100 watt Super Bass with KT88’s

[wpaulvogel]

Here’s a new one I just finished. It’s the best sounding 100 watt I’ve heard.

[statorvane]

Very nice looking and original head!

[harleytech]

Very Nice...

[Thermionic/EL-34]

The 88's seem small these days, maybe its just me.

I remember the Marshall Majors they looked huge.

Did you use Merren or Heyboer iron by chance ?

[wpaulvogel]

It’s a Merren C1998 output and C1999 choke. Used a Hammond 100 watt JMP power transformer

[Thermionic/EL-34]

Merren/Heyboer/Hammond all great stuff.

[ViperDoc]

That’s gorgeous.

[norburybrook]

that's a sweet build. Lovely lead dress and soldering is perfect My JTM45 is a similar colour scheme


M

[ViperDoc]

How do you keep the 4 x KT88s to 100 W?

[pompeiisneaks]

Probably based upon how they're biased. If you bias them to 60% of max diss then they'll be at a lower output wattage. design max for KT88 is supposed to be like 35W. (per tube.)

35 * .6 = 21W which is about 84 watts... often the terms of wattage that get thrown around aren't super accurate.

A 100 W marshall with 4xel34's is supposed to be 'max diss' of 25W per tube. That would mean running at 100W for 4xEL34 is at maximum dissipation which is going to kill the tubes pretty fast.

Actual normal settings are more valuable in understanding 'real' wattage output.

Take a JCM800, they usually run around 450-470 on the plates.

(voltages taken from Mhuss' site: https://mhuss.com/MyJCM/JCM800_2204.pdf)

if the plate current from a bias calculator for EL34's at that voltage to be say 60% diss gives us: 33.3 mA per tube..

Ohms law says:

450 * .0333 = 15 watts per tube, so 4x15 = 60 watts output at that point. not 100W... I think the marketing of those amps was like 'max this can do is 100W because the datasheets say so!" even though the amp would never be able to do that.

even if you biased it to near 100% and the tubes weren't red-plating, the distortion of most guitar amps kicks in well before you can get the full 100% output volume/power before you start clipping (amp wattage is measured at maximum output still clean/non distorting).

I believe the above to be a good assessment of this from my understanding of output wattage, but, I'm also only about 4 years into building amps and I often get things wrong so take that with a grain of salt lol.

~Phil

[dorrisant]

Very slick and clean looking.

Gonna post any clips?

[wpaulvogel]

This amp is biased at 69% of 42 watts (29 watts per tube). Plate voltage at 65mA per tube is 450 volts. I think it’s the output transformer impedance that limits the output power to 110-112 watts clean RMS (42.5 volts on a 16 ohm dummy load) with the KT88’s. Although they chugged up there to a maximum of 57.6 volts (208 watts). It’s an impressive amp.

[Roe]

This amp is biased at 69% of 42 watts (29 watts per tube). Plate voltage at 65mA per tube is 450 volts. I think it’s the output transformer impedance that limits the output power to 110-112 watts clean RMS (42.5 volts on a 16 ohm dummy load) with the KT88’s. Although they chugged up there to a maximum of 57.6 volts (208 watts). It’s an impressive amp.

the PTs sag a lot normally, they are rated for 290-300mA typically.

[ViperDoc]

This amp is biased at 69% of 42 watts (29 watts per tube). Plate voltage at 65mA per tube is 450 volts. I think it’s the output transformer impedance that limits the output power to 110-112 watts clean RMS (42.5 volts on a 16 ohm dummy load) with the KT88’s. Although they chugged up there to a maximum of 57.6 volts (208 watts). It’s an impressive amp.

I (likely meaning anyone on this site as well!) would love to hear this amp. Looks very nice!

[wpaulvogel]

This amp is biased at 69% of 42 watts (29 watts per tube). Plate voltage at 65mA per tube is 450 volts. I think it’s the output transformer impedance that limits the output power to 110-112 watts clean RMS (42.5 volts on a 16 ohm dummy load) with the KT88’s. Although they chugged up there to a maximum of 57.6 volts (208 watts). It’s an impressive amp.

I (likely meaning anyone on this site as well!) would love to hear this amp. Looks very nice!

https://youtu.be/XkHFhf0r6wY
https://soundcloud.com/vogel-instrument ... stratshort
https://soundcloud.com/vogel-instrument ... tstratlong