PRIMA LUNA AMPLIFIERS

Love my Prologue 5. Beautifully built. Zero problems.

Any competent tube amp tech could fix one in the unlikely event that something went wrong.

They have a 'gorgeous, romantic' sound.

I rolled the supplied el34’s to KT 120’s to power sonus faber’s that needed more to drive them.

Installing KT-120s would not change the power appreciably as B+ does not change. Sound and life could change.

EVO Balanced I/O are transformer balanced. This is neither good nor bad, but raises costs and may change sonics with some gear.

IMO, PrimaLuna is losing the plot and just making amps more gimmicky.

The autobias circuit will adjust bias to whatever it is set, not the tube. Different tubes may require a bias change.

Has anyone characterized Hum, Distortion, Power before and after changes?

ksubrama:

The 150 draws considerably more heater current than the EL34. Can the amp supply it?
The operating point will change which will change the distortion considerably.
Do you have the tools / know how to adjust the amplifier to optimize for 150's?

Just WHAT do you expect to achieve other than a thinner wallet?

There is a switch on the side for low and high output tubes. EL34 being low output, and KT120, KT150 etc. are considered high output.

The switch is for EL34 or KT-88 bias. The KT-120 & KT-150 are a whole different tube than the KT-88. The 120 & 150 use up to 25% more heater current. Unless the amp has a regulated heater supply capable of supplying the increased load, an un-regulated supply may struggle with the extra current. If the amp can supply the current for 150's with an unregulated supply, then the heater voltage for the EL34 and drivers is way too high.

Power is determined by the power supply. Adding a beefier tube does not increase the power. Sonics may change depending on the design and transformers.

Additionally, general tube rolling advice is not worth the bits to transmit. Tubes from the same batch vary widely. Tubes change continuously. What is golden in one amp may be less than stellar in another.