Hy all,
I'm new here and this is my first build.
The circuit is the Abbellah KT88 as Gendrano has modified. except for the fact I substituted the 5 mH inductance with 250R resistors and omitted the two 10 uF condenser connected to the 47K res going on the plate of ecc88.
The amp works, so I'm happy (it is a good news for a first builder)
Anyway I have some answers for you experienced builders:
I left off the standby swich, should I include it for some reason like improving tube life?
I hear a little hum, I believe it is 50Hz related hum. what can I do? better B+ filtering or DC on filaments?
when the amp is on I can hear the rectifier rattling. is this normal?
When no source is connected to the amp (I included a source selector) I can hear a Prrrrrrr coming out from the speaker... what the hell is happening? Maybe I was wrong when connected the grounds of the two sources together? hope can understand me
hope someone can help me.
Vincenzo
I'm new here and this is my first build.
The circuit is the Abbellah KT88 as Gendrano has modified. except for the fact I substituted the 5 mH inductance with 250R resistors and omitted the two 10 uF condenser connected to the 47K res going on the plate of ecc88.
The amp works, so I'm happy (it is a good news for a first builder)
Anyway I have some answers for you experienced builders:
I left off the standby swich, should I include it for some reason like improving tube life?
I hear a little hum, I believe it is 50Hz related hum. what can I do? better B+ filtering or DC on filaments?
when the amp is on I can hear the rectifier rattling. is this normal?
When no source is connected to the amp (I included a source selector) I can hear a Prrrrrrr coming out from the speaker... what the hell is happening? Maybe I was wrong when connected the grounds of the two sources together? hope can understand me
hope someone can help me.
Vincenzo
Vincenzo...
On the subject of the "rattling" sound your hearing..Quite probably it is your choke on the power supply. Of course that is assuming it is a choke input PS.
Chokes are notorious for buzzing badly...imparting the buzzing sound into the chassis. One needs to isolate a choke from the chassis with a soft pliant material to absorb vibrations.
Do you have a schematic for us to see??
_______________________________________________Rick........
On the subject of the "rattling" sound your hearing..Quite probably it is your choke on the power supply. Of course that is assuming it is a choke input PS.
Chokes are notorious for buzzing badly...imparting the buzzing sound into the chassis. One needs to isolate a choke from the chassis with a soft pliant material to absorb vibrations.
Do you have a schematic for us to see??
_______________________________________________Rick........
schematic
Thank you Richard for your reply. I will try to put something between the choke and the chassis. The schem I followed can be found at:
http://diyaudioprojects.com/Tubes/KT88/
I found that only one channel hums and if no source is connected the hum stops. Maybe the double triode or a wire too close to heater ac wires?
Vincenzo.
Thank you Richard for your reply. I will try to put something between the choke and the chassis. The schem I followed can be found at:
http://diyaudioprojects.com/Tubes/KT88/
I found that only one channel hums and if no source is connected the hum stops. Maybe the double triode or a wire too close to heater ac wires?
Vincenzo.
Hi Vincenzo-
I built this same amp, and it's dead quiet, so I'm not sure where the hum is coming from.
You say "I found that only one channel hums and if no source is connected the hum stops." This sounds like a ground loop with one of the channels. If you short the input jacks to ground, the center of the RCA connector to the outside, do you still hear the hum?
I'm also not sure where the ecc88 came into this build, I'm using the 6N1P called for on the schematic. Is it possible that the ecc88 has too much gain for this amp? Others more knowledgeable than myself can comment on this.
My KT88 build
Glenn
I built this same amp, and it's dead quiet, so I'm not sure where the hum is coming from.
You say "I found that only one channel hums and if no source is connected the hum stops." This sounds like a ground loop with one of the channels. If you short the input jacks to ground, the center of the RCA connector to the outside, do you still hear the hum?
I'm also not sure where the ecc88 came into this build, I'm using the 6N1P called for on the schematic. Is it possible that the ecc88 has too much gain for this amp? Others more knowledgeable than myself can comment on this.
My KT88 build
Glenn
vince76 said:Hy all,
I'm new here and this is my first build.
The circuit is the Abbellah KT88 as Gendrano has modified. except for the fact I substituted the 5 mH inductance with 250R resistors and omitted the two 10 uF condenser connected to the 47K res going on the plate of ecc88.
The amp works, so I'm happy (it is a good news for a first builder)
Anyway I have some answers for you experienced builders:
I left off the standby swich, should I include it for some reason like improving tube life?
I hear a little hum, I believe it is 50Hz related hum. what can I do? better B+ filtering or DC on filaments?
when the amp is on I can hear the rectifier rattling. is this normal?
When no source is connected to the amp (I included a source selector) I can hear a Prrrrrrr coming out from the speaker... what the hell is happening? Maybe I was wrong when connected the grounds of the two sources together? hope can understand me
hope someone can help me.
Vincenzo
What is the voltage rating for the capacitors that you used on the PSU? If it is 500V or 450V, then you need to use a standby switch as the PSU is capable of producing more than 500V when the tubes are cold.
If you are just hearing the hum on one channel, then please check your wiring and where you have routed the signal wires, it might be close to the heater wiring. BTW, did you twist the heater wires? It can also be a "cold solder" on the side that you hear the hum.
I have built a few of these amps, and all of them are very quiet.
Regards,
Alex
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thank you Alex
I need a standby switch. I didn't put a switch in because I used for on off switch a recicled one from a computer PSU. I wanted to use two of them but realized one was under rated since it says 250V 5A.
The heater wires are well twisted. I will look for a cold solder, but I'm sure it isn't since as I turn off the amp, while the caps are discharging and I can listen to the music, the hum disappear. It have to be 50 Hz!?!?!
Vincenzo
I need a standby switch. I didn't put a switch in because I used for on off switch a recicled one from a computer PSU. I wanted to use two of them but realized one was under rated since it says 250V 5A.
The heater wires are well twisted. I will look for a cold solder, but I'm sure it isn't since as I turn off the amp, while the caps are discharging and I can listen to the music, the hum disappear. It have to be 50 Hz!?!?!
Vincenzo
war to the hum
dear boys,
I'm in a dead point.
I need your advice.
My amp, when no source is connected is super silent.
if I connect one channel of the CD source to the amp using shielded or unshielded wire than the hum starts. The same happens with an Ipod. same if I connect both channels. Volume doesn't affect hum.
don't know what to search for since I don't understand where it comes from (50Hz hum, a loop....?)
thank you,
Vincenzo
dear boys,
I'm in a dead point.
I need your advice.
My amp, when no source is connected is super silent.
if I connect one channel of the CD source to the amp using shielded or unshielded wire than the hum starts. The same happens with an Ipod. same if I connect both channels. Volume doesn't affect hum.
don't know what to search for since I don't understand where it comes from (50Hz hum, a loop....?)
thank you,
Vincenzo
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