5E3 based clone - 6v6s to 6L6s

[stephenhartley]

Hi I'm trying to get a bit more umph and volume out of my 5E3 clone.

It's a standard 5E3 circuit but the transformers are rated at 25w, leading me to believe that I might be able to drive 6L6s.

The PT is rated at:

330v @ 80mA. 6.3v @ 3A heater 5V @ 2.5

OT has a PI of 8500 ohms with 4, 8 & 16 ohm taps.

I have a RCA 5V4GT rectifier in and the tubes (6V6s and 6L6s) are Russian military.

I'm reading plate voltages of ~ 360v on the tubes.

I have 2 questions

1. do I plug the current 8ohm speaker into the 4ohm or 16ohm OT socket to get the best out of the 6L6s - (I can never remember which way round)

2. What's the optimim biasing for this set-up in terms of cathode resistor and dissipation wattage to get the best out of the 6L6s without putting the PT at risk? - I know there isn't enough current to drive them hard, but maybe enough to get a little step up in performance from the 6V6s?

[Jazz P Bass]

My first impression is the 80ma rating.
You won't be able to drive the 6L6's very hard with that limit.

[Bruce / Mission Amps]

My first impression is the 80ma rating.
You won't be able to drive the 6L6's very hard with that limit.

You'll need a power transformer with at least a 120ma rating to run 6L6s in cathode bias with that topology.
Vintage 6L6 tweed amps with cathode biasing used a PT with at least a 160ma rating.
Using the right power transformer, it's higher current available and the right B+ voltage, the bias voltage (however you derive it) should let the 6L6 tubes idle around 18-21 watts each for vintage tweed 6L6 amps.
You need at least a 10 watt 250 to 300 ohm resistor.
I don't think your 80ma power tranny is going to give "that" to you... and still have enough B+ to run the power tube very hard.
You'd run your 8 ohm load on a 16 ohm tap.

What you could do is build a little fixed negative voltage bias supply, use a GZ34/5AR4 or a solid state rectifier and run the 6L6s in fixed bias idling around 12-15 watts each... your PT might be able to run them at reduced power output.... or a few watts over your 6V6s.