Hi, googling around, there seems to be a lot of info on replacing EL34 with KT88. But there seems to be zero info on the opposite.
Can KT88 be replaced with EL34 without changing circuit / components?
Thanks
Can KT88 be replaced with EL34 without changing circuit / components?
Thanks
No, not if the circuit uses typical 6550/kt88 voltages and currents.
el34 can absorb 30w anode losses, 6550/kt88 42w
el34 can absorb 30w anode losses, 6550/kt88 42w
hello ,
the EL 34 is possible change for 6CA7 ; ...caution , look datasheet for use to ampli PP , the SE is not problem 😉
the EL 34 is possible change for 6CA7 ; ...caution , look datasheet for use to ampli PP , the SE is not problem 😉
Even if you changed the plate, screen, and bias the tube wouldn't sound as good as a KT88 or 6550.
Thanks for all the replies.
I bought a PCB which label "diy PCB for EL34 KT88 6L6GC FU7 FU50 6550" (SE amp). The vendor only supply a schematic for KT88 and did not reply when ask for the EL34 schematic.
As I already have the EL34 tubes and the power transformer to go with them, is there any guide line or formula to recalculate required components values?
I bought a PCB which label "diy PCB for EL34 KT88 6L6GC FU7 FU50 6550" (SE amp). The vendor only supply a schematic for KT88 and did not reply when ask for the EL34 schematic.
As I already have the EL34 tubes and the power transformer to go with them, is there any guide line or formula to recalculate required components values?
Shure.
The Valve Wizard -Push-Pull is a good starting point together with tube data : http://www.mif.pg.gda.pl/homepages/frank/sheets/010/e/EL34.pdf
Do you have the B+ voltage, output transformer impedance, and cathode resistor value for the output tubes? EL34 and KT88 share the same pinout and are interchangeable in some circuits.
Where was the PCB purchased? Got a link?
Be careful with substituting EL34 and KT88. Pinouts are not the same.
EL34 pin 1 is connected to suppressor grid and must be strapped to cathode on pin 8.
KT88 sometimes has metal base shell connected to pin 1 and suppressor and cathode are internally connected on pin 8.
EL34 pin 1 is connected to suppressor grid and must be strapped to cathode on pin 8.
KT88 sometimes has metal base shell connected to pin 1 and suppressor and cathode are internally connected on pin 8.
Thanks for correcting me, Richard. This being a PCB, I'm assuming the designer took this into account (but such assumptions are probably dangerous!).
PCB is from ebay 1pc Single-ended tube amplifier bare diy PCB for EL34 KT88 6L6GC FU7 FU50 6550
The transformer has 300-0-300 HT using 5Z3P rectifier tube with a 3H choke. I do not know the value of B+
You should be able to make this work with el34. What does the schematic list as the cathode resistor on the output tubes?
This looks like a pretty straight forward single ended design. If you can upload the schematic, that would also help.
This looks like a pretty straight forward single ended design. If you can upload the schematic, that would also help.
CL, you might want a little higher based on a quick review of the schematic. You can calculate the b+ with a program like Duncan PSU Calculator (free). Also, Tubelab has some great data on the Simple SE pages about octal power tubes and choosing a cathode resistor.
That voltage seems a bit low for KT88 or 6550 and better for EL34. In my experience, read limited, KT88 has more punch in the low end. 6550 has better midbass and highs. And EL34 really blooms in the mid-range. I don't know your skill level but I would suggest fixed bias for the outputs. It would mean building a bias supply but with the little power single ended has available it would be worth it. Also, with the lower current demand of the EL34 the B+ voltage is going to go up.
Wouldn't it make more sense to build it with KT88 and see how it sounds? Circuit boards don't give you as much flexibility as point to point wiring.
Wouldn't it make more sense to build it with KT88 and see how it sounds? Circuit boards don't give you as much flexibility as point to point wiring.
Hi CL, you should have no trouble using an EL34 as long as pins 1 and 8 are connected on the octal power tube socket. I like the 6sl7 front end of this design which is a great sounding tube. And with many different brands to choose from you can roll to your heart's content. Since this design has a tube rectifier you can change the 5z3 to a 5y3 for a lower B+ which might be a better match for the EL34. Conversely, switching the rectifier to a 5V4 will give you about 30 volts more than the 5Z3. This might sound better for the KT88 or you could even use the KT90 for even more power. The only thing would be your OPT needs to handle at least 15 watts. So many choices, so little time. cheers,
Thanks everyone for advise.
I'll be hardwiring SP1/SP4 to 1-2, changing the R11/R23 to 330, C5/C10 to 220uF.
My last touch on tube circuit and amps was 35+ years ago and hence I can say I'm a noob (I'm trying to re live my teen years).
Please advise the purpose of C13 (can i reduce to 0.1uF?), C4/C9 (can I omit them?)
I'm happy in finding this forum, everyone are so helpful. Thank you.
I'll be hardwiring SP1/SP4 to 1-2, changing the R11/R23 to 330, C5/C10 to 220uF.
My last touch on tube circuit and amps was 35+ years ago and hence I can say I'm a noob (I'm trying to re live my teen years).
Please advise the purpose of C13 (can i reduce to 0.1uF?), C4/C9 (can I omit them?)
I'm happy in finding this forum, everyone are so helpful. Thank you.
c13 is a film cap to bypass the large 220uf electrolytic. The value can be changed to a smaller one but in the power supply you would like the bypass cap to be around 1% of the value of the main cap. Changing it won't hurt any but the original value is more effective. c4/c9 also serve the same function of bypassing the large cap. in this instance since it is bypassing the cathode capacitor it is even more critical. The cathode bypass cap has the entire signal going through it so that electrolytic capacitor needs to be the best you can find in that value or slightly smaller would probably be ok. This is the spot where a Black Gate electrolytic would be best served.
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What were your results?
I also purchased one of those PC boards and am in the process of tweaking it for EL34's. Just wondered what your results were and what you have changed.
First off there are two errors on the board. If you are going to use R29, it has no ground connection. A jumper will fix that. Also there is a missing trace between the top of R30 an the top connection of C15 that requires another jumper. I am using regulated DC on the 6SL7 filaments. Also changed R23 to 470 ohms. For pentode mode I am using 33v zeners (vd1, vd2) but I also added another in series to bring the screen voltage down a bit for pentode mode. I included two switches to go from triode, ul, and pentode. I am using Transcendar tt-336 4.2k transformers.
Ron S.
I also purchased one of those PC boards and am in the process of tweaking it for EL34's. Just wondered what your results were and what you have changed.
First off there are two errors on the board. If you are going to use R29, it has no ground connection. A jumper will fix that. Also there is a missing trace between the top of R30 an the top connection of C15 that requires another jumper. I am using regulated DC on the 6SL7 filaments. Also changed R23 to 470 ohms. For pentode mode I am using 33v zeners (vd1, vd2) but I also added another in series to bring the screen voltage down a bit for pentode mode. I included two switches to go from triode, ul, and pentode. I am using Transcendar tt-336 4.2k transformers.
Ron S.
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