• 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.

EC8010 & AD1 & 845

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#45

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#48
6A3sUMMER said:
I guess if you use a 211 tube, u=12, Gm about 3000uMhos, and about 4000 Ohms plate impedance or more at only 55mA quiescent Ip . . .
And then you combine it with a transformer that is not well matched for 211 service, you get what you get.
And, you got it.

Do not increase the B+ voltage; instead, reduce the negative bias voltage until you get 60mA plate current.
(look at the curves at various bias volts and plate volts; check where the slope is curving, not straight. rp is much larger at the curve than at the straight line)

The output transformer is specified at 60mA when set to 11k primary, Right?
I asked you to check that.
Take Lundahl at their word; if it does not meet specs, send it back for a refund ($$$).
Then purchase a less elegant but more capable E-I transformer with a single Air Gap.

I am just thinking out loud.
Click to expand...
Proffessionally you are right, but we diyers sometimes think with their hearts and ears.

You have the measured damping factor and 1620 datasheet, why do you not calculate the exact ri of 845 ?
From what I remember it is much lower than you suspect.
 
#51
A very important factor to troubleshooting the amplifier:

A 20kHz square wave in Post # 12 looks 'textbook perfect' at the input tube, driver tube, AND the output tube Grid.
(There was no negative feedback during that multi trace capture).

The only things left that could cause the odd shaped output from the output transformer secondary are:
The 211 Tube (not likely the cause)
The 211 filament circuit path to ground (not likely the cause)
The non-inductive load resistor on the 8 Ohm tap (not likely the cause) [I hope a good resistor was used, not an open, and not a loudspeaker].
The B+ filtering at the top of the output transformer (not likely the cause)
And, the Only thing left . . . The Output Transformer.

Just my opinions
So . . . how about another 50 Posts to give "fixes" that do not fix that 20kHz square wave shape.
Either Live with the shape; OR Replace the Output transformer; only the original poster can do that.

There is nothing against hearts and ears.

As one trusted reviewer once said: Enjoy the Music
 
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#53
daanve,

You are correct.
My error, 845 tubes not 211 tubes.
Same filament voltage and filament current (10V, 3.25A)

But here are a few important differences:
Approximations:
211 u/2 = 845 u
211 rp/2 = 845 rp

I would say that requires quite different output transformers (but only if you want to have a decent amplifier).

There is No "Plug and Play" here.
It will play alright, but Handel's "Messiah" sounds like the Salvation Army Band.

Just my thoughts.
 
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#55
filenet said:
SQ at 10khz, -6db GNFB, and compensation cap.

Better?


View attachment 1201189
Click to expand...
So it is a problem with capacitances. Nothing to do with saturation, class B and other similar stuff because 6 dB fbk will not remove them like this. Moreover, core saturation you would see already at lower frequency where induction would be higher and higher. As I said, from the practical point of view you might not hear anything strange. Unfortunately cannot compare the sound with and without feedback to tell something SPECIFIC about that SQ feature because feedback completely changes the way the amp drives the speakers. This also means that sound might be better without feedback. Try and see what is better for you.
 
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