tube 45 triode

[xjfx]

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

[studiorp]

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

[Perisphere]

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]

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/

[Simon]

http://shop.ebay.com/items/?_nkw=12ax7+tube&_sacat=0&_trksid=p3286.m270.l1313&_sop=3&_dmpt=Vintage_Electronics_R2&_odkw=12ax7+tubes&_osacat=0

[markrob]

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

[cuttercollector]

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.