JE Labs 300Bdx stereo - troubleshooting

loganlaux · 5th December 2011, 03:35 PM

Hello:
I am a quite inexperienced amp builder and am afraid I have run into a situation that I cant quite figure out... I have assembled a 300B stereo amp based on the JE Labs 300bdx stereo schematic (members.myactv.net/~je2a3/se300b.htm) and have fired up the amp only to find that the line in signal is not being amplified! I have sound coming out of the speakers but no amplification. I have checked the wiring, checked the voltages shown on the schematic and checked about everything else I can think of with no luck...
I was hoping someone could steer me in the right direction- what am I overlooking? Are there other tests I should be running? Any advice would be greatly appreciated.
Specs:
All passive components match the JE labs circuit (note i am using oil can caps in power supply).
Using James 6123HS output tranny @3.5k and 8 ohm.
Have tried a CD player and an MP3 player as sources.
Have insulated RCA jacks and speaker binding posts (both grounded to star ground).
Using 1 star ground scheme.
Thanks,
Logan

Palustris · 5th December 2011, 04:42 PM

What test gear have you available: VOM, signal generator, o'scope?

loganlaux · 5th December 2011, 04:51 PM

I have a few digital multimeters. i could build a signal generating circuit if necessary...

GloBug · 5th December 2011, 05:38 PM

Check your signal path, one of the tubes is not amplifying.

I experienced something similar once, the signal was able to pass through the one tube that was not hooked up properly, I forget now which wire I had disconnected, but the heaters were hooked up for sure.

loganlaux · 5th December 2011, 05:43 PM

will do; i assume im just making sure the wiring to each pin is correct?

If it was wired wrong would i still be getting sound from the speakers??

GloBug · 5th December 2011, 06:00 PM

Yes I think I had the B+ disconnected. - not really "wrong" so much as "incomplete"

loganlaux · 5th December 2011, 06:02 PM

i have posted pictures of the amp on flickr; Flickr: loganlaux's Photostream

euro21 · 5th December 2011, 06:05 PM

First check passive components with multimeter (without mains).

Is it all correct?
300B grid resistor 220K ?

Second, check DC settings.

1.) Check PSU voltages: 436, 430, 320V.
2.) Check first tube anode and cathode voltages: 90V, 3V.
3.) Check second tube anode and cathode voltages:329V, 98V.
4.) Check 300B anode and cathode voltages: 425V, 70v.

Is it all correct?

MikeR · 5th December 2011, 06:08 PM

Both channels are the same? How do your voltages compare to the schem, can you post the numbers.

Please triple check the wiring on the volume pot. This is easy to get wrong. When you rotate the volume control, is there any noticable effect on the sound level?

Can you get closeup photos of the volume pot and the tube sockets and post them?

loganlaux · 5th December 2011, 06:10 PM

yes sir, i have checked all of the voltages to make sure they match those on the schematic. they all do as far as i can tell. should i be checking the grid voltages? i am under the impression they will vary depending on the signal coming into the amp.

5th December 2011, 03:35 PM	#1
loganlaux diyAudio Member Join Date: Nov 2011	JE Labs 300Bdx stereo - troubleshooting Hello: I am a quite inexperienced amp builder and am afraid I have run into a situation that I cant quite figure out... I have assembled a 300B stereo amp based on the JE Labs 300bdx stereo schematic (members.myactv.net/~je2a3/se300b.htm) and have fired up the amp only to find that the line in signal is not being amplified! I have sound coming out of the speakers but no amplification. I have checked the wiring, checked the voltages shown on the schematic and checked about everything else I can think of with no luck... I was hoping someone could steer me in the right direction- what am I overlooking? Are there other tests I should be running? Any advice would be greatly appreciated. Specs: All passive components match the JE labs circuit (note i am using oil can caps in power supply). Using James 6123HS output tranny @3.5k and 8 ohm. Have tried a CD player and an MP3 player as sources. Have insulated RCA jacks and speaker binding posts (both grounded to star ground). Using 1 star ground scheme. Thanks, Logan

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5th December 2011, 04:42 PM	#2
Palustris diyAudio Member Join Date: Aug 2006 Location: Cape Cod	What test gear have you available: VOM, signal generator, o'scope?

5th December 2011, 04:51 PM	#3
loganlaux diyAudio Member Join Date: Nov 2011	I have a few digital multimeters. i could build a signal generating circuit if necessary...

5th December 2011, 05:38 PM	#4
GloBug Banned Join Date: Jun 2011	Check your signal path, one of the tubes is not amplifying. I experienced something similar once, the signal was able to pass through the one tube that was not hooked up properly, I forget now which wire I had disconnected, but the heaters were hooked up for sure.

5th December 2011, 05:43 PM	#5
loganlaux diyAudio Member Join Date: Nov 2011	will do; i assume im just making sure the wiring to each pin is correct? If it was wired wrong would i still be getting sound from the speakers??

5th December 2011, 06:00 PM	#6
GloBug Banned Join Date: Jun 2011	Yes I think I had the B+ disconnected. - not really "wrong" so much as "incomplete"

5th December 2011, 06:02 PM	#7
loganlaux diyAudio Member Join Date: Nov 2011	i have posted pictures of the amp on flickr; Flickr: loganlaux's Photostream

5th December 2011, 06:05 PM	#8
euro21 diyAudio Member Join Date: Sep 2004 Location: Budapest	First check passive components with multimeter (without mains). Is it all correct? 300B grid resistor 220K ? Second, check DC settings. 1.) Check PSU voltages: 436, 430, 320V. 2.) Check first tube anode and cathode voltages: 90V, 3V. 3.) Check second tube anode and cathode voltages:329V, 98V. 4.) Check 300B anode and cathode voltages: 425V, 70v. Is it all correct?

5th December 2011, 06:08 PM	#9
MikeR diyAudio Member Join Date: Feb 2004 Location: Michigan	Both channels are the same? How do your voltages compare to the schem, can you post the numbers. Please triple check the wiring on the volume pot. This is easy to get wrong. When you rotate the volume control, is there any noticable effect on the sound level? Can you get closeup photos of the volume pot and the tube sockets and post them?

5th December 2011, 06:10 PM	#10
loganlaux diyAudio Member Join Date: Nov 2011	yes sir, i have checked all of the voltages to make sure they match those on the schematic. they all do as far as i can tell. should i be checking the grid voltages? i am under the impression they will vary depending on the signal coming into the amp.

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