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12ax7 preamp tube for jolida 1501BRC

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Hi All,
I am new to this forum,just registered today. I have jolida JD1501BRC hybrid amp and planing to roll off 12ax7 tubes,please guide me , I have tried tungsol 12ax7 RI,mullard 12ax7,jj 12ax7,siemens ecc83 NOS,GE 5751 NOS and telefunken ecc83 smooth place, among this I like GE 5751 NOS,but still I am looking for dynamics..... please guide me

Thanks
 
The 5751 has a lower mu than the ECC83. I wouldn't expect huge dynamics from both. Or noteworthy changes in sound unless your amplifier is constructed on the edge and different current draws of different tubes change the behaviour of the circuit.
Did you measure bias of the different tubes you used?
Be aware that emission will rise in the first few hours you are heating a tube.
 
The 5751 has a lower mu than the ECC83. I wouldn't expect huge dynamics from both. Or noteworthy changes in sound unless your amplifier is constructed on the edge and different current draws of different tubes change the behaviour of the circuit.
Did you measure bias of the different tubes you used?
Be aware that emission will rise in the first few hours you are heating a tube.

yes , GE 5751 don't have dynamics, I am expecting tube which can give dynamics. I don't have any idea abt bias.. My amp is hybrid amp ( 2 pair of 12ax7 + sold stage power amp ) .
 
Given the output stage is capable of delivering dynamics the input stage would have to be replaced. There are always many possibilities. If you want to stick with tubes go for a high transconductance low Rp type. These will need considerably higher anode current than a 12AX7, so a new powersupply will be needed as well. A Salas simplistic HV regulator could be used here. Use a CCS as plate load and LEDs on the cathodes to get rid of the cathode resistor and most importantly of the bypass cap. Hopefully you found a tube with enough mu to work with the output stage. DC couple to the output stage, don't use coupling caps.

Do your math.
 
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today I have tried siemens 12ax7 nos tubes, it is nice than ge but low is not like ge. It is very clear representation... it is nice but disappointed with lows


Leave them switched on for a couple of hours. Emission needs to stabilise when an old tube is used for the first time. Current draw usually goes up. Different current draws (operating points) will (if at all) change the sound more than the printing on the glass.
 
I dont have any meter type and even dont know the bias 🙂 . I will burn them for some days....

have one small query , some people who know more abt this amps, they informed this jolida have some limitation,so by changing tube you will not get benefit
 
have one small query , some people who know more abt this amps, they informed this jolida have some limitation,so by changing tube you will not get benefit

I was one of these people. Tube rolling does soooo little for what you are looking for I personally consider it a waste of time. But maybe these little changes are all you need. It just seems very tedious.
 
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