Transformer as tube amp input / phase splitter?

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nielsk

Well-known member
Joined
Nov 12, 2004
Messages
1,758
Location
Megapopulas, Florida
Here's one for the tube amp gurus (as I am not one :'()... I want to build a straight forward Fender Bassman type power amp, and use a transformer as the input / phase splitter. The little reading I have found on this makes it seem like a transformer can work well here.
I have a Lundahl 1517 w/ dual output coils as a candidate, is it as simple as grounding one side of each output coil & using the opposite phase of the outputs to feed the grids of the 6L6s through a .1uF cap?
Could I use an attenuator of "volume knob" type pot (1m wiper out, one side to ground) set-up before the transformer as a master level control?
Thanks forward...
 
Normally you lose both the grid resistor and grid cap, feed the transformer directly to the grid. This gives simplicity and large tolerance of gassy grids.

This was done in the very early gitar amps, in a couple of Garnets (later production of the same models went to R-C coupling for some reason), in Fender's teeny bass-amp, and in Fender's Monster 300 Watt amp.

The fact that 99% of gitar amps ever made do NOT use transformer coupling MAY be a hint. (Yeah, cost is a factor, but Fender's small bass amp says that was not decisive.)

A Bassman's grid drive is quite large, over 45V. Most interstage iron is not made for such levels. Is this one?

Putting a pot with a transformer will seriously screw-up impedance relationships. Certainly 1Meg is way too high..... what impedances is this transformer supposed to work with?

The 5F6A Bassman driver is widely respected and universally plagiarized. What are you hoping to improve?

http://www.schematicheaven.com/bargainbin/garnet_m90_mach5.pdf
http://www.schematicheaven.com/bargainbin/garnet_l260d_bto.pdf
http://www.schematicheaven.com/fenderamps/musicmaster_bass_schem.pdf
http://www.schematicheaven.com/fenderamps/400ps.pdf
 
Thanks for the response. Not really hoping to improve, other than noise floor / hum / interface, but to simplify. I will only need the B+ to the OT-CT, less heater current, lower parts count.
And I happen to have a pair of these Lundahl transformers...and some NOS outputs.
I plan to build a 100 watt & a 50 watt amp, and use them with a crossover and my DIY Alembic type preamp.
These guys got me thinking this way:
http://www.kandkaudio.com/poweramplifier.html
OBTW, would using the coupling caps keep the DC out of the input transformers?
 
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