tube 45 triode

Who are you? Tell us about yourself, get feedback, and provide links to your work.

Moderators: piaptk, tragwag, Steve E., Aussie0zborn

Post Reply
User avatar
xjfx
Posts: 5
Joined: Sun Mar 09, 2008 11:14 am

tube 45 triode

Post: # 3002Unread post xjfx
Thu Jun 26, 2008 11:41 am

hi

is there someone who knows about an equivalent of the tube 45 triode for presto k 8 amp ?
the 45 is pretty expensive..
thanx
jf

User avatar
studiorp
Posts: 761
Joined: Thu Nov 01, 2007 6:55 pm

Post: # 3007Unread post studiorp
Fri Jun 27, 2008 7:48 am

You can try to mount on your Presto amp the 2A3 tubes.
This tubes works to 2.5 V voltage as 85.

User avatar
Perisphere
Posts: 39
Joined: Thu Nov 10, 2005 9:53 pm
Location: Mountain Home, Arkansas

Post: # 3009Unread post Perisphere
Fri Jun 27, 2008 3:02 pm

NOTE--Changing from 45s to 2A3s is NOT plug-and-play even though the pin-outs of the two types are the same.

The filament in a 45 pulls 1.5 amps, the 2A3 2.5 amps. Hence the current draw in a push-pull amp will jump up by 2 amps just changing from one pair of 45s to a pair of 2A3s.

Also, the transconductance of the 2A3 is much greater than that of the 45 so there will also be issues with grid and plate current that will need to be sorted, even if the power transformer can tolerate the increased load on the filament winding.

CipBlole

tube 45 triode

Post: # 5657Unread post CipBlole
Mon Jul 20, 2009 10:39 am

Anybody--help

In a dual triode tube such as the 12ax7, used to amplify both left and
right channels, how is channel separation maintained?

Is there some sort of partition inside the tube or is it dependent on
the distance separating the two sections.?

Thanx for any info.

ESTG/

User avatar
Simon
Posts: 625
Joined: Wed Mar 05, 2008 12:25 pm
Location: London, Brighton - England

Post: # 5658Unread post Simon
Mon Jul 20, 2009 11:30 am

Happy to learn something new.
Wanted: Stylus for Presto, Mono heads Grampian, Fairchild, Presto, Fairchild 740 lathes, Presto 8n, 8d 8dg lathes or parts or Presto or wot ever recording Amps, PM me what you have for sale.

User avatar
markrob
Posts: 1670
Joined: Wed Nov 28, 2007 1:14 am
Location: Philadelphia Area

Re: tube 45 triode

Post: # 5660Unread post markrob
Mon Jul 20, 2009 1:36 pm

CipBlole wrote:Anybody--help

In a dual triode tube such as the 12ax7, used to amplify both left and
right channels, how is channel separation maintained?

Is there some sort of partition inside the tube or is it dependent on
the distance separating the two sections.?

Thanx for any info.

ESTG/
They are seperate sections. If you look at the tube closely, you can see the two sections. There is are common mica insulators that hold the two sections in place, but they operate independently. Crosstalk should not be a big issue as the capacitance between the sections is very small.

Mark

User avatar
cuttercollector
Posts: 431
Joined: Sun Jun 11, 2006 4:49 pm
Location: San Jose, CA

Re: tube 45 triode

Post: # 5701Unread post cuttercollector
Thu Jul 23, 2009 2:17 pm

markrob wrote:
CipBlole wrote:Anybody--help

In a dual triode tube such as the 12ax7, used to amplify both left and
right channels, how is channel separation maintained?

Is there some sort of partition inside the tube or is it dependent on
the distance separating the two sections.?

Thanx for any info.

ESTG/
They are seperate sections. If you look at the tube closely, you can see the two sections. There is are common mica insulators that hold the two sections in place, but they operate independently. Crosstalk should not be a big issue as the capacitance between the sections is very small.

Mark
There is theoretically some crosstalk specification. It is probably worse at frequencies above the audio band. I have seen the sections split for L/R stereo operation, but typically only at higher levels when less gain is needed from the stage. I don't think it was good practice to make the first stage of a preamp for a mic or phono cartridge or tape head be split like that. The other reason is probably for those low level stages it went right into the next stage in the same tube with minimal wire path between the two stages.

Post Reply