Balder lightning guitar amp schematic please!

[bigdrums925]

I am desperately searching for any documentation for a BALDER LIGHTNING GUITAR AMP.
I believe Balder was located in Sweden, then bought out by Nady Systems in Oakland, CA.
I have checked with Nady but they say they got rid of all Balder/Nady docs years ago.
If anyone can point me in a likely direction it would be appreciated greatly.
One of the problems I'm having with this amp is high frequency parasitic oscillation.
I'm told this was an ongoing problem with these, but a great SS amp otherwise

On the circuit board it reads "S.O.S. LIGHTNING LMk 82-2

Thank you

[nickb]

I see you asked once before Balder lightning schematic needed - it's not looking good.

I think you safely say you are on your own with this. Can you post some gut shots so we can see what you are dealing with? How do the controls affect the problem?

[bigdrums925]

Thanks Nick, I wasn't sure if I posted previously or not.


In this pic the 4ea TO3 output transistors have been removed.
When they were in I could not prevent it from going into oscillation.


This pic is of the circuit just before the output. I was able to determine one of the trim pots is for DC offset. Still don't know what the other is for

Recently I found upwards of 166 VAC nearest the missing output transistors. But this only occurs when a plug is inserted into the channel 1 input.
It doesn't have any signal on it, just inserting it causes the high AC voltage to appear, disappears when removed. It does not occur inserted into the
channel 2 input jack. Not sure but it may be related to the tube overdrive circuit in this amp.
The AC is strange but the oscillation is the one I need to tackle.

[J M Fahey]

Just thinking aloud and in no particular order:
1) expensive Darlington output transistors.
2) you can do nothing until you remount them, amp is running and showing nasty oscillation.
3) just a hunch but I would not be surprised if it had some family resemblance to old Hughes Ž Kattner amps.
They also once loved these Darlingtons, this designer might have "borrowed" that design (something way more common than most think), so that *might* help-
4)

How do the controls effect the problem?

5)

I found upwards of 166 VAC nearest the missing output transistors. But this only occurs when a plug is inserted into the channel 1 input.

"near" (physical proximity) means nothing, connections mean everything.
"166VAC" might very well be *60V DC* improperly understood by a cheap multimeter, measuring DC but set to the AC scale.

So in a nutshell:
6) rebuild the amp as original and weīll suggests some tests.

[nickb]

As Juan said + make sure no speaker is connected to avoid stressing the output transistors. Also, loose that badly wired jack plug before it shorts out and destroys the output transistors.

[Jazz P Bass]

What in the world are they using that UPC2002 for?

It's a 5W power amp.

[nickb]

What in the world are they using that UPC2002 for?

It's a 5W power amp.

Reverb driver (with attitude)?

[J M Fahey]

Most certainly.
Roland and Yamaha typically used a "car radio" type chip amp to drive low impedance (8 ohms ) reverb tanks.

They *might* also use it for an independent headphone out although that would be more unlikely.

[bigdrums925]

The UPC2002 probably does drive the reverb. I removed the "tank" to get a better look at the traces, and the "tank" mounts just above the 2002 chip on a set of four springs. Not that it matters but the reverb springs have no cover, never did.
I removed the Darlington's to see if the oscillation occurred prior to and without them in. Results were nonconclusive. It was at that time I noticed the high AC. I understand near means nothing, but the output drivers which connect directly to the Darlington's are there so.....and without the schematic was trying to get a general understanding of the signal flow paths.

[J M Fahey]

Ok.
The main point was that VERY probably you do NOT have 166VAC there, but your meter is lying to you.

[nosaj]

Ok.
The main point was that VERY probably you do NOT have 166VAC there, but your meter is lying to you.

Ground reference could be very important in this case, no?

nosaj

[bigdrums925]

Before I put the Darlington's back in can anyone suggest a way to test them with certainty?
I have a simple transistor tester but it gives me different results depending on which lead I put where.
The manual that came with it suggests it shouldn't matter which lead goes where
However it does say it might not test high gain Darlington's accurately
It is a radio shack cat No. 22-330 electronic components tester

[J M Fahey]

it does say it might not test high gain Darlington's accurately

Test them using the diode function in your multimeter, they will test like any other NPN or PNP transistor with just two minor quirks because of their internal construction:
1) forward bias Vbe will be around 1.3V instead of around 0.65V for the very good reason that you are measuring *two* BE junctions in series
2) in many power Darlingtons , certainly in TIP142/147 , not sure on these, you will find an internal EC diode, connected "backwards" so it does not pass current under normal operation, so if you find it , donīt worry.
Itīs a "parasitic" diode which appears as a byproduct when the transistor is made, but since it does not cause any problem, they leave it there.

Example: TIP142 showing the internal parts, see the two BE junctions in series and the parasitic diode (pointing "the other way" so it does not pass current under normal operation) ; yours shouldnīt be very different.

[Enzo]

And to be thorough, the two internal resistors are parallel the two BE junctions and can confuse readings.

[bigdrums925]

I checked the Darlington's seemed ok but didn't find a double junction in every case, however the were all the same as its pair.
Put them in and brought up the variac with the scope on the output, no load. no input plug either 0-1/2 way very little current draw, then at 50%
the variac amp meter slams on full (1.5 amp meter) and about 20mV of oscillation appears on the scope. Same as before.
Turned it off. Any suggestions?
Btw the ground pin is missing from the power plug.