All things LA2a related

[CJ]

The grid of V3 is fed off the input iron so grid stoppers might not be it, unless the osc. is flying around the circuit, which can happen sometimes.

It might be the AQ5 doiny it by itself.

Increase R35 to 1 meg to drop screen volts, that might help if it is V4 in osc.

 

[Paul B]

thanks guys,

CJ, I am measuring 222VAC on the tube side of C11. With no audio it stays at 222 as I turn the PR and with audio it peaks at about 255 by the time PR is all the way up. On the pin 3 t4b side I get 0V without audio and a max of about 1V with audio and PR maxed. I definitely have a problem in this area so I will trace out with highlighter per your suggestion.

The grid stoppers are in on pin 2 and 7 of V2. I will try a 1meg as R35 tomorrow.

I am measuring 804VAC at C7a and 631V at C7b. just for grins, C7c is 492VAC and C7d is 285.

Steve - I have listened to the signal very, very carefully to see if in fact maybe I was tricking myself with my ears. Im not an electrical engineer (oh,... really???) but I do have a very good ear and I literally am not hearing any compression or volume reduction at all until a setting of about 65-70 on PR. I have tried different inputs, preamped or DI'd or not, with signal levels (audiowise) that would blow the doors off anything else. I am getting the same results - strong input signal, tiny compression. overly strong signal, more compression as the input signal gets stronger/worse(the higher/worse the input level, the earlier the meter shows reduction as I turn PR up)

Steve and Analog, I will have time to mess with the software this weekend. It looks interesting but Im not sure how effective in the hands of someone like myself. The learning curve could be quite flat. I do want to see if I can measure for the oscillations that you are talking about.

Let me know what you think of the C7 voltages and if you have any more ideas about, well, anything.

Paul

 

[Scenaria]

HOLY CRAP

did your really write 804V AC? and 631

dont turn this thing on anymore..

if you are really seeing those numbers... theres some things we need to address.. for the life of me I cant even think of how your seeing those values..

let me sleep on it

 

[CJ]

Paul, be sure you are not reading millivolts ac.

If you are using an auto ranging meter, and measuring low voltage, it will go to mv but you might not see the mv in tiny letters.

I pretty sure you are, otherwise your house would have burned down by now.

If it is AC Volts, check the pwr supply first.

 

[AnalogPackrat]

:shock: :shock: :shock:

Two things. First, what brand/type of meter are you using? Can you please measure ACV at the outlet you are plugging into (put the black probe into one slot and the red probe into the other)?

Wave had a wacky outlet in his apartment and maybe you do too. I once lived in a duplex that had a 220V box for a window mounted air conditioner, but someone had put a standard outlet in it! Luckily the only thing we plugged into it were a string of christmas lights. They seemed awfully bright, so I checked the voltage. 220!

Analog Packrat

 

[Paul B]

The DMM is a cheapo GB and it didnt even occur to me that its capacity is 500VAC so I dont know how I am getting these readings. It is not showing me mv - there is a small 'HV' in the left corner. I am measuring 121-125VAC at the power outlet. Maybe I need to get a better DMM :?:

ugh I am sorry if I am wasting your time. Despite the tribulations and aggravation, I've had a great time building the Bloo and Ive learned a helluva lot, but I need to get back to playing. I am considering sending the unit to Steve to have a look at it. Let me kmow if you have any more ideas.

Thanx for your patience,

Paul B

 

[AnalogPackrat]

Paul,

Hey, we're all volunteering our time. Don't feel guilty. Everyone makes mistakes and I, for one, learn more from mistakes than anything else. CJ has said before that he enjoys the challenge of remote debugging. I do too.

It seems like your DMM works since you got a reasonable reading on your outlet. If you have a manual you might look up what the "HV" indicates besides the obvious "high voltage."

The only other idea I have is to disconnect the power tranny HV secondary and check the voltages there (be very careful not to let the leads touch anything else and keep one hand in your pocket). Something is really wierd. Have you looked at photos of anyone else's build and compared them to yours? I have some at:

http://photobucket.com/albums/a173/AnalogPackrat/Bloo LA2A/

Use "Bloo" as the password to view them. Check the right end of the turret board where the PS stuff is...

Analog Packrat

 

[CJ]

Measure from the center tap to each leg of the secondary of the power transformer. If you measure across the full secondary, you might zap the meter.

Caps disconnected. We can fix it here, but if you want to send it off, that's your choice. I think if we get you a good power supply working, the thing might work right. Don't get mad, get even!

 

[Paul B]

Well since you guys enjoy the challenge of remote troubleshooting, then I wouldnt possibly think of denying you guys such a GREAT time :grin:

Now bear with me, I'll remind you all that you are helping an electrical ignoramus, so write to me like Im in first grade. i dont know terminology like center tap or secondary leg, you will need to say something like "the grey wire from the power transformer"

CJ, are you saying to take out the caps before I make these measurements? (see what I mean?!)

A case of your favorite beer to everyone involved when this thing is fixed. And I mean that!

Paul

 

[CJ]

OK, lets do the pwr supply first. Leave the primary side connected to the power plug/fuse.

Leave the heater wires connected. These are green wires, right?

How many wires are left coming out of the pwr transformer and what color are they?

I suspect two reds and one red/"striped with something" wire. The striped would be grounded as your center tap. No need to unsolder it. Just unsolder the two red wires that go to the diodes, those two small black thingy's with a stripe or arrow on them, that then lead to the big capacitors.

Do you have a digi camera?

What make/model pwr tranny?

We have yet to be skunked on troubleshooting here at the forum.

The harder the problem, the more fun it is, because then we get more of a cyber self esteem boost and get to act like were cool beens for five minutes.

You did read my signature at the bottom, right? :razz:

 

[Scenaria]

his power tranny should be from allied

6K88VG

two blk's are primary

two red's are 250v

red/yellow is 0v (center tap)

two Grn's are heaters

Grn/Yel is the center tap

gray is the shield

 

[Paul B]

The power tranny is the Allied 6K88VG. The other wires out of it are the yellow striped red, yellow striped green and grey. those 3 are to ground.

no digi camera but I can get one. will disconnect reds now.

 

[CJ]

Cool.
While your under the hood, check the polarity of the diodes. What side are the stripes on? The cap side or the transformer side?

Also, what kind of filter caps, they should say 20 uf at 450 volts or siimilar.

How is the minus lead labeled? Black stripe? Where is it soldered?

Hook up one lead of your meter, which I know is set to AC volts with the red jack not in the ma socket, to chassis ground, via an alligator clip lead or alligator on the end of the probe.

other lead gets another alligator flown in fresh from a florida hurricane attached to one of the red wires. black meter lead is fine on the red, since ac is non polarized. (trying to teach ele 101 at the same time)
stand back and lite that bi-atch up!

 

[Scenaria]

light up?

oh you mean the compressor

:green:

 

[Paul B]

Diode stripes on the cap side. C7a & b are 47uf 450V, c& d are 33uf 450V.
The caps have an indentation on one side. that IS the + side isnt it?
:sad: the minus sides of the caps are to ground. measuring each disconnected red wire to the ground where the center taps are, I measure 289 VAC on each.
I apologize, Im not understanding your instruction to attach the black lead to ground, take the red lead out of the ma socket, and do what now??

 

[CJ]

How's the weather, punk?
Yeah, you will have to lite one after I get done cleaning up your customer's mess.
You get the coin, and I get the customer support.
I guess you didn't fall off the hay wagon yesterday, now did ya? :grin:

Don't worry Paul, I was talkin to Austin.

 

[Paul B]

Yeah I'll be lightin one of those when this sucker works. sorry to be such a mess. :evil:

 

[CJ]

OK, that ac is a lil high but no big.
We can mod your supply to get it down a bit.

Those caps should charge to peak voltage of 289 times 1.4 equals 400 volts. Dangerous, but not lethal. We don't wear panties with lace on them like some of the paranoid saftey fanatics around here, so not a problem. Right?

Paul? Come in, Paul! :grin:

The circuit load will draw down the voltage to about 1.3 times 289 which is 375. Plenty of headroom on the filter cap voltage.

Hook up the red wires and measure dc volts on all four caps.

Oh yeah, un plug it first. Don't just turn off the pwr sw.

 

[Paul B]

No sissies here. I picked myself right up after that 289 V went across my chest....

Im getting C7a- 366VDC, b- 288V, c- 227V, d- 131V. Still getting the bizarro AC readings of 809, 636, 498 & 287 respectively; maybe best to throw this info to the side for now (?)

 

[CJ]

Yeah, forget about it. It's rf messing with your meter.

Your probably driving the next door neighbor's dog nuts, but thats tough on them.

OK, how are you sittin as far as having a few resitors laying around the house?