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Old 26th January 2013, 11:26 PM   #1
zilch99 is offline zilch99  United States
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Default first tube amp

OK
I bought the 16-LS tube amp plus add-on tone control from tube depot. I have assembled the PC boards. It looks pretty cool, ceramic sockets, clean layout, beefy power xformer. Studied the schematics and already see some potential tweaks and a couple questions. Anyway, I'll finish it and see how it plays before messing with it. When I'm happy, I plan a "steampunk" style enclosure for it.
Of course it will have a window in the front so we can see the glow from all those pretty firebottles.
I have to go to Philly tomorrow to work on a project so I won't get back to the amp till late in the week. See WALKING PIANO to see what I'll be up to .
I build some of the electronics for these guys.
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Old 27th January 2013, 12:32 AM   #2
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I built this amp too and it is a fun little thing. As-is it sounds pretty good but I highly recommend getting output transformers from Edcor (CXPP 25-8-5K or if you are running 4 ohm speakers the CXPP 25-4-5K) I would say out of all the mods I have done to this little amp the Edcors made the most pronounced difference. (I also used Orange Drops for all the coupling caps and used tube rectifiers.) The steampunk enclosure sounds cool please post some pics when you get it built. I decided to go with an industrial look for mine and used polished treadplate. Here's mine.
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Old 3rd February 2013, 10:06 PM   #3
zilch99 is offline zilch99  United States
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Default first tube amp con't

OK
I'm back from Philly.
Finished assembling the 16-LS amp with the add-on tone control/preamp.
I mounted the whole mess on a piece of wood as intended. It works OK But:
HUM! lots of background hum. A bit of investigating shows it to be from grounding issues. The "chassis" is a piece of wood, bad. The input RCA connectors are brought out through some shielded cables to the back side rather than the pcb mounted connectors on the front of the main pcb. they are held by a simple metal bracket. this is all far away from the pwr transformer. These cables pick up tons of hum. Adding a short heavy wire from the bracket directly to the ground trace on the tone control/preamp board greatly reduces the hum. Still, touching the bracket or the (grounded) control pots reduces the hum still more. More grounding issues.
So, looking at the main pcb I see the ground traces are less than 1/8" wide and they loop all around the board. One side of the output secondaries connect to this skinny trace too. Not good.
Clearly this amp could benefit from a real metal chassis but more importantly, I need to go through it and re-do the grounding scheme to a star arrangement with everything going to a common point at the - side of the filter caps.
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Old 4th February 2013, 07:50 AM   #4
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Bad filtering is first reason of hmmm. Do You have a choke?
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