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Old 15th October 2003, 11:46 PM   #1
effindi is offline effindi  Singapore
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Default Beefing up EL34 PP

Hi all,

I am trying to beef up my long service EL34 PP amplifier.

I recently changed the origincal Shuguang tube to Electro Harmonix EL34 EH.

It is using 5670WA as driver and ECC88 as phase splitter.

It seems to lacking in the lower end region. High is fine but mids lack the weight.

I am using the Brines FT1600 Full range driver as my speaker and Marantz CD63 SE for my CDP.

Since I have used this amp for more than 10 years. I thought of giving it a new life but not sure where to start.

Looking forward to great advice from here.
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Old 16th October 2003, 12:09 AM   #2
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For the lower frequencies you need to utilize current sinks in both your phase splitter if it is a long tail pair and in your output stage. You can install a current sink in your output stage if it is a cathode bias but replacing the resistor and cap with a suitable sink, sinking the same amount of current. This is similar to the long tail pair. This forces balance in both the phase splitter almost identical phase splitting and at the output stage too. Also with identical or almost identical amount of current flowing thru the tubes ( phase splitter and output tubes) the interaction at the power supply would be minimize as both tubes are out of phase current demands thus cancelling each other theoretically. But in pratice some amount of interaction will take place, that why some designers biased the pp into class a and use a smaller power supply. This is because class a load is consider constant and pp would not need so much LC to clear up the ripple. I have tried both cathode biased and ltp with resistor and after with ccs and found the bass region and mid improve alot. I speculate that
in the mids, since both tubes are almost identical and out of phase waveform, the run almost identical out of phase and not smearing the sound or distorting with not perfect phase splittering.
For the mids, are you using utralinear or triode. Normally the el34 when run in triode mode does not utilize feedback and this would be a plus point. Ultralinear gives you more power but will have to utilize some amount of feedback. This could ruin the mids. BUt in triode, the lower bass would be not firm due to low damping factor. Feedback improves on this. I go around this by using a stepdown transformer after the output transformer was a 4:1 impedance stepdown. This allowed by damping factor to increase to 12.5 without feedback at a cost of power
my pp are 6922 driving a el34 into a 6k:8 then into a 4:1 stepdown trans.
if you like i could post the schematic here for you to get a rough idea on the implementation or you could visit my website at
www.geocities.com\nickchua81
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Old 16th October 2003, 12:29 AM   #3
SY is offline SY  United States
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Some Qs:

How is the output stage configured (i.e., triode, pentode, UL)?

Plate to plate output transformer impedance?

Plate supply voltage?
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Old 17th October 2003, 03:59 AM   #4
effindi is offline effindi  Singapore
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Default how about CCS with LM317

Hi Nick and SY,

That's a chokeful of information for a newbie like.

I think posting my current schematics will be a good idea. Will try to do that but not sure what software to use. Any suggestion on that?

In the mean time, after looking at Nick web page, I like the CCS of using LM317 with 50ohm resistor.

Let me try if this work out some wonders or warn me if it will cost me more problem...

REgards,
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Old 17th October 2003, 05:42 AM   #5
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Quote:
Originally posted by NickC
You can install a current sink in your output stage if it is a cathode bias but replacing the resistor and cap with a suitable sink, sinking the same amount of current.
If it's class A.
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Old 17th October 2003, 06:37 AM   #6
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sorry about mention about that

Quote:
You can install a current sink in your output stage if it is a cathode bias but replacing the resistor and cap with a suitable sink, sinking the same amount of current.
effendi
remember to heatsink the lm317
the resistor value should be =1.25/current
My current value is different from yours

I would install cathode degeneration resistor to balance the current in both tubes and as well as measuring the current
this can be done by

cathode--------resistor ------resistor -------Cathode
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Old 17th October 2003, 06:38 AM   #7
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sorry about mention about that

Quote:
You can install a current sink in your output stage if it is a cathode bias but replacing the resistor and cap with a suitable sink, sinking the same amount of current.
effendi
remember to heatsink the lm317
the resistor value should be =1.25/current
My current value is different from yours

I would install cathode degeneration resistor to balance the current in both tubes and as well as measuring the current
this can be done by

cathode--------resistor ------resistor -------Cathode
|
CCS
You could opt to use a variable resistor to balance the current.
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