D-LA2A Support Thread

[[silent:arts]]

Anyone can post EU BOM?becouse i cant buy from mouser and other sites...

everything needed should be available from
www.tubetown.de
and
www.reichelt.de
or
www.conrad.de

 

[benlindell]

Back to troubleshooting this beast.

So I swapped tubes between channels and now both channels are almost no signal, very faint thin sound, wtf is going on?

I've probed and found signal on my input transformer molex but nowhere else, any ideas?

 

[Cardinen]

Hi,

i've finally finished my unit (but i'm still waiting for the VU meters since 4 months...  ).

after some initial debug the unit is working fine, but i've a minor problem.

One of the neon lamp (Ch. 2) don't make glow, so i've checked the voltages:
Neon 1 : 53-54 V
Neon 2 : 49-50 V

Maybe a little too lows ??

I've tried to change the dead neon with another but is the same. Sometimes it glow for a few seconds at startup.
I've checked the voltages before R128-228 and i have 7V of difference between them. (the same difference coming from the AC of PSU) so i guess is OK.

Any advices ??

Anyway i'm happy with the sound of this beast, thank's Volker for make this possible !!

regards,

Cardinen

 

[bernbrue]

Hi,
sonic warrior compiled a pdf file with things to keep in mind. Read the passage about the neon lights. Might be better to replace them with zener diodes. PDF attached.
regards
Bernd

 

[Cardinen]

thank's bernbrue,

i had read that pdf.  I don't have here some zener to try, but i'll do soon.
However the voltages i have on lamps are fine ??

regards

 

[bernbrue]

Hi,
they are a bit low but should work. Don´t care too much about the differences between the channels. The neon lamps need 60V or more to glow. Zener diodes are more reliable. Replace the neons and you are on the saver side.
regards
Bernd

 

[MicDaddy]

a few simple questions I hope.

Regarding:

-1.)  R125/225  what is the 'cleanest' way to mount a 100K trimmer? 

-2.)  "Changing those 220k plate resistors to something lower is indeed a good idea." 
                  How about sockets for easily swapping of resistors (100K etc) depending on which
                  tube 12AY7/12AX7 etc..??  Good idea or waste of time?

-3.)  C8 listed as 100n, can anyone verify 0.1uF wima (V?)

-4.)  On the Azone US BOM, there were only 4x 9 pin sockets listed.  Though there are 6
                  allotted positions for 9 pin sockets.  I went ahead and ordered 6x sockets, is there
                  something I should be aware of for the 12BH7A?

-5.)  I'm planning on sockets for C104/204 but what are folks generally satisfied using?
                I opted for the edcor wsm600:15K  wsm15K:600  Is anyone using these xformers
                that care to share which cap used in designation C104/C204?


Just read this entire thread for the second time today. 

Thanks again for all of your inspiring builds

 

[desol]

-1.)  R125/225  what is the 'cleanest' way to mount a 100K trimmer?

I just used the default that was suggested. 33kohms?? (Can't remember right now) Otherwise, you could solder the middle leg to one side(underneath) of a trimmer....verify lead spacing...and should fit ok.

-2.)  "Changing those 220k plate resistors to something lower is indeed a good idea." 
                  How about sockets for easily swapping of resistors (100K etc) depending on which
                  tube 12AY7/12AX7 etc..??  Good idea or waste of time?

I used 12AY7's and put in 100k(or whatever) resistors permanently. I don't plan on changing it back to 12ax7.
Your call here...

-3.)  C8 listed as 100n, can anyone verify 0.1uF wima (V?)

Not sure what your asking, but yes, 100nf is .1uf. Whatever voltage you can find in that lead spacing.
Probably 100v-300v.

-4.)  On the Azone US BOM, there were only 4x 9 pin sockets listed.  Though there are 6
                  allotted positions for 9 pin sockets.  I went ahead and ordered 6x sockets, is there
                  something I should be aware of for the 12BH7A?

Nope. The BOM must be wrong. I must have noticed this too at some point???  ???

-5.)  I'm planning on sockets for C104/204 but what are folks generally satisfied using?
                I opted for the edcor wsm600:15K  wsm15K:600  Is anyone using these xformers
                that care to share which cap used in designation C104/C204?

I broke singles off of a sip strip and soldered those in. Seemed to work well enough. Single sockets were hard to source and the ones that i ended up buying(pricey) didn't work in the end cause the hole was ever so slightly oversized. For the value, I used the default suggested.

Everything seems to be working, sounding well. Oh yeah, and yes i used those transformers.

 

[MicDaddy]

Thanks desol

..yet another project you hold my hand through  ;D

Another question if I may regarding Grid Stoppers..

Did you install 1K for GS101/102 GS201/202?

Thanks again!!

 

[desol]

yep...

 

[benlindell]

Back to troubleshooting this beast.

So I swapped tubes between channels and now both channels are almost no signal, very faint thin sound, wtf is going on?

I've probed and found signal on my input transformer molex but nowhere else, any ideas?

Anyone have some clues for what might be going on with mine?

 

[bernbrue]

Only a guess, it might help:
check
- transformer wiring and molex connectors
- XLRs wiring
- grounding
- bypass relays (switch wiring)
- heater wiring (has to be wired on solderside)
- correct voltages
- bad tubes
- .....
I´m shure there is an easy to find mistake. Don´t give up, the compressor is worth every hour you spend in building and troubleshooting.
regards
Bernd

 

[benlindell]

I double checked the transformer and xlr wiring, they appear to be good, my grounding appears fine, the relays are clicking and working (signal to no signal).

The Heaters.... I measure 6.5V between pin 4 and pin 9 on all but the 6aq5a (pin 3 and 4). But whats weird is that on the left channel I get 3.3V between pin 4 and every pin but 5, that shouldn't happen right?

 

[bernbrue]

For all tubes (except 6AQ5) heater is wired to pins 4&5. For the 6AQ5 heater is connected to pins 3&4 (pcb turned around and counted clockwise)
check left channel for bad tube, soldering of the tube sockets, heater wiring, power transformer specs & wiring, values of R1&R2. So you´ve already narrowed the problem, you should be quite close to find the mistake. Go on!
regards
Bernd

 

[benlindell]

Yea I'm getting 6.7V on pins 4 and 5 (referenced to pin 9) but I'm getting 3.3V from the rest of the pins (still referenced to pin 9), why would this be?

 

[bernbrue]

Pin 9 is useless for measuring. You´ll get half the heater voltage. If you´ve got 6,3V between 4&5 everything is allright with the heater. What are the other voltages? There is a schematic with correct measured voltages out there. Take it for reference and compare your voltages with them. Check the voltages at R129 and R229 (attention !!!!!!!!! , very high voltages). Measure with reference to ground.
regards
Bernd

 

[benlindell]

ok so if I shouldn't reference pin 9, should I be referencing the star ground? if so then I'm getting even weirder voltage readings. I'm getting +350VDC on R129 and R229 though

 

[bernbrue]

Yes, always measure the voltages with reference to star ground. Your voltages are fine. There should be about 350V before (on the right side of) R129 and R229. After the resistors (other leg of the resistors) there should be something like 275V. Have a look at the schematics below and compare your voltages with those shown in the schematic. Keep in mind that heater voltage is AC whereas H.T. voltage is DC.

http://www.twin-x.com/groupdiy/albums/userpics/LA2A-deconstructed.jpg

http://www.waltzingbear.com/Schematics/Urei/Urei_LA-2A.JPG

Hope this helps.
regards
Bernd

 

[benlindell]

Yes, always measure the voltages with reference to star ground. Your voltages are fine. There should be about 350V before (on the right side of) R129 and R229. After the resistors (other leg of the resistors) there should be something like 275V. Have a look at the schematics below and compare your voltages with those shown in the schematic. Keep in mind that heater voltage is AC whereas H.T. voltage is DC.

http://www.twin-x.com/groupdiy/albums/userpics/LA2A-deconstructed.jpg

http://www.waltzingbear.com/Schematics/Urei/Urei_LA-2A.JPG

Hope this helps.
regards
Bernd

Thanks for sharing those. I just had a chance to run through one channel and all the voltages are close but generally under by a little bit (250V instead of 275V)

Both with and without the t4b installed I'm getting super quiet and thin sound that goes up and down with the gain pot.

I just went through resistor by resistor and verified they are the correct values, and also the caps. I continuity checked all the molexes as well.

When I measure the heaters referenced to star ground on the left channel at pin 4&5 I get 3.3v and pin 9 I get 3.2V, all the other pins are 0V now. but on the right channel at pin 4&5 I get 0.2V and pin 9 i have 6.3V. What would be causing this?

I've swapped input and output transformers.

The only thing I haven't tried yet is new tubes I've been mixing up the 8 original ones I put in, before using another set I wanted to make sure it's not something I'm doing that killed these ones.

 

[benlindell]

I should also add that this one did definitely work a few months ago when I wired it up on the bench, then I left it for a couple months and then finally put it in the case, makes this all even weirder