Using Wards SE EL84 Transformers for Decware Zenkit1 - diyAudio
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Old 24th March 2013, 09:01 PM   #1
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Smile Using Wards SE EL84 Transformers for Decware Zenkit1


Hi All,
My Friend and I are building a ZenKit1 Modified from using a Wards
console SE EL84 Transformers. Now, this amplifier as shown in the .pdf
is all the tweaks, mods, suggestions from others and I need to know few things:
1.) Will the Transformers work in this design?
2.) Can I use a 5AU4 Type or 5Y3GT Rectifier tube instead of the 6CA4?
3.) Can someone calculate a Choke size for me in the PSU....Please
4.) Can someone Calculate Voltage and amperes going to be if we use 5AU4?
5.) What about the SV83's will they work with the 500 Ohm OutputTrans?
6.) Any suggestions on the Pre-amp 6DJ8 tube? will there be enough current?
7.) Voltage loss across the Plates on the SV83,Will I have enough?
8.) Any suggestions on the EFB Biasing? this is Dave Gillespie's design, and we are going to use it, in this SE Amplifier, Yes?!!!
Any Comments would be appreciated... blonde-pianist
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File Type: pdf SE EL84 WARDS_processed.pdf (815.4 KB, 54 views)
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Old 24th March 2013, 09:18 PM   #2
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The original SE84 uses a 125 mA. 5Y3 rectifier. The 150 mA. 6CA4/EZ81 is, obviously, adequate. Also, you lack a 5 VAC winding. I would switch to SS rectified B+, to raise the rail voltage. My SE84Bs use Hammond 272FX power trafos, whose B+ winding is 300-0-300. You can't afford vacuum rectification forward drop losses.

I suspect your measurement is DC resistance. A reflected impedance in the 4 to 5 KOhm range is "routine" in EL84/6BQ5 SE amps.
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Old 24th March 2013, 09:56 PM   #3
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It is also recommended to use a separate regulator for each EL84, since it is a stereo setup, why would you want to join your EL84's?
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Old 24th March 2013, 10:02 PM   #4
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Default In Reply to EFB

Quote:
Originally Posted by costis_n View Post
It is also recommended to use a separate regulator for each EL84, since it is a stereo setup, why would you want to join your EL84's?
Because by doing this, one can achieve a balance between output tubes...
More Linear control.
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Old 24th March 2013, 10:07 PM   #5
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Well. we are concerned with balance in push-pull pairs (to avoid magnetising the transformer core) Here we have two separate channels. Nothing to balance with.

By the way sharing a cathode resistor is the wrong way to achieve balance.

Amplifier auto bias circuits: Alan Dower Blumlein's garter circuit
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Old 24th March 2013, 10:46 PM   #6
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Quote:
Originally Posted by costis_n View Post
Well. we are concerned with balance in push-pull pairs (to avoid magnetising the transformer core) Here we have two separate channels. Nothing to balance with.

By the way sharing a cathode resistor is the wrong way to achieve balance.

Amplifier auto bias circuits: Alan Dower Blumlein's garter circuit
to ensure idle current balance between two output tubes; and nine OpAmps can be used with ten output tubes, as each OpAmp finds the same reference voltage: the cathode voltage of the lead tube, whose idle current is set with a potentiometer/Trimmer and this is where I got the Idea to use Dave Gillespies EFB, i know he meant that for PP Dynaco SCA35, But really, I think the Negative voltage regulator will work. In Dave's schematic of the SCA35, He used the LM337 and connected two pairs of 10 ohm resistors in parallel with a jumper, for both pairs of EL84's he wanted to maintain what was described above, keeping the idle current equal no matter the voltage spikes, I assume this also helps out in unmatched output tubes to be able to have a coherency of sorts. Also Dave mentioned the effect of a type of floating Bias for lower distortion. Results are supposed to be cleaner clearer more dynamic output! Any thoughts on this? I could have misunderstood him.
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Old 25th March 2013, 12:50 AM   #7
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Quote:
Originally Posted by pianolydia View Post

1.) Will the Transformers work in this design?
a little late for that question I would have thought, but none the less, as Eli says, yes they should be perfectly acceptable (assuming htey are still sound condition)


Quote:
Originally Posted by pianolydia View Post
3.) Can someone calculate a Choke size for me in the PSU....Please
4.) Can someone Calculate Voltage and amperes going to be if we use 5AU4?
No but you can teach yourself to fish here PSUD2

The "balancing" of your finals is covered by costis. You are comparing apples to volkswagens. The two output tubes are effectively in independent circuits and do not need to be balanced for all practical purposes, regardless of who devised the balancing scheme.
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