All things LA2a related

[dripelectronics]

(edit )

the 10k R34 screws every ones voltages up ,
replace it with a 22k along with r36 to a 1k
and your 6aq5a voltages will all fall into place.

like i said , i dont speak bloo , so i cant help you on the turret board.
but i bet the 22k replacement will help alot ,

hell it set me back a year in my designs because the voltages were
messed up due to it ,

brand x uses the 22k / 1k combo too.

 

[dripelectronics]

V1
____

#1-108V FINE (reissue is 133v /la2a 96v /schematic is 146v)
#3-1V FINE
#6-113 FINE (reissue is 135v / la2a 101v / schematic is 120v)

V2
____

#1-109V FINE
#2-0.02 NORMALLY READS 0 (but that seems fine)
#3(through 1kResistor to TurretA6)-0V (SHOULD BE 4 VOLTS) trace all
conexions to this pin , something might be loose or wrong.
#6-220 FINE
#7-70 FINE
#8-111 FINE

V3 (12AX7#2 ?)
______

#1 and #6-82V FINE ( reissue is 105v/la2a is 90v/schematic is 100v)
#3 and #8- 0.834v FINE
#7-0.003 FINE (USUALLY READS ZERO)


V4
_____

#2-7.3 to 7.5V FINE (reissue is 10.4 / la2a is 2.8/ la2 is 5.8)
#5-116 A LITTLE HOT , TRY THE R36 1K / 22K COMBO will correct this
#6-133 FINE

hope this helps ,

g,

 

[emx]

I noticed you stated that in a previous post to someone so I ordered some 22k resistors to try it out that came in about a week ago so I'll try that too. R36 on mine is already 1k so I won't need to change that then.

 

[emx]

R36? I thought it was R31 that had to be changed to 1k, OK maybe I need to change that one too.

 

[dripelectronics]

(edit)

r36 and r31 should be 1k

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

yeah i figured as much , because your voltage was right on with pin
2 of the 6aq5a ,

the 22k will fix the other one ,

seems like your almost ready to roll her out of the shop.

just trace the wireing to the tube pin thats lacking the 4 volts.

g.

 

[emx]

As for R29, does it stay 4.7k?

 

[dripelectronics]

that one stays 4.7k

g,

 

[Purusha]

I have a question. With my silver T4B came a resistor and on the manual it
says that I need to use it in the R25 place if I remember it right. Do I use
it on the R25 place on the Drip boards too or is this only meant for the original LA-2A boards?

 

[dripelectronics]

yes ,youll replace that resistor ,
ill bet money that it's a 33k , they all seem to be 33k from urei

nice cases by the way ,

could you email me the price and shipping to the united states of america.

best ,

g.

 

[Purusha]

E-mail sent.

 

[Purusha]

I am almost there with my LA-2A :grin:

Is there anything wrong if the PCB is mounted so that the tubes
come near the back side of the case? I have my doubts as in this
way the main power wires have to run all over from left back side
to the right front side of the case.

Should I turn the PCB for 180 degrees around?

 

[Neil]

Wouldn't you want the tubes in the front, since that's where your slots for cooling are? Edit: Never mind, was looking at the pic backwards! D'oh!

 

[dripelectronics]

I usually have it so the power section is right near the power x former.
,
seems to work out better this way , makes it so the wires to the
gain and reduction pots is shorter.


and less power wires on the inside.

it's hard , because you put the metering section closer to the front , but you also put the audio path of the gain and limit controls more
near the transformer .

try it with the power section near the transformer ,

you can use shielded wire for the meter if you want ,
it would be compairable to a point to point la-2a ,
the metering section does have some nice long wire runs in it.


g.

 

[emx]

Hey Drip,

I did the resistor switch and was wondering what the B+ value should be with this setup, just curious as I inititially had somewhere around 265 and now am closer to 300.
I think their may have been some confusion as to what my reading on V2 pin #3 as I was checking the voltage on this after the resistor which on my layout goes directly to be connected to R10 and connected with Transformer #2 directly to ground so the 0 reading doesn't worry me much, maybe you check yours before the resistor,directly off of the tube? My pin #3 is covered with shrink tubing so I can't get to it without problems, it's a really tight squeeze in that area as it is.

Anyone here have any info on the output cap placement? I ran the unit and it ticked until I pulled it out away from the unit near V1, V2 and the neon, it is passing audio however.
I'm assuming I should place it somewhere else away from all tubes, neon, and transformers? :grin:

 

[dripelectronics]

this is odd ,

so to sum up ,

you replaced r34 with a 22k and you replaced r36 with a 1k.

correct ?

this shouldnt have brought the b+ power rail up more.

it's normally 275 ish ,

your running hot ,

wich probably means one of the tubes is mis wired and not doing it's share of sucking juice.

(so to speak)

lemme post some voltages.

1 sec

 

[dripelectronics]

12ax7#1

pin#________brand x___schematic_____la2_____la2a
1___________133_________146_________111_____96
2___________---------------------------------
3____________1__________1.2_________.9______1v
6____________135v_______120_________122_____101
7____________--------------------------------
8____________1___________NA________1.4_____1v

12bh7a
pin#________brand x___schematic____la2______la2a
1___________105_________100_________95______92
2___________--------------------------------
3___________4.6__________NA_________3.4_____3.8
6___________226__________220________195_____200
7___________77___________NA__________65_____65
8___________111__________NA_________100_____98

12AX7#2
pin#________brand x___schematic____la2_____la2a

1_____________98_________NA______89_____90
2_____________---------------------------------
3_____________.8________.75_______.70____.75
6_____________98_________NA______89_____90
7_____________-------------------------------
8_____________.8_________NA_______.7____.75

6AQ5A
pin#________brand x___schematic____la2_____la2a

1_____________---------------------------------
2_____________10.4_______NA________5.8_____3.8
5_____________85_________85________125_____100
6_____________134________NA________104_____70



sheesh !

'note pad' was giving me hell

 

[Purusha]

[quote author="Neil"]Wouldn't you want the tubes in the front, since that's where your slots for cooling are? Edit: Never mind, was looking at the pic backwards! D'oh![/quote]

That is the thing. The cooling slots are in the back... :? Should have known better.

 

[dripelectronics]

i think as long as the case is vented , it will be fine ,

everyting in there can handle alot of heat.

gosh i could cook eggs on my avalons that i got rid of.

best ,

g,

ps thanks for the email.

 

[Purusha]

Hi,

I need a bit of a help with wiring my Hammond power juicer and both Sowter transformers. Is there any info on this in regard to the LA-2A project? I have the PDF called LA-2A hook up notes but the colours on my Hammond are not the same as in those notes :?

Hammond 369JX - http://www.hammondmfg.com/pdf/5c0028.pdf

Two more things.

How do you ground the T4B? Mine is in aluminium case. The only thing I can do is connect the wire to the screw on the side of the T4B case.

And regarding the comp/lim switch, when 1 and 2 connected LA-2A works in LIM or COMP mode?

 

[sintech]

Regarding In and Out trafos:

Sowter input:

XLR Pin 1: Chassis
XLR Pin 2: Green
XLR Pin 3: Brown

Trafo Blue : Input signal to limiter
Trafo Grey tied with Black: Ground


Sowter Output:

Trafo Yellow : Is output signal from the limiter
Trafo Green tied with Black : is ground

XLR Pin 1: Chassis
XLR Pin 2: Pink
XLR Pin 3: Grey