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EL84 ECC83 SE Amp schematic

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#2
ECC83 gain is rather high for this application and it has a high output impedance and not great linearity. This suggests applying lots of global feedback to resolve these issues.

The ECC83 seems more applicable to a guitar amp, think about using a ECC88 or 5687 which are overall better matches to your plan.

Shoog
 
#3
Hi
Thanks for the reply I can always sell
The ECC83 and use others valves as
You suggested there seems to be a lot
Schematics with ECC82 / El84

I do not want to spend my time building
A poor amp

And appreciate any help

Thank you
 
#6
honestly, its a hard circuit to make a hash of if you set your target parameters reasonably.

Moreover, a typical EL84 SE circuit will have so few parts that if you don't like the implementation once its built, its a matter of 2 hours and a handful of passive components and you have a new different circuit
 
#7
The ECC82 is certainly better than the ECC83 in this application, though I still think that the ECC88 is slightly better.

I found that feedback to the cathode of the driver from the plate of the EL84 produces an excellent result.

Shoog
 
#8
Hi

All the parts I have came from a reel to
Reel tape recorder

2 x El84. 3 x ECC83 1 x EM801
And the transformers

My plan was to salvage what I can

I will measure the output voltages of the
Mains transformer (which used a sold state
Bridge rectifier for the HT)
I can also measure the inductance of the
Outputs transformers and work out the turns
Ratio

Will post any info I have when I can

Thanks
 
#9
Shoog said:
ECC83 gain is rather high for this application and it has a high output impedance and not great linearity. This suggests applying lots of global feedback to resolve these issues.
Click to expand...

The gain of ECC83 can be adjusted if needed. The linearity of ECC83 is far better than ECC82 but this is not a problem at all.
The THD developed by ECC83 voltage amplifier is well below 1 %. At the same time the EL84 output stage produces some 5 % of THD.
So do we need GNFB due to ECC83 or EL84 ?
 
#10
artosalo said:
The gain of ECC83 can be adjusted if needed. The linearity of ECC83 is far better than ECC82 but this is not a problem at all.
The THD developed by ECC83 voltage amplifier is well below 1 %. At the same time the EL84 output stage produces some 5 % of THD.
So do we need GNFB due to ECC83 or EL84 ?
Click to expand...
Taming the excessive gain will introduce some noise or require a considerable amount of feedback. I still think its a bad option and I think that the ECC88 is better than the ECC82 for a few reasons.
Why compromise when the ECC88 can be had for less than €20.00

Why use a high gain triode when high gain is not needed ?

However this is just my personal opinion and if the builder wants to pursue the ECC83 EL84 combination he might look at this thread:

http://www.diyaudio.com/forums/tubes-valves/145369-help-el84-ecc83-se-project-very-low-volume.html

Shoog
 
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#11
Hi again

Thanks for all the info

I am quite happy to use another triode
I have the ECC83 to hand
But if useing another triode ECC88 or
Whatever is a better option then for the
Cost involved I will go that way

After all that is way I asked the question
For some recommendations

Thank you
 
#13
Shoog said:
...Why use a high gain triode when high gain is not needed ?
Click to expand...

EL84 SE as UL or triode connected requires some 6.5 Vrms drive for full output power,
which in case of triode is some 1.5 W and in case of UL some 4 W.

If one accepts an amplifier without GNFB ( and high THD) and some 1 Vrms sensitivity is OK, then the gain of 1st stage should be about 16 dB minimum. So one ECC82 would be sufficient is this case.

If some moderate amount (~10 dB) of GNFB is used and the required sensitivity is less than 0.5 Vrms, then the gain of the 1st stage needs to be minimum 32 dB. Now ECC83 is a right choice.

Below is one example of well considered version with UL-output stage.
Some distortion cancelling takes place at the voltage amplifier (12AX7), the GNFB is 10 dB, Pout = 4 W, THD is some 2% and sensitivity is just below .5 Vrms.
 

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  • EL84_UL-12AX7.jpg
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#14
I agree with Artsalo. The real question is pentode or triode strapped. I normally would pick triode strapped, but for EL84 I would go for pentode.

Actually EL84 is hard to beat in push-pull if you are inclinded to try that out using ecc88 - Morgan Jones' "Bevois Valley" amplifier is a nice one to start out with if it your first build.

Have you only got the tubes or do you have any iron yet?

Ian
 
#15
Try this circuit, I'm currently building it at the moment. I reckon it'll give the best performance of any EL84 SE design out there 😛.

It uses the an ultra-linear EDCOR output transformer. You can buy them at their site for a very reasonable price and they ship worldwide. They also look pretty cool 😉.
 

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#16
Hi

With regard to the output connection
The transformers I have do not have
Taps on the primary so I can not
Use UL unless I am totally incorrect as
I am new to valve amps

So that leaves me triode or pentode
I think I will look how the EL84 where
Connected originally with the transformers
I have and go with that

My theory being that is what the output
Transformers where intended for

Regards
 
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