Hartke HA-3500 static noise. Traced to output board thus far.

[Indyryder02]

Need to clarify which transistor is which. Which one connects to R318 ?

318 goes to base of Q067

[Indyryder02]

DO NOT connect a capacitor between R318 and ground. It will take off and become unstable. I have seen them destroy the power transistors. The noise, will pass through R318 and Q301 will cancel it, if Q301 is working correctly.

Shorting all three pins together gives you no noise? Please confirm that shorting the pins stops the problem you have or just stops the static noise.

If it does;
That means the noise is coming in BEFORE that point, nothing tp do with the power amplifier at all !!!!

It silenced the overlaying static.. the problem remains on the output board.

[Indyryder02]

Hope I answered those questions clearly and correctly.

[Indyryder02]

Get a chance to look at this amp again since I have another good one here to compare to.
so. Looking again at the no name pair of transistors…
(q301 & q067). The emitters have around 1.5v on the noisy amp, and about .7v on the good amp. This definitely seems to be the issue, or an issue. Trying to figure out what causing this. Suspecting Q302.. it tests fine with a diode test. Haven’t found any shorted caps or open resistors near these..

what else should I look for?

[g1]

Compare voltages at Q302 and Q303 with good amp.

[Indyryder02]

Compare voltages at Q302 and Q303 with good amp.

Bad amp.
Q302
E -24.4v
B -1.9
C -26.5

Q303
E -24.4
B -23.9
C -23.9

D301 & D302 +/- .6v.
both sides of
SVR301 @ +/- 260mv
both sides of
SVR302 @ -1.5v

Good Amp
Q302
E -32.9
B -1v
C -32.2

Q303
E -32.8
B -32.2
C -32.2

D301 & D302 +/- .5v
both sides of
SVR301 @ +/- 230mv
both sides of
SVR302 @ -.5

I found another thread on here with this same issue.. unfortunately it ended unresolved.

sadly this amp is a pain to work on taking the board from the heat sink etc.. and simply not worth the time I’ve invested in it..
I need to just stop taking stuff like this in. There’s plenty of other tube amps etc I could make money on. Ugh..

[g1]

Q302 collector can't be more negative than the emitter (bad amp).
Not sure why the difference in B- supply voltage, are you on a limiter lamp?
As it is just a noise issue, there is no reason for a limiter lamp and it will just confuse readings. Limiter lamps and variacs are only needed for issues like blowing fuses/burning components etc.

[Indyryder02]

Q302 collector can't be more negative than the emitter (bad amp).
Not sure why the difference in B- supply voltage, are you on a limiter lamp?
As it is just a noise issue, there is no reason for a limiter lamp and it will just confuse readings. Limiter lamps and variacs are only needed for issues like blowing fuses/burning components etc.

I did both amp tests on a lamp as the components are so hard to access confidently.. so just to prevent a short while probing.
I usually don’t use one for anything but replacing blown outputs etc in general.

[g1]

The differences in supply voltages (when on bulb) between the two amps suggests there is more going on than just noise.
Suggest going off-bulb at least to check for supply voltages and if any DC offset at output.

[Helmholtz]

Bases of Q302 and Q303 are connected, so sit at the same voltage. Check again transistor leads.
Probably base and collector leads mixed up.

[The Dude]

^^^^^^ That! Those measurements don't make sense unless you have the pin configuration wrong.

[Helmholtz]

DCV at speaker output?

[Indyryder02]

The differences in supply voltages (when on bulb) between the two amps suggests there is more going on than just noise.
Suggest going off-bulb at least to check for supply voltages and if any DC offset at output.

More like 48v on both. Without lamp. I had a load hooked up to one I forgot about that may have caused the difference .

[Indyryder02]

Bases of Q302 and Q303 are connected, so sit at the same voltage. Check again transistor leads.
Probably base and collector leads mixed up.

Yes.. apologies. I did have the base and collectors backwards.

I’ll try this again without the limiter..

Bad amp..
Q302
E -50. (This and the other -50 was 48v I suspect just wall fluctuation while testing)
C -1.8 (seems to be the main difference)
B -50

Q303
E -50
C -50
B -50

sides of SVR301 145mv & 283mv
SVR302 -1.3 & -1.3 (this is also the main difference)

Good amp

Q302
E -48
C -.8
B -48

Q303
E -49
C -48
B -48

sides or SVR301 168mv & -275mv
SVR302 -.5. & -.45

hopefully this is better.
I should really prob just stick to tube amps. (But of course many of them have solid state devices as well to deal with)
Ive repaired a lot of solid state amps, many with help from you guys.
Chalk this all up as more learning!

[Indyryder02]

DCV at speaker output?

Yes.. about -1vdc. I should have checked this first! I’m familiar with this from hifi amps I’ve repaired in the past, usually they had a lot of distortion or hum though. Never hiss / static noise.
So I’ve gone about this one all wrong from the beginning unfortunately.

No recovering time now. So just trying to better understand thes damned transistors!

I see the main difference is the .8 v on collector of Q302 on the good amp and the -1.5 on the bad amp. But don’t fully understand the cause.. diodes / transistors etc.. .7v usually.. just means q302 isn’t working? Even though it tested ok with a diode and transistor tester. Hmm…