• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Vacuum Tube OTL power amp!!

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M Gregg

M Gregg

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Joined 2010
Just for interest,

Mozeners fitted started burn in.... A couple of orange drop 716 in the 1st to second stage coupling just for a test.. :) :)


Regards
M. Gregg
 

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M Gregg

M Gregg

Disabled Account
Joined 2010
flatheadmurre said:
How´s first impression ?
Click to expand...

It's very loud..

With two heaters on it's a bit much to stand in front of the speakers...I am also concerned about damage to the speakers the cones are being driven quite hard... at these volumes...YMMV

sound is clear and powerfull...its a bit early to tell yet it needs to burn in.. :)

I'm only using the mozener as a clamp....so the heat will be less spread across the resistor and FET.. cap still in place at the moment...

I don't want to use the trim pot its another pain in the ....like fixed bias..
:D...it's almost cheating....so I might change a few resistors to get it close..LOL


Regards
M. Gregg
 
M Gregg

M Gregg

Disabled Account
Joined 2010
The mozener,

Does clamp the cap voltage and prevents the increase of cap voltage when two heaters are switched in... << just an observation :)

The only thing I can think of is my speakers must drive well with just a few watts.. I have no other explanation...

Regards
M. Gregg
 
Last edited:
M Gregg

M Gregg

Disabled Account
Joined 2010
flatheadmurre said:
You´re only benefitting from the constant voltage when running it hard.

At low OP it should perform the same as katodbias.
Click to expand...

I agree ,,if the voltage across the cap was to remain the same ie change with number of heaters running... 40v (one heater) 46V(two heaters)<<<resistor bias

If the voltage across the cap/resistor remains the same voltage more current must be flowing through the FET to reduce the voltage across the resistor?

This must effect the bias at idle?

Regards
M. Gregg
 
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M Gregg

M Gregg

Disabled Account
Joined 2010
Last edited:
M Gregg

M Gregg

Disabled Account
Joined 2010
Alastair E said:
Worth remembering the Impedance presented to the amp by the speaker at or near its freq of resonance, --for the Alpair 7 70 Hz, its many times the DC or quoted nominal impedance...

For the Alpair, its approaching something like 50 ohms at 70 Hz, therefore an easier load for the amp and more effective power can be realised.....:eek:
Click to expand...

The only trouble is..

When you power them for the first time you can only have them at transistor radio volumes (I have a feeling you would damage them if you try to push them their so tight) and they produce what sounds like "0" bass...Then a very slow break in period over 6 Months..LOL

Then your stuffing polyfluff in the vent to reduce the bass...cuz its so loud..LOL :D :D

Regards
M. Gregg
 
M Gregg

M Gregg

Disabled Account
Joined 2010
OK just an update,

The toroids now have cork pads under the rubber pads made from cork tiles..
Result reduced Tx noise (mechanical).. :)
(Tx under rated no heat issue)

The 0.22 interstage cap was changed just for a laugh to Obbligato 630V <<(seem to like violin don't know why)
I would never have tried them except I was interested in price Vs performance...Compared to jupiter HT in this part of this circuit..Well yes different..for the price you have got to try these :D

Switched on Jessie J and goose bumps..LOL


So as it stands now for a laugh orange drop to Op tubes and as above..LOL

The saga continues...

Regards
M. Gregg
 
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