Antek OPT

[LinuksGuru]

@Jeb-D

Check out this thread: http://www.diyaudio.com/forums/tubes-valves/144443-experience-antek-opts.html

I did a few tests. Nothing that could be used to make a datasheet, but the results were consistent. Huge drop off after 6k. It is apparent there was no quality control.

It means leakage inductance is too high, they seem to be wound without sectioning, just secondary over primary.

 

[jrenkin]

Try this for size, its where I got the idea;

The Tube CAD Journal,Three-Pin Regulators

The power toroidals I have used are all the same manufacturer - European unfortunately - I think the brand is Telema. I found the polarity of the primary quite critical as to induced resonances - so try both directions. The winding stratergy is quite straightforward been bifilar primary next to the core and then biflar secondary on top. No screening, nothing.

Shoog

How do you apply the CCS to a P-P output stage? Just tune to the deisired combined current, or one CCS per tube?

 

[piano3]

350V is the highest I have gone. It was with a 807 amp.

Shoog

Many thanks, Shoog.

Best wishes, N.A.

 

[Tubelab_com]

How do you apply the CCS to a P-P output stage? Just tune to the deisired combined current, or one CCS per tube?

There are two ways that I have used.

1) tie both cathodes together and run one unbypassed CCS to ground (or a negative supply). Set the CCS for the total desired current for both tubes. This makes the output stage a differential pair but forces strict class A1 operation. Grid current upsets the balance. It also works best with triodes or triode wired pentodes (no screen current to upset the baance). Sweep tubes operating in pentode at a low screen current seem to work OK too. If the entire amp is fully differential it will sound magical with a very high dynamic range. A good clean power supply is essential.

2) build any ordinary cathode biased P-P amp. Install a bypassed CCS in place of each cathode resistor set for the desired current in each tube. The bypass cap will allow some AB operation.

 

[jrenkin]

There are two ways that I have used.

1) tie both cathodes together and run one unbypassed CCS to ground (or a negative supply). Set the CCS for the total desired current for both tubes. This makes the output stage a differential pair but forces strict class A1 operation. Grid current upsets the balance. It also works best with triodes or triode wired pentodes (no screen current to upset the baance). Sweep tubes operating in pentode at a low screen current seem to work OK too. If the entire amp is fully differential it will sound magical with a very high dynamic range. A good clean power supply is essential.

2) build any ordinary cathode biased P-P amp. Install a bypassed CCS in place of each cathode resistor set for the desired current in each tube. The bypass cap will allow some AB operation.

Perfect! Thanks! I am building a two stage P-P differential amp with 12AT7 as input and driver LTP with CCS driving EL34s, but I hadn't planned a CCS in the tail of the output tubes. Now I will, what the heck! Magic, until I try to output through my Anteks... might be time to buy something else.

 

[Shoog]

2) build any ordinary cathode biased P-P amp. Install a bypassed CCS in place of each cathode resistor set for the desired current in each tube. The bypass cap will allow some AB operation.

A slight variation on this approach is to take the bypass caps and tie their negative terminals together and then run a 1meg bleed resistor to ground. This makes the output stage class A differential again - but with no chance of DC in the output transformer.

Shoog

 

[Shoog]

It means leakage inductance is too high, they seem to be wound without sectioning, just secondary over primary.

Toroidals have almost no leakage inductance and winding as you describe creates a transformer with bandwidth out to 50Khz.
Its something else, and probably capacitance which is the issue.

Shoog

 

[LinuksGuru]

Toroidals have almost no leakage inductance and winding as you describe creates a transformer with bandwidth out to 50Khz.
Its something else, and probably capacitance which is the issue.

Shoog

It is common misconception floating around. Audio transformer have much more primary turns then standard 220/127V power unit, and therefore, higher leakage inductance. It is impossible to measure leakage inductance of standard power transformer and use the same value for audio output unit wound on the same core. I have a software for designing audio transformers and can evaluate different design outcomes. Audio output transformers can be made as toroids, but this is really tricky and expensive venture.