Could someone knowledgeable comfirm please:
If I want to replace the current KT88 tubes in my amp with EL34 (to compare sound) I need to make a connection between pins 1 and 8 of the tube sockets and properly adjust bias.
Is this correct? From what I've found using the search function that should be all.
Thanks in advance guys.
If I want to replace the current KT88 tubes in my amp with EL34 (to compare sound) I need to make a connection between pins 1 and 8 of the tube sockets and properly adjust bias.
Is this correct? From what I've found using the search function that should be all.
Thanks in advance guys.
Well connecting g3 ( pin 1) to the cathode (k) pin 8 is a step in the right direction but they have vastly different vg voltages and anode (plate ) current settings .
OF course you can --"just plug it in " but it amazes me that expectations in the "tube rolling " section are going to make a tube "sound better" when its operating under circuit component conditions set up for a completely different tube .
Personally if the KT88 is a good quality make there is no way on this earth I would put an EL34 in its place .
Read up on the KT series of UK tubes , they were designed specifically for high quality audio even the ones I fitted to old tube radios .
Look when I worked in a hospital a guy came in to change the EL34,s in an old fashioned doctors valve call system transmitter --he went through a lot .
Not once was the KT series used for general industrial systems except in tube radios the EL34 just wasn't in the same league as a KT 66/88.
I can only comment on the British made ones Osram for example as I don't know all those "Golden Lion " Chinese versions and others .
OF course you can --"just plug it in " but it amazes me that expectations in the "tube rolling " section are going to make a tube "sound better" when its operating under circuit component conditions set up for a completely different tube .
Personally if the KT88 is a good quality make there is no way on this earth I would put an EL34 in its place .
Read up on the KT series of UK tubes , they were designed specifically for high quality audio even the ones I fitted to old tube radios .
Look when I worked in a hospital a guy came in to change the EL34,s in an old fashioned doctors valve call system transmitter --he went through a lot .
Not once was the KT series used for general industrial systems except in tube radios the EL34 just wasn't in the same league as a KT 66/88.
I can only comment on the British made ones Osram for example as I don't know all those "Golden Lion " Chinese versions and others .
As to why, long story short: I always wanted that lush warm jazzy sound of old tube amps but simply couldn't afford one until my uncle gave me his Cayin A-55t which he already modded with better caps and other parts, so selling it for an other is out of the question.
This amp came in a EL34 version A-50t and the more expensive KT88 version A-55t.
Don't get me wrong it sounds fantastic, but it can still get a bit agressive in the upper mids.
Newer models come with a switch to let you choose between EL34 and KT88 so I figured it might not need much modding to try some EL34s in it? The loss of power is no issue since I never listen past the halfway point of the volume pot.
The schematic:
404 Not Found
Currently researching which NOS 12ax7 to get for the pre amp section in the hopes to achieve my preferred sound that way.
This amp came in a EL34 version A-50t and the more expensive KT88 version A-55t.
Don't get me wrong it sounds fantastic, but it can still get a bit agressive in the upper mids.
Newer models come with a switch to let you choose between EL34 and KT88 so I figured it might not need much modding to try some EL34s in it? The loss of power is no issue since I never listen past the halfway point of the volume pot.
The schematic:
404 Not Found
Currently researching which NOS 12ax7 to get for the pre amp section in the hopes to achieve my preferred sound that way.
I see the schematic link doesn't work. How can I share a pdf file here?
By the way, I'm not dead set on using EL34s, open to any suggestion to add a bit of warmth; different power tubes (Gold Lion KT88 currently), 6550, different pre amp section tubes, exchanging 12ax7 for 5751 or 12at7, etc.
By the way, I'm not dead set on using EL34s, open to any suggestion to add a bit of warmth; different power tubes (Gold Lion KT88 currently), 6550, different pre amp section tubes, exchanging 12ax7 for 5751 or 12at7, etc.
the link for the schematic is missing a colon http://images.tubebbs.com/clone/c/Cayin-A55-int-sch.PDF
I am far from an expert on any of this but it looks like it would be easily reversible if you didn't like the EL34 by just changing back the bias resistor.
I've seen amps before where they have the correct bias resistor for the EL34 and then a switch adds a parallel resistor that takes it down to the correct bias resistance for the KT88 for easily moving back and forth.
I don't have a push pull amp to try them in but I've switched my DIY SE amp from EL34 to 6550 and back before. Overall I prefer the EL34 but amp design, driver tubes, speakers and room all play into the sound as well as personal preference so there is no one perfect answer. If there was one perfect answer then there would only be one amp and one speaker sold at every price point because it would be perfect for everyone.
I am far from an expert on any of this but it looks like it would be easily reversible if you didn't like the EL34 by just changing back the bias resistor.
I've seen amps before where they have the correct bias resistor for the EL34 and then a switch adds a parallel resistor that takes it down to the correct bias resistance for the KT88 for easily moving back and forth.
I don't have a push pull amp to try them in but I've switched my DIY SE amp from EL34 to 6550 and back before. Overall I prefer the EL34 but amp design, driver tubes, speakers and room all play into the sound as well as personal preference so there is no one perfect answer. If there was one perfect answer then there would only be one amp and one speaker sold at every price point because it would be perfect for everyone.
Last edited:
There are no "bias resistors" in there - that amp has fixed bias.
Running the EL34 at ~420..425V plate voltage and 40mA (as per schematics) requires about -36V bias. Running the KT88 at the same operating point requires about -55V bias.
The only way to achieve this is to modify the bias adjustment circuitry, but it looks like there may be not enough voltage. If you can measure the voltage at the top of the bias pots (marked red) relative to the ground when the amp is running, then we can tell for sure.
Running the EL34 at ~420..425V plate voltage and 40mA (as per schematics) requires about -36V bias. Running the KT88 at the same operating point requires about -55V bias.
The only way to achieve this is to modify the bias adjustment circuitry, but it looks like there may be not enough voltage. If you can measure the voltage at the top of the bias pots (marked red) relative to the ground when the amp is running, then we can tell for sure.
Attachments
As Egellings says -- output transformers different .
What he means is the input AC impedance of the OT is different ,that's apart from the different wattage rating .
KT88=3500ohms .
EL34=2000ohms .
While it would work it will sound "different " if "different " pleases you then well and good but I have to be honest I am not a fan of "tube rolling " but each to his own.
Electrically it is incorrect.
Also what voltage are you running the KT88 at ?
What he means is the input AC impedance of the OT is different ,that's apart from the different wattage rating .
KT88=3500ohms .
EL34=2000ohms .
While it would work it will sound "different " if "different " pleases you then well and good but I have to be honest I am not a fan of "tube rolling " but each to his own.
Electrically it is incorrect.
Also what voltage are you running the KT88 at ?
EL34's will work fine in your amp, but you may need to change the resistors in the bias circuit to hit the correct operating point for the tubes, as TG pointed out.
My first tube amp was a Jolida 302b. The company also offered the same amp (502b) that was setup to run KT88's. The two amps were the same, except for the resistors in the bias network.
jeff
The amp in question is fixed bias push-pull. Did you look an the schematic?
jeff
I'm considering adding a small circuit to the bias pcd so you could exchange different tube types at the flick of a switch.
I only quickly copied part of the schematic and resistor values aren't mentioned.
Still figuring out how I'll do the switching, 4 pole relay, 2 x 2 pole relay with a switch, 4 pole switch...
I only quickly copied part of the schematic and resistor values aren't mentioned.
Still figuring out how I'll do the switching, 4 pole relay, 2 x 2 pole relay with a switch, 4 pole switch...
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.