Bass Amp for a friend

[Guy77]

Hi Dave. I was also leaning towards Svetlana (new production). I was leasing to a shootout on Youtube between the JJs and Svetlana and I preferred the openness of the Svetlana 6550C over the darker sounding JJ.
Thanks!

Guy

[Colossal]

Hi Dave. I was also leaning towards Svetlana (new production). I was leasing to a shootout on Youtube between the JJs and Svetlana and I preferred the openness of the Svetlana 6550C over the darker sounding JJ.
Thanks!

Guy

I want to give the Gold Lions a try, as TubeDude suggested, but in another amp. I like the Gold Lion KT66s. Right, I think open is a good way to describe the Svetlanas. It's a great sound. Rich and warm and clear, but not strident, harsh or "forward" sounding (at least with this bass amp).

Dave

[pompeiisneaks]

Most definitely. That amp will destroy the world and surely if the Higg's Boson was not discovered at CERN, it will be confirmed with that GU-50 amp.

Just call it the Higgs Boson Destroyer



~Phil

[Reeltarded]

and choose inner for tubes.. inner... tubes. that head is a tube top. those speakers make the bottom end..

lets cll this thing T3h PuN

[roberto]

Hi Dave,

what is the current rating of the anode power supply?
The amp is supposed, with 450V B+ and 2k2 on a quad of 6550 with 40% UL, to go up to around 750 mA peak.
I don't remember if we talked about it, but I think you have designed it to have a bit of sag on full power.

[Colossal]

Hi Dave,

what is the current rating of the anode power supply?
The amp is supposed, with 450V B+ and 2k2 on a quad of 6550 with 40% UL, to go up to around 750 mA peak.
I don't remember if we talked about it, but I think you have designed it to have a bit of sag on full power.

Hi Roberto,

Yes, the entire DC power supply is CLC filtered; 100uF - 10H/31R - 100uF and if current is suddenly tripled, the rail is pulled down hard, so this should limit the stress on the PT. I wanted very low ripple from the start since the OT is U/L. The choke is about the size of a 50W Plexi OT. The tubes idle at 50mA with the AB2 driver, this worked out to something like -48V on the grids. It was over engineered and I think the secondary is rated to 750mA (IIRC?). The amp was, in fact, in for service yesterday and that new quad of Svetlana 6550s finally got installed. I have not gotten any of the voltages from the tech, but it got a clean bill of health.

It was my friend's 50th birthday yesterday and after getting the amp serviced and back home, he said:
"Been playing for an hour. This amp is responsive AF! It literally produces EXACTLY what you play — f-ups included. That Rumble 100 is a LOT less articulate."

[Roe]

A schematic would be great!

[Colossal]

A schematic would be great!

Here is the schematic

Bass Amp For A Friend.pdf

[roberto]

Nice! So the AB2 is not really to go into AB2, because the pentode won't go much deeper than 50V, but to avoid blocking distortion.
It should have around 150W, is it correct?

6550 43UL 450B+ 4k4Raa.png

[Colossal]

Nice! So the AB2 is not really to go into AB2, because the pentode won't go much deeper than 50V, but to avoid blocking distortion.
It should have around 150W, is it correct?

6550 43UL 450B+ 4k4Raa.png

Hi Roberto,

Yes, I don't think it will ever get to AB2, the power supply should limit that, but yes, you can definitely hear the increased bandwidth of the U/L output and the driver stage. It's very, very present but not strident. I didn't bother with a Presence control as U/L is a type of NFB and the amp is fine without it. The tone stack is quite effective. Yes, I think I estimated 140Wrms.

[Roe]

A schematic would be great!

Here is the schematic


Bass Amp For A Friend.pdf

thanks! looks pretty impressive
PS: any idea how much the HTS-7475 might cost?

[roberto]

Thanks Dave,

I like it! I actually do dc coupled driving of the output tubes with mosfets ccs loaded, and I really appreciate their effect on the sound.

On the other side I prefer lower UL percentages used together with other local feedback methods, because you can squeeze some more watts and still keep the sinplicity of the UL to supply screens.

UL is a great feature for bass amps, and the lack of gnfb plus the triodized curves give a nice overdrive behaviour to the amp.

[Colossal]

thanks! looks pretty impressive
PS: any idea how much the HTS-7475 might cost?

Hi Roe,

I'm sorry, I can't remember what that transformer cost (maybe $250US?). You can email Phil or Arlen at Heyboer and they will give you a quote. It weighs about 12kg!

[Colossal]

Thanks Dave,

I like it! I actually do dc coupled driving of the output tubes with mosfets ccs loaded, and I really appreciate their effect on the sound.

On the other side I prefer lower UL percentages used together with other local feedback methods, because you can squeeze some more watts and still keep the sinplicity of the UL to supply screens.

UL is a great feature for bass amps, and the lack of gnfb plus the triodized curves give a nice overdrive behaviour to the amp.

I'm quite happy with how it came out. I played guitar through the amp and two Thiele cabs and it's just massive. Probably too much! For bass though, yes, you are right. It sounds great. Very clear and articulate, but still warm and rich.

[ViperDoc]

Always looked forward to seeing that. Very cool!