First stereo tube amp build advice

[Tom Kamphuys]

The Triad N-77U is not available in my country: Due to government regulations, Mouser is unable to sell this product in your country. I get your point though.

@Eli: I appreciate your list of amps. Now I can search more focussed. However... Could you point me to the best info w.r.t. el Cheapo? I read you were involved. It is not that easy to find concise info about it on the internet.

[Tom Kamphuys]

Originally Posted by 6A3sUMMER

Eli,

That is a good way to get the B+.
But just be sure to keep all of the doubler circuit in a local loop. Extending it out to
other areas of the amplifier, it will cause terrible hum/hum upper harmonics noise.
But it requires one more tran$former, the filament tran$former.

Choke input full wave with center tap, or with bridge, has the quietest hum/hum upper harmonics ground loop noise. Again, be sure to keep the circuit to just a local loop (at least the secondary, rectifiers, choke, and the first cap (and resistor and second cap).
But the power transformer is more expen$ive, and heavy; and so is the added choke more expen$ive and heavy. And, the choke needs to be far away from the output transformers, and oriented properly.

That amazes me about hifi tube amps: the output transformers are mostly very close to the power transformer. I used the headphone trick on my guitar amp and I had to position the OT over 30cm (12") away from the PT to hear no hum. Why is that not the case for hifi?!

[6A3sUMMER]

Generally, headphones on your ears are many times more sensitive, versus loudspeakers.

I often ask why HI Fi Stereo manufacturers do what they do.
Lack of knowledge.
Average customer base that is fairly easily satisfied.
Customer's speaker efficiency, distance to listener, room size and absorbent items, etc.
Price to a Point (save money, more profit)
Think of your own reasons that they act that way.

I try very hard to reduce the hum and noise on my amplifiers.
Almost all of them have less than 100uV at the output;
I use them with medium efficiency loudspeakers that are only 2 or 3 feet away from me.

But . . . I do not consider my amplifiers to be good enough for most headphones . . .
Unless the output is sent to a resistor load, plus a pair of resistors to attenuate what goes to the headphones. That way, you turn the volume up a little, and the signal level, versus the hum and noise level is improved (good enough for almost all systems).

In the 50s and early 60s, the accepted way to get a good Hi Fi Stereo, was to tie together a number of individual specialized products into what was called a 'component system'.
Many thought that all of the individual components were compatible with each other; not always true.

Now, in 2020, so many think they can tie a number of products together, and get what thay want.
Again, that is not always true.
A system is complex, involves signal voltage levels, magnetic pickup of nearby fields (like a magnetic cartridge and a turntable motor, or placing it on top of a power amplifier), gain, input and output impedances, speaker efficiency, room size, music selection, what volume is desired, etc.

One of the most important ways to get a system that satisfies, is to completely and accurately describe both the wants and needs of such a system.
Without that, it is like shooting an arrow, blindfolded, in the dark, at an unknown target (the target is 'safe' it hardly ever gets hit).

Many a dollar has been $pent on all kinds of gear, that is then replaced with other gear, and never satisfies.
That is because of two things:
The target was never hit.
Some are never satisfied.

Listen to the Music. Do not listen to the sound of the system.
Enjoy the music.
Then you might like the system.

[Eli Duttman]

The method employed by Hegeman and others was used in "El Cheapo" (schematic provided). The LC reservoir section is critical to high performance. A refinement is inserting a LC "hash" filter made from a high current RF choke and a 1000 pF. mica or high quality ceramic (NP0/C0G) cap. between the doubler stack and the reservoir section.

Large valued caps. at the I/P of a PSU filter "crush" the ripple fundamental, but they generate ripple overtones up into the RF range in doing so. (TANSTAAFL strikes again) I've discussed the mechanism many times both here and AA. A "hash" filter keeps the trash out of the ultimate PSU product.

[Schmitz77]

Originally Posted by 6A3sUMMER

Generally, headphones on your ears are many times more sensitive, versus loudspeakers.

I often ask why HI Fi Stereo manufacturers do what they do.
Lack of knowledge.
Average customer base that is fairly easily satisfied.
Customer's speaker efficiency, distance to listener, room size and absorbent items, etc.
Price to a Point (save money, more profit)
Think of your own reasons that they act that way.

I try very hard to reduce the hum and noise on my amplifiers.
Almost all of them have less than 100uV at the output;
I use them with medium efficiency loudspeakers that are only 2 or 3 feet away from me.

But . . . I do not consider my amplifiers to be good enough for most headphones . . .
Unless the output is sent to a resistor load, plus a pair of resistors to attenuate what goes to the headphones. That way, you turn the volume up a little, and the signal level, versus the hum and noise level is improved (good enough for almost all systems).

In the 50s and early 60s, the accepted way to get a good Hi Fi Stereo, was to tie together a number of individual specialized products into what was called a 'component system'.
Many thought that all of the individual components were compatible with each other; not always true.

Now, in 2020, so many think they can tie a number of products together, and get what thay want.
Again, that is not always true.
A system is complex, involves signal voltage levels, magnetic pickup of nearby fields (like a magnetic cartridge and a turntable motor, or placing it on top of a power amplifier), gain, input and output impedances, speaker efficiency, room size, music selection, what volume is desired, etc.

One of the most important ways to get a system that satisfies, is to completely and accurately describe both the wants and needs of such a system.
Without that, it is like shooting an arrow, blindfolded, in the dark, at an unknown target (the target is 'safe' it hardly ever gets hit).

Many a dollar has been $pent on all kinds of gear, that is then replaced with other gear, and never satisfies.
That is because of two things:
The target was never hit.
Some are never satisfied.

Listen to the Music. Do not listen to the sound of the system.
Enjoy the music.
Then you might like the system.

Perfect. Some call it "the music mind".

[6A3sUMMER]

Eli,

Of course that schematic of El Cheapo is a good power supply . . .

Using 3 separate power transformers is sometimes considered a luxury.
More real estate, weight . . . and expensive.
1 B+, and 2 separate filament transformers.

That helps to isolate the noise from one power supply getting into another supply
(has to cross from the 1st secondary, to the 1st primary;
and then onto a 2nd primary, back to a 2nd secondary.

[Eli Duttman]

Believe it or not, 3 transformers were (sic) the inexpensive route. Triad's N-77U and N-68X are bargains for getting 300+ V. of B+.

Things change over time. Anybody in North America considering an "El Cheapo" build can get a complete set of power "iron" from Allied Electronics.
Stock # 70218190 = main B+ $32.59
Stock # 70218344 = 2 "12" VAC windings for B+ boost and heater power. $16.73
Stock # 70009000 = B- feed and 12AT7 heater power. $16.83
Stock # 70218145 = B+ filter choke $8.62
Approx. $75 for a reasonably sophisticated set of power "iron" is (IMO) a pretty good deal. FWIW, Triode Electronics charges approx. $100 for a ST-35 power trafo and that chunk of "iron" will not completely satisfy the needs of an "El Cheapo".

Something additional is provided to show the versatility of the Triad isolation transformers. Here's a vacuum rectified "300" V./60 mA. B+ supply, for preamp projects.

[6A3sUMMER]

So the only expen$ive thing about the EL Cheapo having 3 transformers . . .
is the extra large chassis to be able to fit those on.

1 transformer = more hum and noise cross coupling; but a smaller chassis.

3 transformers, and 2 output transformers that need to be spaced away from them = a larger chassis.

Tradeoffs.

[Eli Duttman]

The N-77U is pretty good sized, but the B- trafo and twin "12" VAC items are not especially large.

Consider mounting some power "iron" item on the side wall.

[OldHector]

Artosolo lade this suggestion for a power transformer on another thread ...
tsl180_001/transformers-with-fastening/indel/tsl-180-001/

For €57 it has lots of versatility.