Luxman MB-3045: Convert from Triode (KT88 sort of) to 300B Push-pull?

[richp4003]

Hi Everyone,

I have a pair of Luxman MB3045 monoblocks, that are currently wired with KT88 in a triode, push/pull setup making about 42 watts. For those who know the amplifiers, they originally ran a 8045G tube that was made by NEC, no longer in production.

I have high efficiency speakers (Zu Druid V) so the wattage output isnt a huge concern. Ive been interested in the whole 300B/SET thing, and I was wondering the following:

- Is most of the 300B magic in the SET or in the tube itself?
- Is it possible to convert the amplifiers I have to 300B?
- Would there be any real point to such a conversion?

Ive attached a basic wiring diagram, not sure if this is a fantastic idea or a terrible one..

 

[kevinkr]

The supply voltages in the MB3045 are too high for easy use with the 300B, and you don't have the requisite filament supplies either, many other modifications would be required.

You'd be better off selling the 3045s and replacing them with a PP 300B amplifier.

 

[richp4003]

Kevin,

That was exactly what I was looking for.. Im a bit new to this stuff, and obviously when you get to a certain point in the hifi search its well beyond going to the store to listen to things.

PS. Nice Thomas Paine quote!

 

[kevinkr]

Good observation there, I design and build all my own gear, originally decades ago as a matter of expediency since I couldn't afford anything good.

Now I can't afford to buy/find the sorts of things I can make at home. LOL

Paine definitely had a way with words and ideas. One my favorite quotes.

 

[kevinkr]

FWIW in view of your question I am 100% SET here, active system with six channels of amplification driving each driver in my system individually. Four channels (mids and highs) are 300B SE and two channels (bass) are GM70..

Working on a new electronic crossover design to replace the EVs I currently use.

I would think the 300B or one of its EML cousins would probably provide sufficient power for the Druids. The GM70 could be another option if you are not scared of high voltages and transmitting triodes.

 

[6A3sUMMER]

richp4003,

You might consider Parallel Single Ended 300B if the GM70 high voltage is too scary.

For PSE it is better to use individual bias, can use individual self bias, or individual fixed bias adjustments. Exact current balance is not needed like it would be in push pull, but it is a very good idea to have nearly equal currents, nice to have matched tubes, and be able to adjust or self bias them (and you can easily test them after hundreds of hours of use). Using individual self bias also requires separate filament supplies when using DHTs.

PSE The driver will need to drive 120pF, twice that of a single 300B (Miller C). You use an SE output transformer with Half the primary impedance, Two Times the current, and Two Times the volume of laminations versus a single 300B SE OPT. The driver only has to swing the same voltage for PSE as it does for single SE.

I was one of the Authors of "Paralleling Tubes Effects", Glass Audio, Volume 12, Number 5, 2000. Parallel tubes CAN sound great!

I need to go and listen to a friends Zu's soon.

Have fun building and listening.

kevinkr, Yes, the old Thomas Paine quote applies well today.

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ALL generalizations have exceptions - me

 

[richp4003]

Thanks again guys; the question of necessary power and if 300B on its own is going to be sufficient is a question. Ive read different things about the good and bad about PSE. Zu said their favorite amps for the druid V are 300B setups, and that push/pull gets a bit harsh. I haven't really found that but I don't have a reference point for what SET would sound like. In addition luxman stuff is generally pretty liquid-smooth so that could be part of it.

I talked to abszero (Radu) who only lives a few towns over from me; he has been gracious enough to offer to bring one of his 300B creations over to try out. if I found that was the sound to have, I would probably work with him to design something and build something. Im not quite there yet with doing something from scratch!

As to high voltage tubes.. Im not married to it being 300B; heck.. I was even ogling over some of the 833 tube setups! (I wouldnt build to their crazy top outputs.. maybe 40-50 watts or so)

 

[TonyTecson]

fwiw, i have a quad of 8045G tubes, these tubes like the 6ac10's looked like tv scanning tubes wired internally as a triode.....

 

[richp4003]

Those are like gold! I have the original set my amps came with (I did the KT88 conversion) I decided to convert because I use these amplifiers a lot and I didn't want the rarity of the original tubes to become a factor in how often I would use them.