Kt88 Pin alignement problem=did a mistake= HELP NEEDED
Someone sold me a Amp ( Quicksilver V4) with a set of JJ kt88 . Some of the central pins of the tube are missing ... ( the plastic guide in the middle) I instaled the the tubes, but I think a mis- aligne a tube... Now my amp don't bias. I've broken my wonderfull amp... Can someone tell me the problem ( a capacitor? , a resistor is damaged? )
Someone sold me a Amp ( Quicksilver V4) with a set of JJ kt88 . Some of the central pins of the tube are missing ... ( the plastic guide in the middle) I instaled the the tubes, but I think a mis- aligne a tube... Now my amp don't bias. I've broken my wonderfull amp... Can someone tell me the problem ( a capacitor? , a resistor is damaged? )
Last edited:
I would suspect the tube. Can you swap the KT88s with another amp (assuming you have two mono blocks)?
If the problem follows the tubes than you know what you need to do.
Without a scematic it will be mostly guesswork.
So let's see if we can guess in the right direction...
Do you know how the KT88 was oriented? One, two,... pins (counter)clockwise? Perhaps we can deduct what might have happened.
With the powercord and the KT88's removed, can you measure the resistance of pins 1 & 8 (the ones next to the locator notch) to ground? Comparing that to the resistance in the good amp will tell you if there is a problem with the kathode resistors (assuming there are kathode risistors).
So let's see if we can guess in the right direction...
Do you know how the KT88 was oriented? One, two,... pins (counter)clockwise? Perhaps we can deduct what might have happened.
With the powercord and the KT88's removed, can you measure the resistance of pins 1 & 8 (the ones next to the locator notch) to ground? Comparing that to the resistance in the good amp will tell you if there is a problem with the kathode resistors (assuming there are kathode risistors).
Great info ' thanks! It was almost a the right aligment. But I can not say counter or clockwise.... I will have the amp check by a tech. But I will tell him want you just said about the kathode risistor . Thanks!
I bias tubes individually with a meter on my amp ( meter integrated in the face plate) Normally I bias my kt88 to 45ma. Now all tubes bias 20ma max.
These are ultra-linear amplifiers based pretty closely on the old Williamson design and usually with ridiculously huge electrolytic caps in the supply (tube rectification by 5AR4 which usually don't live that long in these amplifiers.)
Most likely the screen stopper resistors are fried if fitted, check them first (pin 4 of each KT88) if present.
Quicksilver does not provide schematics for servicing any of their products as best I have been able to figure out. Many years ago I attempted to get schematics for a pair of monos I was servicing and was unable to do so. They aren't particularly complex, but there have been a number of variations. I no longer remember all of the details but this particular pair utilized 8417 output tubes and I converted them for KT88. (Note that I no longer service anything!
)
Most likely the screen stopper resistors are fried if fitted, check them first (pin 4 of each KT88) if present.
Quicksilver does not provide schematics for servicing any of their products as best I have been able to figure out. Many years ago I attempted to get schematics for a pair of monos I was servicing and was unable to do so. They aren't particularly complex, but there have been a number of variations. I no longer remember all of the details but this particular pair utilized 8417 output tubes and I converted them for KT88. (Note that I no longer service anything!
)
jrenkin's comments about the bias supply are worth heeding as well, and I have just looked at that amplifier on line and realize it differs in significant ways from the much older ones I have worked on. You might also want to check the power supply voltages.
Note that the fact that you can't set the bias any higher than 20mA could indicate that bias supply voltages are too high for the tubes used. It may also indicate problems with screen resistors if indeed it is UL or with the screen supply if tetrode mode is employed.
Take the bottom cover off and snap some very detailed pictures which might give us all a clue as to what might be going on since you can't get the schematic.
I would recommend you find a good local tech unless you have test equipment and are comfortable working on tube amps which I suspect you may not be.
Note that the fact that you can't set the bias any higher than 20mA could indicate that bias supply voltages are too high for the tubes used. It may also indicate problems with screen resistors if indeed it is UL or with the screen supply if tetrode mode is employed.
Take the bottom cover off and snap some very detailed pictures which might give us all a clue as to what might be going on since you can't get the schematic.
I would recommend you find a good local tech unless you have test equipment and are comfortable working on tube amps which I suspect you may not be.
I will try to post some pictures this week ( the inside) I'm bringing the amp to a tech monday night and I will give him a copie of this discussion..
The amp was checked by my tech.... I destroyed the meter... It can not be fixed... I will have to order another one from Quicksilver. ( got some help from them too. they are a good company) It is only 40 dollars for a new one. Here is a pic of the amp ( bottom) . I will be happy when it is all fixed....
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.