Yamamoto 09S 300B SE Amp Problem - diyAudio
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Old 18th September 2012, 04:03 PM   #1
kcshyan is offline kcshyan  Malaysia
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Default Yamamoto 09S 300B SE Amp Problem

Dear all experts.

Recently I build up 300B Se Amp based on Yamamoto schematics following are part being using in this setup.
300B as power stage
Siemens C3M as drivers stage ( Pentode configuration )
Lundahl LL1664 100ma as Output Tran.
Power tran, get from vt4c (HK). 400v-0-400v

After finished & power up. doesn't work up well at all. After measuring the voltage of the system, noticed the c3m plate voltage drop to 10v after few second. But the rest of the measurement point still OK.

Some debugging status.
Disconnected driver stage to output stage. c3m VOLTAGE also drop.
Plug in my c3m tube to my friend Yamamoto system. work well to confirm c3m still GOOD.
Measuring the c3m bias voltage, look WELL.
Now I really out of idea what going wrong. is it possible tube socket problem or others. Need advises from the diyers...

Thanks in advance.
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Old 18th September 2012, 04:26 PM   #2
kevinkr is offline kevinkr  United States
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Please post some detailed pictures, and hand drawn schematics of how you actually built the amplifier..

Check for socket wiring errors in the driver stage.
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Old 18th September 2012, 04:54 PM   #3
palmas is offline palmas  Portugal
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Yes, without schematics it's difficult, but it might be bad contact in the valve socket, or a bad resistor.
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Old 18th September 2012, 11:53 PM   #4
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well the first thing to do is to check the connections. its common for people to get turned around on the pin number on the tube socket. The second thing you have to double check is the tube pin out with the data sheet. common typos that happen with prints is the mislabeling of pin numbers on vacuum tubes.
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Old 19th September 2012, 12:01 AM   #5
kcshyan is offline kcshyan  Malaysia
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Thanks for reply, I had checked the pin layout again & again. I even took out the tube & plug into my friend system & it working well.
I also measure the heater current & stay stable @ 125ma +- 5ma.
For the resistor connected to driver stage also replaced & doesn't help.
Following is the schematics I used.
Yamamoto A-09s

The only problem is on c3m plate voltage after 110K resistor. the voltage before 110K resistor remain unchanged. only after 110K resistor it drop from 300++ V to 10V.
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Old 19th September 2012, 12:23 AM   #6
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both channels have same problem?
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Old 19th September 2012, 01:01 AM   #7
kcshyan is offline kcshyan  Malaysia
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Commstech, thanks for reply.
YES both channel are same problem / symptoms.
I tried to disconnect 1 channel to verify single channel. still same problem.
really out of ideas.
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Old 19th September 2012, 02:46 AM   #8
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Quote:
Originally Posted by kcshyan View Post
Commstech, thanks for reply.
YES both channel are same problem / symptoms.
I tried to disconnect 1 channel to verify single channel. still same problem.
really out of ideas.
if both channels have the same problem, it is of high possibility that u have wrong connections for the C3M. You sure u have got the pinouts of C3M correct?

perhaps u should post a pic of your amp for us to scrutinise on your connections.

I have built this circuit with no problem at all. it is the amp in the middle of the pic.
Click the image to open in full size.
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Old 19th September 2012, 02:50 AM   #9
kcshyan is offline kcshyan  Malaysia
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Thanks Commtech, Your system look very perfect. I like it.
btw, just to let you understand my grounding can cause problem or not.
I have 2 star ground point. 1 for left & 1 for right. Driver stage & power stage ground connected to their own Left / Right star ground.
Then this 2 star ground go separate wire to p/s ground.
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Old 19th September 2012, 02:54 AM   #10
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Quote:
Originally Posted by kcshyan View Post
Thanks Commtech, Your system look very perfect. I like it.
btw, just to let you understand my grounding can cause problem or not.
I have 2 star ground point. 1 for left & 1 for right. Driver stage & power stage ground connected to their own Left / Right star ground.
Then this 2 star ground go separate wire to p/s ground.
i doubt so. i have a hunch u have connected the C3M incorrectly.
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