power transistors

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#21
check output offset

You must disconnect the speakers and disconnect the input cables.
Then insert a zero ohms dummy RCA/Phono plug into both inputs.
Power ON.
Clip your voltmeter black probe to power ground (the speaker return should be the same as power ground).
Clip the voltmeter red probe to the speaker output. What is the DC volts reading on Left output and on right output?
Power OFF.
 
#23
Oh Geez...OK.
Let me do this again, sorry about that.
When you say Left output and Right output...you are talking about a "stereo" amp right.?
This amp has two mono outs in //.
So i assume i will just be taking one reading for DC off-set.?
Sorry about all the questions, but you guys probably forget how much You Know and how much i Do Not know.
Thank You
 
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#26
you've got a Peavey BH 400 output module what do you have for a pre-amp ?

common fault with those is usually CR20,21 the regulators for the low voltage rails(hum, and no or faint sound) but sounds like you've now got blown outputs as well.
 
#29
jaycee said:
I also see now this is a Peavey amplifier. Peavey love to use their own transistor markings, so the part numbers on them will probably not read to anything you recognise.

For the output and driver transistors, I would go with these:
Q4-Q6: MJ15003, MJ15022, MJ15024
Q14-Q16: MJ15004, MJ15023, MJ15025
Q3: MJE15032
Q13: MJE15033

Aha, just found a crossreference list:
http://adrsoundsense.co.uk/technical/peavey/PV_Semi_Cross_Ref.pdf
Click to expand...

Sorry, but the Peavey 400BH power amp module is of the quasi complementary type with NPN/PNP predrivers, NPN drivers and NPN output devices. So the correct cross reference should read:

Q2: MJE15032
Q12: MJE15033
Q3-Q6, Q13-Q16: MJ15003 or MJ15022

Best regards
 
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#32
AndrewT said:
"no input"
I told you to
Click to expand...
.....Zero Ohms is a short, right.?
These In Jacks are all switched and their default is short not open.
I can insert a shorted jack but the number will be the same won't it.?
Both Pre and Post gain knobs are also at Zero.
Even with the Input Jacks open, the VDC was still that same... 5.7
Of course, with no speaker plugged in, the Out Impedance is huge, but that is what you guys said to do.?
 
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#34
fuse said:
Sorry if i am still confused about the off-set.
Am i supposed to measure between the +52 and -52.?
That number is about 15.5 Volts.
+52V to speaker jack tip is about 13.5V
and
-52V to speaker jack tip is about -2.2V
Is that the numbers you guys are looking for.?
Thank You
Click to expand...

Maybe I'm misunderstanding you, but if you measure between both rails the reading should be about 104 volts. What ist the exact voltage of each rail with respect to ground?

Best regards!
 
#35
AndrewT said:
The output impedance is not huge. It is very likely to be less one ohm.
The load impedance is huge when no load is attached. Probably close to infinite.
Click to expand...
Sorry, i am Completely Lost.
You guys all have WAY MORE knowledge/Experience than i do.
Where are you calculating these numbers.?
If i put a meter across the Out Jacks it will say OL...Infinite Ohms.
If i put a meter across the In Jacks it will say Zero...Zero Ohms
Let me ask this:
What type of plug do you want me to insert to the In Jacks...Open or Short.?
What type of plug do you want me to insert to the Out Jacks.....Open or Short.?
Right now, with no plugs inserted, the in jacks read short and the out jacks read open.
 
#37
fuse said:
Even with this amp is on a limiter.?
If that is true, i have huge problems with the B+ as well.
Click to expand...

Sorry, I didn't notice you're using a limiter. Is this a light bulb in series with the power trafo? Does it light, even with no input signal applied? A dark red glow would seem to be normal, but the rail voltages should be equal. Otherwise (unequal rail voltages, bright glow), check all predriver, driver and output devices, one by one. Yes, you'd have to desolder each one carefully...

Best regards and good luck!
 
#38
Hey KP -
Yes, you are correct...a 100 Watt light bulb in series with the hot wire of the Mains.
I understand what you are saying. It does not glow, or flash then glow, the bulb lights bright as soon as the amp powers up and it stays bright the whole time.
Yeah, it would seem i need to pull and check or just pull and replace all that stuff.
No doubt all The Elytics in the DC Supplies are past due as well.
Thank You
 
#39
fuse said:
............ the bulb lights bright as soon as the amp powers up and it stays bright the whole time............
Click to expand...
Did you test the Mains Bulb Tester after you built it?
a.) Does the bulb light with the output socket empty?
b.) Does the bulb light when a low power appliance is plugged in?
c.) Does the bulb light when a high power appliance is plugged in?
Try a radio tuner for b.) and then a hair dryer or fan heater for c.).

If your tester is good, then move back to the amp.

Disconnect the transformer primary wires (easier to remove the mains fuse). Does the bulb light?
reconnect the primary and disconnect the secondary. Does the bulb light?
reconnect the secondary and disconnect the rectifier from the PSU. Does the bulb light?
reconnect the rectifier and disconnect the smoothing caps. Does the bulb light?
reconnect the caps and disconnect the amplifier/s. Does the bulb light?
 
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#40
Hey Andrew -
I have only used it with tube guitar amps. It does not light with a "good" amp, and i have used it with success in the past.
I have never tested it, as in your examples, but i will give that a shot.
Thanks
 
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