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Old 14th May 2010, 05:55 AM   #21
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Quote:
Originally Posted by tubelab.com View Post
When all automobile engines were of similar design and all had 2 valves per cylinder, the saying was true. Today it is hard to judge an engines output potential by displacement alone.

When all transformers were of EI construction, mass was a suitable means to judge the power capabilities of a transformer. In this case we are comparing a 2 valve cast iron engine, the EI constructed Hammond, to a 4 valve VVT aluminum headed high RPM screamer, the toroidal Plitron. Since a toroid makes more efficient use of the magnetic flux, it can have less iron (but about the same copper) for a given power output.
I'm not sold on toroids being that much better, based on "flux efficiency".
The 1650W is 0.1lbs/watt and Sowter is about 0.24lbs/watt. The PAT 4141 is 0.0588lbs/watt. I think that's about 24%-58% less and I'd guess less iron is due to running higher flux density.
The Plitron PAT 4141-00 has no specs on distortion and DC imbalance. It's easy to fudge frequency response curves when no operating level and source/load impedance is mentioned. I can get 117kHz out of anything at low levels with low Z drive. So I find it strange to have all this glam yet missing some of the real measurements.
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Old 14th May 2010, 07:29 AM   #22
Arnulf is offline Arnulf  Europe
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Quote:
Originally Posted by dggs View Post
For OTL, it's possible. 500W MA-3
Only $147,100.00/pair
$?????? if you DIY
I like how they put this in two consecutive lines:

Quote:
- Zero feedback
- Automatic Bias and DC Offset control
I'd like to see this automatic bias system that doesn't work by the means of feedback Before anybody jumps up to point out that they were probably referring to audio feedback so this doesn't affect audio output - any bias shifting affects audio output.

Impressive power output nevertheless, if only they skipped the audiophool marketing gimmicks ...
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Old 14th May 2010, 03:34 PM   #23
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Quote:
Originally Posted by prairiemystic View Post
I'm not sold on toroids being that much better, based on "flux efficiency".
The 1650W is 0.1lbs/watt and Sowter is about 0.24lbs/watt. The PAT 4141 is 0.0588lbs/watt. I think that's about 24%-58% less and I'd guess less iron is due to running higher flux density.
The Plitron PAT 4141-00 has no specs on distortion and DC imbalance. It's easy to fudge frequency response curves when no operating level and source/load impedance is mentioned. I can get 117kHz out of anything at low levels with low Z drive. So I find it strange to have all this glam yet missing some of the real measurements.
It totally bugs me when products are sold without good specs or test reports. That alone keeps me away from certain products...

However, the core material should make a difference.

I believe that the core material used in the toroid may have a higher saturation flux density and may be operated at higher V/turn.

The core material may also have better high frequency properties.

There also needs to be enough core cross-section to handle the power.

I think it's possible for the toroid to equal the power performance of an EI iron core at less weight if these conditions are met.

I don't know about the small signal performance; could be better due to more flux at lower levels, or could be worse due the core material having higher remanance. Probably pretty good as long as there is zero DC bias.

I have tried to get a DC current spec from a few transformer makers and for these toroids the number I get is usually zero; not <1mA, not <1 uA, not <1pA, but zero...

But there are toroids that handle DC current, but using so-called "distributed gap" toriod cores. Apparently there is a dielectric material compounded in with the core material which has the effect of a magnetic gap. I've never tried one, but you see them in flyback switchers and used as filter chokes.

Maybe someone could test the Plitrons and write a report.

Michael

Last edited by Michael Koster; 14th May 2010 at 03:47 PM.
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Old 14th May 2010, 03:44 PM   #24
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Quote:
Originally Posted by Arnulf View Post
...
I'd like to see this automatic bias system that doesn't work by the means of feedback Before anybody jumps up to point out that they were probably referring to audio feedback so this doesn't affect audio output - any bias shifting affects audio output.
Agreed, but I can imagine a low frequency balancing loop I can live with.

Anyway, it's not negative feedback per se that is the problem. The problem is when a circuit with poor open loop bandwidth is "fixed" by using huge open-loop gain and loads of NFB. (can you say "741"? I knew you could)

If NFB is applied to a circuit that has good open loop bandwidth already, for purposes of lower output impedance or linearity correction there is not going to be a problem.

IOW, it's not about the feedback being "too slow", it about the circuit without feedback being too slow.

Cheers,

Michael

PS increasing NFB can certainly change the sound by supressing the second harmonic, resulting in a "dry" sound.

Last edited by Michael Koster; 14th May 2010 at 03:49 PM.
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Old 14th May 2010, 06:55 PM   #25
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What about OTL with 6C33C? Maybe 12 or 16 per channel? Power >250W. The tube costs only 12-15$ per piece. It operates on 180 - 200 volts. The problem is maybe only on size of the tube - it is a huge.
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Old 19th May 2010, 10:34 PM   #26
MI-9448 is offline MI-9448  United States
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If you would be content with it being a commercially made amp that you would have to mildly mod,why not look for a pair of Ampeg model SVT bass amps? I know they are bass amps but the players they were designed for are the fusion and jazz guys that love that crisp SLAP as they pluck the strings.So the high end is definitely there.Very impressive build too.Monsterous output trifilar wound output trans fed by 6X 6550;s. Monster plate trans and big filament trans too. haven't worked on one in awhile but it was a separate power amp and preamp chassis affair.Only trouble is finding two for sale as they have a MAJOR cult following among players
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Old 20th May 2010, 07:47 AM   #27
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200 - 500W pure vacuum tube amplifier doesn't seem to be a practical approach (although I have schematic for 30kW tube amp buried somewhere in my book library).

IMHO better solution would be low-frequency high-quality solid-state amplifier (e.g. 2 x Sansui G8700DB or Beng&Olufsen IcePower) running subwoofers, and 2-way 2-channel vacuum tube amp for mid and high frequencies, plus electronic cross-over of course.
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Old 20th May 2010, 09:17 AM   #28
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Making a 200W tube amp isn't an issue. The cost is, also alot of watchdog thrown in. One just needs a proper bench and instrumentation for such poke.

Putting in separate amps for separate frequency bandwidths adds to speaker phase problems and with a well designed tube amp is unnecessary. I heard alot of Hipower SS amps with fantastic bandwidths but there's often something wrong with the sound. Too many cables, leads about and I 've seen many setups working on the verge of oscillation on signal peaks without anyone knowing what the heck is going on..

richy
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Old 20th May 2010, 11:55 AM   #29
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Bi/tri-amping it would make less power needed and more manageable to construct I reckon
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Old 20th May 2010, 06:27 PM   #30
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Quote:
Originally Posted by Arnulf View Post
I like how they put this in two consecutive lines:



I'd like to see this automatic bias system that doesn't work by the means of feedback Before anybody jumps up to point out that they were probably referring to audio feedback so this doesn't affect audio output - any bias shifting affects audio output.

Impressive power output nevertheless, if only they skipped the audiophool marketing gimmicks ...
The way it does it is there is no feedback loop anywhere in the amp. There is a DC servo control; it is a 2-pole design that is unresponsive to inputs above about 1 Hz or so. It measures the voltage drops on the cathode resistors of the output section and adjusts the DC Offset and Bias on this basis. So it really is zero feedback and bias/DC offset automatic.

Contrary to assertion, blah blah shifting the bias does not alter the output level, that is to say power output is unaffected. If the bias were to be lowered far enough, you would get a bit less gain, but the circuit does not have the amp shut down like that and so its not relevant.

This amp has a lot of extra stuff in it that you really don't need if you want to build a really big amp, like the AC voltage regulator and the tube tester. If you eliminated those things it would be a lot easier to build. I think the AC line voltage regulator is an issue though; unless you have several dedicated 20-amp lines, the amp will draw the AC voltage down and keep it down!

A schematic that is very similar is published on page 3 of this thread: What tubes for a tube amp?

It varies only in scale. The MA-3 uses +/- 400V for the driver supply, but all the other voltages are similar.
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