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Dynaco MKIII vs ST-70 MK2 and a few questions.

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#43

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#44
baudouin0 said:
I used the Hammond transformers in a number of amps and they perform well and to the specs they publish. I would go for the 1650N myself. digikey have them. You may need to adjust the NFB a little.
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NA is described as "easy wiring" and I have it in my local store.
Can you share some projects?

And does anybody knows some amp with toroidy's transformers? (Btw, its my local company 😀 )
 
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#48
Looks intresting! I see there's also a version with Hammond 1650N.
Three questions about it:
1. What can you say about this Baby Huey amplifier? I mean, how does it sounds? Good alternative for classic Dynaco amp?
2. Which version would be better? With Hammond transformer or Toroidy? Some advantages and disadvantages?
3. If Hammond transformer, can be 1650N replaced with 1650NA?
 
#49
The 1650NA is probably not as good on just the 4R output as the 1650N as less of the secondary windings are engaged. At 8R I would think they are not dissimilar. They have good primary inductance reasonable leakage inductance and good for at least 17dB of GNF. I have used both Hammond and Toroidy and are pleased with both. Toroids need more accurate DC current balance. Depends on what you would like your amp to look like. There's also https://www.amplimo.nl/images/downloads/ds vdv/vdv6040.pdf
https://www.amplimo.nl/images/downloads/ds opt/40pp4k0s.pdf
 
#53
I cannot answer your first for I have not built one. The second well for toroid's watch the DC balance. It's how you wish your amp to be styled. Any well-designed amp with a moderate amount of NFB should not contribute any audio colouration of its own. As for the third the leakage inductance will be worse making feedback less stable.

This is what Sowter have to say:

OPTIONS We normally provide a single 8 ohm secondary or 4 separate secondary windings which can be arranged for loads of 16, 8, 4 or 1 ohms as shown in the tables below. Alternatively we can provide a single 4, or 16 ohms or 8 tapped at 4 ohms. Also we can provide twin 4 ohm windings which can be connected in series for 16 ohms or in parallel for 4 ohms. Tapped secondary windings will have somewhat increased losses, reduced HF response and reduced damping when the load is connected to a tap. This is particularly true when a 4 ohm tap on a 16 ohm winding is used. Please be sure to specify your preferred option if you wish to have a non-standard secondary option or a screen tap %.

If you intend to use the 4R maybe the 1650N is a better choice.
https://www.mouser.co.uk/c/?q=1650N
 
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#54
If your asking me what I would build probably something like a beefed up mullard 5-20 or maybe a double stage LPT and some EL34/KT77 output stage with fixed bias and a 1650N but it's really up to you. There's lots and lots of designs out there.
 
#58
OK so EL34 maybe best 50W. The problem is at 450V you may exceed the screen dissipation pop the screen and the valve will glow like a light. If you are looking for +50W then you need to really move over to the KT77.

I know I will get slaughtered for this. I would not build this amp. It does not have any FB from the speaker but uses plate to plate feedback. This is easier to design but will result in the damping factor (important with modern speakers to control the bass) being higher. Just two stages of valve amplification is not quite enough to provide a decent amount of GNF. There does seem to be overuse of semiconductors in the design where a simple buffer between the first stage and second would be fine. Looks like design by committee to me. So not one I would build myself. But its popular in diyaudio and its only an opinion
 
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#60
baudouin0 said:
I know I will get slaughtered for this. I would not build this amp. It does not have any FB from the speaker but uses plate to plate feedback. This is easier to design but will result in the damping factor (important with modern speakers to control the bass) being higher. Just two stages of valve amplification is not quite enough to provide a decent amount of GNF. There does seem to be overuse of semiconductors in the design where a simple buffer between the first stage and second would be fine. Looks like design by committee to me. So not one I would build myself.
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Damn, I already thought I had found the perfect project 😀 But it looks a little bit complicated to me, too. Maybe ST70 or MK4 will be really the best for me.
 
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