5c5 build-troubleshooting hum

dangelico603 · April 1st, 2008, 06:21 PM

Hey guys, I got it wired up finally and got a chance to play through it a little today. I was encouraged that it didn't blow up but a little discouraged because it hums pretty bad. The hum is pretty loud at idle but the tone knob seams to make it louder the higher up it goes. I'm guessing it's a grounding issue but where do I start looking? Come to think of it it had a bad hum before I gutted it. Would a bad transformer cause it? Thanks guys.
Jason

jh45gun · April 1st, 2008, 08:41 PM

Refresh our memories what did you build it out of and what did you change and what did you keep?

dangelico603 · April 1st, 2008, 11:14 PM

Well, I built it out of a Stromberg-Carlton AU-33 PA head. I gutted it though and built the board from all new components and ran all new everything except transformer wires. So basically I used the original transformers and chassis and just built a 5C5 inside it and that's about it. I also used 1meg resistors on all the inputs and wired it up for 6SL7's instead of the 6SC7's. I could tell I'll like the sound of it if I can ditch the hum.
Jason

jh45gun · April 2nd, 2008, 01:26 AM

I would double check everything to see to make sure you have every thing wired right. As far as the tranny goes I do not know if they get noisy or not. Just wondering did you run double heater wires or go with the old single method?

dangelico603 · April 2nd, 2008, 11:17 AM

I ran double heater wires and I think that may be the culprit. I didn't do any kind of hum balance. I ran all the pin 7's (heater) together and all pin 8's together, is this how it's done or not? I'll try and post some pics later.

dangelico603 · April 2nd, 2008, 11:57 AM

Here is a camera phone pic of heater wires. The tape on the transformers was just so I didn't accidentaly get something in there.
Jason

jh45gun · April 2nd, 2008, 02:39 PM

Thats how I did it on my 5e3 build and I have no hum issues and your wire twisting is neater than mine. Same with my Super build I ran the wires parallel and I have not fired that one up yet I am waiting for parts though I fire it up to make sure the heaters lit up which they did along with the pilot light. I guess I would check grounds too and make sure every thing is right on the board layout. From what I have read so far on these builds on the forums it is usually something simple you overlook or a bad ground.

jh45gun · April 2nd, 2008, 02:49 PM

The hard part I would guess is that you had a hum before so you would figure ok new filter caps will take care of that and now you still have a hum so you wonder if it is the PT (which I cannot help you with there as I do not know how a bad PT acts except smoke) So while you suspect that maybe this hum could be a whole new issue and maybe the PT is fine. I do not know for sure but I would think either a PT is good or bad I do not think there is a middle ground I would think if a PT is shorted there would be smoke and if open your not going to get anything out of it.

dangelico603 · April 2nd, 2008, 03:39 PM

I keep thinking of things that were the same from the first time I fired it up to now and I'll try and swap things one at a time and see if I can't find something. I used the same tubes, the cord for the speaker (which is super-ghetto) and the transformers.

dangelico603 · April 2nd, 2008, 05:50 PM

Well I fired it up today and now there is smoke! I can't tell where the smoke came from as I shut it down as soon as I smelled something and I saw the smoke after I had turned it off. I did nothing between yesterday and today. I also heard a kind of hum but not out of the speakers tell me please that the trasformers aren't gone because that was the reason I used an old PA in the first place. What now?

dangelico603 · April 2nd, 2008, 06:58 PM

OK the dust has settled and I've found one of the 10K dropping resistors has been turned into a little charcoal briquette. Same problem or new problem?
Jason

jh45gun · April 2nd, 2008, 09:58 PM

Sorry I cannot help ya with that one if no one gives ya the advice you need here try the gear page.

dangelico603 · April 3rd, 2008, 05:10 PM

Any ideas?

April 1st, 2008, 06:21 PM	#1 (permalink)
dangelico603 Tele-Meister Join Date: Jan 2007 Location: Oklahoma City Posts: 222	5c5 build-troubleshooting hum Hey guys, I got it wired up finally and got a chance to play through it a little today. I was encouraged that it didn't blow up but a little discouraged because it hums pretty bad. The hum is pretty loud at idle but the tone knob seams to make it louder the higher up it goes. I'm guessing it's a grounding issue but where do I start looking? Come to think of it it had a bad hum before I gutted it. Would a bad transformer cause it? Thanks guys. Jason __________________ "Don't just play something, stand there."

April 1st, 2008, 11:14 PM	#3 (permalink)
dangelico603 Tele-Meister Join Date: Jan 2007 Location: Oklahoma City Posts: 222	Well, I built it out of a Stromberg-Carlton AU-33 PA head. I gutted it though and built the board from all new components and ran all new everything except transformer wires. So basically I used the original transformers and chassis and just built a 5C5 inside it and that's about it. I also used 1meg resistors on all the inputs and wired it up for 6SL7's instead of the 6SC7's. I could tell I'll like the sound of it if I can ditch the hum. Jason __________________ "Don't just play something, stand there."

April 2nd, 2008, 11:17 AM	#5 (permalink)
dangelico603 Tele-Meister Join Date: Jan 2007 Location: Oklahoma City Posts: 222	I ran double heater wires and I think that may be the culprit. I didn't do any kind of hum balance. I ran all the pin 7's (heater) together and all pin 8's together, is this how it's done or not? I'll try and post some pics later. __________________ "Don't just play something, stand there."

April 2nd, 2008, 03:39 PM	#9 (permalink)
dangelico603 Tele-Meister Join Date: Jan 2007 Location: Oklahoma City Posts: 222	I keep thinking of things that were the same from the first time I fired it up to now and I'll try and swap things one at a time and see if I can't find something. I used the same tubes, the cord for the speaker (which is super-ghetto) and the transformers. __________________ "Don't just play something, stand there."

April 2nd, 2008, 05:50 PM	#10 (permalink)
dangelico603 Tele-Meister Join Date: Jan 2007 Location: Oklahoma City Posts: 222	let there be smoke Well I fired it up today and now there is smoke! I can't tell where the smoke came from as I shut it down as soon as I smelled something and I saw the smoke after I had turned it off. I did nothing between yesterday and today. I also heard a kind of hum but not out of the speakers tell me please that the trasformers aren't gone because that was the reason I used an old PA in the first place. What now? __________________ "Don't just play something, stand there."

April 1st, 2008, 08:41 PM	#2 (permalink)
jh45gun Tele-Afflicted Join Date: Jan 2006 Posts: 1,109	Refresh our memories what did you build it out of and what did you change and what did you keep?

April 2nd, 2008, 01:26 AM	#4 (permalink)
jh45gun Tele-Afflicted Join Date: Jan 2006 Posts: 1,109	I would double check everything to see to make sure you have every thing wired right. As far as the tranny goes I do not know if they get noisy or not. Just wondering did you run double heater wires or go with the old single method?

April 2nd, 2008, 02:39 PM	#7 (permalink)
jh45gun Tele-Afflicted Join Date: Jan 2006 Posts: 1,109	Thats how I did it on my 5e3 build and I have no hum issues and your wire twisting is neater than mine. Same with my Super build I ran the wires parallel and I have not fired that one up yet I am waiting for parts though I fire it up to make sure the heaters lit up which they did along with the pilot light. I guess I would check grounds too and make sure every thing is right on the board layout. From what I have read so far on these builds on the forums it is usually something simple you overlook or a bad ground.

April 2nd, 2008, 02:49 PM	#8 (permalink)
jh45gun Tele-Afflicted Join Date: Jan 2006 Posts: 1,109	The hard part I would guess is that you had a hum before so you would figure ok new filter caps will take care of that and now you still have a hum so you wonder if it is the PT (which I cannot help you with there as I do not know how a bad PT acts except smoke) So while you suspect that maybe this hum could be a whole new issue and maybe the PT is fine. I do not know for sure but I would think either a PT is good or bad I do not think there is a middle ground I would think if a PT is shorted there would be smoke and if open your not going to get anything out of it.

April 2nd, 2008, 06:58 PM	#11 (permalink)
dangelico603 Tele-Meister Join Date: Jan 2007 Location: Oklahoma City Posts: 222	OK the dust has settled and I've found one of the 10K dropping resistors has been turned into a little charcoal briquette. Same problem or new problem? Jason __________________ "Don't just play something, stand there."

April 2nd, 2008, 09:58 PM	#12 (permalink)
jh45gun Tele-Afflicted Join Date: Jan 2006 Posts: 1,109	Sorry I cannot help ya with that one if no one gives ya the advice you need here try the gear page.

April 3rd, 2008, 05:10 PM	#13 (permalink)
dangelico603 Tele-Meister Join Date: Jan 2007 Location: Oklahoma City Posts: 222	Any ideas? __________________ "Don't just play something, stand there."