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Messages - Jazz P Bass

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1
Amplifier Discussion / Re: Rickenbacker TR25 Noise
« on: January 21, 2020, 10:10:43 AM »
That puppy was manufactured in 1977.
So any interboard connections are suspect (wipe them with DeOxit).
The controls & reverb jacks should also be gone over.
As to the squealing: do any controls affect it?
Be careful in there as there are quite a few obsolete transistors in it.
The slight distortion may be a bad speaker. Try another one.

2
Guitar News / Re: Nutube is the word of the day at NAMM - Vox and Korg Nutube pedals
« on: January 11, 2020, 11:05:55 AM »
Ibanez also uses a NuTube in the new Tube Screamer.

3
Amplifier Discussion / Re: Crate CR112 tone stack
« on: January 05, 2020, 09:33:05 PM »
The 'Bright' capacitor C41 is 680 pf.
You could try a lower value, like 220pf.

4
Amplifier Discussion / Re: 1988 Randall RG100ES
« on: January 03, 2020, 01:30:01 AM »
I am stuck on the squirrely voltages on Q8.

5
Amplifier Discussion / Re: 1988 Randall RG100ES
« on: January 01, 2020, 08:59:11 PM »
Q8 according to the schematic:
B:Not specified (47K from ground, it's an NPN transistor so I would expect minimal Vdc)
C: +38Vdc
E: -1Vdc

Q12 should have a negative voltage on the base: 0.6Vdc

(You do have the schematic don't you?
The expected static voltages are well marked.

6
Amplifier Discussion / Re: 1988 Randall RG100ES
« on: January 01, 2020, 04:47:26 PM »
Not too sure what you are seeing.

Reverb output ic looks good but Q8 base looks bad.
That makes no sense unless Q8 is toast.

Q10 should have +49 Vdc on it.
Q11 should have +1.2 Vdc on it.
Which leads me to believe Q10 is bad.

You have more problems here than I think you can solve on a forum.

7
Amplifier Discussion / Re: 1988 Randall RG100ES
« on: January 01, 2020, 03:02:15 PM »
What does the signal look like at the base of Q8?
Q10?
Q11?
Q12?
Take care that the specified 250mv AC signal into Q8 is NOT exceeded.

8
Amplifier Discussion / Re: 1988 Randall RG100ES
« on: December 31, 2019, 06:13:29 PM »
What does "Q8 is irregular pattern" this mean?


9
Schematics and Layouts / Re: shcematics for true tone/ western auto amp mod# 5dc 9528e
« on: December 31, 2019, 06:08:02 PM »
First of all, you need to be aware that this amplifier configuration is called 'The Widow Maker'.
The ac mains voltage is directly coupled to the rectifier.
There is not a transformer to supply the secondary voltages.
To work on and operate these safely you must have an isolation transformer that would separate the mains voltage from the amp (110-110Vac)

10
Amplifier Discussion / Re: 1988 Randall RG100ES
« on: December 31, 2019, 02:35:06 PM »
Follow the signal into the power amp.
You do have a scope, correct?
What does the signal look like at the base of Q8?
Q10?
Q11?
Q12?

11
Amplifier Discussion / Re: 1988 Randall RG100ES
« on: December 30, 2019, 05:24:49 PM »
So you feel the output is 'low'.
What is the maximum Vac out into an 8 ohm load before clipping?

12
Amplifier Discussion / Re: 1988 Randall RG100ES
« on: December 30, 2019, 12:25:26 PM »
Other than having the designators wrong on the outputs and the leg assignments wrong on the Negative outputs, I see nothing majorly wrong with the static voltages.

The schematic indicates a 225mv AC signal entering the amplifier.
What value do you read coming in there?

13
Amplifier Discussion / Re: 1988 Randall RG100ES
« on: December 29, 2019, 09:42:57 PM »
Where is the schematic?
Can you please post it?
On the last three transistors, what are the designated 'Q' numbers?

14
Amplifier Discussion / Re: Gallien Kruger GT200
« on: December 25, 2019, 08:26:43 PM »
Not too sure what you are attempting to fix here.

Yes there is a small x over notch at higher settings.
I really doubt that you could here that.

What I see from the image is a gross mismatch in the top & bottom width of the waveform.
THAT will be noticeable.


15
Amplifier Discussion / Re: Gallien Kruger GT200
« on: December 20, 2019, 01:06:31 AM »
Can you take a picture of the distortion as it appears on a scope?

If so, upload it.

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