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Discussion in 'Shock Brother's DIY Amps' started by Preacher, Oct 15, 2017.
Pic is great but I still can’t tell for sure. Is your bus soldered to the pots?
The input jacks are and the tone control is through the orange drop cap. But the two volume controls are grounded to the back of the pot. I will try to throw a ground line on there and see what happens. If could be a hum that is coming through them, and going through the tone pot at the end.
Anybody looked at the voltages? Do they seem OK?
V2 is looking a little fishy but having a 12au in there may be the reason. Do you have an ax to put in there so we can see a more common reading
Au type can be noisy too
you can swap the tubes around so the ax is V2 and the au is V1. Then notice if the noise is affected by the volume and tone controls. and take voltage readings from the V2
your PT is ever so elusive in your pictures... Does your PT have a heater center tap?
I have a spare AX so I will check it with that.
Your photos are hard to follow and the lighting isn't great. Maybe take separate close-up pics of each component that folks have asked about, i.e.: the 5Y3 socket, the PT wiring, power tubes, preamp tubes.
This is the schematic that the tranny was used. I think it is an old VTX model.
Working with a camera phone is not the best... will work on getting some better pics.
I did see that I am missing joining the grounds on the volume controls. I am going to ground them to the bus and see if that maybe helps the grounding issue.
As I said a few post back, if I push down on the board it seems like there is a bad ground as the hum stops. I may have a ground loop that is caused by the pots attached to the chassis and nowhere else.
If pushing on the board changes things... I always look for cold joints.
Preacher, did you build your Cab? Curious as I am starting mine in a couple of weeks.
Well no, but I have a good excuse.
The surgery seems to be good, I have better flexibility in that finger but the stitches just came out on Friday, and I am still gaining strength in that finger. So no wood working for a little while.
And the fact that I had a 1x12 of really nice white pine for the cab in my shop that somehow grew legs and walked away, or is hiding in a corner, or I cut it up and used for kindling...
but stay tuned, I got a new table saw so finger joints are an option!
I hope all goes well!!!
Well here’s an update.
In my last post I had sound but a bad 60cycle hum that went away when I pushed down on the board.
So I checked a bunch of stuff and finally decided I must have a lead on the bottom of the board that was making contact with the chassis.
So I pulled all my leads and yanked the board. Nothing stood out to me so I trimmed a few possibles and reflowed the eyelets.
I reinstalled the board, put the leads back and checked it all over again. Did my lightbulb limiter and turned it on. Everything looked good. Hooked up the speaker and installed the tubes and turned it back on. No hum! Yea!!
So I go to strum the guitar, no noise at all.
Back to the drawing board.
I went back and checked my connections and everything looks good.
So I checked my power leads, the light bulb lights up but when I check voltage at the switch I am not seeing 120. I am getting 6.1 at the bulb, and somewhere around 1 volt at the switch which seems weird.
And then my meter batteries died so I just quit to clear my head.
Later today I will post some voltages and pics if I can’t figure it out.
Dead baterry will cause confusion for sure. I would have like to see some type of insulator between the board and the chassis to reduce the chance of short to chassis. If your stand offs are tall enough you may be fine tho. I would suggest a fresh copy of your layout/schematic and go through your connections and highlight/confirm every component and connection one at a time.
Take a break watch some football... Post some new pictures if you need help spotting a wiring issue.
Yeah I started getting “those” readings where you wrinkle your nose and say “what?” out loud. Lol
I have about 1/8” stand offs I made from an old ball point pen to raise the board off the chassis.
One question is on my input jacks. I originally had them all grounded to the bus bar. But after thinking it through they are grounded to the chasis at the connection point. So do I need to add insulated washers or eliminate the grounds to the bus and let them ground directly to the chasis?
As I always say, I’m the opposite of an expert but I think most people just ground one jack to the bus and ground the others to the first. Merlin and others do suggest isolation of the jacks from the chassis but it is kind of a pain especially if you have four input jacks. Most people don’t find the small potential ground loops created there a big source of noise.
I do it on my own builds but my VibroChamp and 5e3 don’t. And they’re pretty quiet.
Again I could be totally wrong.