Welllllllll, after a whole rainy day of tinkering I now know a whole bunch more things that don't work. I got my output stage and PI up and running. It makes 15 watts with a real OPT.
Some of the budget transformers I tried couldn't make more than a watt or two without distorting badly. The Cheap P-P OPT from AES can do 12 watts which isn't bad since the real one that I used weighs 5 pounds. I found a tiny little power transformer that will make 8 watts, but the DC resistance is so high it starts smoking after an hour even at idle.
I had planned on using the N-68X for a power transformer but even though the Kill a Watt reads 44 VA the transformer is too hot to touch. If I switch to a choke input supply I go over budget and lose half of my power.
Time to rethink a few things.
Some of the budget transformers I tried couldn't make more than a watt or two without distorting badly. The Cheap P-P OPT from AES can do 12 watts which isn't bad since the real one that I used weighs 5 pounds. I found a tiny little power transformer that will make 8 watts, but the DC resistance is so high it starts smoking after an hour even at idle.
I had planned on using the N-68X for a power transformer but even though the Kill a Watt reads 44 VA the transformer is too hot to touch. If I switch to a choke input supply I go over budget and lose half of my power.
Time to rethink a few things.
I thought, I tested. Repeat.....The more I tinkered the worse things got. Before long my mighty amp was making 3 watts, I could get that out of the PI if I stuffed the right tube in there.......not a bad idea........
I decided to put it all back the way it was before I started messing with it. Crank the bias back up to what it takes to feed some hungry tubes. Power at clip is 14 watts and the Kill A Watt reads 65VA. Time to get a bigger transformer and rethink what I'll need to leave out to make budget.
So far this circuit is far too HiFi. I couldn't make a HiFi amp this cheap and this clean if I tried. At 5 watts the distortion is 0.85%, at 10 watts it is 1.8%.
OH, that was the little version.......The board with the plate capped sweep tubes hasn't been powered up yet. Don't think that one fits in the budget...yet, but I had time to kill while I was up north, so I laid it out anyway.
The $100 guitar amp thread interrupted my thoughts with respect to the 6P41S as a potential SE amp.
Tonight I finally got around to wiring up a servo to control the bias supply and flogged it to 8W out thorough an Edcor 3.5K opt with a B+= of 300V.
Glowing like a metal on the edge of a knife...
350 V b+ and the whole side begins to glow with an output of 9W.
The 2.5K opt does not do any better even thought the load line looked better.
Tonight I finally got around to wiring up a servo to control the bias supply and flogged it to 8W out thorough an Edcor 3.5K opt with a B+= of 300V.
Glowing like a metal on the edge of a knife...
350 V b+ and the whole side begins to glow with an output of 9W.
The 2.5K opt does not do any better even thought the load line looked better.
Gday Printer2,
Yeah it has a very smooth transition at breakup, it's not to bad for the first attempt from paper to actual circuit.
I am just running some more numbers to try to get it closer to what I want.
For myself I find it more useful to do the prototype work in a chassis, for safety & so there is little change in sound between say breadboarding or open circuit work on a bench to the actual finished thing in a chassis.
It never ceases to amaze me how things can change soundwise from a prototype on a bench to the actual finished thing in a chassis.
I have some new idea's I will try out with this circuit, just hope they work out ok.
How about some of you other builders put up some sound clips, as you can see the response is overwhelming haha!
Can't wait to hear some.
Cheers
My apologies wdcw. It seems my fingers messed up again. I can't seem to edit my message to fix my typo. Hence this post to correct my mistake.
Gday hunoz,
Yes this is a cheap solution to the problem of chassis, this is 150mm wide Galvinised Steel Purlin--used for sheds, roofs etc.
This piece is 150 X 350mm long & cost $4.00 or you can buy a 6Mtr length for $69.00 & cut it up which is what I do.
You Can get 100mm wide or 200mm etc & it's perfect for chassis.
No need to worry about typo's, I make plenty of mistakes.
Just remember-- VOTE for wdcw hahaha!
Hope this helps out.
Cheers
Thanks mate.
I just found it on the net too as your reply arrived. They got it in Williamstown which is a bit too far from here, but I hope they have it at Bunnings or some other building supply place closer to me. It sure looks good to me for chassis.
I too prefer to test my ideas as the finished product will be as I also found that parts placement can be critical to the final sound.
Voting for you? SURE thing! that is, if I like your project the most
Thanks mate.
I just found it on the net too as your reply arrived. They got it in Williamstown which is a bit too far from here, but I hope they have it at Bunnings or some other building supply place closer to me. It sure looks good to me for chassis.
I too prefer to test my ideas as the finished product will be as I also found that parts placement can be critical to the final sound.
Voting for you? SURE thing! that is, if I like your project the most
No problem glad to help out, steel merchants also sell it, shop around as prices vary a lot, you know what it's like.
Cheers
I'm after this fat, greasy tone. No success yet, dammit!!
1948 McKinney / Valco Supreme ( Supro ) guitar tube amp demo - YouTube
I believe this is the schematic:
Field coil speakers are used in that Valco, LOL, that is some old technology:
The Field-Coil Guitar Amplifier | Preservation Sound
The Field-Coil Guitar Amplifier | Preservation Sound
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I can get such tones, but I can't play so well! Damn!
Those old Valco's are mean, but its not a had tone to get either.
build a 5E3, LOL
Even with 6aq5's you can get that.
It defies all of the rules, split load PI, no negative feedback, plate voltages just over specs sheets.
Richter Tweed Deluxe - Tim Brundage - YouTube
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One possibility for those galvanized steel chassis is construction sites. A lot of steel is used in home construction now days and it might be possible to get scraps for free if you talk to the site foreman.
The 6P41S is proving to be a tank of a tube. I blew the bias servo circuit (Tried to run power-drive in addition to the providing power to the input stage for biasing). The MPS92 didn't like 20+ma at 100V. Once the bias went, the tube went for a run with .25A current at 250V. The plate took on a nice orange glow before I hit the breaker.
I'm putting it aside for now and going back to the 6F4P circuit.
The 6P41S is proving to be a tank of a tube. I blew the bias servo circuit (Tried to run power-drive in addition to the providing power to the input stage for biasing). The MPS92 didn't like 20+ma at 100V. Once the bias went, the tube went for a run with .25A current at 250V. The plate took on a nice orange glow before I hit the breaker.
I'm putting it aside for now and going back to the 6F4P circuit.
Because they ROCK.......the 6V6 sings the blues.......just my dummmazzz opinion.
Glad to see that I am not the only one that got some sand into my amp.
Yeah I have fried a few parts. Amp 1.0 blew up when I didn't like the sound so I spun the power supply knob to the right until it blew up. Turns out the 1/4 watt screen resistors did the job of saving the 150 volt tubes from nearly 400 volts. It's alive again but still sounds like #*^&. I think it has too many parts in it so it is becoming an exercize in Muntz design. Anyone here old enough to remember Mad Man Muntz TV sets.