| Miles Prower |
"It is an High End amplifier?"
Doesn't look like it to me. The performance is determined largely by that chip amp up front. These are mediocre performers useful for a quick 'n' dirty solution where fidelity isn't all that important.
Secondly, Class AB2 and cathode bias do not mix. You need a stable source of fixed bias if you're going Class AB2 and you want sound quality above what you'd get from any PA amp.
The 6A3 has a Pd= 15W. You're not gonna get 50W from a pair of those, at least not for very long.
I'd take a pass on this one. |
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| anatech |
Sorry Jaime,
I have to agree with Miles.
Hey, I saw a couple schematics that didn't use that chip! He must have a drawer full of TDA2030's to use up.
| quote: | | The power is 50w using 2 x 6A3 !!! |
You really have to be careful with claims like that. Output power is not the most important consideration with a tube amp. This one may put out that power - possibly - maybe. IT would be here for a semi good time, not a long time.
| quote: | | It have a wide band? |
Errr, depends on the transformers mostly. I am doubtful.
| quote: | | It is an High End amplifier? |
I have trouble with that too. I'll bet they could sell it as high end in some shops. It has TOOOBS!
Yeah, skip this and look for something more conventional.
-Chris |
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| astouffer |
| Link is down for now but VTL used to claim similar ratings. 50 watts from a pair of 807s triode strapped :bomb: |
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| anatech |
Yes they did,
They did it at HIGH voltages. At least they attempted 50 W with a 25 W plate type tube (EL34). I didn't see the 807 deal, but it makes sense given the voltages they liked to run.
-Chris |
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| corne |
There's no way two 6A3 tubes in A2 PP will give you 50W output power.
The maximum efficiency for a class A2 amp is 50% so the theoretical max. power output is 30Watt.
Even running two 300B tubes A2 the power output is restricted to 40W.
If you want 50W from two 6A3's you'll need to run it class B2 requiring fixed bias.
| quote: |
Miles Prower wrote:
The performance is determined largely by that chip amp up front. |
It's a big factor but even worse is the way the grid current is supplied.
The transformer is in series with the 380ohm cathode resistor. For a large part this amp will run class1 (no grid current) so the transformer sees a load of 20k. As it goes into grid current the load changes to 380ohm and due to the grid current a significant portion of the signal is lost in the cathode resistor.
The amplification for class1 and class2 is different, this will give a very nasty distortion at the class1 to class2 transition
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It is an High End amplifier?. |
No not even close.
Corne |
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| corne |
| quote: | | The maximum efficiency for a class A2 amp is 50% so the theoretical max. power output is 30Watt. |
That should be 15Watt not 30Watt.
Corne |
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| corne |
I've read the Electra-print article on A2.
This is my opinion:
It has bits of truth, alternative explanations to what is really going on (shifting bias), a solution to a problem (shifting bias) but fail to tell the real solution (don't use a coupling capacitor in A2), compares two completely different things (chips drivers with FB and tube drivers without FB) and leaves out key issues (effective driver impedance at the output tube grid).
In my experience it's possible to design a good tube A2 driver.
Use a high transconductance Cathode Follower (low output impedance) directly coupled (no bias shift) to the output tube grid and a driver with local FB from the CF output.
This will ensure low output impedance and therefore the driver signal doesn't get distorted when the output tube draws grid current. And don't use cathode resistors when using A2.
Corne
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