KT66 to EL34

[bmi]

Does somebody see any issue to swap KT66 with EL34 in the JTM45/100?
I have an old siemens/mullard duet that i want to try on one side.

[surfnorthwest]

Sometimes depending on the board or the transformers you can make the swap and will only have to re-bias.

Or it could be your transformer is not ideal for EL34s or you need a mod to the board. I am not a amp tech but yes it can be done, just don't know what work needs to be done in your case to make it happen.

Not sure you would like the EL34 sound over the KT66 sound. Would be best to PM Steve and ask this.

[SteveD]

The output transformer primaries are in parallel so there is no 'one side'. Only the secondaries are separate and isolated from each other. If you wanted to do that you would have to install the valves in the usual positions 1 and 4 or 2 and 3 and then rebias (if the range on the trim pot allows).

[bmi]

Wow it seems that i'm using half of both push pull.
So if i use 1&4 or 2&3 i will get sound on both speaker outputs?
And i can use only one speaker output because the hot-point of the jack is grounded when nothing is plugged and so protect the circuit?(it's not open)
I am right?

[SteveD]

Because the primaries are in parallel there will always be signal at both outputs regardless of what valves are plugged in where.

The power amp's output signals are NEVER grounded when nothing is plugged in on any amp or at least they shouldn't be. Only input signals are grounded to prevent transmission of noise and interference into the preamplifier.

[bmi]

Thanks for these informations Steve, it helps me to correct things but i disagree with one point.
I know that inputs are grounded to avoid noise when using the other jacks but you can find output jacks grounded thru a resistor to protect the secondary of the OT when nothing is plugged. What is dangerous for the OT is to have an open circuit.IMO

[SteveD]

'Grounded through a resistor' is not the same as grounded.