sw#2 for La-2a

[kazper]

What are you planing on using for Iron and a T4B?

I'd recommend Peter (Grandmasteraudio) for a nice front panel.

 

[college101]

I got my T4B from Kenetek

My chassis...I still have not found exactly what I'm looking for yet...

Irons
For PT-going with the Hammond 369JX
input and output-probably with cinemag

going to go with orange drop and sozo mustrds caps...have not worked out exactly what I want yet

switches, I want to go with Grayhill's...everyone agree's on their quality and durabillity

 

[college101]

SO...off of the Neg(com) side of the Vu meter(which is essentialy the chassis ground side)...is the fist set of positions, where the POS side has the second set of positions...(which is essentialy wired into the output transformer)TB2 in the 68 schematic

Now I have never worked a DIY project with a switch like this before...first time for everything huh?

 

[kazper]

Yea the greyhills are good stuff... If you haven't got it yet and want it PM me your email and I'll shoot over the build docs for the drip stuff. It's another source of info for you and may help you a little in sourcing some of the parts.

I've built a couple LA2A's from drips pcb's. Jensen and Sowter also make transformers for the LA2A and I'm sure you could find others as well

KaZ

 

[Sredna]

SO...off of the Neg(com) side of the Vu meter(which is essentialy the chassis ground side)...is the fist set of positions, where the POS side has the second set of positions...(which is essentialy wired into the output transformer)TB2 in the 68 schematic

I dont really understand what you want to ask/say here?

There is no first or second set of positions, the switch is ganged and you have three positions and two connections per position.

Dont confuse the negative (-) side of something with ground. With help of the switch the meter
is strapped either between the secondary of the output transformer or the GR signal.
Notice that in pos 2 the + of the meter is connected to a (fixed) voltage divider and the - to
another voltage divider that is depending on the zero adjust pot and the second photoresistor in the T4B.

 

[college101]

Sredna...your right...at first,when I was looking at the switch...I was thinking the wiring would be split into two different sections...BUT I didn't see why I couldn't just set it up, as you had stated...setting up 3 positions 

In wiring a greyhill...a 4 pole switch has a pole and 3 positions

At first glance, I had it in my head, that it would be a 8 position type switch, where 1 and 5 were ganged together...as the +4...hopefullly you understand what Im trying explain...but now I see... 

I was also saying positions where I meant poles...

I understand the grounding...just not explaining myself too well right now...off to sleep finally

 

[college101]

think I maybe going with sowters now...They look like they me be the best fit...

I like cinemag just cause they are so small and an ideal size for set up on the backside

 

[Sredna]

Found a picture of SW#2.

Mybe it helps....

 

[college101]

ok..so update...I have all the caps and res ordered today...

 

[kazper]

Did the docs I sent help you a bit?

his newer docs have more Hi-fi parts..

Found Here

 

[college101]

They did...Im still having trouble figuring out the wiring off of R2

the middle tab goes to (7)R32 over V3 which is 12AX7#2...

Looking at Cayacosta's set up, over R2-it shows a white and a gray cable off of R2..but only the white cable goes to pin7 in line with R32

Compared to the schematic from 68..I would think there is only supposed to be one cable? Am I missing something?

 

[Sredna]

The gray "cable" is the shield.

You have to use a shielded cable (ie guitar cable) and connect the shield to ground = the left tab of the pot.
The other (tube) end youll leave unconnected.
Same for the right tab cable that's going to R6/R7.

 

[college101]

oh,,,OK...I saw that, but if its not connected to anything, it really serves no purpose right?

 

[Sredna]

Think again, it is connected.  

The purpouse of the gray "cable" is to shield the white one and just need (or should)
be connected at one point.

 

[college101]

Sorry Sredna, I need to be more specific! I understand the shielding aspect, but the second cable that is run to no where...makes no sense to me!?!  If it were to go to a ground, then maybe it would make sense, but just left hangin out-not connected to anything?

I got my carbon comp resistors in yesterday...

I got my first order in from tubedepot.com ...I picked all the wrong wires, and have to place a second order...or go up to FRYES electronics and see if they have any deals...

 

[Sredna]

Do you with the "second cable" mean the grey line connected to the left tab of R2 in Cayacostas layout?

If yes, there you have the connection! The left tab is connected to ground and therefore the grey "cable" is a part of the ground.

THe grey cable is actually a pipe woven of copper strains surrounding the white (signal) cable and shields it from interference.
Such a shield should be connected on only one side. It doesnt transport a signal from A to B but takes interference induced on the cable itself
to the ground and therefore protects the white one = shielding.

Id suggest you to read up on grounding in general, there is lots of info here and your instructor should be able to help you out.
Cayacostas layout is good to study because its concidering grounding issues.

Hope this helps.

 

[college101]

I did some reading on grounding...And I have a much better understanding of it now! I understand the purpose as well...

I got a bunch of parts in today...still waiting on a few more caps to come in...

 

[college101]

ok..so I guess there are some hard to find resistors that I can not get in stock for a while, that are 5% 1/2 watt per the 68 schematic....guess Ill be using some 1% resistors in place till I can get the proper 5% that I want

 

[kazper]

guess Ill be using some 1% resistors in place till I can get the proper 5% that I want

Probably better that way anyways

 

[bdubya]

To add to what the astute gentleman just above mentioned:

a bag of 100ohm/1% resistors will have actual values of between 99 ohms and 101 ohms,

a bag of 100ohm/5% resistors will have actual values of between 95 ohms and 105 ohms


the "%" is the "tolerance", if you have a list of "to google" items going.  Cheers, and have fun with the build!



ben