anyone in NY area have a p2p la2a build?

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

sr1200

Well-known member
Joined
Dec 6, 2010
Messages
2,094
Location
Long Island, NY USA
I finished mine up and have rewired the thing 3 times now and cannot for the life of me figure out why im getting RIDICULOUS voltages in places they shouldn't be.  (maybe its just my meter?) but im getting readings of 350v for my B+ and at tube socket pins where I should have only 100v.  Was hoping i could compare/contrast what is going on with this thing.  Certainly would pay for the time.
 
The first warning sign is
sr1200 said:
... (maybe its just my meter?) but im getting readings of 350v for my B+ and at tube socket pins where I should have only 100v.

What kinda of meter do you have? Did you replace or check the battery?

Verify the meter then report?
 
Will do.  Only reason why id think it wasn't my meter is that the heater voltages are all spot on.  But couldn't hurt to replace the battery.
 
Once, years ago, when I was a young tech... I chased down "wrong/crazy" voltages for what seemed like hours... only to find out it was a weak battery in my fluke! haha!

Anyways, if the heater voltages look all right, then I would trust the meter for now and look at where you are "supposed" to measure the voltage "across."

 
Tell me exactly where the two probes are touching for your 350v

http://www.recproaudio.com/diy_pro_audio/diy_files/la2a/la2a_layout.jpg

Use this and MS paint!
 
thats the diagram i used to wire it (i noticed that the 6aq tube is missing the connection between pin 1 and 7 thats on the schematic) but on the bottom where it says B+ red probe there and black on ground.  (am i doing this wrong?)
 
350v is not what the raw B+ is supposed to be?

What pins have 350v on them?

What do you have across the secondary of T3?

What do you have across any of the C7 caps?

Is there a problem with the unit?

Does it pass audio etc?
 
i tried measuring with tubes and without.  (thought the same thign that without tubes voltages might be messed up).  Ill take a full reading tonight when I get back to the "lab" which as of late has been my kitchen table.

Dunno if this is any consequence... but I'm using cinemag transformers not the UTC or remakes of the UTC.  Dont think any voltage per-se is going through them though.

Being that my voltages are SOOO off from the schematic voltages, I didn't even try to hook it up to audio source.  Last think i want it to spew a few hundred volts into my converters lol.
 
b+ = 362v

V1
1 311
2 0
3 359
4 6.4ac
5 "
6 183
7 0
8 1.65
9 6.4ac

V2
1 359
2 341
3 359
4 6.4ac
5 "
6 359
7 322
8 358
9 6.4ac

V3
1 352
2 0
3 357
4 6.4ac
5 "
6 353
7 0
8 356
9 6.4ac

V4
1 233
2 357
3 6.4ac
4 "
5 360
6 357
7 233
 
For reference: im using a hammond 369JX Transformer for power. Cinemag CM2810 for output and Cinemag cmqee-3440A for input.

Measured im getting 534 VAC from the Red leads (should only be 500v max)  Bad Transformer?
 
Sounds to me like your primary is just a little high... Which pri taps are you running?

What is the voltage across R29 4.7k 2w?
 
At the front of 29 i have 369.3 at the back i have 363.2 (DC)

EDIT:(directly across i have 6.25v)

oh i have the 2 120 taps also from main (black white blue and brown)
 
you aren't pulling any current through R29 or it's the wrong value. In order for a resistor to drop voltage there must be a current "running through it"

Power down... wait until the caps discharge and or run them dry and check the resistance of R29
 
Will try in a couple min (after caps discharge... this B&#&@#^ has already bit me twice during my build)  I also noticed that the 2 pots in teh back were not set fully clockwise, i just changed that. (dunno if that matters)
 
Best is to monitor the voltage as it drops... put your probes across the main c7 cap if you can... and watch it drain from there... those are going to be the ouchy ones if you get bit again
 
got 4.4-4.5 k (2w) resistor.  Do i need grid stoppers since im using the cinemag transformers? (would that have anything to do with anything?  Ive been reading the "all things LA2A" for a couple of days now trying to figure this out.
 

Latest posts

Back
Top