Welcome To the Hoffman Amplifiers Forum

September 07, 2025, 03:41:09 pm
guest image
Welcome, Guest. Please login or register.
-User Name
-Password



Hoffman Amps Forum image Author Topic: Columbia 360 phono OT ?  (Read 1986 times)

0 Members and 1 Guest are viewing this topic.

Offline tubenit

  • Global Moderator
  • Level 5
  • ******
  • Posts: 10274
  • Life is a daring adventure or nothing at all!
Hoffman Amps Forum image
Columbia 360 phono OT ?
« on: December 10, 2017, 01:21:37 pm »
I was given a Columbia 360 phono that was quite beat up.  Turned out it had one of those "tube amps" without a power transformer in it. It had 35L6GT tubes which put out about 1.5w to 3w (I think?)

http://tdsl.duncanamps.com/show.php?des=35L6GT

I think the amp is a push/pull circuit?  There is a schematic to the amp here:

https://www.audioasylum.com/forums/tubediy/messages/17/175068.html

I kept the OT from the amp thinking it might be useable for the pentode section on ECL84 tubes which have a similar output (I think?):

http://tdsl.duncanamps.com/show.php?des=ECL84

Do you guys think the OT could be used for ECL84's  which I used on the SoLowWatt amp I built years ago?

With respect, Tubenit




Offline PRR

  • Level 5
  • *******
  • Posts: 17082
  • Maine USA
Hoffman Amps Forum image
Re: Columbia 360 phono OT ?
« Reply #1 on: December 10, 2017, 11:22:13 pm »
You sudda kept the whole chassis and speakers, got an isolation transformer. Those upper-class phonos were sometimes magical.

The 3W is at 200V. The Columbia ran less than the 110V which gives the 1.5W result. So push-pull barely 3 Watts.

The ECL84 is nowhere near a 35L6. It needs twice the B+ just to make half the current. It is not a good match for that OT. The most available tubes suitable for that OT will BE the 25/35/50L6 or 6Y6. And at ~~100V supply; much more and the bass will just fart.

But what are you building? A stadium blaster? I guess not. A couple ECL84 @ 100V will make nearly a Watt push-pull in this low-Z load. A lame Champ, but push-pull.

Offline tubenit

  • Global Moderator
  • Level 5
  • ******
  • Posts: 10274
  • Life is a daring adventure or nothing at all!
Hoffman Amps Forum image
Re: Columbia 360 phono OT ?
« Reply #2 on: December 11, 2017, 06:12:01 am »
PRR,  thanks for the response!  I appreciate it.  I didn't know that it could have been a reasonable or good idea to have used it.   :dontknow:

Anyhow, I still have the OT and tubes available to me. 

With respect, Tubenit

 


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


password