I just finished wiring up this SE KT88 amp
the only difference I used a 560 ohm cathode resistor
across pin 1 & 8 of KT88 socket.
was getting ready to try her out for the first time
and need to know where to check voltages and
what voltage readings should I be getting at critical spots.
Scott
the only difference I used a 560 ohm cathode resistor
across pin 1 & 8 of KT88 socket.
was getting ready to try her out for the first time
and need to know where to check voltages and
what voltage readings should I be getting at critical spots.
Scott
Is there a schematic you were using to work from? Could you post it here so others can see it? That way it would be much easier to see what you are referring to.
It's kind of hard to understand why a resistor would be placed from pin 1 to pin 8 on a KT88. Usually pin 1 and pin 8 are shorted together, and then 560 ohms might be the cathode load resistor to ground. A schematic should make all that easier to understand.
--
It's kind of hard to understand why a resistor would be placed from pin 1 to pin 8 on a KT88. Usually pin 1 and pin 8 are shorted together, and then 560 ohms might be the cathode load resistor to ground. A schematic should make all that easier to understand.
--
You are correct 560 ohm resistor goes to pin 1 & 8 and feeds ground.
here is the schematic.
http://diyaudioprojects.com/Tubes/KT88/F01-KT88-Amplifier.png
here is the schematic.
http://diyaudioprojects.com/Tubes/KT88/F01-KT88-Amplifier.png
First check the voltages in red in the schematic. Do yours match the schematic's? If they do, then you're probably in business. It looks like the 6N1P should be drawing 4mA per triode, and each KT88 should be drawing 70mA.
You could also measure the voltages at the plates of the 6N1P. That would be pins 1 and 6 (if I'm not mistaken). The voltages there should be 188V lower than the voltage measured at the other side of the 47k resistor, coming off the 10uF polypro cap.
Do you have a schematic for the power supply?
--
You could also measure the voltages at the plates of the 6N1P. That would be pins 1 and 6 (if I'm not mistaken). The voltages there should be 188V lower than the voltage measured at the other side of the 47k resistor, coming off the 10uF polypro cap.
Do you have a schematic for the power supply?
--
Usually pin 1 and pin 8 are shorted together, and then 560 ohms might be the cathode load resistor to ground.
Pin 1 of the KT88 is connected to the exposed metal base. Why should it be at cathode potential rather than ground?
Are you saying pin 1 would just go to ground and not
connect to pin 8.
I thought 1 & 8 should always tie together.
connect to pin 8.
I thought 1 & 8 should always tie together.
Pin 1 of the KT88 is connected to the exposed metal base. Why should it be at cathode potential rather than ground?
Last edited:
How about 6L6.
Pin 1 is unused on the KT88 & the 6550. It does not need to be connected. If you want to run EL34/6CA7 in your amp though, pin 1 & 8 need to be connected. Take a look at the data sheets for all of the tubes and you will see.
How about 6L6.
http://frank.pocnet.net/sheets/049/6/6L6.pdf
I don't think I would run a 6L6 in that amp. The max plate voltage is 275V for the 6L6.
Is it not 500v max plate for 6L6GC.
I hope so because I just bought a Quad of them.
I hope so because I just bought a Quad of them.
http://frank.pocnet.net/sheets/049/6/6L6.pdf
I don't think I would run a 6L6 in that amp. The max plate voltage is 275V for the 6L6.
Last edited:
So should I disconnect pin 1 on 6L6gc or will it matter
as I use KT88 6L6gc & EL34.
as I use KT88 6L6gc & EL34.
So the safest thing to do would be no connection to pin 1
as I will use KT88 & 6L6gc primarily correct.
as I will use KT88 & 6L6gc primarily correct.
If you plan on using the different tubes, then connect pin 1 & 8. You could install a toggle switch to either connect or not connect pin 1 & 8 if you are concerned about the metal base of the KT88 being at cathode potential.
Basically that power supply with diode bridge rectifier.
Are you getting +400V at pin 3 of the KT88, or something much higher?
So the safest thing to do would be no connection to pin 1
as I will use KT88 & 6L6gc primarily correct.
You can leave pins 1 and 8 connected, and then you can use EL34 if you like. I've never heard of any harm being done by pins 1 and 8 being connected on a 6L6, 6550 or KT88.
http://frank.pocnet.net/sheets/049/6/6L6.pdf
I don't think I would run a 6L6 in that amp. The max plate voltage is 275V for the 6L6.
6L6 is the old metal tube.
6L6G is the coke bottle glass version.
6L6GB is the straight glass tube with higher ratings. 19W max plate dissipation, something like 360V max plate volts.
6L6GC is the bigger straight glass tube with 30W max plate dissipation and higher max voltage ratings. You can probably use that in your amp with no harm done. The GE datasheet states max plate voltage is 450V for triode operation, 500V for pentode.
Since your heater supply is designed for KT88, which draws 1.6A heater current, you might want to check your heater voltage when you have a 6L6GC in the amp. 6L6GC draws on 900mA heater current. If the heater voltage is much higher than about 6.6V, that is likely to decrease the life of the tube. Ideally the heater voltage should be between 6.0 and 6.3V AC.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
- Home
- Amplifiers
- Tubes / Valves
- Mikael‑Abdellah‑SE‑KT88 Bias & Voltage readings Help?