Holton AV800 Schematic

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#101
thylantyr said:
I see something else odd on your screenshot.

<SNIP>
R28, R29 doesn't look like it's 100 ohms. It looks like 47 ohms or
47 something ohms :hot:
Click to expand...


OK I systematically went through the board with the schematic and a copy of the silkscreen beside me and checked every resistor... Nice catch on R28 and R29, they were 47 ohms as per the parts list. :up:

I had a thought that kind of worries me but I am going to do it anyway... I have made all the changes to the as yet untested board, hmmm do you see where this is going?, so I figured what the heck, I am going to set it up and test it, if it works I will remove all my semiconductors on the other board and just replace them, even though my Sencore TF46 shows that all are good, I can't be bothered testing them all again, time is money and it would be cheaper to just replace them all, about $10 worth of semiconductors.😉
 
#102
Failure

Well the experiment was a failure.

The new board with all the changes made prior to testing responded the exact same way right from the start.

I raised the power supply up to 15Vdc and measured across R1 and got over 5v. Not good considering R1 is only supposed to measure 1.6v when the power supply is at a full 90Vdc.

It can't be the Zeners, I was testing the amp at 15Vdc so that I could rule out the Zeners.

:bawling: :bawling: :bawling: :bawling: :bawling: :bawling:
 
#103
Have you verified the values of those suspicious resistors
I posted? There was quite a few of them 🙂

Have you verified the Q1 and Q2 installation to make sure
the transistor pins are in the right pcb holes?

Take new closeup pics of your new changes for re-examination 🙂

Not that it matters, but are you testing using +15VDC or
+15VDC and -15VDC ?

The measured zener voltage is?
 
#104
thylantyr said:
Have you verified the values of those suspicious resistors
I posted? There was quite a few of them 🙂

Have you verified the Q1 and Q2 installation to make sure
the transistor pins are in the right pcb holes?

Take new closeup pics of your new changes for re-examination 🙂

Not that it matters, but are you testing using +15VDC or
+15VDC and -15VDC ?

The measured zener voltage is?
Click to expand...



Yes I checked all the resistors you mentioned, even measured them, all were correct except R28 and R29 which I have changed on both of my AV800's.

I again verified the new orientation of Q1 and Q2. Tested all four 2SC2240's and all test exactly as a brand new one does for both gain and leakage.

I am testing using +15vdc and -15vdc supplies.

As for the zener, I took one out and tested, look at the picture.

An externally hosted image should be here but it was not working when we last tested it.


The meter on the right is supply voltage, the meter on the left is zener voltage, whats with the 14.10V it is a 1N4744 it is supposed to be 15v.
 
#106
Some Success.... WOO HOO!!!

OK...

R54 IS supposed to be 10K, that is a fact!
I checked my zeners again and replaced Q23 (BD681) and fired it up...

Here is what I got, board #1

R1= 1.274v Supposed to be 1.6v
R2= 1.333v Supposed to be 1.6v
R3= .786v Supposed to be 1.0v
R55= .645v Supposed to be 500mv
R56= .763v Supposed to be 500mv

Offset Voltage at R37 was .03v

Here is what I got, board #2

R1= 1.207v Supposed to be 1.6v
R2= 1.281v Supposed to be 1.6v
R3= .716v Supposed to be 1.0v
R55= .594v Supposed to be 500mv
R56= .703v Supposed to be 500mv

Offset Voltage at R37 was .032v

These values are pretty darn close, but I need to get them a bit better, especially R55 and R56 before I try installing the O/P devices.

I am close guys, I am really close. WOO HOO!😀 😀 😀 😀 😀
 
#111
No, I wouldn't mind at all.
But the revisions would only be applicable to the first version boards, mostly, but I think the information would still be useful to all trying to build the amplifier.

I am going to try a board with the O/P devices installed later tonight, and if all goes well I will give it the old music test.

Keep your fingers crossed for me.:nod:
 
#113
Re: Some Success.... WOO HOO!!!

Frazzled said:
Here is what I got, board #1

R1= 1.274v Supposed to be 1.6v
R2= 1.333v Supposed to be 1.6v
R3= .786v Supposed to be 1.0v
R55= .645v Supposed to be 500mv
R56= .763v Supposed to be 500mv

Offset Voltage at R37 was .03v

Here is what I got, board #2

R1= 1.207v Supposed to be 1.6v
R2= 1.281v Supposed to be 1.6v
R3= .716v Supposed to be 1.0v
R55= .594v Supposed to be 500mv
R56= .703v Supposed to be 500mv

Offset Voltage at R37 was .032v
Click to expand...


Anyone care to comment on these values before I commit to installing output devices?

I am a little worried about the measurement at R56, this is almost 50% higher than what the construction guide states that it should be, I would rather address this concern than risk damaging more parts especially output devices.
:$: :$: :$: :$: :$:
 
#115
Almost ready.

An externally hosted image should be here but it was not working when we last tested it.


Well I removed the 10 ohm resistor, soldered in all the output devices, drilled and tapped the mounting bar for Q8, bolted the amp down to my wind tunnel heatsink insulators used and attached Q8 to the mounting bar.

I am about ready to do final testing and bias adjustment.

I am going to take my dogs for a walk and then feed them, then I will go down to my basement shop and I just might fire the whole thing up.

Stay tuned... I may wait until tomorrow when I am rested and might be able to spot any potential problems.

Frazzled🙂
 
#117
YUP... Gonna sleep on it.

I got everything ready for a test tomorrow morning.
As soon as I have had a chance to fire it up and do the tests, I will update.

Thanks to everyone for their help and encouragement and a special thanks to thylantyr who was my second set of eyes and was constantly giving me new ideas to try, I am pretty sure he was mostly responsible for getting me through the pre-flight testing.

Until tomorrow then...
😴 😴 😴 😴 😴 😴 😴 😴 😴
 
#119
Does anyone have an idea what the idle current of this amp should be?

I started powering it up and my offset voltage was way out of whack and at less than 10v from the power supply I was getting a reading of 3.5A.

I checked all the output devices for shorts and found none.

No Joy!🙄

Oh and I am getting a negative offset voltage???
I have the + lead of my meter at the + output of the amp and my - lead at ground and I am getting a negative offset voltage and a oscillation at the output all at less than 10v on the power supply.:xeye:
 
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