Welcome To the Hoffman Amplifiers Forum

September 08, 2025, 05:56:52 am
guest image
Welcome, Guest. Please login or register.
-User Name
-Password



Hoffman Amps Forum image Author Topic: OT Position compromise  (Read 1839 times)

0 Members and 1 Guest are viewing this topic.

Offline dennyg

  • Level 2
  • **
  • Posts: 153
  • Hillbilly in Philly
Hoffman Amps Forum image
OT Position compromise
« on: December 16, 2016, 07:47:31 am »
I've just about completed a rebuild of my first amp, a 2-channel version of the AX84 SEL design, completed a couple years ago.  The last bit of tidying up is OT placement. When I first built the amp, I'd mounted the OT right next to the PT per layout, but upon learning of the headphone trick, had moved it to the lowest hum position - directly over the preamp.  After a few weeks of researching squeal and oscillation causes, learned about how OT's work and then moved the OT to middle of the chassis where it's remained since.  The rebuild has been very rewarding, yielding a very quiet, amazing marshally tone machine, thunderous at full throttle.  At idle, there is no hum until MV is past 90%, but then only slight and not a concern.
But the secondary leads run beneath the tone stack filters on the board (see gut shot below), which just bothers me out of principle.  One thought would be to run those leads on top of the chassis and drop them in right next to the speaker jacks (which are also near the preamp but fortunately did not repeat that error on later builds!).  Also for my later builds, the OT was happy right next to the PT, so not sure why this isn't the case with this pair. 

Would you guys leave it as is, or is there a benefit (or caution) for running the secondary leads across top of chassis?  Or other suggestions regarding placement compromise when the OT is happier further from the PT vs right next to it? 
What's last thing a hillbilly says before an untimely death?
"Hey ya'll, watch this!"

Offline PRR

  • Level 5
  • *******
  • Posts: 17082
  • Maine USA
Hoffman Amps Forum image
Re: OT Position compromise
« Reply #1 on: December 16, 2016, 01:33:26 pm »
I would not obsess about secondary leads as they are not a lot higher voltage than many internal signals.

I have run Primary leads outside the box to keep the much higher audio voltages away from small stages. That does demand much care for user safety.

 


Choose a link from the
Hoffman Amplifiers parts catalog
Mobile Device
Catalog Link
Yard Sale
Discontinued
Misc. Hardware
What's New Board Building
 Parts
Amp trim
Handles
Lamps
Diodes
Hoffman Turret
 Boards
Channel
Switching
Resistors Fender Eyelet
 Boards
Screws/Nuts
Washers
Jacks/Plugs
Connectors
Misc Eyelet
Boards
Tools
Capacitors Custom Boards
Tubes
Valves
Pots
Knobs
Fuses/Cords Chassis
Tube
Sockets
Switches Wire
Cable


Handy Links
Tube Amp Library
Tube Amp
Schematics library
Design a custom Eyelet or
Turret Board
DIY Layout Creator
File analyzer program
DIY Layout Creator
File library
Transformer Wiring
Diagrams
Hoffmanamps
Facebook page
Hoffman Amplifiers
Discount Program