Merlin Blencowe talks about 'switching noise' in his hifi preamp book. He states fast diodes and a snubbing network will do the job and the quietness of a tube rectifier is because of its internal resistance which can be purposely be added to a ss one.
I'm a big fan of his work, especially his guitar book and website. I value his opinion a lot.
I'm a big fan of his work, especially his guitar book and website. I value his opinion a lot.
Experience has shown that it is necessary to boost the N-77U's O/P, in order to obtain a sufficiently "tall" B+ rail. "Stealing" volts for the negative supply is a very bad idea.
Does anybody know the specific reason the Triad N-77U is forbidden in The Netherlands and (possibly) other EU countries?
How tightly matched are the O/P tube pairs going to be? Close matching of gm is always required. A shared bias network per pair saves some money and also compensates for minor cathode cathode current imbalance. Substantial differences in cathode current are not acceptable.
Does anybody know the specific reason the Triad N-77U is forbidden in The Netherlands and (possibly) other EU countries?
How tightly matched are the O/P tube pairs going to be? Close matching of gm is always required. A shared bias network per pair saves some money and also compensates for minor cathode cathode current imbalance. Substantial differences in cathode current are not acceptable.
There will be little demand for 115V mains transformers over here 😉 Filling up the sea container and stocking products that do not sell is commercially uninteresting. It is probably as simple as that.
Digikey does not say it is forbidden (Mouser does). I think I read it was conform some ROHS from 2017 onwards. Can't find it anymore though.
I'm keeping the N-67A on my list. Just for the end bells.
I'm keeping the N-67A on my list. Just for the end bells.
I wouldn't recommend a toroidal output transformer for a first-time project. It does not take a lot of DC to saturate the toroid core, so one has to be very careful with DC balancing the output stage, and to keep it perfectly balanced in the long run. This is possible, but requires some extra circuitry that may not be ideal for a first-time project.
While the N-67A is more than adequate in the VA department, it still requires boosting.
Triad's N-67A, N-77U, and N-68X have dual primaries, which makes them "universal". The dual "12" VAC Triad item previously mentioned also has dual primaries. The B- trafo is the "problem child".
Triad's N-67A, N-77U, and N-68X have dual primaries, which makes them "universal". The dual "12" VAC Triad item previously mentioned also has dual primaries. The B- trafo is the "problem child".
Well 5V from 350V is
less then 1,5%.No big deal.
Here in Europ one could use the TSTA60/002 from Toroidy (Poland).
It is 230V in and 250V + 2x 3,15V out.Skip the doubler and use a bridge rectifier.
And only 6AQ5 😱 but also no heater transformer 🙂 .
Mona
Here is my collection of quotes from all over the place: The original decware thread, diyaudio threads and others.
Far from ready, but it's a start.
Far from ready, but it's a start.
There are also TRA300 and TRA400 from Ask Jan First which are cheaper and have windings for the negative supply
The Polish transformer seems to be rather expensive.
A cheap alternative could be the NTR110 from Rohren Trafos | TBT Trafobau | Trafo | Siebdrossel
Mona
A cheap alternative could be the NTR110 from Rohren Trafos | TBT Trafobau | Trafo | Siebdrossel
Mona
Not necessarily true as long as the core is large enough / transformer is designed for power. When I interleave two Triad PTs, a pair of 250VA coils allows for almost 500mA of misbalance before it becomes audible. I found this out when one side of the PP output stage was disconnected making it an SE using half a PP output. YMMV.
For the record, I have built about 15 amplifiers now. Only two of them used EI outputs. A friend comments on how much better it sounds than the Hammond 1650N coils on a more traditional amp build 🙂
Last edited:
Is it common knowledge that CC resistors are better at blocking heat from e.g. tubes? I can't find anything about it.
That's not about heat.
Grid stopper resistors are used to suppress oscillation. They introduce a non-inductive resistance into the grid circuit that interacts with the Miller capacitance of the tube's grid (input) to form a low pass filter (LPF) that passes everything in the audio band, but attenuates radio frequencies.
The third statement is about using a carbon composition resistor in the negative feedback loop, where an inductive resistor would introduce an unwanted filter element into the signal there. I can't believe the tiny little bit of inductance in a typical half-watt metal film resistor would make a difference in a typical circuit, especially at the relatively low levels of NFB used in a tube amp, but I can see the basis for it.
But that still has nothing to do with heat, per se.
--
I don't see any mention of a carbon composition resistor in that passage.
CF = carbon film (not carbon composition)
CCS = constant current sink
??
The resistors wattage rating is relevant to heat (power dissipation).
A metal oxide or wirewound resistor would do just as well dropping volts. Possibly even better, as long as it was rated for a high enough voltage drop and high enough power (heat) dissipation (in watts).
CF = carbon film (not carbon composition)
CCS = constant current sink
??
The resistors wattage rating is relevant to heat (power dissipation).
A metal oxide or wirewound resistor would do just as well dropping volts. Possibly even better, as long as it was rated for a high enough voltage drop and high enough power (heat) dissipation (in watts).
Last edited: