Home » VintageKustom.com » Repairing Kustom Amps » Upgrade input transitor - may be repeted question (Upgrade for Q1400 (PC1400) or Q1500 (PC1500))
Upgrade input transitor - may be repeted question [message #26178] Sat, 03 June 2017 19:46 Go to next message
Saransk is currently offline  Saransk
Messages: 20
Registered: February 2017
Location: Northern Virginia
Junior Member
A common thread is that Q1400/ Q1500 (the first input transistor on the 1400/1500 (SE4002)) is prone to "destruction" when overdriven.
Since the various vintage Kustom amplifiers were designed when the output of most guitar pickups was lower than the "hot" pickups which are now standard on most guitars, the first input transistor often is blown by pedal boards and high output pickups.
At the risk of asking a previously discussed question, is there a simple upgrade for the first input transistor that will handle the higher input voltages of today. Either a darlington configuration or just a "stronger" transistor for that first position that can handle a higher input.
While I could put a transistor socket in the first position to facilitate quick replacement, it might be nice to avoid the issue altogether.
Thanks
Michael
Re: Upgrade input transitor - may be repeted question [message #26179 is a reply to message #26178] Mon, 05 June 2017 08:48 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4728
Registered: June 2004
Location: NY
Senior Member
Even today's hottest non active pickups will not blow out the factory transistor .
Most failures I believe have been for 2 reasons, ( 1) static discharge, or (2) hitting the transistor with big signal level from a stomp box.
SS amps are no where near forgiving in regards to number 2 like at tube amp is, I don't even think that if you could mod the amp to take a dirt cheap 5558 chip would buy you better protection?
Re: Upgrade input transitor - may be repeted question [message #26180 is a reply to message #26178] Mon, 05 June 2017 13:26 Go to previous messageGo to next message
chicagobill
Messages: 2005
Registered: April 2003
Senior Member
Agree with Steve about the input transistors being reasonably immune from damage. If they were that bad, there would be no working amps out there with original transistors.

Transistors can die from any number of things, the fact that some of them have given out, doesn't mean that they all should be replaced. It's like getting a flat tire and supposing that all 4 tires are defective because one went flat.
Re: Upgrade input transitor - may be repeted question [message #26210 is a reply to message #26178] Sun, 25 June 2017 21:49 Go to previous messageGo to next message
Saransk is currently offline  Saransk
Messages: 20
Registered: February 2017
Location: Northern Virginia
Junior Member
I think the comment about "hammering" the Q1 input transistor of vintage Kustom amp with a "hot" stomp box is probably very true. Maybe the way to avoid this is to rewire the input jacks, changing them from the design that had a capacitor used to cut the frequency response to the more common design, even used in the later Kustom 150 series, of having a jack with high and low sensitivity using a pair of 68K resistors and the switching jacks.

As for the transistors, maybe a little less gain might match today's higher signals and pedalboards.






Re: Upgrade input transitor - may be repeted question [message #26213 is a reply to message #26178] Mon, 26 June 2017 06:08 Go to previous message
stevem is currently offline  stevem
Messages: 4728
Registered: June 2004
Location: NY
Senior Member
Its funny you mention the hammering effect , but you need to think about the era even the metal face amps where made in, as there where no overeound hot pickups back then unless you had them made for you.

The metal face amps that came about in 71 did as you posted have the two different inputs with one being 3 db down ( 1/2 volume ) from the other, but in general Kustom was getting complaints from six string player about needing more gain out of the 5066 preamp board ( the preamp without selectone )so the engineers issued a mod in Nov of 71 for the 72 production run of the 150 and 250 series amp that provided more gain.

They also sent out to all there dealers info on how to do this mod on the earlier amps should a customer want such.
The mod is a simple swap out of 3 resistors and 1 cap.
Previous Topic: Kustom Kombo Organ repair
Next Topic: 1969 kustom k100c8
Goto Forum:
  


Current Time: Thu Mar #d 09:11:37 EDT 2024
.:: Contact :: Home ::.

Powered by: FUDforum 3.0.9.