Need Valco "Chicago 51" schematic

tim · 06-05-2007, 02:05 AM

Hey all,
I have an old Valco that's giving me fits...hums loudly, varying from nothing to loud as I adjust volume control. I have replaced all the tubes, filter caps, checked all resistors for proper value and checked bypass and interstage caps, replacing anything that looked questionable. I have checked all grounds and they are fine. At this point, I need to find a schematic for this beastie. Tube line up is as follows ===> 6SQ7 > 6SC7 > a pair of 6V6's with a 5Y3 rectifier tube....
Thanks boys
Tim
Electronic Sound Technologies

Enzo · 06-05-2007, 06:03 AM

Schematic Heaven has about 17 Valco drawings, most by chassis number. See if any of those match up.

tim · 06-08-2007, 02:33 AM

Enzo
Thanks for the "hint"....I was able to find the schematic under Gretsch on Schematic Heaven...it's the same as the model Gretsch G6155 . I'd forgotten that Gretsch, Valco, Supro, etc etc were all made by the same company and it seems they just slapped names on whatever was ordered by the different companies.

Anyway amp has a nasty hum and I've pretty much decided that it is being caused by bad grounds....every ground is dependent on a rivet and there are many grounds in this amp...These amps were made very cheaply originally and after 50 years, the rivets loosen up and you start having bad grounds and ground loops...the only way I can seen to get rid of the hum is to star ground everything but I don't think the guy is going to go for the labor that it will take.
Thanks again
Tim
Electronic Sound Technologies

06-05-2007, 02:05 AM	#1
tim Senior Member Join Date: Sep 2006 Location: Boscawen, NH Posts: 212	Need Valco "Chicago 51" schematic Hey all, I have an old Valco that's giving me fits...hums loudly, varying from nothing to loud as I adjust volume control. I have replaced all the tubes, filter caps, checked all resistors for proper value and checked bypass and interstage caps, replacing anything that looked questionable. I have checked all grounds and they are fine. At this point, I need to find a schematic for this beastie. Tube line up is as follows ===> 6SQ7 > 6SC7 > a pair of 6V6's with a 5Y3 rectifier tube.... Thanks boys Tim Electronic Sound Technologies

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06-05-2007, 06:03 AM	#2
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,366	Schematic Heaven has about 17 Valco drawings, most by chassis number. See if any of those match up.

06-08-2007, 02:33 AM	#3
tim Senior Member Join Date: Sep 2006 Location: Boscawen, NH Posts: 212	Enzo Thanks for the "hint"....I was able to find the schematic under Gretsch on Schematic Heaven...it's the same as the model Gretsch G6155 . I'd forgotten that Gretsch, Valco, Supro, etc etc were all made by the same company and it seems they just slapped names on whatever was ordered by the different companies. Anyway amp has a nasty hum and I've pretty much decided that it is being caused by bad grounds....every ground is dependent on a rivet and there are many grounds in this amp...These amps were made very cheaply originally and after 50 years, the rivets loosen up and you start having bad grounds and ground loops...the only way I can seen to get rid of the hum is to star ground everything but I don't think the guy is going to go for the labor that it will take. Thanks again Tim Electronic Sound Technologies

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