Lead Dress re wire tips

[Pochie45566]

So, this is the final thread for this amp. Someone rather inexperienced (like me) built this back in 75. It is a clone of a 2204 but built on a sunn chassis. I have fixed everything with the help of you wonderful people and the last thing is, It hums like hell ( and yes have replaced caps) It oscillates when sitting in certain positions and just hums a hell of a lot. The lead dress looks horrible but I am not quite sure what to do or how to start on this. Here are some pictures! Please tell me what I should do.   

[John]

If it uses NFB, try unhooking that resistor first; if the oscillation disappears, you just need to swap your plate leads from the OT.


Lead dress... hmmm      Look at your signal wires (any connected to grid pins) They should be as far away as possible from heater wires and the B+ wires. If they're shielded, make sure the shield is connected at one end only. The most critical (IMO) place is right at the first tube. Every tiny noise there will be magnified throughout the amp.


Oh, check your grounds. Ideally, your PT center tap and the first 1 or 2 filter caps all connect to 1 ground point, as close to the PT as possible (usually using a PT mounting screw) Some people also ground the output tube cathodes to this point also. The only other ground point then, should be right at the input jack. IOW, instead of having each ground point where it's most convenient, they only ground at one spot instead of 6 or so.


FWIW, I'd disconnect all but one of those 4 input jacks, unless it's a 2 channel amp, and then I'd only connect 2 (1 to each channel) I've never yet seen a player plug into the low input side. 

[pompeiisneaks]

I'd get a wooden chopstick, get it to reproduce the hum issue, and then chopstick around slightly moving any wires you think could be coupling with others, if the sound gets worse or better that will give you indications on where things may be best changed.  make sure to keep signal wires away from noisy areas.  You may just want to replace all wires in the signal path with shielded wires. 

~Phil

[shooter]

are you following these 2 builds?  lots of things can be learned just by peeking

http://el34world.com/Forum/index.php?topic=22149.0

http://el34world.com/Forum/index.php?topic=22182.0

[John]

If he tries to emulate Sluckey, he'll only get discouraged. At least, I do! ;)

[shooter]

If he tries to emulate Sluckey

I've always lived by the adage; you strive for 100% but sleep well if you wind up at 87%

[pompeiisneaks]

If he tries to emulate Sluckey

I've always lived by the adage; you strive for 100% but sleep well if you wind up at 87%

then how does Sluckey always hit 100? :P

~Phil

[shooter]

how does Sluckey always hit 100

genetics blow to the head as a youth many, many years honing a skill set that most of us give up on

[PRR]

> how does Sluckey always hit 100?

Decades of work where accuracy *MATTERS* (aircraft systems).

Neatness is next to accuracy. Ugly wiring may work fine, but is far too much effort to verify or troubleshoot. Between being knuckle-rapped for early slop-work, and seeing the consequences of messy work, he grew into good work.

[Ed_Chambley]

I will tell you how I learned.  I ignored everything everyone told me on my first scratch build.  I did not make a schematic, not did make a layout.  I built it backwards.  Had way too long lead dress and I turned it into a what you have.  Still thought I could 'Fix' it.  I took it apart and removed the bottom of the chassis by sawing it and welding it back.


Still I payed no attention to Lead dress and did not make a layout.  This time I fried a Power Transformer.


Guess what.  I drew a schematic and then a layout.  The layout was to actual size.  While doing this I began to understand a method that worked, a method I use today on circuit board amps.  This happened only after Sluckey (lovingly) yea right, told me what I needed to do.  I found no one would help me and now I now why.


I began studying layouts and by golly there are a lot of consistencies in successful builds.  Imagine that.


Will I build without a layout today, you bet ya! Without a schematic I draw, no way!  Most layouts are common even if they are tube up or tube down.  You have the iron and a chassis.  Get a board and wire it up and do not give any rats a home.