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
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
Ugh, I forgot to include the schematics.
Here it is:
Here it is:
An externally hosted image should be here but it was not working when we last tested it.
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.
"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 said:
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.
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.
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.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Honour to Mapletree Audio Design for the artwork! I have never dared to do such a job for any customer.
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
http://www.audiotropic.net/Projects/mmPow.html
An externally hosted image should be here but it was not working when we last tested it.
Here is a pictures from the inside with some parts installed:
1: Black Gate filer caps bank
2: Tamura 14VDC heater transformer
3: Brackets for JJ filter caps
4: HEXFRED rectifiers
5: Voltage regulator for 12VDC heater.
6: Socket for soft start relay.
7: IEC 230v input
8: Octal socket for power output (2x6.3VAC, 12VDC, 560VDC, GND)
9: On/Stby LEDs
10: On/Stby switch
11: Power resistors, soft start.
12: Main fuse
13: Terminal strips
14: Stiffening
An externally hosted image should be here but it was not working when we last tested it.
Hi, I just can't get excited about another version of the 60's commercial amps. Loop NFB, Class AB2 operation...nothing all that special. Sort of like a Heathkit W6M. At least the Heathkits go for about what it would cost to buy the 16431 OPTx for.
May I suggest not selling to the same power hungry folks who will see a bigger number in the SS offerings, and go for instead those who would pay real money for an amp which delivers that which cannot easily be found.
Just my opinion, and I am sure it will sound OK. For the money you'll need to charge, I'd expect a bitmore than OK though.
cheers,
Douglas
May I suggest not selling to the same power hungry folks who will see a bigger number in the SS offerings, and go for instead those who would pay real money for an amp which delivers that which cannot easily be found.
Just my opinion, and I am sure it will sound OK. For the money you'll need to charge, I'd expect a bitmore than OK though.
cheers,
Douglas
Jane:
Speaking of Norway and just for grins, here's a picture of my son with our 6 toed, double jointed, Puffin hunting Norwegian Lundehund on the lake....
Nice amp project, where and how much $$ was that chassis work?
dr._sleep
Speaking of Norway and just for grins, here's a picture of my son with our 6 toed, double jointed, Puffin hunting Norwegian Lundehund on the lake....
An externally hosted image should be here but it was not working when we last tested it.
Nice amp project, where and how much $$ was that chassis work?
dr._sleep
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