LA2A voltage prob re: R34/36

Gents,

I've read 40+ pages of the LA2A meta and still have a voltage anomaly.  I have followed some of CJs mods I found and removed the limit switch and response pot. 

All of my voltages are very close except for the grid and plate voltages on the 6AQ5.  This seems to be a common issue but here's my values-

as per 1968 schemo

R34 - 10k, 3w
R36 - 470r
R38 - 22k

6AQ5
pin 5 - 124v
pin 6 - 139v
pin 2 - 7.3v

In the meta I read that pin5 should be approx 90v.  Would using the 22k and 1k for the resistors, removing R38, and changing the cathode cap value solve this issue or is there something else I need to address?  BTW I'm using JAN 6005 Sylvania for 6AQ5 if that might change any readings.

The unit passes audio fine and does compress some but I think the el panel(diy night light/nsl-5910) isn't lighting fully and wondered if the off voltages may be to blame.  Has there been a night light or other commonly available that has worked best for others?

Thanks, Nathan

22k/1k or 10k/470r for R34/36 on LA2A?  I also didn't get more than 17vac to the T4 until I disconnected R30 and C6 - Is there a reason why?  I'm getting approx 144v ac to the T4 presently - is that about right?

Thanks 

do you have the stereo pot in there?

the voltages on that el driver tube are always all over the place,

different schematics and stuff, tube voltages are way looser than transistors, you get used to the 20%,

Thanks CJ for the reply,

I don't have the stereo pot, lim. response, or lim. sw as per some of your posted schemos here when you were thinking about an octal LA2A.  I printed out a possibly early mod idea with the 6V6GT instead of the 6AQ5 to simplify it.  In the schemo I saw you had C6(.01) after C12(.001) and R30(47k) to gnd but I saw on other schematics it was going to the 1meg above ground and pins 1/7.  Once I disconnected C6 and R30 I had what seemed to be a good output of 144v AC to the el panel esp. compared to the 17v I had b4.

After all the searching I did, it seems there ought to be a wider diff between the supply voltage to the screen and plate.  Some I have seen are approx 90-100v to pin 6 and 135v to pin 5 which is certainly more than the 15v-ish  diff I have.  Aren't the difference between these voltages important on the output drive characteristics of the panel.

I am using all A-B 5% c-comps, PIO's, and mica's and have measured the resistors in the psu and they are all within 2% tol.

If I got rid of C13(510pf) and R38(22k) and just left the 30uF to pin 5 as per your schematic reduce the voltage on pin 6 of the 6AQ5 or are these specific tweaks to allow use of the 6V6? 

CJ - I saw mention if you using an el panel from an alarm clock etc for a diy T4 and see why these are an amazing nut to crack/tweak.  Have you found a non-LSI panel that is easily available to play with

Again, thanks for the reply, Nathan

that alarm clock thing was ok for a while, but give her the real thing, thats what i say,

what if you bought your girl artificial flowers, what would she say?

you have healthy voltage on the panel, i think it was meant to run at 120 steady ac for back lighting,

if anything, your meter might need a little cal. job.

you should be able to almost squash the audio so you can barely hear it, if everything is speced out,

that is with a healthy line input, like a cd level over compressed POS like they sell nowdays,

mastering engineers, shame on you for selling out!

but your cd's make a good squashing test, ever hear a squashed cd getting squashed again?

it's like a mack truck ran over it, sheesh ka bob,  ;D

CJ,

Thanks for the input - looks like I'm getting close.  I saw your info on the LSI panels - do they still have the high purchase number requirement?  If not I'd be interested.

I'm a bit of a ghetto gear maker - I've been off work from an injury on the job as an electrician so my funds are limited.  I was just able to solder again 3 weeks ago after another shoulder surgury.  The part I spent the most on this product was 6 photocells I bought from Allied to try to find a decent pair. 

I bought most of the project gear I have and scavange from was back when the 'bay had killer deals 7+ yrs ago like 5 50's era RCA trafos for $140, V672/2s for $200/pr but didn't know wtf I was doing until the last few of years until this forum helped tons.   

I decided to do this project as the only thing I had to buy were a couple c-comps, NSL-s, el night light, RS plastic encl. for T4ish unit, and a JAN 6005.  Other than what I had on hand to scavenge I spent under $75.  I am in no way trying to duplicate an LA2A but was going for a reasonable clone.  I'm not using any standard trafos, just the stuff I have on hand that ought to work - a couple Freed 'ouncer' sized trafos with 15k:50,200,500 for in and output.  They say +-2dB 20-20k but they have a similar hi rolloff as the original specs of the '2A around 16k. 

I'm never gonna screenprint a faceplate, use a pcb, etc.  If I want to make something I'm gonna figure the cheapest possible way to get a great end product regardless how ugly it is.  A decent vu meter, some hammerite for the faceplate and some quality pots.  Not trying to impress on the visuals just sound - kinda like taping over the meter, right? 

The pics of the gear many make on this forum are absolutely amazing and I aspire to that level of a quality end product.  I'm just not at the point where I want to pay anyone for something other than the guts that makes the reels go round pretty.

Many thanks to the guys that make this forum so invaluable!

Regards, Nathan