Welcome To the Hoffman Amplifiers Forum

September 06, 2025, 12:37:29 pm
guest image
Welcome, Guest. Please login or register.
-User Name
-Password



Hoffman Amps Forum image Author Topic: Valve Junior Layout Error  (Read 4380 times)

0 Members and 1 Guest are viewing this topic.

Offline plexi50

  • Level 4
  • *****
  • Posts: 4649
  • Tube Tone
Hoffman Amps Forum image
Valve Junior Layout Error
« on: August 20, 2010, 10:38:47 pm »
Do you see any errors in this layout file? If so what and where are they?

Offline PRR

  • Level 5
  • *******
  • Posts: 17082
  • Maine USA
Hoffman Amps Forum image
Re: Valve Junior Layout Error
« Reply #1 on: August 21, 2010, 10:03:15 pm »
IEC jack pinning is unclear to my eye.

Offline RicharD

  • SMG
  • Level 4
  • *****
  • Posts: 2057
    • Toxic Water
Hoffman Amps Forum image
Re: Valve Junior Layout Error
« Reply #2 on: August 21, 2010, 10:58:12 pm »
Seems like R2 should be a 33k, not a 68k.  They "omitted" cathode bypass caps for R8 & R9 but didn't say why.  No tone control...cool!  The flow of the board looks fine as does the grounding scheme.  Not that it's "wrong", but I'm not a fan of separate jacks for the different speaker impedances.  I prefer a single shorting jack with a selector switch.

>IEC jack pinning is unclear to my eye.

Ditto.  Where is the fuse and power switch?  Where is the pilot light? 

Offline sluckey

  • Level 5
  • *******
  • Posts: 5075
    • Sluckey Amps
Hoffman Amps Forum image
Re: Valve Junior Layout Error
« Reply #3 on: August 21, 2010, 11:04:44 pm »
Maybe the fuse is in the IEC and the pilot is in the double pole switch?
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline plexi50

  • Level 4
  • *****
  • Posts: 4649
  • Tube Tone
Hoffman Amps Forum image
Re: Valve Junior Layout Error
« Reply #4 on: August 22, 2010, 08:19:49 am »
The fuse is in the IEC and the pilot is in the double pole switch. I almost burned up a second PT when i looked at the rectifier diodes. I lifted there ends and tested them. They were reading good. I replaced them anyway seeing as they are a dime a dozen. I wound up wiring the PS caps neg to chassis ground and the rectifier diodes the old Fender way with each HT lead to it's own diode

Amp fired right up with no light bulb current limiter dimming this time
Tested all preamp and power tube socket voltages before installing power tube
Working fine now / What was the issue?
« Last Edit: August 22, 2010, 08:25:45 am by plexi50 »

Offline sluckey

  • Level 5
  • *******
  • Posts: 5075
    • Sluckey Amps
Hoffman Amps Forum image
Re: Valve Junior Layout Error
« Reply #5 on: August 22, 2010, 08:29:39 am »
Quote
I wound up wiring the PS caps neg to chassis ground and the rectifier diodes the old Fender way with each HT lead to it's own diode
That statment suggests there is a center tap for the HT winding. If so, AND you had the CT connected to chassis with the bridge rectifier shown in the drawing, that's the reason you burned up the PT.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline plexi50

  • Level 4
  • *****
  • Posts: 4649
  • Tube Tone
Hoffman Amps Forum image
Re: Valve Junior Layout Error
« Reply #6 on: August 22, 2010, 09:10:06 am »
Yes the second PT had a CT. The original PT had no CT lead that i recall. The shell is all that is left. Im using the old PT as a paper weight for projects
« Last Edit: August 22, 2010, 09:14:20 am by plexi50 »

Offline sluckey

  • Level 5
  • *******
  • Posts: 5075
    • Sluckey Amps
Hoffman Amps Forum image
Re: Valve Junior Layout Error
« Reply #7 on: August 22, 2010, 09:39:38 am »
Quote
Yes the second PT had a CT. The original PT had no CT lead that i recall.
That explains why the second PT began smoking. Gotta be careful when replacing a PT. Just because it has a center tap doesn't mean it's gotta be connected to chassis. Only the shadow knows why the original failed.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline plexi50

  • Level 4
  • *****
  • Posts: 4649
  • Tube Tone
Hoffman Amps Forum image
Re: Valve Junior Layout Error
« Reply #8 on: August 22, 2010, 11:22:15 am »
Thanks. The Shadow is unavailable. All worked out. I will remember this one

Offline J Rindt

  • Level 2
  • **
  • Posts: 427
Hoffman Amps Forum image
Re: Valve Junior Layout Error
« Reply #9 on: August 22, 2010, 03:52:30 pm »
What is the advantage of that .1uf poly-film cap in parallel with C8?
Is there some advantage of a small, non-elytic cap?
Thank You

 


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