Will 6L6GC work in a Leslie 147 that uses 6550 tubes

[1CMA1082]

Hello all,

Would it be safe to use 6L6GC tubes in a Leslie 147 amplifier that came stock with 6550 tubes?

I have tested the Leslie with 6L6GC's and it sounds great, but I wonder if there would perhaps be any damage to the 6l6's.

Looking at the Leslie schematic it seems we have 415 volts going to the plates of the 6550/6L6GC, which seems fine for 6L6GC which has a max plate voltage of 450/500 according to the datasheets.

Also, would it be wise to change any resistor or cap values. I also need to learn how to bias!

http://bentonelectronics.com/wp-content ... lie147.gif
https://frank.pocnet.net/sheets/164/6/6L6GC.pdf
https://frank.pocnet.net/sheets/127/6/6L6GC.pdf

Thanks

[thetragichero]

All things being equal shouldn't the 6L6 be drawing less HT current resulting in higher plate voltage? not saying it won't work, just that there are some measurements I would be taking to ensure longer life

[martin manning]

What are the idle voltages on the 6L6GC pins? Is it wired exactly the same as the schematic you posted?

[Stevem]

That is a cathode biased output stage so really the tube used is seeing the plate voltage minus the cathode voltage.

So in effect with less then 400 volts on the plate a 6l6 will work fine, the only real big consideration is how high the filament voltage goes up to since two 6L6 tubes need 1.8 amps less then the 6550s did to light up!

If you find the the 6L6 tubes are running higher then 7.1 VAC on the heater then your going to eat them up fast, and yes that 12AU7 will eat up its cathode fast also!

Your comment on the 147 sounding great with the 6L6 tubes is likely more due to the added gain of the 12AU7 making a lot more gain due to that high heater voltage!