow Audio mini 5wpc integrated on some 6.5" 2 way Quads, big soft dome tweeters. The soundstage was just amazing. Some sort of Nordost flat cables instead of the alloy the guy usually uses at his shop.

About the impedance matching of toroidal output transformers; this was something I hoped to learn about advanced levels of in the course of making these amps. And tube circuits, impedance matching/level matching amongst tubes, caps, resistors, etc.

Any good books with simple explanations for advanced tube circuit ideas? Highly visual learning is easiest for me. I have no formal schooling with electronics, but since I was always around it and repairing it; I have an decent intuitive knowledge of how to fix things or what is wrong. Sometimes I am not sure how something is working, but once I get an explanation it's fairly easy. Basically, I know what not to touch when there is voltage on or in.
 
Only thing is if your wanting to use the tubes you have,

"7 pairs of 12AU7
11 6SN7
5 6CG7"

Then the one I built Dennis mentions won't have enough drive, that circuit needs like
a 12AT7 or 6SL7 type tube for drive as it has only 1 gain stage in it.

Using your tubes I would do something simular to what Bricktop posted, or a say 6SN7
driver to 6CG7 LTP splitter and out to the finals (or switch it around).
 
You could use say a 6SN7 or 6CG7 to power a stereo 6V6 (or EL84) SE UL amp using the
inexpensive Edcor open frame outputs, that would be a very simple amp to build an would
give good sound quite easily.
 
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