"Fiddy" 50-watt build log
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"Fiddy" 50-watt build log
Fine, I admit to being a masochist: I am deviating from existing layouts and schematics, which leads to Questions, Problems, and Hair Pulling. But hopefully ends in Solutions and pride in a job well done. We'll see.
I'm launching another "beaks and feet" build, meaning I'm using parts from the bin, donated transformers, a cheap Weber chassis, and a pine head box I'll build myself. The last one, 18 Bone Monkey, came out really well, and is a favorite of mine.
I'm aiming at a 50-watt, EL34 powered, Plexi Lead 1987, parallel/cascading mashup. Because the Weber chassis is weird, I'm modifying the layout to fit, and I have been looking at Hiwatt builds for inspiration.
My layout so far is attached. I use Adobe Illustrator, in case anyone wants the parts, which I've drawn to scale.
I'm launching another "beaks and feet" build, meaning I'm using parts from the bin, donated transformers, a cheap Weber chassis, and a pine head box I'll build myself. The last one, 18 Bone Monkey, came out really well, and is a favorite of mine.
I'm aiming at a 50-watt, EL34 powered, Plexi Lead 1987, parallel/cascading mashup. Because the Weber chassis is weird, I'm modifying the layout to fit, and I have been looking at Hiwatt builds for inspiration.
My layout so far is attached. I use Adobe Illustrator, in case anyone wants the parts, which I've drawn to scale.
You do not have the required permissions to view the files attached to this post.
Re: "Fiddy" 50-watt build log
Looks good. I did a 6V6 Plexi with a parallel/cascade switch and it was a great sounding amp. I like your alternate layout where V1 and V2 are up front. It will make for less risk of oscillation in cascade mode with the runs being much shorter and more direct. The zone around the mixing resistors can be microphonic in traditional builds (in cascade mode) so the way you've shown it is nice and discreet. No need for long shielded runs; should sound really good.
Re: "Fiddy" 50-watt build log
Refined layout, proofread, and staked turret board.
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Re: "Fiddy" 50-watt build log
Nice layout idea!
Is that being built on the 6MX chassis from Weber?
[img:500:233]https://taweber.powweb.com/store/chassis/6mxch.jpg[/img]
4 octal, 2-9 pin socket holes. .090" aluminum chassis
1 Channel, 2 Inputs, Nine 3/8" control holes, PWR, STBY, Pilot Lamp
Generic 50 to 100 watt head chassis. Same size as a standard '45 chassis. Standup PT and OT with large grommet holes to fit just about any transformer wiring.
PT and OT foot mounting holes are slotted. Also includes mounting for choke. Mounting holes provided for 2-1/2" by 10" fiber board.
Output tube socket holes are positioned to accept 6L6's, 6V6's, EL34's, KT66's, and KT88's.
*
Is that being built on the 6MX chassis from Weber?
[img:500:233]https://taweber.powweb.com/store/chassis/6mxch.jpg[/img]
4 octal, 2-9 pin socket holes. .090" aluminum chassis
1 Channel, 2 Inputs, Nine 3/8" control holes, PWR, STBY, Pilot Lamp
Generic 50 to 100 watt head chassis. Same size as a standard '45 chassis. Standup PT and OT with large grommet holes to fit just about any transformer wiring.
PT and OT foot mounting holes are slotted. Also includes mounting for choke. Mounting holes provided for 2-1/2" by 10" fiber board.
Output tube socket holes are positioned to accept 6L6's, 6V6's, EL34's, KT66's, and KT88's.
*
Last edited by topbrent on Thu Sep 06, 2012 11:05 pm, edited 1 time in total.
dealer: allparts, weber, antique electronic supply
Re: "Fiddy" 50-watt build log
I used that chassis for my Matchless Lightning build not the best for what I needed but it worked.
Mark
Mark
Re: "Fiddy" 50-watt build log
Yes, that's the Weber 6Mx chassis. Only $30 plus shipping!
Got all the parts mounted today; took a lot of work drilling, milling, and Skilling. Check out the custom PT brackets! Yah!
Got all the parts mounted today; took a lot of work drilling, milling, and Skilling. Check out the custom PT brackets! Yah!
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Re: "Fiddy" 50-watt build log
Got the board all soldered up. BUT I accidentally ordered a bunch of 0.0022uF caps, instead of 0.022uF. Damn. Now I have to wait for replacements.
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Re: "Fiddy" 50-watt build log
Board mounted.
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Re: "Fiddy" 50-watt build log
I hate when that happens.xtian wrote:Got the board all soldered up. BUT I accidentally ordered a bunch of 0.0022uF caps, instead of 0.022uF. Damn. Now I have to wait for replacements.
I got a bunch of extra parts like that.
Nice looking build!
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: "Fiddy" 50-watt build log
All parts in, all wired up. Have not proofed yet. Gotta rest my brain hole.
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Re: "Fiddy" 50-watt build log
Nice job.
I have a couple of those 6MX chassis hanging around, waiting for a project
to develop. Couldn't resist the price.
I built a D'Lite into a Natalie chassis, similar size as 6MX, and it is
very crowded, so there's a limit to what you can do.
Good luck with it.
Love the attitude-hmmmm, let's try this.
I have a couple of those 6MX chassis hanging around, waiting for a project
to develop. Couldn't resist the price.
I built a D'Lite into a Natalie chassis, similar size as 6MX, and it is
very crowded, so there's a limit to what you can do.
Good luck with it.
Love the attitude-hmmmm, let's try this.
Re: "Fiddy" 50-watt build log
Fiddy lives! Breathes fire! Almost literally!
Tubes are running very hot. One (crappy old mismatched one) started to red plate.
I've got 460vdc plate voltage, and 60mV across the 1ohm resistor at the cathodes. Bias calc tells me I want about 35mV. But I cannot turn the current down any further with my bias adjustment pot.
So, I'm looking at the 47K resistor in series with the bias pot. I think I want to INCREASE the value of this resistor in order to allow the bias voltage to be more negative, thus DECREASING the current through the power tubes. Did I get that right?
Here is my voltage chart:
Tubes are running very hot. One (crappy old mismatched one) started to red plate.
I've got 460vdc plate voltage, and 60mV across the 1ohm resistor at the cathodes. Bias calc tells me I want about 35mV. But I cannot turn the current down any further with my bias adjustment pot.
So, I'm looking at the 47K resistor in series with the bias pot. I think I want to INCREASE the value of this resistor in order to allow the bias voltage to be more negative, thus DECREASING the current through the power tubes. Did I get that right?
Here is my voltage chart:
Code: Select all
1 2 3 6 7 8
V1 169 0 1.07 210 0 1.8
V2 180 0 1.11 286 180 181
V3 222 44 68.5 220 43.6 68.5
1+8 3 4 5
V4 .045 465 461 -40.5
V5 .060 465 458 -40.6
B+ = 468
wall AC = 120
- martin manning
- Posts: 13335
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: "Fiddy" 50-watt build log
Ya you got that right, or you could decrease the resistor right off the HT.
Re: "Fiddy" 50-watt build log
The simplest thing to try is to tack in another resistor in parallel to the one off the HT before the diode. Once you see the result of that, even if it's not right, you can pretty well guess from there a value that will produce the result you want.
Re: "Fiddy" 50-watt build log
Nailed it. Had to try a couple different values, but 75K is right on the button. A matched pair of Mesa Boogie EL34s now easily biases at 32ma.
So finally I got to play a little, quietly. First: WOW! Awesome! This build is extremely quiet. No hum, barely any hiss. LarMar master is excellent.
I put in a parallel/cascade switch (basically the "one wire mod"). In normal (stock) mode, opening both Volume pots and turning the Master way down to bedroom levels, the gain is what I'd call HIGH gain. And with the cascade switch thrown, the gain is literally overwhelming--I have to turn the Vol pots down to about 75% to avoid runaway oscillation and blocking distortion.
Will have to wait until house is empty tomorrow to see how much clean headroom is available. Will report.
Color me extremely self satisfied.
So finally I got to play a little, quietly. First: WOW! Awesome! This build is extremely quiet. No hum, barely any hiss. LarMar master is excellent.
I put in a parallel/cascade switch (basically the "one wire mod"). In normal (stock) mode, opening both Volume pots and turning the Master way down to bedroom levels, the gain is what I'd call HIGH gain. And with the cascade switch thrown, the gain is literally overwhelming--I have to turn the Vol pots down to about 75% to avoid runaway oscillation and blocking distortion.
Will have to wait until house is empty tomorrow to see how much clean headroom is available. Will report.
Color me extremely self satisfied.