Increasing OPT Primary

[clyde]

For 4 EL84's, common value is 4k, I have a 6k transformer on hand and am wondering what it will do to the tone, power output and the effect on the tubes if I use it.  Thank you.

[Merlin]

Higher impedance puts greater stress on the screen grids, so it may be a good idea to increase the screen stoppers. You will also get a little less power, althought that may hardly be perceivable in terms of volume. Tonally it's difficult to say. You'll be running more in Class-A than AB, for what it's worth.

[Glenn]

I have. 6.6 k OT in my Liverpool and i can’t tell the difference between my Rocket which has a 4K OT in terms of sound loudness, they are both too loud for my house.

I believe the is a 4x el84 Orange amp that also uses a 6k OT
Just my 2 cents….

[clyde]

Higher impedance puts greater stress on the screen grids, so it may be a good idea to increase the screen stoppers. You will also get a little less power, althought that may hardly be perceivable in terms of volume. Tonally it's difficult to say. You'll be running more in Class-A than AB, for what it's worth.

1k?

[Merlin]

1k?

1k is standard, I'd go for 2.2k or even 4.7k.

[shooter]

fwiw
did a qSE PA 6BQ5's into a 1250:8 ohm OT, 2 speakers for 4 ohms.  probably my best mono-block audio amp.  did pretty good with guitar n pedals up front also.

[HotBluePlates]

I have. 6.6 k OT in my Liverpool and i can’t tell the difference between my Rocket which has a 4K OT ...

The "right" impedance is about balancing factors:
   - Supply Voltage
   - Tube Current Capability (at the Supply Voltage)

What is Ohm's Law?
   - Volts / Current = Impedance


What often happens is the supply volts are raised and the tube can't manage more current, so the OT impedance is increased.  That results in same-current dropping more-volts across the output transformer.

If a tube is shifted to running in Class AB rather than Class A, peak plate current goes up (often a lot).  To allow more-current with same-voltage, the OT impedance is reduced.
   - If nothing else changed, the tube would overheat (because same-voltage, more-current).
   - But when we go from Class A to Class AB, we also cool off the idle bias, so the tube spends a greater period of time cooler to offset the added heat when conducting hard.