Millett "Starving Student" hybrid amp
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livewire

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Hello all!
I'm kind of late to the party, I've been lurking the past few days reading this fine thread.
So far, I've only digested 175 pages, about half. Whew this is a long read!
Got all of the parts together to do this build, scrounged an old finned heatpipe cpu cooler
from the junk parts bin to put up top for the fets. Below is a blurry pic of the mock-up,
hope to have it wired this weekend. Wish me luck!
 
BTW as an intro, I love all things audio.
My hobby is restoring 1920's - 1950's tube radios and 1960's - 1970's stereo receivers.
Just did a Marantz 2275, at the moment I'm rebuilding a 1963 Sansui 1000.
 

 
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Beftus

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Nice looking case you got there. Love the CPU cooler. Well done!
 
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the_equalizer

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Quote:
SNIP  
My hobby is restoring 1920's - 1950's tube radios
 
SNIP
 
 
 
I used to do that back in my early twenties!   I still have a (working) 1940's Pilot tube radio in my living room, with a lovely Art Deco bakelite case
 
Your 'mock-up' looks great !  It seems to me that you managed to get your hands on a couple of the coveted 19J6 tubes? 
 
Given your background in electronics I'm not sure you need any luck to get this little amp working! And please post pics of your built and working amp !
 
cheers
 
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livewire

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Quote:Originally Posted by the_equalizer /img/forum/go_quote.gif


 
It seems to me that you managed to get your hands on a couple of the coveted 19J6 tubes? 
 
 
Funny you mention that!
What a mixed bag that was. So far, the "hardest part" of this build.
Let's see, Antique Electronic Supply had one left at the "old" price of $1.10,
(or maybe they were limiting what one could order?) I snapped that one up.
The next guy I contacted has them in stock advertised at $10 each.
So I contacted him and he says that the going price is now $20 each + $10 shipping.
No thank you. Sheesh! I can find them on fleabay for that price.
The last guy I contacted only had two left in stock at $10 each, so I bought those as well.
They all seem like new old stock in the original boxes, mixed bag, no matching.
Two D-ring getters and one halo. I hope they work, they test good on my B&K tube tester.




 
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livewire

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Quote:
Nice looking case you got there. Love the CPU cooler. Well done!


Thank you!
I'll post more pics next week when it is done. (and hopefuly working) 
The aluminum case will be painted with a "granite look" finish.
 
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Beftus

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Quote:
I hope they work


 

In the event that they don't work you can modify if and make the 12AU7 version. My 12AU7 version sounds delightful. While 12AU7 tubes aren't the cheapest tubes around, they are very easily sourced. The 12AU7 version also allows you to play with higher gain tubes from the same 12A.7 family. The 19J6 is a bit of a dead end street as finding them becomes difficult and should you have found them prices are very high.
 
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Ikarios

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Quote:
In the event that they don't work you can modify if and make the 12AU7 version. My 12AU7 version sounds delightful. While 12AU7 tubes aren't the cheapest tubes around, they are very easily sourced. The 12AU7 version also allows you to play with higher gain tubes from the same 12A.7 family. The 19J6 is a bit of a dead end street as finding them becomes difficult and should you have found them prices are very high.

also apparently, the 12AU7 mod can also swap in 17EW8 tubes (which ARE cheap) with apparently no modification. I plan on trying it at some point down the road when my finances are a little more free and I have a way to get tubes without getting charged for shipping.
 
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the_equalizer

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Quote:
also apparently, the 12AU7 mod can also swap in 17EW8 tubes (which ARE cheap) with apparently no modification. I plan on trying it at some point down the road when my finances are a little more free and I have a way to get tubes without getting charged for shipping.
 
That is correct, another builder tried it and reported it worked. I then tested in my build and indeed it works.
 
cheers!
 
 
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Beftus

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For the 17EW8 mod, shouldn't R2 and R8 be around 250K - 260K? In practice this could be a 270K resistor. Correct?
 
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vrenlos

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I just found one hell of a score of NOS tubes buried in my lab at work, does anyone happen to have a list of tube models that have been tried/verified working?  I was trying to look through but 360+ pages is a lot to comb.
 
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vrenlos

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Excellent, thanks.  I'm going to cart these home over the next few days and I'll try to catalog what I've got.  I'm pretty sure I saw a handful of 12AT7's, but there's probably a total of a few hundred to look through.
 
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Beftus

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Tubes you don't need/want or have in adundance could be sold here... 

 
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vrenlos

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Very true...also found two old tube testers - one from circa 1946 and another from probably 60-70's with updated charts for testing.  Both work.
 
It's probably going to take me a few days to haul most of this stuff home but I'll catalog it all and let everyone know what I've got.  As of now I see plenty of 12AU7's and 12AT7's.
 
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the_equalizer

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Quote:
For the 17EW8 mod, shouldn't R2 and R8 be around 250K - 260K? In practice this could be a 270K resistor. Correct?

Technically yes, it should be a ~250K ohm; but the 220K value of the 19J6 version does nicely.  A 270K will work too, after all, it works with the 390K that a 12A_7 version uses.
 
cheers!
 
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