Humdinger question

[passfan]

Just to be clear, the hum is too bad to play the amp correct ? At this point it goes without saying that the color codes must be checked to ensure the correct resistors. Double and triple check everything. I have to be honest, I'm not a fan of the layout, especially the main ground buss. I know it works but at times it has seemed problematic. I feel you have the area narrowed down... perhaps it's time to take the iron and re-sweat the solder connections in this area and possibly check out Merlins article on grounding.

[passfan]

Oops

[surfsup]

I just got done re-running all the heater wires. Same hum. At this point having completely re-run the heaters, I have to assume its not the heater wires?

I have to be honest, I'm not a fan of the layout, especially the main ground buss. I know it works but at times it has seemed problematic. I feel you have the area narrowed down... perhaps it's time to take the iron and re-sweat the solder connections in this area

I reread merlin (pg 275) and he says a ground buss is fine for hand wired applications with a bare copper wire. What am I missing?

I can play the amp yes, but with everything maxxed, the humming is very loud - its simply too loud.

[passfan]

I just got done re-running all the heater wires. Same hum. At this point having completely re-run the heaters, I have to assume its not the heater wires?

I have to be honest, I'm not a fan of the layout, especially the main ground buss. I know it works but at times it has seemed problematic. I feel you have the area narrowed down... perhaps it's time to take the iron and re-sweat the solder connections in this area

I reread merlin (pg 275) and he says a ground buss is fine for hand wired applications with a bare copper wire. What am I missing?

I can play the amp yes, but with everything maxxed, the humming is very loud - its simply too loud.

I feel it's easier to stumble into a ground loop with this method and have done so before. I use a star type through the chassis with points at various spots along the signal path. I also use 6SL7 preamp tubes (notorious for heater hum) without a problem. One thing I noticed in your pics is your ground buss is not made up of a solid wire all the way through, is it ? It appears they are individual pieces from eyelet to eyelet. I might reheat those just to be sure they're solid. Chopsticking around v2 could be worth the effort as well.

[surfsup]

EDIT : If I have no tube in V2, but have the EL34 and V1 in there, with everything maxxed it is quiet. With no tune in V1, but V2 and EL34 are in, with everything maxxed, the humming is louder and there is some static present.

Also, does anyone have any idea why my voltages are all low? This is the case with either the EL84 or EL34 as output tube. New readings with the EL84:

WITHOUT TUBES:
Before the diodes: 215.1 (schematic 214)
B+ 269.1
B1 269.4
B2 271.1
B3 270.2

WITH TUBES
B+ 237.5 (supposed to be 264)
B1 233.2 (supposed to be 259)
B2 226.0 (supposed to be 250)
B3 211.1 (supposed to be 234)

[martin manning]

In a post above I noted that the schematic shows 120VAC on the 115VAC primary, and you have 125 on the 125. There's 4.3% of of your 11.1% difference right there. Switch to the other primary tap and you ought to get B+ up to ~258.

Is this noise definitely a hum (not a hiss or Shhhhhhh-type noise), and if so what frequency? 60Hz or 120? If it's 60Hz, it's PT primary or heater circuit related. If it's 120, it's something after the rectifier.

[surfsup]

There's a 60hz hum which doesnt seem to be a big deal, because there's a higher pitched hiss on top of it, as well. So i think i have both problems! The hum does get louder but its hard to tell b/c of the hiss.

My wall measures 125v, which is why i used the 125. I'll try the gray lead to see if that fixes the voltages.

[Structo]

Sorry if I missed it but what are you using for a pilot light?

Voltage and where is it supplied from?

[surfsup]

Pilot light was w/the amp kit. In 2nd photo at top right it is easily visible...

http://chicagocadcam.com/ChrisHahn/amp.html

Thanks for looking! i really appreciate it guys!

[martin manning]

How is it that your photos don't look like the layout? It seems you are shifted over one chassis-hole from V2 onward.

Re the hiss, could it be a parasitic oscillation? You described it as a high-pitched noise on top of the low hum, and if it's at the edge of your hearing it could sound like a hiss. If so, you will need an oscilloscope to see it.

[surfsup]

martin, it is a static and it gets loud. as for changes, I simply moved V2 over and V3 to the other side of the octal. I wanted to add a FX loop later so I wanted room for a tube before the power section. The octal was predrilled so I couldn't shift that so the EL84 moved all the way over.

The lead lengths are practically unaffected by this. I used the octal as the main socket from the circuitboard this time, shortened some lines, re-did the heaters (twisted a bit tighter and run along the chassis edge), reflowed the turrets (again), ahhhh I love it!

It's a bit cleaner (the turrets have been flowed many times so apologies for the messiness). I uploaded new pics. First four shots are the sockets up close, EL84, Octal, V2 then V1. Then the switches, the input and pots, then a couple glamour shots...

http://chicagocadcam.com/ChrisHahn/amp2.html

Everything looks good, well placed (as good as I can think to place it), the only issue is the second to last photo at bottom right the lines from the mains. I did splice and solder, then shrink, this line. Is this a problem?

[martin manning]

I dunno... some of those wires have to be longer the way you did it, like the grid wire that goes to the EL84 and then back to the octal. The 5k6 grid stopper R8 should be as close to the grid pin as possible (and zero lead length is best), so run it to the octal first. I noticed in the documentation that it is suggested to get it working without the octal option installed first... sounds like they are warning that there might be some sensitivity there.

[passfan]

What kind of ground wire are you using ? Is it magnet wire ?

[Structo]

Are you positive you have ruled tubes out?

A bad tube can just about mimic every bad noise symptom there is.

Also, how is the heater wire dress?

Is it well away from grids and other signal carrying wires?

[surfsup]

martin, yes, how did I miss that green wire? I planned to do it and per the new photos I went direct to the octal with the yellow but didn't do the green. Doh. I will change that.

passfan, the wire is "copper wire 20gauge" per the package from Ace Hardware. Doesn't say anything about magnetic on it.

Structo, the amp takes two 12ax7s. I have three total. I have rotated the three (two in, one out) many times. I think one tube is indeed microphonic and have stopped using it. One is definitely fine as it works fine in my other amp. The third? I wonder if the two amp kit tubes were both bad - wouldn't that just be my luck. I'll try that tube in the other amp. That should solve the issue.

As for lead dress I invite you to see all the pics (the first 4 are all socket shots up close):

http://chicagocadcam.com/ChrisHahn/amp2.html

Keep in mind I've soldered/unsoldered several times. But they look pretty clean to me - but I'm a noob.

I do have an update. I replaced the leads running from the 3prong plug to the fuse, to the main switch. The amp is noticeably quieter (about 20% - when I crank everything, the speaker cab doesn't shake from the hum/static anymore so it IS quieter). But, now when I plugged in a guitar, there was a grounding issue that didn't exist before (touch the strings or amp and the humming drops slighly).

Thanks for the continued help guys. I can't tell you how much, but I really appreciate it.