Dual OTs Dual Pro

[Mats]

Im wondering how this schematic of an Dual Pro amp works, with two OTs.
Its an early amp about 1946, I think. In that amp, its power tubes is 6L6s.
Lets say if I have two 6V6s and they want 8k-10k of reflected load.
I use two Hammond 125E.
Are the two OT paralleled so I hook up each 125E for about 20k // 20k = 10k
Is this correct ?
Or are the two OTs not paralleled and they should be hooked up 5k and 5k = 10k
How are they hooked up in this config. ?
Sorry I don´t know how to load up an image of this amp.
/Mats

[sluckey]

We need to see the schematic. When you reply to this message, click on the "Additional Options..." link. Then you will be able to attach a file.

[Ed_Chambley]

In 46, I believe you will have a field coil speaker which looks like another transformer on a schematic.  If this is correct, you can simply eliminate it and use a standard 8k OT and a modern speaker.

[Willabe]

Maybe this schemo?

http://www.el34world.com/charts/Schematics/files/fender/pro_5b5_schem.pdf

BTW, this ^ 5B5 pro ^ above ^ is listed as 5A5 pro in the Dave Funk tube amp workbook.

I think this is the same amp? Listed as 46 pro in Doug's library.

http://www.el34world.com/charts/Schematics/files/fender/1946_pro.pdf


             Brad      
  

[Willabe]

Im wondering how this schematic of an Dual Pro amp works, with two OTs.

Wait a minute. Are you talking about the old V-front tweed amp with the chrome stripe down the middle splitting the speaker baffle in two?

They were named Dual Professional by Fender and had 2x10" speakers. They have also through the years been called V-front supers as a nick name.

Billy Gibbons loves them and claims he's got 20 to 25 of them.

Funk book has a foot note on the 5B4 Super 2x10" (all octal tubes) that says that the OT is mounted on the speaker.

Same book shows 5B5 Pro 1x15" (all octal tubes) with same foot note and the 2 schemos are very similar.  


                   Brad      

Edit; Found on line where somebody said in a forum that the Dual Professional and V-Front Super were the same amp with different.  

[Willabe]

Hey I found this;

The Dual Professional used two output transformers mounted to the speaker frames. The Dual Professional included two 10″ Jensen speakers. It was renamed the Super in fall of 1947.

But found this too;

Circa 1949 Fender Dual Professional/Super Tweed Guitar Amplifier, Serial # 490. Replaced handle with several extra screw holes. Grill cloth appears to be replaced but material is correct with numerous staples. Some caps have been replaced. Speakers are Jensens with date codes of 22083 and 22084. Field coil appears to be correct.

But I agree with Ed, the 46 amp probably had a field coil for the speakers. Maybe a later year but still a very early Fender amp had gotten rid of the field coil and did use 2 OT's mounted to the speakers for a short time?

I've looked and can't find a schematic for an old Dual Professional.  


               Brad    

[Willabe]

Here's the earliest Fender Super schemo in Doug's library, it's only a layout drawing. Notice it shows for 6L6's pin 3 "to speakers."

That could be/should be 1 OT mounted on the speaker frame? Or did they use 2 OT's wired in series, 1 mounted on each speaker?

http://www.el34world.com/charts/Schematics/files/fender/super_5b4_LAYOUT.pdf


              Brad     

[Willabe]

Here's a Sears Silver tone amp 4x6L6 PP with 2 OT's.

http://www.el34world.com/charts/Schematics/files/silvertone/silvertone1474.pdf

And;

http://www.el34world.com/charts/Schematics/files/silvertone/silvertone1485.pdf
              

             Brad    

[Mats]

Here is the schematic that I found.
Thanks for help about attachments.
Its much like the Silvertone amps and the double OTs

[Willabe]

Ok, that drawing shows 2x6L6 going to 2 OT's wired in parallel and a single speaker field coil.

I have no idea if you can use 1 field coil for 2 separate speakers. 2nd field coil might have been left out of the drawing by mistake?


                     Brad     

 

[sluckey]

Each speaker must have it's own field coil since the field coil is part of the electromagnet.

But his drawing does not show a field coil. Instead, it shows a typical filter choke. At least that's how it's labeled.

[Willabe]

Sorry I misread that.


               Brad     

[jjasilli]

Absent a subjective preference for lots of iron    I do not see the point of having 2 trannies.  One alternative: since the plate impedances all match have the 4 power tubes in PP to the OT primary -- one pair of el84's & one pair of 6V6's. Use a pot at the signal end as a mixer to send all signal to one pair / blend both / or just to the other pair. 

[PRR]

At one time, OTs came with speakers. (This made additional sense with field-coils since one end of the FC and the CT on the OT are common, saves wiring.)

And usta be that speakers (and OTs) over 15W were rare, or costly. Who would EVER need THAT much power?? Only 1,000-seat movie houses, and they had custom parts and complicated networks.

Yeah, well, too much is never enough.

A 6L6 pair can do 30W, but how do you load it with 15W OTs and speakers?

Double-up. You can double the OTs fine.

WHY do you want to know? Do you have a true Dual Pro? Or are you, like Leo in 1947, scrounging up leftovers to assemble a killer amp?

[Mats]

Thanks for all your answers.
No I have not this amp, wish I could say that.
Yes it make sense to use two "smaller OTs", if you want to get use of them, in a little bigger amp.
Im trying to understand this about dual OT and yes I have two 125C (not 125E)  
I recall, that also Marshall did this with two OTs

So if I understand this correct, the dual OTs will be connected at 20k load each,
the OTs in parallel, so the two 6V6 will get 10k
Is this correct ?

[jjasilli]

I continue to question the practicality of this approach, though it might be fun to build anyway.  It's all about the B+ supply voltage.  Per the 6V6 data sheets --

@ 250 plate volts 2X 6V6's in PP put out 10W.  You can do this with one 125C, rated at 8W.  You can build 2 amps; or go stereo!!!  Either of these last two approaches seems more practical to me.  

@ 285 plate volts 2X 6V6's in PP put out 14W.  Maybe borderline doable with one 8W tranny, IF you install a fan to cool the tranny.  You'll get saturation which may be desirable; but nifty if you're into a saturated tone.  You can combine 2 trannies for a 16W rating.  But as a practical matter the difference between 10W (previous choice) and 14W is probably undetectable in terms of volume.  

@ 360 plate volts 2X 6V6's in PP put out 23W.  2 trannies are again under-rated but borderline doable.  A fan may still be a good idea.  Again, saturation is likely to result.  

For the impedance effects of combining trannies, see this thread:  http://www.el34world.com/Forum/index.php?topic=8471.msg76062

EDIT:  This reinforces PRR's comments.  It was more practical to do this with bigger 30W power tubes, when only 15W trannies were readily available.