Special 130 sounds "dirty"

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RussW
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Special 130 sounds "dirty"

Post by RussW » Sat Nov 12, 2022 5:18 pm

My Special 130, audio when quiet while playing. I replaced ALL the Electrolytic capacitors. I now have volume back.
However, it does not sound clean. With a scope, and a 1khz signal the preamp signal seems clean and amplified

I then found the screws for one of the power transistors Q6 (T03), were loose. I tighten them.
These Transistors are indicated as 2J6392.

What is the correct replacement for this transistor, there are 4

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Pappy B
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Re: Special 130 sounds "dirty"

Post by Pappy B » Wed Nov 16, 2022 9:42 am

According to my schematic Q6 is a JSE-5331, a TO-126 case. The 4 Power transistors ,Q-7, 8, 11 &12 are SJ-6392's and Peavey's cross Reference List says the field replacements are MJ-15015 or 2n3055A.

I would double check the polarity of the replaced capacitors and also look for any bad solder joints. Power resistors should be checked also.

Diodes cr36 and cr37 is another possible source of the problem.
The more I learn the more I realize how much I don't know.

RussW
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Re: Special 130 sounds "dirty"

Post by RussW » Fri Nov 18, 2022 3:06 pm

Thanks, I did have C47 reversed prior to starting this thread. I replaced it with a new one.

I did not test the new caps with my cap tester,

Measurements I took today based on the schematic

Q13 = 2n3904
B = +0.12vdc Volume at 0, increases to 2.2vdc
C = +32vdc
E = 0.8vdc

Q14= 2n3904
B = [b-][/b]8.1 vdc Volume at 0, increases to -6.5vdc
C = +39vdc
E = 0.8vdc

+42v = 39vdc
-42v = -36vdc
-13v = -8 vdc (measured at R82)

I have a Four (4) ohm / 200w resistor load connected. What I did notice, is the output waveform did not look right when scoped

I will look into your suggestions

rogue777
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Re: Special 130 sounds "dirty"

Post by rogue777 » Sat Nov 19, 2022 1:37 am

Pay attention to the dc voltages written on the schematic in the power amp. imo These are quiescent no-signal condition dc voltages. Don’t be turning any knobs for measurements. Keep the volume at zero. Focus on dc voltage, what you measure vs the schematic values. Your measurements of Q13, Q14 look off balance. Especially Q14 base to emitter values, unless that’s your typo-the 8.1V on the base? Try replacing those two transistors (if you have 8.1V on the base) and go from there. And did you replace C49? If not, replace that cap too.

PV Special 130.pdf
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RussW
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Re: Special 130 sounds "dirty"

Post by RussW » Sat Nov 19, 2022 10:50 am

volume at 0, no input connected.


Yes 8.1v is measured at the base of Q14, of note I had previously installed C47 in reversed when I replaced it.
I see the how this may have damaged Q14. I will investigate this.

On a side not, I am getting 120hz from the speaker with volume at 0, with or without an input connected, it does not seem to increase with volume.
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RussW
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Re: Special 130 sounds "dirty"

Post by RussW » Sat Nov 19, 2022 12:51 pm

I remeasured; I have attached the measurements. Yes, C49 was replaced, I will check it again.
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rogue777
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Re: Special 130 sounds "dirty"

Post by rogue777 » Tue Nov 22, 2022 7:55 pm

Thanks Russ for the effort. Yes Q14 needs to be replaced. Also replace Q13 at the same time considering the effort vs cost of a 2N3904.
I'm not sure what effect that will have, hopefully positive. Its like they control the whole amp, so that part needs to work right. Both the positive and negative sides are conducting way too much. The supplies being pulled down from +/- 42V vs 39V. Now I need some help in figuring out this. Some values are close but a couple are way off. Hopefully some more educated person will help out.

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Pappy B
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Re: Special 130 sounds "dirty"

Post by Pappy B » Wed Nov 23, 2022 9:28 am

2N3904 is a common transistor and not expensive. It would be best if they were matching.
The more I learn the more I realize how much I don't know.

RussW
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Re: Special 130 sounds "dirty"

Post by RussW » Thu Nov 24, 2022 3:17 pm

Well, some good news. Q6 was shorted Base to emitter. it was an SJE-5331, I replaced it with an MJE-243, plus changed out Q10 for an MJE-253.

And replaced Q13, Q14 with 3904 (SPS-7239 were in), Q4 for an MJE-253, and Q5 and Q9 as well. and the 120hz hum is gone as well

I got some re-education here, never really got into analog / audio.

Added some LEDS to indicate Reverb is ON, and LEAD or NORMAL channel active. LEDS are to Upper left of the volume knobs
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Pappy B
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Re: Special 130 sounds "dirty"

Post by Pappy B » Sat Nov 26, 2022 9:54 am

Glad to hear it's working again. I think the Special 130 if a great amp in the Combo category. I like the Mid Tone Control on this one. You can tweak your sound more than the typical one knob mid. And I think the 4 ohm Scorpion used in this model is great. And though I like the tone of good tube amps, I am a big fan of solid state amps and Peavey's are at the top of my "favorites" list.
The more I learn the more I realize how much I don't know.

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