A high plate Hiwatt?

[lord preset]

I have a PT and OT from a 1980's 100 watt KMD. It was a UK made amp that was very close to a Musicman 65/100 watt design with 700volt plates and 350volt grids wringing 100 watts out of 2 6l6gcs. I was going to use them for my 1st build -a D'Lite but chickened out and bought a standard 50 watt PT/OT set. So now for what will be my third build I'm thinking of a Hiwatt circuit.

My thought was to run a Hiwatt preamp stage into a MM-style voltage doubled high plate power stage. Certainly it can be done, but the question is will it sound good and/or will it in any way resemble Hiwatt tone? Or it this a dumb idea that we will never speak of again?

Any insights from the Hiwatt brain trust would be appreciated.

[bb5000]

The Hiwatt DR201 and DR405 runs with 700Vp and 400 Vg2, so I guess that that's how it would sound like.

[lord preset]

The Hiwatt DR201 and DR405 runs with 700Vp and 400 Vg2, so I guess that that's how it would sound like.

Hmm, I knew that the DR201 had a voltage doubler in the power supply but I didn't know the voltages were that high. Cool. So I could build a DR201 with 2 power tubes rather than 6. The KMD transformers are labeled "100 watts" but I don't know their current specs so I wouldn't want to draw much more current than the original amp did.

Thanks.

[bb5000]

The Hiwatt DR201 and DR405 runs with 700Vp and 400 Vg2, so I guess that that's how it would sound like.

Hmm, I knew that the DR201 had a voltage doubler in the power supply but I didn't know the voltages were that high. Cool. So I could build a DR201 with 2 power tubes rather than 6. The KMD transformers are labeled "100 watts" but I don't know their current specs so I wouldn't want to draw much more current than the original amp did.

Thanks.

The PT has two high voltage secondary windings and the rectifier bridges are stacked on top of each other to achieve the 700 V.

http://hiwatt.org/Schematics/DR_200wPS.gif

[Stevem]

You can not get 100 watts out of 2 6l6s unless the amp class AB2.

[JazzGuitarGimp]

+1 for Class AB2 if you're expecting 100 watts from a pair of 6L6's. You could probably accomplish this using a direct coupled CF 12AU7 driver tube between the PI and output stage.

[lord preset]

+1 for Class AB2 if you're expecting 100 watts from a pair of 6L6's. You could probably accomplish this using a direct coupled CF 12AU7 driver tube between the PI and output stage.

I'm not fixated on getting 100 watts from this build, although I am considering using KT88s to goose things up a bit. But I am curious about the 12au7 driver idea. Like Musicman, KMD used a transistor driver. As for the 12au7' why does it need to be direct coupled? I ask because in this article, http://lenardaudio.com/education/14_valve_amps_3.html direct coupled drivers are described as being problematic, although this was in the context of HI Fi applications.

[lord preset]

Thinking some more on this, I'm leaning toward combining the Trinity Triwatt preamp design with a 6L6-based power amp running the plates at 700v and screens at 350V.

I was interested in trying a pair of KT88s (basically 1/2 of a DR201 power amp) but I'm concerned that I may not have enough filament current to run the KT88s and 4 12ax7s. There is literally zero info online regarding the specs of the power transformer I pulled from the KMD. I only know that it worked in a circuit that is a direct copy of a 100watt high plate Music Man design - 2 -6L6s, voltage doubling PS, solid state preamp. Original Music Man iron is known to be capable of running all-tube configurations, but I don't know if that's true for the "Tranilamp 100 watt" transformer I have from the KMD. KT88s (and EL34s for that matter) draw significantly more current than 6L6s. Also, I know that the OT I have was speced to work with 6L6s. Again, I don't care what wattage this ends up being as long as I can get Hiwatt cleans at band volumes.

[Stevem]

Well you can do the math to nail down the full amp circuits current needs for 100 watts with duel KT88s, wire up the recto and filter part of the amp and have that feed a bank of resistors to measure said current and then note the current output where it starts to nose downward.
This will be your current output for max RMS power.
In regards to KT88, even with only 550 volts on the plate two of them will need a max of 290 ma to pump out 100 RMS, with higer voltage from a voltage doubler you should need only some 250 ma for the output stage and then very litlle more even for 4 duel triodes in a preamp.
Also there is nothing to stop you from using a sperate filament PT for the heaters of the KTs!
Even 40 watts RMS can cover clean power needs thru 2 or more 12" drivers with SPL ratings of 96 db or better.

[lord preset]

Thanks. I was mainly concerned about heater current. Given the size of the PT I was perhaps rashly assuming that B+ current wouldn't be an issue. A filament transformer is always an option. The other major unknown for me is whether the OT will play well with a pair of KT88s. I've been searching about but I haven't figured out what primary impedance a pair of KT-88s running at 700v/350v would want to see. Tube data sheets don't address that application. KT-88s and 6L6GCs are not generally thought of as interchangeable re plate loads but the OT has 4 and 8 ohm taps to play with if adjusting speaker impedance could bring things into the proper range.