My audionote Kit one have problem on 300B cathode terminal

ramnmic · 12th January 2005, 07:09 AM

After completed the construction of Kit One, I measure the voltage according to manual, without any tubes plug-in, it seems all in normal rating. But when I plug-in all tubes and test it again, I found the terminal 3 of front 300B (cathode pin) was arround 7v (indicated 70v on manual), and the back 300B was 65v firstly and drop down then. The front 300B was so hot then the back one which just a little bit warm. (touch the glass)

I tried to swap the 300B tubes, cathode pin capacitor but still in vain.

BTW, all the high voltage seems drop down step by step as times goes by. say the HT on 300B terminal 1 from 0v to 320v after powered on, after 5 secs, it begin to drop down from 320v...315v, 310v, 300v and so on. I turn it off immediately so I don't know how low it will drop down. But the front 300B's cathode terminal (pin 3) was stayed at 7v from power on. So I think the problem is on it but I cannot identify it.

Anyone can help me!!!

analog_sa · 12th January 2005, 07:32 AM

Very possibly you have a simple wiring error. I don't have the AN circuit in front of me but it probably has a paralleled resistor and cap in the cathode. If the cap is reversely connected you may experience the symptoms you describe. As a first step measure the resistance between cathode and ground when the amp is not powered and if you get a value lower than Rk try to find out why.

Alternatively the resistor between grid and ground may be missing.

ramnmic · 12th January 2005, 09:25 AM

Thx,
I check it once and once again and confirmed the cathode capacitor solder in correct position. The capacitor positive terminal solder to cathode pin and the negative solder to the ground.
Also the cathode resistor was worked fine and measured in 900R.

No resistor between grid and ground directly according to the schmatics.

analog_sa · 12th January 2005, 10:03 AM

I am talking of the 330k resistor. When measuring from 300B grid to ground do you measure 333k?

If this doesn't help disconnect one side of the .22uF cap and see if the fault persists.

ramnmic · 13th January 2005, 06:56 AM

thanks~~

I found it. It causing by 7805 5V filament reglator for the 300B tube. the GND (case of 7805) was touched chassis, after I re-sit the 7805 and heatsink, the symptom disappeared and my kit one sounded great~~

It is careless mistake....
anyway, thanks for your help, analog_sa!
nice to talk to you!!

12th January 2005, 07:09 AM	#1
ramnmic diyAudio Member Join Date: Jan 2005 Location: HK	My audionote Kit one have problem on 300B cathode terminal After completed the construction of Kit One, I measure the voltage according to manual, without any tubes plug-in, it seems all in normal rating. But when I plug-in all tubes and test it again, I found the terminal 3 of front 300B (cathode pin) was arround 7v (indicated 70v on manual), and the back 300B was 65v firstly and drop down then. The front 300B was so hot then the back one which just a little bit warm. (touch the glass) I tried to swap the 300B tubes, cathode pin capacitor but still in vain. BTW, all the high voltage seems drop down step by step as times goes by. say the HT on 300B terminal 1 from 0v to 320v after powered on, after 5 secs, it begin to drop down from 320v...315v, 310v, 300v and so on. I turn it off immediately so I don't know how low it will drop down. But the front 300B's cathode terminal (pin 3) was stayed at 7v from power on. So I think the problem is on it but I cannot identify it. Anyone can help me!!!

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
300B SE cathode feedback to grid?	alan_982002	Tubes / Valves	3	29th March 2010 01:04 PM
300B Cathode Feedback + Cathode Bias	korneluk	Tubes / Valves	13	7th January 2009 08:07 PM
What are terminal 1 & 4 of 300B tube	andy2	Tubes / Valves	45	24th January 2005 09:28 PM
Transfomer Too hot on my AudioNote 300B kit one	audionote	Tubes / Valves	7	6th November 2003 11:20 AM
Best way to connect 300B cathode	Ralph	Tubes / Valves	12	3rd February 2003 10:39 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

12th January 2005, 07:32 AM	#2
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Very possibly you have a simple wiring error. I don't have the AN circuit in front of me but it probably has a paralleled resistor and cap in the cathode. If the cap is reversely connected you may experience the symptoms you describe. As a first step measure the resistance between cathode and ground when the amp is not powered and if you get a value lower than Rk try to find out why. Alternatively the resistor between grid and ground may be missing.

12th January 2005, 09:25 AM	#3
ramnmic diyAudio Member Join Date: Jan 2005 Location: HK	Thx, I check it once and once again and confirmed the cathode capacitor solder in correct position. The capacitor positive terminal solder to cathode pin and the negative solder to the ground. Also the cathode resistor was worked fine and measured in 900R. No resistor between grid and ground directly according to the schmatics.

12th January 2005, 10:03 AM	#4
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	I am talking of the 330k resistor. When measuring from 300B grid to ground do you measure 333k? If this doesn't help disconnect one side of the .22uF cap and see if the fault persists.

13th January 2005, 06:56 AM	#5
ramnmic diyAudio Member Join Date: Jan 2005 Location: HK	thanks~~ I found it. It causing by 7805 5V filament reglator for the 300B tube. the GND (case of 7805) was touched chassis, after I re-sit the 7805 and heatsink, the symptom disappeared and my kit one sounded great~~ It is careless mistake.... anyway, thanks for your help, analog_sa! nice to talk to you!!

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)