Millett "Starving Student" hybrid amp
Apr 15, 2010 at 2:06 PM Post #5,131 of 7,269

the_equalizer

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Quote:

Originally Posted by fogmachine /img/forum/go_quote.gif
it just made sense, if your planning on building something like this and there is that much help, suggestions, issues etc all ready documented, make the most of them or at least use the search function and stop asking the same questions over and over again! tbh i'm surprised some of you are still replying to some of the questions that have been asked soo many times already.
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I agree... but still nearly 350 pages !!


Quote:

Originally Posted by fogmachine /img/forum/go_quote.gif
</snip>
right back to the breadboards, got a birdsnest to unpick, looking forward to see how much the 12sr7gt glow, both 12au7 and 12ax7s dont glow nearly as much at the 19j6's, but of couse its not all about how it looks
biggrin.gif


cheers for the help, my initial guess was to ground them, but is always good to check. thank you head-fi'ers



No problem... so I take it you've already built prototypes with those three other tubes?

cheers!
 
Apr 15, 2010 at 2:21 PM Post #5,132 of 7,269

the_equalizer

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Quote:

Originally Posted by fogmachine /img/forum/go_quote.gif
wicked, works just great


Nice! hmmm... no tube sockets ?
 
Apr 15, 2010 at 3:49 PM Post #5,133 of 7,269

fogmachine

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Quote:

Originally Posted by the_equalizer /img/forum/go_quote.gif
Nice! hmmm... no tube sockets ?


ha, i knew if i started posting pics i'd get some questions about it, trying to keep it as a little surprise as i've put quite alot of work into the chassis so far, and if all goes to plan will be looking very nice. the 12sr7gt's are in sockets but due to their long pins they happily slot in the socket via a piece of acrylic, the socket will be mounted from the underside, the brackets on them are easily prized off and flipped around to make this possible, been running it fairly hot for a couple of hours now and the acrylic isnt even slightly warm either side, so seems safe enough.

the only down side is that i dont think you can mount a led in the middle of the socket due to the central pin of the valve. correct me if i'm wrong but this central pin is purely for the orientation of the valve, has anyone ever drilled into this? would love to see if you could stick an led in it but dont fancy ruining my valves as they all still work! - anyone got any old dead ones they fancy sticking a drill bit in?

cheers ears
 
Apr 19, 2010 at 4:05 AM Post #5,134 of 7,269

c12mech

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the equalizer,

In your 17ew8 mod, are all the caps electrolytics? In the original I thought that c2 and c4 were film. I'm ordering parts this week to start this along with several other projects and just want to make sure I've got it all right. I'm going to try my hand at building the power supply for this also.

Thanks,
Bryant
 
Apr 19, 2010 at 4:06 AM Post #5,135 of 7,269

c12mech

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the equalizer,

In your 17ew8 mod, are all the caps electrolytics? In the original I thought that c2 and c4 were film. I'm ordering parts this week to start this along with several other projects and just want to make sure I've got it all right. I'm going to try my hand at building the power supply for this also.

Thanks,
Bryant
 
Apr 19, 2010 at 11:28 AM Post #5,136 of 7,269

the_equalizer

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Quote:

Originally Posted by c12mech /img/forum/go_quote.gif
the equalizer,

In your 17ew8 mod, are all the caps electrolytics? In the original I thought that c2 and c4 were film. I'm ordering parts this week to start this along with several other projects and just want to make sure I've got it all right. I'm going to try my hand at building the power supply for this also.

Thanks,
Bryant



Hello Bryant,

C2 and C4 are film caps indeed. You can either use the original value in Pete Millett's BOM (0.1 uF) or the value set by Dsavitsk's modified BOM ( 0.22 uF ).

cheers!
 
Apr 20, 2010 at 6:56 AM Post #5,137 of 7,269

blippster

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Finished a 12AU7 version last week in a recycled Hammond case, after missing the old 19J6 version I built and sold enough to give this a second spin. 12AU7s are a lot more widely available, so I won't have to ditch this amp for a fear of lack of tubes again.

Had a couple of failed attempts along the way until traced the problem to the MOSFETs not working and so preventing the heaters from coming up. One had a failed gate and the drain leg of the other broke off before I could figure out what was wrong. Using Cerafines gave a ~1V DC offset at the output at first, until switching to Nichicon KWs solved the problem.

The increased 7-volt drop does seem to make the amp run hotter, but manageably so with the Aavids - though the case was heating up much faster that the sinks until the application of thermal paste.

Have a pair of 17EW8s that should (hopefully) be on the way, so will try those when they arrive. In the meantime though, thank you to the_equalizer for providing the impetus to come back to this.

ssmh-12au7-f.jpg

ssmh-12au7-r.jpg
 
Apr 20, 2010 at 6:23 PM Post #5,139 of 7,269

the_equalizer

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Very nice job, indeed!
smily_headphones1.gif


Question: if the on/off switch is in the back of the unit, what does that red-tipped switch in the front panel do?

Remember that even though you can directly plug 17EW8's in place of the 12AU7's, their higher heater voltage requires to change R2 and R8 = 220 Kohms

I'd love to read your impressions on both the 12AU7 and 17EW8 versions.
smily_headphones1.gif


cheers!
 
Apr 20, 2010 at 7:06 PM Post #5,140 of 7,269

Juaquin

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Quote:

Originally Posted by the_equalizer /img/forum/go_quote.gif
Question: if the on/off switch is in the back of the unit, what does that red-tipped switch in the front panel do?


It looks like there's two inputs on the back, possibly source select.
 
Apr 21, 2010 at 12:33 AM Post #5,141 of 7,269

blippster

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Thank you tomb. Your SSMH site was very useful when deciding how to construct it, and the suggested heatsinks were nice big ones that didn't look ugly..
smile.gif


Quote:

Originally Posted by the_equalizer /img/forum/go_quote.gif
Question: if the on/off switch is in the back of the unit, what does that red-tipped switch in the front panel do?

Remember that even though you can directly plug 17EW8's in place of the 12AU7's, their higher heater voltage requires to change R2 and R8 = 220 Kohms

I'd love to read your impressions on both the 12AU7 and 17EW8 versions.
smily_headphones1.gif



The front switch is a DPDT for mute, connected after the output capacitors to the 2K dummy load, so they can charge without needing to the headphones. Wait a bit and flick the switch - no pop!

I'll probably wire up an internal DPDT for switching between the 17EW8s and the 12AU7s following your suggestion a bit back, but for now that's a moot point until the postal service brings those tubes over
rolleyes.gif
 
Apr 21, 2010 at 3:16 AM Post #5,142 of 7,269

the_equalizer

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Quote:

Originally Posted by blippster /img/forum/go_quote.gif
<snip>
The front switch is a DPDT for mute, connected after the output capacitors to the 2K dummy load, so they can charge without needing to the headphones. Wait a bit and flick the switch - no pop!

I'll probably wire up an internal DPDT for switching between the 17EW8s and the 12AU7s following your suggestion a bit back, but for now that's a moot point until the postal service brings those tubes over
rolleyes.gif



Cool, kind of like the 'Standby' switch on old Fender tube amps.

Enjoy!
 
Apr 21, 2010 at 7:48 AM Post #5,143 of 7,269

m11a1

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Hey Equalizer,

You have mentioned many times that you especially love the sound of the K701 coupled with the SSMH. However, have you tried the K701 with the MiniMax? I'm thinking about building a MiniMax but I'm not sure how much of an upgrade it truly is.

Thanks
 
Apr 21, 2010 at 3:27 PM Post #5,144 of 7,269

the_equalizer

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Quote:

Originally Posted by m11a1 /img/forum/go_quote.gif
Hey Equalizer,

You have mentioned many times that you especially love the sound of the K701 coupled with the SSMH. However, have you tried the K701 with the MiniMax? I'm thinking about building a MiniMax but I'm not sure how much of an upgrade it truly is.

Thanks



Yes, I do own a MiniMAX. I'll respond in PM with my impressions on these two amps.

cheers!
 
Apr 21, 2010 at 6:33 PM Post #5,145 of 7,269

c12mech

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I'm finally getting all the parts together for this build. I found a power supply on evilbay yesterday.

Would there be any issues with mounting the power supply in the enclosure and just wiring in direct instead of using the plug? I'm not sure about heat dissipation of the PS. Just a thought. I'll be making my own enclosure, so size is not a problem.

the equalizer,
I would like to here what you have to say about the K701's also since the MilletMax is most likely next on the list. I'm planning on picking up some K701's in the next week or so.
 

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