distortion at low volume

Electar · 15th January 2009, 04:32 AM

I have an old guitar amp that is only 5 or so watts. It has an 80,6l6 and a 6sj7. a field coil speaker. I can play it for about 20 minutes at any volume and it sounds fine ,then it starts distorting .with the volume low!

jerluwoo · 15th January 2009, 08:33 AM

Do you know the manufacturer or model of the amp?. First suspect in all old amps are electrolytic capacitors. Could also be old resistors drifting with heat? Need more info on it.

Geek · 15th January 2009, 09:41 AM

Hi,

If it's that old that it has a field coil speaker, a recap job is in order, as mentioned.

Cheers!

Frank Berry · 15th January 2009, 09:47 AM

Could be a capacitor on the cathode of the output tube that is shorting. This would cause the tube to draw excessive current.

Electar · 15th January 2009, 12:19 PM

Its a 1939 Epiphone amp, someone has changed the filter caps already to 20 uf 450vdc theres only 2 of em. the rest of the caps are very early.

Tom Bavis · 15th January 2009, 01:14 PM

Quote:

Originally posted by Electar
Its a 1939 Epiphone amp, someone has changed the filter caps already to 20 uf 450vdc theres only 2 of em. the rest of the caps are very early.

The rest of the caps are very leaky. Replace them. Another possibility is a 6L6 with grid leakage when hot. But that usually doesn't take 20 minutes to show up.

jerluwoo · 15th January 2009, 06:08 PM

Been digging around google looking for pre Gibson Epiphone schematics for nearly an hour with no luck. Got me curious what the differences were in them before Gibson bought them out.

Electar · 21st January 2009, 06:39 AM

Thanks, it makes prefect sense.

15th January 2009, 04:32 AM	#1
Electar diyAudio Member Join Date: Jan 2009	distortion at low volume I have an old guitar amp that is only 5 or so watts. It has an 80,6l6 and a 6sj7. a field coil speaker. I can play it for about 20 minutes at any volume and it sounds fine ,then it starts distorting .with the volume low!

15th January 2009, 09:47 AM	#4
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	Could be a capacitor on the cathode of the output tube that is shorting. This would cause the tube to draw excessive current. __________________ Frank

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15th January 2009, 08:33 AM	#2
jerluwoo diyAudio Member Join Date: Feb 2006 Location: Ashland,Ky U.S	Do you know the manufacturer or model of the amp?. First suspect in all old amps are electrolytic capacitors. Could also be old resistors drifting with heat? Need more info on it.

15th January 2009, 09:41 AM	#3
Geek diyAudio Member Join Date: Sep 2004	Hi, If it's that old that it has a field coil speaker, a recap job is in order, as mentioned. Cheers!

15th January 2009, 12:19 PM	#5
Electar diyAudio Member Join Date: Jan 2009	Its a 1939 Epiphone amp, someone has changed the filter caps already to 20 uf 450vdc theres only 2 of em. the rest of the caps are very early.

15th January 2009, 06:08 PM	#7
jerluwoo diyAudio Member Join Date: Feb 2006 Location: Ashland,Ky U.S	Been digging around google looking for pre Gibson Epiphone schematics for nearly an hour with no luck. Got me curious what the differences were in them before Gibson bought them out.

21st January 2009, 06:39 AM	#8
Electar diyAudio Member Join Date: Jan 2009	Thanks, it makes prefect sense.