The Valhalla power amplifier project

[jane]

The Valhalla power amplifier project:

A conservative rated 2x75w power amp with DC-coupled output driver stage and Mullard topology input board. PTs will be Hammond, OPT Sowter UN70 (8 ohms versions of the U070) and for coupling caps I will use Cardas and some old Phillips "mustard" caps. All resistors, except for 1W+ will be NOS Phillips carbon film.

A short walk through: Input stage will feed 60-70v p-p (maximum) into the first driver tube, a 6SN7. This tube will do 2.5x amplification and is supported with local NFB for linearity. Next is a cathode follower, the driver for the output tubes, this 6SN7 is DC-couplet to the KT88s. Hopefully--this will prevent blocking.

The amp will be build into two separate 19" chassis, one for the power supply and one for the amp. The chassis will be painted in a camouflage color scheme; black, dark brown and olive green. Any text will be in yellow stencil fonts.

All the chassis work will we done in Canada by Mapletree Audio Design. The input board is also from MAD, it's a modified version of Lloyd Peppard's Special Red Driver for the Dynaco ST70. The final assembling work and testing will be done here in Norway.

Please, wish me luck

[jane]

Ugh, I forgot to include the schematics.
Here it is:

[aletheian]

That's quite an undertaking! Good luck man. BTW, is that a UO70 or a UA70 output tranny? I have never heard of a UN70.

And what's the Zout of your first stage looking like, if you don't mind me asking? Looks like somwhere around 90K... just a rough guess.

[aletheian]

I tried to view your webpace through a Norewgian to English translator... comes out kinda funny:

"Entire step am except elektrolytter in signalveien. Koblingskondensatorene am Auricula and Cardas. Resistance am easily admixture between carbon composition (NOS Phillips) and metall movie for 2W and other effektmotstander."

I'll definately try out those 2W metall movies in my effektmotstander.

[jane]

Originally posted by aletheian
That's quite an undertaking! Good luck man. BTW, is that a UO70 or a UA70 output tranny? I have never heard of a UN70.

And what's the Zout of your first stage looking like, if you don't mind me asking? Looks like somwhere around 90K... just a rough guess.

Thanks aletheian

The OPT (UN70) is a drop through style 8 ohms custom version of the Sowter U070.

Rout, if you are talking about the LTP is not far away from your guess. Rp||rp (150k||60k)=42k, I believe.

[jane]

Originally posted by aletheian
I tried to view your webpace through a Norewgian to English translator... comes out kinda funny:

"Entire step am except elektrolytter in signalveien. Koblingskondensatorene am Auricula and Cardas. Resistance am easily admixture between carbon composition (NOS Phillips) and metall movie for 2W and other effektmotstander."

I'll definately try out those 2W metall movies in my effektmotstander.

Norwegian is a funny language...

Yes, I'm writing a "blog" about the project progress.
Well, the pictures tells the story, more than the strange language, I'll guess..

[aletheian]

Originally posted by jane



Norwegian is a funny language...

Yes, I'm writing a "blog" about the project progress.
Well, the pictures tells the story, more than the strange language, I'll guess..

Yeah, the translator translates "tubes" as "pipes" and "film" as "movie" prety funny, but for the most part I can figure it out.

I have some friends from Norway. Their sense of houmer is strange. They don't understand why hyperbolie is funny, and they take sarcastic statements as literal. So if they do something extrordinary and I say "man, that sucked" as a joke... being funny beacuse it is obvious that it did not suck, but rather it was very good. In America, that is funny, but they get insulted until you tell them that you were joking.

Seeing Norwigans watch "The Simpsons" was one of the funniest experiences of my life. They just stared at the TV and shook their heads.

[jane]

Yesterday the power supply chassis arrived from Canada.
I have all the time since I decided to use a camouflage paint scheme wondered what it would look like. I think the result is quite impressive. With the big clocks on the front panel, it looks like an illegal radio transmitter from WW2, very authentic. The only thing that is missing are some scratches here and there...
Maybe I'll use black hex nuts instead of machine screws.





Honour to Mapletree Audio Design for the artwork! I have never dared to do such a job for any customer.

[Cassiel]

it looks like an illegal radio transmitter from WW2,

COOL!!!!!!

[Cassiel]

Jane i was looking at your schematic and liked the way you get your bias voltage. I need also -140 for a PP 6v6 i am building. If i copy your idea i wouldn't have to search for a 120 ac transformer, but i am not sure if it will work in my amp. Here's the schematic:

http://www.audiotropic.net/Projects/mmPow.html