All things LA2a related

[JerryPbury]

[quote author="Scenaria"]hmmm....

mine dont take that long to drain (when the tubes are in) I would say under 10 seconds...


so when you power it up with GR selected where is the needle sitting? at zero or a lot lower?[/quote]

Takes several minutes to drain. Checked all of my grounds etc. for continuity and everything checks OK. Tubes are in. I thought that it was a long time. I'm used to them draining much faster.

After adjusting my VU zero, it moves to zero in GR at startup.

 

[Scenaria]

then the tubes must not be loading the p/s down...

this is a first ive seen of this one..

wanna mail one down for me to take a look at?

 

[JerryPbury]

[quote author="Scenaria"]then the tubes must not be loading the p/s down...

this is a first ive seen of this one..

wanna mail one down for me to take a look at?[/quote]

6AQ5A? This is where I have all of the high voltages at the connections to this tube.

I have swapped all tubes with the same results. Both 6AQ5A's, etc.

If that's the one I'll send it out when I get back.

Thanks,

Jerry

 

[cayocosta]

The 6AQ5 is not biased correctly. It's not pulling any current, that's why your B+ is high and you're not dropping any voltage across the plate resistor - R34.

This could be caused by:

DC on the grid - pin 7. (That could occur with a leaky capacitor - C9)

A bad cathode ground.

A reversed electrolytic capacitor on the cathode - C10.

The heaters are not on.

 

[JerryPbury]

[quote author="cayocosta"]The 6AQ5 is not biased correctly. It's not pulling any current, that's why your B+ is high and you're not dropping any voltage across the plate resistor - R34.

This could be caused by:

DC on the grid - pin 7. (That could occur with a leaky capacitor - C9)

A bad cathode ground.

A reversed electrolytic capacitor on the cathode - C10.

The heaters are not on.[/quote]

DC on grid. Will check. C9 did check OK but I did not check for leak.

Verified all grounds.

Verified cap orientation. Electrolytics do get ugly when put in wrong (did this once in a old Dynaco ST70).

All heaters checked OK. Verified voltages and continuity & connections. As well as a visual that all heaters were on.

Thanks! I'll check for leak past the cap. Will check everything else again and if it solves the problem will let you know which one it is.

Jerry

 

[cannikin]

Ok I'm finally at the initial testing stage, Here are my measurements without Tubes and T4B:

AC Volts Between A24 & A25 - 7.14 AC
B21 - 379.5 dcV
B20 - 380 dcV


My Neon Isn't illuminating

A1 - 23.68 dcV

Any thoughts??

 

[cayocosta]

I say pop in the tubes.

 

[cannikin]

[quote author="cayocosta"]I say pop in the tubes.[/quote]

Really? pop in the tubes...

but whats up with my neon and the low voltage on A1

 

[cayocosta]

Is your B+ voltage at the top of the 470k (R28) the same as the B+ voltage at the top of the 10k (R34)?

 

[cannikin]

[quote author="cayocosta"]Is your B+ voltage at the top of the 470k (R28) the same as the B+ voltage at the top of the 10k (R34)?[/quote]

They are exactly the same :grin:

 

[cayocosta]

I don't know what voltage to expect at the NE-2 with the power supply unloaded. But your voltages appear to be good. Put the tubes in - and be careful.

 

[Scenaria]

double check your wiring on the rotary switch...

I just fixed wil's and it had a similar problem... neon didnt light and the VU didnt swing up to zero (it was shorted to ground)... found the GR wiring off the rotary to be incorrect...


the neon should light even if the tubes arent in

 

[cannikin]

thanks scenaria;

That was it, I had a little short near SW3.


Anyway the Neon is glowing and my A1 reading is 57 dcV.

 

[Scenaria]

rock-n-roll

plug those tubes in


and share pix!!! you all put in all of this time but never post pix

:roll:

 

[Scenaria]

oh and be sure to turn the two pots on the back fully clockwise...

 

[cannikin]

Hey LA2a Gurus;

Despite my initial (no Tubes) voltage values being correct, I haven't put the tubes in the unit yet, because I have one snag....

The unit is in permanent power "ON" mode. :shock:

The wiring of the P. trannie:
Primary:
1 Black to Live on power connector (Wire to B24)
1 Black to Neutral

Secondary:
Center Tap 6.3v (green w/yellow stripe) to ground Bus/TAG 3
Center Tap 250v (red w/yellow stripe) to ground bus/TAG 3

2 - 6.3v (green) to A24 & A25 with heater Wire.
2 - 250v (red) to A22 & A23
Ground:
Grey to Gound on the Power Connector.

The wiring from B24 & B25 to the SW1 are correct.

What is eluding me is the connection of B25 to the Power Trannie.
Right now I have nothing connected to B25 other than SW1
I know thats not right - I'm missing a connection, which is disabling SW1

 

[Scenaria]

B24 should come from the hot coming out of the IEC connector... and tied to one side of the power switch

B25 should be tied to the other side of the switch and also tied to the black primary lead of the power transformer...

the neutrl should go right from the IEC to the power transformer

 

[cannikin]

Ok The Tubes are in, Here are my #'s:

B21 - 351V
B20 - 351V** Should be roughly 275V
A1 - 56.1V
A14 - 233V** Should be roughly 216V
A17 - 7.1V** Should be roughly 90V
A19 - 146.1V** Should be roughly 105V
A20 - 156V** Should be roughly 131V

** Are Suspect.

Whatcha Think?

 

[Scenaria]

what values are you using for:

R36
R31
R34
R29

?

do you have BOTH R37 and R3 turned fully clockwise? (looking at them from the back of the chassis)

 

[cannikin]

R36 - 470R
R31 - 1K
R34 - 22K 2W
R29 - 4.7K 2W

Both R37 & R3 are 100% Clockwise