Dual La2a - [silent:arts] version

[[silent:arts]]

non latching

[Infernal_Death]

Since i have finished my 1081 the completion of the Dual LA2A is my next task.
Unfortunately after finishing the wiring, both channels don't work right now. Channel 2 seems to have a defective input relay as i can't get the signal to the input transformer. So while waiting for new relais i want to get Channel 1 working.
Channel 1 passes a signal but it's very low and distorted (of course the T4B is pulled).
I traced the signal and it's fine at the "output" of C101 (the orange drop 22n). At the "output" of C103 (the solen fast 100nf, to the 470K and grid of V102B) the signal is already distorted.
So now my problem is that i cannot trace between both those points as there is a much too high voltage which would kill my test speakers.
The Problem seems to be at either V101B or V102A.
Any tips how i can proceed ?

Thanks for reading.

Flo

[Infernal_Death]

I measured some voltages on V102:
Pin 1: 123V
Pin 6: 223V
Pin 7: 82V
Pin 8: 130V

Anyone got some reference values ? Both channels have around the same values on V102/V202.

Flo

[[silent:arts]]

Flo,

CJs Voltage Chart for the LA2A should work here too:
http://vacuumbrain.com/The_Lab/LA2/la2_voltages.jpg

for a cross reference the D-LA2A schematic:
http://www.silentarts.de/DIY/D-LA2A/D-L ... ematic.pdf

[Infernal_Death]

Thanks Volker. I hope this helps as i am quite clueless at the moment where to search. Tubes seem to be ok as i swapped them and the problem remains.

Flo

[[silent:arts]]

did you check heater voltages ?

[Infernal_Death]

I did, they are both a bit high at around 6,8V.

Flo

[[silent:arts]]

Thanks Volker. I hope this helps as i am quite clueless at the moment where to search. Tubes seem to be ok as i swapped them and the problem remains

sorry for the delay, have missed this
do you have any other tube for testing V101 ?
just a guess, this tube seams to be critical.
Waldorfcave had noise issues there, replaced with a (very good) tube solved the problem.

[rob_gould]

Hi All,

First post on here though I'm a regular Prodigy-Pro reader.

My board is mostly stuffed, but I was hoping that someone could point me in the right direction for sockets for the 7 pin tube position and the T4B. I have the 9 pin sockets already. I have seen that there are various options at most suppliers and I'm not sure which to go for.

Tube Town and Banzai are where I normally get this stuff from, but any supplier will do

Thanks

Rob

[bernbrue]

Hi Rob,
extract from my order at tubetown:



hope this helps.
regards
Bernd

[rob_gould]

Perfect thanks Bernd

[Infernal_Death]

Sorry Volker, seems like i too have missed your reply

Anyway i don't think it's a problem with V101 as i have already swapped it and it made no difference. Also i think the noise has it's origin somewhere else as it sounds like something major isn't working at all in my build. For example when i switch the vu's from gain reduction to vu level, on both channels the needle goes immediately to the max right side. Even on the second channel which doesn't pass any audio.
Right now i think it's best to tear the board out of the case and have a real close look as there seems to be something very wrong.

However i don't have any time right now to look at it so the project goes on the shelf until i find some more time to work on it.

Thanks for the help so far.

Flo

[Infernal_Death]

Ok got a bit further on this project. I found two dead relays, the output relay on channel 1 and the input relay on channel 2. First time i bought Omron relais (normally i am buying finder relais) and surely the last time. 2 dead out of 4 ain't that good and also those are the first broken relais i ever got.

The broken input relay was easy to find as i couldn't trace my signal at the input transformer so i knew it was the relay. The broken output relay however wasn't so obvious. Even with a dead relay, i still got some signal at the output jack, not sure how that happened. I was pretty clueless so i just measured the resistance on between the poles on the relais, that's how i found out it wasn't even working.

Anyway it's still not working 100% but at least i made a step in the right direction and got some motivation again

Flo

[[silent:arts]]

Ok got a bit further on this project. I found two dead relays, the output relay on channel 1 and the input relay on channel 2. First time i bought Omron relais (normally i am buying finder relais) and surely the last time. 2 dead out of 4 ain't that good and also those are the first broken relais i ever got.

mhm - have used loads of Omron relays with no problems yet.
(never bought them from angie - did you ?)

Anyway it's still not working 100% but at least i made a step in the right direction and got some motivation again

good to hear you are on the way.
it is an easy project, and what we have seen from you before

[Infernal_Death]

Worked on it a bit more and i really have a strange problem.
I can pass audio on one channel (other channel gain is turned down) until i hit around 3-4 on the gain control. Then the audio signal fades away and i get hum on the test speakers. When i reach this point, the meter in output mode goes immediately from -20 to full right.
Now the strange thing is that i can interfere with the second channel in this.
If i set the gain on channel 1 (where the audio signal is) to around 2, it's fine. As soon as i start to add gain on the second channel (nothing connected to the second channel) i can start the same behaviour on the first channel by turning the gain to 2 on the second channel. The audio signal fades, the hum surfaces and the meter goes to full right position.
The reverse is also possible, making the problem on the second channel by turning the gain poti on the first channel (while the audio signal is connected to the second channel).
I am wondering if there are some problems with grounding or what could be the reason for this behaviour.
Anyone got some tips ?

Flo