Fairchild 670 DIY In Progress
- Thread starter CJ
- Start date
Help Support GroupDIY Audio Forum:
CJ
Well-known member
lead poisoning usually takes place by 2 am so i have to quit,
using the old kester 60/40 rosin core, thick, low melting point, have to re adjust solder method otherwise you get flooded tube sockets,
only way to clear a flooded pin is to heat up the solder inside and hit it quick with some contack cleaner, hold you breath, i do not know what henious chemicals are formed when contact cleaner hits a hot soldering iron, but it can't be good, one of the cans at radio shack was only 1/4 full, i asked the cash register guy who was huffin the cleaner and he gave me the stank eye so i left and did a quick hit off the new can in the parking lot, hey jus kidin,
GE 12BH&a came in, looks like a good match, almost the same code,
will pick up a JJ 34 thanks for that Volker!
oh, one trick for soldering with low temp solder is to put a junk tube in the 9 pin tube socket while you solder, this will heat sink the pin which means the solder will not flow down the pin as quickly and also the pins will block the solder and will not stick,
another good thing about the ground bus is that you can lay the heater wires down against the chassis instead of twisting them all over the tops of the tube sockets, those turrets would make that look real ugly anyway, so they sit on the chassis.
using the old kester 60/40 rosin core, thick, low melting point, have to re adjust solder method otherwise you get flooded tube sockets,
only way to clear a flooded pin is to heat up the solder inside and hit it quick with some contack cleaner, hold you breath, i do not know what henious chemicals are formed when contact cleaner hits a hot soldering iron, but it can't be good, one of the cans at radio shack was only 1/4 full, i asked the cash register guy who was huffin the cleaner and he gave me the stank eye so i left and did a quick hit off the new can in the parking lot, hey jus kidin,
GE 12BH&a came in, looks like a good match, almost the same code,
will pick up a JJ 34 thanks for that Volker!
oh, one trick for soldering with low temp solder is to put a junk tube in the 9 pin tube socket while you solder, this will heat sink the pin which means the solder will not flow down the pin as quickly and also the pins will block the solder and will not stick,
another good thing about the ground bus is that you can lay the heater wires down against the chassis instead of twisting them all over the tops of the tube sockets, those turrets would make that look real ugly anyway, so they sit on the chassis.
radiance
Well-known member
CJ said:
LOL!
CJ
Well-known member
ruairioflaherty
Well-known member
CJ said:what a project, i should have bought the plug in,
No, we should have bought you a video camera to document the build!
CJ
Well-known member
thanks! it is a fun chassis, no doh, everything else will seem like building a crystal radio set or something,
not much action so just a pic of the back, all the tube sockets but missing the utc and triad stuff,
there is a faceplate blueprint is on file in the docs section of drip, has all the dims and everything, however, there seems to be some drama with the VU meters, old ones read different, old ones were not VU but dc micrometers, etc,
old ones used copper disc diodes, i wonder if this could be the reason for the difference,
i found a cool resto link here:
http://www.youtube.com/watch?v=C-5iEBR1Ii4
vintage king
notice the bigger 12 henry choke as we are running the choke input transformer set,
i win the heaviest compressor award with the bigger choke,
should come in at about 65 and 1/2 pounds, or 2 lbs per db input level,
not much action so just a pic of the back, all the tube sockets but missing the utc and triad stuff,
there is a faceplate blueprint is on file in the docs section of drip, has all the dims and everything, however, there seems to be some drama with the VU meters, old ones read different, old ones were not VU but dc micrometers, etc,
old ones used copper disc diodes, i wonder if this could be the reason for the difference,
i found a cool resto link here:
http://www.youtube.com/watch?v=C-5iEBR1Ii4
vintage king
notice the bigger 12 henry choke as we are running the choke input transformer set,
i win the heaviest compressor award with the bigger choke,
should come in at about 65 and 1/2 pounds, or 2 lbs per db input level,
Attachments
Kid Squid
Well-known member
Absolutely blinding work CJ !!
You is the bomb, bro
Hope the herbals are keeping you sane !!!,
Steve
You is the bomb, bro
Hope the herbals are keeping you sane !!!,
Steve
CJ,
By my reckoning you are going to be paying ~$1200 for the 6386's if you get them from JJ, is that the plan?
There are posts in the forum where 6BA6's in triode mode are tested back to back on a valve tester and they came out practically the same, but they will need B7G sockets, so too late for that now.
Is the plan to sell it later?
It looks really nice work by the way.
best
DaveP
By my reckoning you are going to be paying ~$1200 for the 6386's if you get them from JJ, is that the plan?
There are posts in the forum where 6BA6's in triode mode are tested back to back on a valve tester and they came out practically the same, but they will need B7G sockets, so too late for that now.
Is the plan to sell it later?
It looks really nice work by the way.
best
DaveP
CJ
Well-known member
ok we have a 6.3 volt aux heater transformer installed,
this is for the power supply tubes, the el34 and the ef86,
the center tap of the xfmr is connected to a 100k/100k voltage divider, 240 volts cut in half is 120 dc, because the el34 cathode sits at 240 dc, so if the heater is 0, and the cathode is 240, so the cathode can become a plate and suck electrons off the heater, that is not good, so we get the heaters on the el34 up to 120 and hope for the best, the ef86 has it a bit easier, the cathode sits on the regulator tube at about 85 volts dc. so 120 is a compromise. the circuit is too busy already without adding another transformer to heat the tubes individually,
this is a UTC rated at 2 amps, el 34 draws 2 amps and then the ef86, but now days, the new stuff draws less heater current, more like 1.5 so i should be alright with the nice utc.
this location saves some wire, closer to the el 34 and ef86.
this is for the power supply tubes, the el34 and the ef86,
the center tap of the xfmr is connected to a 100k/100k voltage divider, 240 volts cut in half is 120 dc, because the el34 cathode sits at 240 dc, so if the heater is 0, and the cathode is 240, so the cathode can become a plate and suck electrons off the heater, that is not good, so we get the heaters on the el34 up to 120 and hope for the best, the ef86 has it a bit easier, the cathode sits on the regulator tube at about 85 volts dc. so 120 is a compromise. the circuit is too busy already without adding another transformer to heat the tubes individually,
this is a UTC rated at 2 amps, el 34 draws 2 amps and then the ef86, but now days, the new stuff draws less heater current, more like 1.5 so i should be alright with the nice utc.
this location saves some wire, closer to the el 34 and ef86.
Attachments
CJ
Well-known member
here is the transformer coming up thru the chassis, had to file the square hole, elbow is toast, that wood panel is coming off pretty soon, so i will have room to hook up the pri , the sec is hooked to the heaters, looking for a place to put the 2 watt 100K resistors for the heater elevator,
normally the 6.3 aux tranny sits on the bottom plate of the chassis near the time constant board, so putting it outside the chassis saves some space,
UTC A-26 on the way in,
normally the 6.3 aux tranny sits on the bottom plate of the chassis near the time constant board, so putting it outside the chassis saves some space,
UTC A-26 on the way in,
Attachments
okgb
Well-known member
Like the solid bus bar ! and the resister tree is also cool
keeping it neat for something that involved , go Cj [ wtf over ? ]
keeping it neat for something that involved , go Cj [ wtf over ? ]
Kingston
Well-known member
DaveP said:
You can always make adapters. It's a chore, but levels the playing field. 6K4P(EV) out there too. Probably more consistent than the multitudes of 6BA6 brands.
CJ
Well-known member
got a bunch of 6ba6, and the military number, forget what that is, and i have a 6386, and i can get some JJ's so we can scope out some dc dynamics on all three,
CJ
Well-known member
today we add a hammond 6.3 volt at 6 amps heater transformer for the 6386 tubes.
this chassis is finally starting to get a little heavy, probably about 20 lbs, i bet we can add another 20 if we add more iron and some sheet metal,
the 6386 only draw about 0.35 amps times 8 = 2.8 amps, but if the voltage goes up, the current goes up to 3.2 amps, or if the new JJ tubes take 0.45 amps or something, this will let the xfmr run cool inside this hot chassis and also take on anything i put in the socket, plus the hammond's are rated right at what they can put out,
this tranny also has a center tap, something the original did not have,
we need that since this is the audio section, keeps the hum down, gives us the option to raise the heaters to further stop heater hum but this is a push pull circuit, so a lot of hum will cancel,
this chassis is finally starting to get a little heavy, probably about 20 lbs, i bet we can add another 20 if we add more iron and some sheet metal,
the 6386 only draw about 0.35 amps times 8 = 2.8 amps, but if the voltage goes up, the current goes up to 3.2 amps, or if the new JJ tubes take 0.45 amps or something, this will let the xfmr run cool inside this hot chassis and also take on anything i put in the socket, plus the hammond's are rated right at what they can put out,
this tranny also has a center tap, something the original did not have,
we need that since this is the audio section, keeps the hum down, gives us the option to raise the heaters to further stop heater hum but this is a push pull circuit, so a lot of hum will cancel,
Attachments
Mike Cleaver
Well-known member
This is one honking mother of a build.
Takes me back to my teen years as apprentice engineer at my first radio station where we built nearly everything because the owner didn't like spending money.
We'd scavenge things such as old cab tube two way radios and other electronic detritus and build what we needed.
Great to see that old tradition being carried on today.
Multiple thumbs up!
Takes me back to my teen years as apprentice engineer at my first radio station where we built nearly everything because the owner didn't like spending money.
We'd scavenge things such as old cab tube two way radios and other electronic detritus and build what we needed.
Great to see that old tradition being carried on today.
Multiple thumbs up!
I can't recall if anyone has an actual working "670" with 6K4P?Kingston said:
They're cheap, but I also heard that they're prone to failure.
CJ, if you'd like to check 'em out I volunteer to send you like, 20pcs?
Or however many is needed?
8)
CJ
Well-known member
you don't have to rewire all 8 sockets to try new tubes which is goo,
since one tube is used for the top and the bottom of the push pull, this means you can run the ting with one tube instead of four,
Eric Barbour wrote a dumpeter article in Vacuum Tube Valley that featured the 6386, it was about 5 bucks back then, but you know how that goes,
got a turret board for the time constant parts, so we are slowly gonna finish this thing off,
looking forward to playing with this thing, maybe add a matrix switch,
since one tube is used for the top and the bottom of the push pull, this means you can run the ting with one tube instead of four,
Eric Barbour wrote a dumpeter article in Vacuum Tube Valley that featured the 6386, it was about 5 bucks back then, but you know how that goes,
got a turret board for the time constant parts, so we are slowly gonna finish this thing off,
looking forward to playing with this thing, maybe add a matrix switch,
