Home » VintageKustom.com » Repairing Kustom Amps » 1967 Kustom 200A4 update (I'm sure I've bored you all to tears by now...)
Re: 1967 Kustom 200A4 update [message #24555 is a reply to message #24464] Fri, 29 January 2016 14:10 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4728
Registered: June 2004
Location: NY
Senior Member
No, the output transistors run on the + and - 40 volts which is good by your last checks.
Re: 1967 Kustom 200A4 update [message #24556 is a reply to message #24464] Fri, 29 January 2016 14:25 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
I'll try explaining this to you again. The positive regulator circuit PC502 sets the 23 volt level. The negative regulator circuit PC602 matches or follows the output of the positive side.

If there is +39 dc volts coming out of PC502 then there should be -39 dc volts coming out of PC602.

While there is no problem with working on PC602 first, in order for you to tell if it is working correctly or not, you need to fix PC502 first and then fix PC602.

And yes, if the floor transistor connected to PC502 is shorted, it would pass the entire +40 volts to the output of the regulator circuit.
Re: 1967 Kustom 200A4 update [message #24558 is a reply to message #24556] Fri, 29 January 2016 19:35 Go to previous messageGo to next message
Shaun_Musings is currently offline  Shaun_Musings
Messages: 323
Registered: April 2009
Location: Reading, MA
Senior Member

looking at the transistors on PC502, it appears I had the BCE reversed on two transistors NTE123). I replaced these, and battened down the hatches. I didn't check for bridges; I really should have and will do that tomorrow.

Green: 9.91
Red: 25.2

Like I said, I'll check for any bridges tomorrow and update...


Born on the Baaaaayou (Ok, in Massachusetts)
Re: 1967 Kustom 200A4 update [message #24559 is a reply to message #24558] Fri, 29 January 2016 20:51 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
Shaun_Musings wrote on Fri, 29 January 2016 18:35
Green: 9.91
Red: 25.2

Okay, the +25.2 is in the ballpark and can be called good.

Now your problem is on the negative regulator board PC602.
Re: 1967 Kustom 200A4 update [message #24561 is a reply to message #24559] Fri, 29 January 2016 22:36 Go to previous messageGo to next message
Shaun_Musings is currently offline  Shaun_Musings
Messages: 323
Registered: April 2009
Location: Reading, MA
Senior Member

Alright, we're getting somewhere. I'm going to double check all the transistors on PC602 tomorrow. I am using a 22/50 volt capacitor, and all the transistors on the board are NTE123s, correct? Any helpful suggestions on what I might be looking for? I'm just glad this has been isolated to PC502. One thing I should mention is that I replaced Q1 and the other 36982 transistors with MJ15015. I understand this is an upgrade. I replaced the regular resistors on both of these boards, except for R604 and R605, which are blue metal film 1%.

Now, I have done some work on PC102, changing the transistors there, and I am going to also double check to make sure there are no bridges or transistors in wrong.

I apologize if I gave the impression I just started changing things; some of the transistors on PC102, 502, and 602 had been snapped off previously and somebody soldered them back on; one was barely hanging on by a thread when I opened up the case. The reverb, trem/vibe, selective boost, and harmonic clipper do not appear to have been touched. Once I've figured all this out, I will begin work on the other boards.


Born on the Baaaaayou (Ok, in Massachusetts)
Re: 1967 Kustom 200A4 update [message #24569 is a reply to message #24464] Sat, 30 January 2016 11:50 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
All three transistors on PC602 are 2N3638, PNP. I think that NTE123 are NPN. Check your lists. Maybe NTE129?

Unlikely that the transistors were snapped off, some people will cut transistor leads to test them without having to remove the board or unsoldering the leads. Then they will try to solder the cut leads back together. Maybe that's what was done to your amp.

Yes, start by getting the power supply working correctly, then the power amp, then the two preamp boards and finally the effect boards. This way you will be only working on one section of the amp at a time and will be able to tell if what you have changed is for the better or for the worse.
Re: 1967 Kustom 200A4 update [message #24572 is a reply to message #24464] Sat, 30 January 2016 12:01 Go to previous message
stevem is currently offline  stevem
Messages: 4728
Registered: June 2004
Location: NY
Senior Member
Maybe we can start a new thread for this as my finger is getting tired of all the scrolling!
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