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November 28, 2020, 02:25:50 PM

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1
Amplifier Discussion / Current sources for input stage and VAS
« Last post by shasam on Today at 02:16:09 PM »
Hi!

I would like to use current source for the input stage and for the VAS of my amplifier, and I see different implementations of these, but I don't realy understand what it does change...

When using current sources for the input stage and for the VAS, with a transistor used for voltage reference, sometimes the base of this transistor is connected on the emiter of the LTP curent source transistor, sometimes it is on the VAS one. Could someone explain me what difference does it make please?

Also, resistors are sometime used on the base of one or more of those three transistors. Randy Slone write 1k is a good value, but I haven't find any further information about this. What is their purpose please?

Thanks a lot for your help!
Please apologise my poor English.
2
Amplifier Discussion / Re: baldwin c2 solid state amp rebuild question?
« Last post by thejunkman on November 27, 2020, 08:48:25 AM »
excellent..

 thank you
4
Amplifier Discussion / Re: baldwin c2 solid state amp rebuild question?
« Last post by thejunkman on November 26, 2020, 08:50:24 AM »
thanks for the reply..off hand bill bickers and vern tisdale have been putting out jukebox cap kits for years.i believe they still do.while these were not mandatory they made things easy for me.but if thats not available so be it..could you or anyone else recommend a vendor or 2 that i can order the parts i need.and possibly even a schematic?
 regards
 j 
   
5
Amplifier Discussion / Re: baldwin c2 solid state amp rebuild question?
« Last post by Enzo on November 25, 2020, 09:05:18 PM »
I rebuilt many many many jukebox amps over the years.  Mostly Seeburg tube amp and Rockola solid state.  But Rowe or AMI or whatever, we did it all.   I don't recall ever seeing cap kits.  I don't doubt they exist, but I just maintained a stock of parts and had no need.  I did a ton of CRT monitor repairs for the arcade trade, and they did offer cap kits for those.

That said, I am not aware of any cap kits for amplifiers, and especially for a relatively unusual one like that.  But such parts are easily available.
6
Amplifier Discussion / baldwin c2 solid state amp rebuild question?
« Last post by thejunkman on November 25, 2020, 01:14:04 PM »
 1st off thanks for having me.
 ok i have baldwin c2 amp that Ive had for years.use to have a great sound to it. not anymore it now is making all kinds of popping noises and its even putting out fairly high voltage through the inputs.i guess its in need of a rebuild? Ive rebuilt jukebox tube amps before.just wondering with jukeboxes you could buy a complete cap kits.is something like that available for a guitar amp? or will i have to source each part.(caps,resistors,etc).again any info on how to get this amp up and running again will be greatly appreciated.   
7
Amplifier Discussion / Re: Fender Champion 30 - No output and channel switch frozen
« Last post by phatt on November 24, 2020, 07:59:49 PM »
You have lost the neg rail so the power supply is the issue. with TP4 dead none of the other TP's will read correct.
so first check the filter Caps and Bridge rectifier.
  Suspect parts are D13,14,15,16. and C36.  (If C36 is dead then I would replace C35 as well)
Once those are fixed the rest of the circuit TP's will likely be normal,, but check them after PSU is fixed just in case something else has been stressed.
Phil.
8
Amplifier Discussion / Re: Fender Champion 30 - No output and channel switch frozen
« Last post by TSheld on November 24, 2020, 05:45:42 PM »
Checked some supply voltages as best I could with my old multimeter. See amounts below on the the first 6 test points and then the 27volt supply rails going to the speaker output.  Definitely some weird stuff going on.
Any thoughts you have much appreciated. Thx

   Rated      Meter
TP1   20.3   V   AC   20.1    
TP2   20.3   V   AC   20.1
TP3   25.9   V   DC   26.0 
TP4   -25.9V   DC   0.8    
TP5   15.1   V   DC   14.2
TP6   -14.8V   DC   0.7    

TP17  2.97  V      AC    2.8   
U6-6   27   V   AC   58.5    
U6-4   -27   V   AC   1.2    
D22   27   V   AC   58.5    
D23   -27   V   AC   1.2    
R52   15   V   AC   30.2    
R55   -15   V   AC   28.3    
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Amplifier Discussion / Re: peavey musician series 400
« Last post by dmeek on November 22, 2020, 03:23:29 PM »
The last few Peaveys of this vintage that I've seen had either shorted or open main filter capacitors.
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Amplifier Discussion / Re: peavey musician series 400
« Last post by Jazz P Bass on November 21, 2020, 11:59:23 AM »
Here is the Cross Ref sheet.
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