new la-2 pcb

[norman_nomad]

For the 6.3v 2 amp secondary... does the la2a actually need the full 2 amps? Does anyone know the approx amps that the tubes consume?

Thanks!

 

[dripelectronics]

im unsure of the heater filliment minimum amps needed to
power the four tubes ,

what transformer you thinking of using ?

.......................................................

the v2.0 boards arrive in a week , give an email for details.

the t4s are coming along , i got caught up in testing ,
ill have 13 ready at the end of the week ,
still waiting on the panels , man their lead time is months.
the v72 project is going well , just dismantled my v72
and put it back togeather.

i didnt know the ef804 tubes were scarce (up to 40 bucks each) .
pcb almost ready , waiting for the sowter xformers to test out .

g.

 

[babyhead]

Greg-

What are the chances of your new T4bs being matched?

I want to build a stereo version of this project.

:guinness:

 

[norman_nomad]

[quote author="dripelectronics"]im unsure of the heater filliment minimum amps needed to
power the four tubes ,

what transformer you thinking of using ?

[/quote]

I e-mailed you about this.... Wanting to know if it's possible to connect up to 4 units with one transformer... I can figure it out if I know what the tubes need to run properly...

I found this quote earlier in the thread:

"This is high voltage but relatively low current. You probably don't need thicker wire for the H.T because the total current for the H.T on the La-2a is only about 50mA. The insulation rating for the wire can be more of a problem with valve gear than the current rating, and it is probably worth checking that your wires insulation can handle maybe 400v to be on th safe side

On the other hand you do want the heater wire to be able to cope with maybe 3 Amps to be safe"

Is this to say that 50ma is all the unit draws on the secondaries? Sorry for the newb question... :sad:

 

[dripelectronics]

i was wrong on that ,

the la-2a main high voltage has about 305Ma at the 1n4007s
and about 245mA at r29.

i would stick to saying that the tubes need 6.3 volts @ 2 amps
per la2a.

so it would be my assumtion to say if you were doing 2 you would
need 6.3 volts @ 4 amps .

for 4 you would need 6.3v @ 8 amps.

some heafty amprage.

im not sure how to proceed on this one ,
because you might be the first to try this ,
you might post a thread on this in the drawing board.
your getting into the danger zone of amps .
one mistake and youll fry your self.

have you built one of the la-2's as a single unit ?
it might be best to complete one full , then proceed after that.

ive shocked my self a bunch of times by stupid mistakes.
and it does bite a little ,
you get shocked by a 4 unit power supply and , well ,
you know the story.

i designed the board as a mono unit ,
with the intention of two mono units being combined
to make two .

im going to design induvidual tube boards and power supplies,
(basically the boards devided into sections so you can put them
into a lay out as you choose. )
along with induvidual metering /xformer boards.

in the coming months .




g.

ps ,

on the t4s matching for stereo units is ok.

g.

 

[norman_nomad]

Good. Thanks for the words of warning Greg.

PRR posted the info in another thread.

Here it is for reference.

Power demand of an LA2a:

12BH7 - 4mA to 8mA
6BQ5 - 15mA
12AX7 - 1mA each * 4
meter - 0.5mA
=============
28mA total at 280VDC

heaters
12AX7 - 0.3A * 2
6BQ5 - 0.45A
12BH7 - 0.6A
=============
1.85A at 6VAC

 

[tomcat]

1st: Supercool Project!!!!

2nd: I did read through all 55 pages during the last weeks, so if i overlooked this ... sorry
Whats about the plans for the Stereo version (you mentioned it once)? I like to build a stereo la2a and im not in hurry. So when you plan to do one i can wait

Sooo:
2x new PCBs or 1x Stereo PCB + the necessary T4s are on my wishlist, just tell me (us) when youre ready
Transformater dtto, but this depends on the usage for stereo unit and price

Btw. Does anybody know why brand-x states 4 T4 cells used for Stereo LA-2A?

 

[dripelectronics]

hi there ,

thanks!,

the 'brand x' stereo la2a uses 4 , t4b's because one pair is a slow
recovery and the other pair is for fast recovery.
(it could be attack time not sure , just glanced over the web page )

ive been working on the stereo idea for some time ,

it's been a matter of just crunching things to fit in a single unit.
a stereo la2a is simply two units connected with 2 wires. ( actually
a shield and one wire )

i think the best course of action is to make a la-2a pcb in parts ,

tube section , power section , metering and transformer section .

i think the main problem was that i was so hell bent in eliminating
'all' wires thats i had not taken this approach.
an easy task , should only take a small amount of time,

im in the middle of re-designing the ver1 board
more of an up dated ver 1 Pcb.
im going to change a few things and make the silk screen
to match sowters , simply not so many use the utc-a24 and hax 100
due to their now astronomical price.

i might be sold out of ver 1 board for a couple of weeks.
(untill i get the update done)

ver2 has arrived and is available (more expensive , but well worth the price)


email me for specs and details.

g,

 

[tomcat]

[quote author="dripelectronics"]the 'brand x' stereo la2a uses 4 , t4b's because one pair is a slow
recovery and the other pair is for fast recovery.
(it could be attack time not sure , just glanced over the web page )[/quote]

Hmm, would be a nice option for the drip modular la2 pcb set, especially when the t4 problem is solved

 

[tomcat]

[quote author="norman_nomad"]12BH7 - 4mA to 8mA
6BQ5 - 15mA
12AX7 - 1mA each * 4
meter - 0.5mA
=============
28mA total at 280VDC

heaters
12AX7 - 0.3A * 2
6BQ5 - 0.45A
12BH7 - 0.6A
=============
1.85A at 6VAC[/quote]

Pls dont beat me up if this question was already asked 1000 times

On the pics of the new boards the tubes are marked with

6AQ5A

you mentioned 6BQ5. Soo im starting to get confused I can get my hands on

6AQ5 (no A at the end)

are these also ok?

<sillyaskmodus off>

Thanks! :grin:

 

[dripelectronics]

oh no prob !
that wasnt written by me ,

but for the PCB ,

it's a '6AQ5A'

from what i understand . the 'A' if for low noise.

6aq5 should work , ill double check with tubes.com.

g.

 

[tomcat]

Did some further research and found a thread:

http://www.groupdiy.com/index.php?topic=18530&highlight=12ax7+tubes

 

[MrZpliff]

Hi Tomcat !

Would be nice if you know where you're from...
I've got a couple of spare 6AQ5A that I can part from.
The brand is General Electric and I believe they are NOS , but I'm not shure- they could be slightly used.... they all work fine in my clone.

 

[babyhead]

Greg-

If you are designing a new mono unit, can I recommend a small tweak?

Through hole pads next to the heater pins to solder the heater wires into.

On my build I had to solder the heaters to some clipped component wires...


:guinness:

 

[ruairioflaherty]

Babyhead,

could be wrong but I think Gregory has eliminated the heater wires altogether in V2 of the pcb,

cheers,
Ruairi

 

[tomcat]

@ Magnus: send you pm

 

[mata_haze]

Hi dripeletronics,

i would like to take TWO board.
I've sent you an email with my info.

Let me know.

Thanks

 

[dripelectronics]

thanks babyhead ,

im redesigning the ver 1 over the next 5 weeks ,
there's a lot of corrections like that i need to do ,
simple things like make the radial caps spaced properly.
etc.

plus sprucing up the design with my new skills aquired from designing the
ver 2 'opto' la2a pcb.

it is true that the heaters are already connected on ver 2.o
along with the fuse , and transformers (works with leaded x formers
also)

i just built one with utc ha100x and a-24
really sounds great.!


heres the pcb , notice how the heaters are on the top side of the
board , i used a much thicker board in manufacturing to insulate between
the heaters and the signal side , (that prettymuch doubled manufacturing
costs in it's self) then add the 3oz copper surface ,
2 amps needs some pretty thick copper , or the trace sizes were
going to be pretty thick.


it was pretty tricky getting the heaters to fit into the design ,
after a million designs i finally came up with the 'stadium' (tm) concept
where the heaters go 'around' the signal circuit instead of 'through'
the circuit.

and then was able to position all the signal traces to avoid intersecting
with the heater traces.

the worlds greatest puzzle.
glad im OCD , lol.

 

[tomcat]

:thumb:

Whats the dimensions of the V2 board?

Btw. the 3 internal and 2 external Pots are all lin or some log?

 

[dripelectronics]

the dimensions are 6"x15.75"

there are 3 pots @ 1 meg ohm 'lin' taper
and 2 pots @ 100k ohm 'audio' taper

the mil spec pots are carbon @ 2 watts

it is possible to use vishay ' spectrols' rated at 1 watt pcb
mount for stereo adj , limiter response and the zero adj.

that is if your building a mono unit .

other wise use shielded 3 conductor plus shield cable
for the st ADJ / LIM pad to connect to their pots.


i found it best for the zero adj to be mounted on the chasis , because
sometimes it needs a little adjusting here and there.

youll need access to the lim response/ stereo adj pots if your gonna use stereo hook up.

g.