Primary Impedance

[beta]

Hello all,
I have been searching for an affordable output transformer for my '69 Sentura II for some time now. I finally found one from Parts Express, but I'm unsure which one I need. There are two types I can buy,

Type 1,
Cat. No.-1650N  
Audio Watts-60
Primary Impedance-4,300 ct
Max. DC Per Side-318 ma.
Secondary Impedance-4-8-16    
Wt. Lbs-8

Type 2
Cat. No.-1650P
Audio Watts-60  
Primary Impedance-6,600 ct
Max. DC Per Side-200ma.  
Secondary Impedance-4-8-16  
Wt. Lbs-8  

I don't know what the primary impedance of the output transformer I need is. So I'm not sure if I need the 1650N or the 1650P.  Please help out a fellow Sunn enthusiast if you can.

Thanks........Wil

[Anonymous]

6600 ohms is a good primary impedance match for 6L6GC's, but is a bit too high for 6550's.

The 1650N is a much better match for 6550's.

The Sunn power amps are generally ultralinear.  Does the transformer have the (generally) 40% tap to connect the screen grid connections?

[TubeMan]

To add to what guest said, the max dc of type 2 will be a bit low for 6550s or KT88s. I would go with type 1.

If the tranny doesnt have a 40% ultralinear tap, dont fret. if you are using a power tetrode like a 6550 or KT88, you can connect the tubes in triode mode. you will get a bit higher tube saturation and a bit lower volume output, but it will work.

basically what triode connection does is to delete the 40% connection to the control grid on the tube, and connects the grid to the OT grid supply instead.

If you want to stick with the particular big and clean sound of the ultralinear setup though, a 40% OT tap is required.

[Anonymous]

Tubeman, I'm sure you really meant "screen" and not control grid.  A triode connection of a pentode connects the screen to the plate, usually through a screen resistor (highly recommended to limit screen current).

[TubeMan]

I am assuming that you are the same person as in the 2000s thread, here again, to pick apart my posts.      If you are the same person, i find it interesting that you do not log in. Instead you find it better to crap on my posts anonymously.  

Be that as it may, I will clarify.

Pentodes in triode connection have the tube's grid 1 connected to the cathode, and the input singnal is routed to grid 2.
Grid 3 is of no use in this connection, and can be either connected to the anode (ground), or left alone.

[TubeMan]

due to a typo i incorrectly stated that the anode is connected to ground.    long day.

also: here is a wealth of information regarding triode connected pentodes, tetrodes, and beam power tubes.

http://www.webace.com.au/~electron/tubes/triode.htm

[JoeArthur]

Interesting argument.  I have to side with "guest" on this one - triode operation of a pentode does tie the screen grid to the plate.

Tubeman... you have your grid numbers and connections mixed up also.  I'm sure you know this, but for those that don't, it is tradition to number the grids in this manner, which reflects the history of grid evolution:

Grid #1 is the control grid,
Grid #2 is the screen grid,
Grid #3 is the suppressor grid.

In some tubes, such as the 6550, there is no choice as to where to tie the supressor (grid #3) as it is internally connected to the cathode.  Other tubes, such as the EL34, do give you this option.

[TubeMan]

Joe,

considering that i was tired enough to confuse something as elementary as the anode with the ground side of the tube in my post, im not surprised that i numbered the grids backwards.  

its always worse when you already know the proper way, but you advertise the wrong way by accident.  

i hope no one was hurt. bzzzt    

thanks for clearing that up joe