Welcome To the Hoffman Amplifiers Forum

September 07, 2025, 08:09:21 am
guest image
Welcome, Guest. Please login or register.
-User Name
-Password



Hoffman Amps Forum image Author Topic: Looking for PT candidate for JMP-1watt Clone  (Read 2332 times)

0 Members and 1 Guest are viewing this topic.

Offline Rp3703

  • Level 2
  • **
  • Posts: 120
  • Inexperienced Expert
Hoffman Amps Forum image
Looking for PT candidate for JMP-1watt Clone
« on: July 17, 2021, 12:51:57 pm »
I am looking at building a JMP-1 watt clone. I found this schematic and have for the most part confirmed it’s accuracy. I plan on using a Hammond 125A for the OT but am having trouble figuring out the PT. The Dragnall puts out 0-200V/ 0-11.5V on the secondary. Does anyone know of a hammond or other manufacturer with something similar or an alternative power amp solution that uses a commonly available PT? Is there an advantage to running the filament supply DC?

Offline Willabe

  • Global Moderator
  • Level 5
  • ******
  • Posts: 10524
Hoffman Amps Forum image
Re: Looking for PT candidate for JMP-1watt Clone
« Reply #1 on: July 17, 2021, 01:40:35 pm »
Is there an advantage to running the filament supply DC?

DC heaters can actually at times be nosier.   

I like to use dcv elevated heaters with a humdinger pot. (I use 70 to 80dcv.) 

Read this;

http://www.valvewizard.co.uk/heater.html
« Last Edit: July 17, 2021, 01:49:16 pm by Willabe »

Offline Rp3703

  • Level 2
  • **
  • Posts: 120
  • Inexperienced Expert
Hoffman Amps Forum image
Re: Looking for PT candidate for JMP-1watt Clone
« Reply #2 on: July 17, 2021, 03:37:33 pm »
Are DC filaments just a PCB thing?

Offline sluckey

  • Level 5
  • *******
  • Posts: 5075
    • Sluckey Amps
Hoffman Amps Forum image
Re: Looking for PT candidate for JMP-1watt Clone
« Reply #3 on: July 17, 2021, 04:00:21 pm »
no
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline Rp3703

  • Level 2
  • **
  • Posts: 120
  • Inexperienced Expert
Hoffman Amps Forum image
Re: Looking for PT candidate for JMP-1watt Clone
« Reply #4 on: July 17, 2021, 04:15:11 pm »
But other than reducing hum, they do not contribute to the tone of an amp, right? So going with regular AC heaters would be fine if implemented correctly.

Offline thetragichero

  • Level 3
  • ***
  • Posts: 582
Hoffman Amps Forum image
Re: Looking for PT candidate for JMP-1watt Clone
« Reply #5 on: July 17, 2021, 04:36:40 pm »
i built a ~4w single-ended el84 plexi clone using the hammond 269ex transformer (probably most known for the ax84 high octane) i had lying around and it worked well for me

Offline Willabe

  • Global Moderator
  • Level 5
  • ******
  • Posts: 10524
Hoffman Amps Forum image
Re: Looking for PT candidate for JMP-1watt Clone
« Reply #6 on: July 17, 2021, 06:16:42 pm »
But other than reducing hum, they do not contribute to the tone of an amp, right? So going with regular AC heaters would be fine if implemented correctly.

They do not change the tone of the amp. Very few guitar amps have dc heaters, and their quiet.   

Offline Rp3703

  • Level 2
  • **
  • Posts: 120
  • Inexperienced Expert
Hoffman Amps Forum image
Re: Looking for PT candidate for JMP-1watt Clone
« Reply #7 on: July 17, 2021, 07:38:20 pm »
Thanks Willabe, I think I’ll try AC filaments and see what happens.
Tragichero, I actually have a spare 269EX from a Firefly I built, I’ll give that a try and see how that goes as well. Thanks.

 


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