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Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 02, 2017 9:07 am
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You can put any kind of cap (non'lytic) tone might be different , good for test.


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 02, 2017 9:16 am
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In line RS have only 0.01 mfd , put two in parallel to have 0.02 mfd


https://www.radioshack.com/collections/ ... citor-pk-2


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 02, 2017 9:19 am
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stratele52 wrote:
mud wrote:

Yes the 0.02mfd coming from pin 6 of the 12AX7 ( Coupling Cap from preamp to power amp ) this has more than spec calls for I am getting 258VDC going in ,


That is good , old power transformer work with 115 volts house outlet, today we have 125 volts

The bass, mid, and treble caps all have 23VDC going in

You must have more the 200 volts going in and 1, 2 volts going out, look at the schematic

mud

This one you write about, is coming off of pin 1 of the 12AX7, I see 205 v on the schematic. I measured it after the resistor, would that drop some voltage. Tonight when I get home I will meter pin 1 on the 12AX7 and see what I get
Thank you
mud


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Thu Nov 02, 2017 7:44 pm
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Might be a good idea to measure all the voltages posted on the schematic and layout. Just to be sure you have no issues with the power supply and conduction through the tubes.

http://www.electronicstudio.net/schemat ... _schem.pdf

http://www.electronicstudio.net/schemat ... layout.pdf


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Fri Nov 03, 2017 8:07 am
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BMW2002Ti wrote:
Might be a good idea to measure all the voltages posted on the schematic and layout. Just to be sure you have no issues with the power supply and conduction through the tubes.

http://www.electronicstudio.net/schemat ... _schem.pdf

http://www.electronicstudio.net/schemat ... layout.pdf


Yeah I was thinking on those terms, could not get to it yesterday an event came in late in the day and I got home kinda late last night, and being I have off this Saturday I will break it back out and poke around
thanks
mud


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Fri Nov 03, 2017 6:21 pm
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Good luck with the readings. I usually measure a few times, just to be sure I'm getting consistency.

Remember, higher outlet voltage = higher VDC readings.


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Sat Nov 04, 2017 2:54 pm
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BMW2002Ti wrote:
Good luck with the readings. I usually measure a few times, just to be sure I'm getting consistency.

Remember, higher outlet voltage = higher VDC readings.


stratele52 wrote:
mud wrote:

Yes the 0.02mfd coming from pin 6 of the 12AX7 ( Coupling Cap from preamp to power amp ) this has more than spec calls for I am getting 258VDC going in ,


That is good , old power transformer work with 115 volts house outlet, today we have 125 volts

The bass, mid, and treble caps all have 23VDC going in

You must have more the 200 volts going in and 1, 2 volts going out, look at the schematic

mud
Thanks OK so it was early I needed to get to work just had coffee and misread the meter :oops:
The VDC coming from pin 1 of the 12AX7 and going into the caps were 236VDC
Theses values below were pretty much the same, as the meter was up and down between theses numbers
Bass Cap .007 to -.005 VDC
Mid Cap .002 to -008 VDC
Treble Cap .001 to 000 VDC
Coupling Cap .061 to 010 VDC before the resister and 000 VDC after.

This .02MFD Coupling Cap from preamp to power amp does it have anything to do with my issue

mud


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Sat Nov 04, 2017 5:42 pm
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Be sure the RS cap is rated for 400vdc to handle the plate voltage.
The capacitor leakage you reported is nominal.
Another way the signal can leak through is if the last filter cap is bad. It goes from the plate resistor on pin one through to the plate resistor on pin 6 if the filter isn't there to decouple the signal.
You might try clipping in an electrolytic 22/450 where the plate resistors come together and see if it works right.


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Sat Nov 04, 2017 6:31 pm
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TimsAudio wrote:
Be sure the RS cap is rated for 400vdc to handle the plate voltage.
The capacitor leakage you reported is nominal.
Another way the signal can leak through is if the last filter cap is bad. It goes from the plate resistor on pin one through to the plate resistor on pin 6 if the filter isn't there to decouple the signal.
You might try clipping in an electrolytic 22/450 where the plate resistors come together and see if it works right.


Thanks for this info. I have a 20/20/20/20 cap in there now, so if I move the 3rd stage over to the unused leg I believe that should help see if that is the issue.
I will be sure to get 400vdc if needed
I can't get to it tonight, and I work tomorrow, I hope to get to it tomorrow evening and I'll get back after I move the the 3rd stage over
mud
mud


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Sun Nov 05, 2017 11:37 am
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mud wrote:
TimsAudio wrote:
Be sure the RS cap is rated for 400vdc to handle the plate voltage.
The capacitor leakage you reported is nominal.
Another way the signal can leak through is if the last filter cap is bad. It goes from the plate resistor on pin one through to the plate resistor on pin 6 if the filter isn't there to decouple the signal.
You might try clipping in an electrolytic 22/450 where the plate resistors come together and see if it works right.


Thanks for this info. I have a 20/20/20/20 cap in there now, so if I move the 3rd stage over to the unused leg I believe that should help see if that is the issue.
I will be sure to get 400vdc if needed
I can't get to it tonight, and I work tomorrow, I hope to get to it tomorrow evening and I'll get back after I move the the 3rd stage over
mud
mud


Well I decided before work to move the leg to the unused 20 on the 20/20/20/20 and it did not change anything, that was a good suggestion,as I see how it is related, the preamp side. The Bass and Treble pot do work to some extent, but not like there suppose to, and when there set all the way down, Knob states 1 (fenders all the way down) I am not suppose to get any volume even with the volume pot turned up.
Well I am at work, when I get home I will poke around some more
Thanks for the help
mud


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Mon Nov 06, 2017 9:58 am
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Poking around last night took some measurements, all higher than whats called for on the Layout and Schematic that came with amp,( it has my serial in pencil on it ), as my house puts out more than 117V:
...........12AX7 Peamp, all in VDC
..................Results.........Schematic
pin 1..........244..............205
pin 3...............1.89............1.6
pin 6...........260.............200
pin 8...............2.03.............1.5
............6V6 All in VDC
pin 3...........408.............342
pin 4...........407.............340
pin 8.............23................21
...........Filter Cap All in VDC
1st stage....419.............355
2nd stage..410.............355
3rd Stage..384..............320
Now listening closer the Treble and Bass are doing some, again there should be no sound when tone pot are down and volume pot is up.
I do hear a crackle sound when I DIG into my guitar, and when I hit lower notes heavy, it is hard to hear as it is in the background of the music and stops as I stop playing.
When I power down I hear sizzling crackle, that fades after, I don't know, seconds. I measured the filter cap after and it was 13 VDC and falling.
1 My Question is; Should the filter cap discharge that quick ?
2 My second Question; Do you think I should just swap out the .02 coupling cap from preamp to power amp, that has debris under it, If so should I use 2 x 1uf Ceramic Disk @ 400VDC in parallel, or 2 x 1uf Metalized Film @ 400VDC, that I have in my possession, or should I order a proper .02
Image
Thanks
mud


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Mon Nov 06, 2017 1:45 pm
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You should use a proper 0.02mfd cap. I'd go for a polypropylene (like SBE-716) 0.02mds/400 or better yet, 600VDC cap.

But, as for that crackling noise... sounds like main power supply section. You said you have a new cap can in the amp? How about the resistors, in the PSU's rail? They are the ones (10K and 1K, 1-watt) on the left edge of the circuit board, in this photo:


Image


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Mon Nov 06, 2017 1:53 pm
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BMW2002Ti wrote:
You said you have a new cap can in the amp?



Is it ?
How mud did you solder the cap can on chassis ?

You must show some picture of you own amp


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Post subject: Re: 1967 Vibro Champ Issue
Posted: Mon Nov 06, 2017 2:48 pm
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[quote="BMW2002Ti"]You should use a proper 0.02mfd cap. I'd go for a polypropylene (like SBE-716) 0.02mds/400 or better yet, 600VDC cap.

But, as for that crackling noise... sounds like main power supply section. You said you have a new cap can in the amp? How about the resistors, in the PSU's rail? They are the ones (10K and 1K, 1-watt) on the left edge of the circuit board, in this photo:

I did change the cap can about 1.5 years ago, did not change the resistors on the rail, I guess I will need to check them and see if they had drifted, or should I just replace them.
I will order me a SBE-716 and replace the ceramic disk
mud


Last edited by mud on Mon Nov 06, 2017 2:59 pm, edited 1 time in total.

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Post subject: Re: 1967 Vibro Champ Issue
Posted: Mon Nov 06, 2017 2:55 pm
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Read resistor if they are under 20 % ,
Crakling in power supply are most of the time some bad solders.


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