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charger bass amp [message #14750]

Sun, 28 November 2010 17:35

rptrsn2
Messages: 28
Registered: September 2010
Location: canton mo

Junior Member

looking for a some help wth a squeal from this amp. if you turn the treble or volume up much it gets a real loud squeal, is there something common with these i should look for? thanks

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Re: charger bass amp [message #14752 is a reply to message #14750]

Mon, 29 November 2010 07:49

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

It could be a number of things and I will assume you mean it squeals with nothing plugged into it.
The first thing to check is the Molex connectors that these amps use to connect the preamp board to the driver board.
These need to be checked for tarnish/corrosion build up and for tention.
You can retention the male pins by using a sharpened machinist scribe to poke into the center of the male pin and spread it some.
Then some radio shack contact cleaner can be sprayed onto them.

The next problem could be a bad solder conection, more on the need a tech side of things would be a circuit cap that has changed value with age and is increasing the gain beyond the design spec`s.

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Re: charger bass amp [message #14754 is a reply to message #14752]

Mon, 29 November 2010 09:07

rptrsn2
Messages: 28
Registered: September 2010
Location: canton mo

Junior Member

I found that if I have my hands on the power sw and chasis it sounds fine. I'm thinking ground concern or problem with the power sw. The switch seems to be designed to reverse polarity depending on which way it is turned on. I might try a normal modern on/off sw and ground the chasis. It looks like the sw and power cord have been replaced.

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Re: charger bass amp [message #14755 is a reply to message #14750]

Mon, 29 November 2010 10:08

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

The switch and grounding schem of the amp are in no way related to the problem being there or going away, you are just seing the results of your bodys influence on the operation of the amp.
The effect is just like when you grab a car antenna and the station you are set on goes in and out.
Your amp has a circuit problem that grounding and changing out switches will not fix!

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Re: charger bass amp [message #14756 is a reply to message #14755]

Mon, 29 November 2010 11:14

rptrsn2
Messages: 28
Registered: September 2010
Location: canton mo

Junior Member

Any idea where I might get a preamp board for this amp?

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Re: charger bass amp [message #14757 is a reply to message #14750]

Mon, 29 November 2010 12:19

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Prospects for turning up a used preamp board will be slim if anything, and the problem may not be on that board.

Try pumping the signal from the monitor and the tape out jack into another amp, if one and not the other of them also has the problem then that can narrow it down to one board or the other.

If you find its the preamp board that can be pulled out and taken to a repair shop the all they need to do is power it up with a 12 volt differential supply and trouble shoot it on a 0-scope for its output.

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Re: charger bass amp [message #14762 is a reply to message #14757]

Mon, 29 November 2010 16:30

pleat
Messages: 1452
Registered: June 2004
Location: Belding, Mi

Senior Member

good suggestions, and I'm not a tech, but it might be easier to to take the complete chassis to a qualified tech to go through the complete amp, make sure all parts are working and the connection plugs are clean and making a solid connection. Depending on the age of the amp, kustom sent a memo out to the dealers to replace all white diodes with a RED band with 1N4007 diodes. If the Charger has the older diodes, it would be a great time to change them.
pleat

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Re: charger bass amp [message #14770 is a reply to message #14750]

Tue, 30 November 2010 07:02

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

I never heard of that Kustom revision meno, thanks for passing that along Pleat!
I would then also assume that the tad cheaper 1N4005 diode with just a 600 volt rating instead of a 1K rating would be a fine retro fit also.

[Updated on: Tue, 30 November 2010 07:05]

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Re: charger bass amp [message #14777 is a reply to message #14750]

Tue, 30 November 2010 12:48

rptrsn2
Messages: 28
Registered: September 2010
Location: canton mo

Junior Member

Even though it is probably not the problem, the power switch on this amp is pretty toasted looking, will it hurt to replace with a new on off sw, what is the purpose of having the reverse polarity sw. is this like having a ground lift on newer amps?

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Re: charger bass amp [message #14778 is a reply to message #14750]

Tue, 30 November 2010 14:36

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

No. there is no bad side effects of replacing the power switch with a new one if its done properly.
The ground lift switch on newer amps does just that, the polarity switch on these and other old amps with only a two conductor power cord switches the amps ground reference from one side of the A/C line to the other.

[Updated on: Tue, 30 November 2010 14:36]

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Re: charger bass amp [message #14779 is a reply to message #14752]

Tue, 30 November 2010 14:48

rptrsn2
Messages: 28
Registered: September 2010
Location: canton mo

Junior Member

This amp has had a new 3 wire cord installed.I am going to install a straight on/off switch in place of the polarity switch,will this be ok since it now has the ground wire?

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Re: charger bass amp [message #14781 is a reply to message #14750]

Wed, 01 December 2010 07:43

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

I see there is a Charger up for sale now on Ebay and it has no tape out jack, but is still labled for it.

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Re: charger bass amp [message #14782 is a reply to message #14781]

Wed, 01 December 2010 09:05

LesS
Messages: 477
Registered: December 2002

Senior Member

Hey Steve,
If you look real close at that Charger picture, there are marks where something was mounted where the tape jack goes - so I think a prior owner just removed the jack.
-Les S.

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Re: charger bass amp [message #14783 is a reply to message #14782]

Wed, 01 December 2010 09:09

rptrsn2
Messages: 28
Registered: September 2010
Location: canton mo

Junior Member

No Message Body

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Re: charger bass amp [message #14784 is a reply to message #14750]

Wed, 01 December 2010 09:14

rptrsn2
Messages: 28
Registered: September 2010
Location: canton mo

Junior Member

So with a grounded cord is the polarity sw no longer nessecary and ok to be replaced with a normal on/off?

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Re: charger bass amp [message #14785 is a reply to message #14750]

Wed, 01 December 2010 10:05

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

On many 1969 and latter Kustoms they deleted these output jacks but the chassie was already punched out for it, so nothing was done by the owner.
If you have a grounded AC cord the Polarity swt is no longer needed and the cap that goes to ground off of the swt can just be snipped out.

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Re: charger bass amp [message #14790 is a reply to message #14785]

Wed, 01 December 2010 17:10

pleat
Messages: 1452
Registered: June 2004
Location: Belding, Mi

Senior Member

We seem to be losing track. The amp in question is the charger that wasn't made until late 71 and it did come with a record out jack on the back panel.
The SC100's and SC150's came with a monitor out and footswitch jack. Not sure what a blank hole would be doing on the SS series of amps.
pleat

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Re: charger bass amp [message #14791 is a reply to message #14790]

Wed, 01 December 2010 17:31

rptrsn2
Messages: 28
Registered: September 2010
Location: canton mo

Junior Member

Mine has a date 12/71 it has a tape out and speaker out,no monitor or footswitch jacks if that helps

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Re: charger bass amp [message #14793 is a reply to message #14791]

Wed, 01 December 2010 17:39

pleat
Messages: 1452
Registered: June 2004
Location: Belding, Mi

Senior Member

Since the charger has no effects such as reverb or vibrato, you wouldn't have a footswitch jack. The tape out and monitor out jacks are about the same, it depends on where the tap was taken as to how it was labeled. One of the guys asked if the squeal occurs with an instrument plugged in or if the amp makes the noise without anything plugged in. Did we find that out?
I had a kustom K150 head that the grounding tab of the input jack was not making a connection when nothing was plugged in, and it made a high pitch squeal if you turned up the controls. You may want to check the input jacks.
pleat

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Re: charger bass amp [message #14794 is a reply to message #14793]

Wed, 01 December 2010 17:48

rptrsn2
Messages: 28
Registered: September 2010
Location: canton mo

Junior Member

It will sqeal with or with out instrument.it will start when volume about 1/4 and all eq down. If set volume just below where it starts it will squeal when you boost bass or treble on eq to about 1/4, not so much with mids,mids can boost 1/2 or more before squeals

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Re: charger bass amp [message #14799 is a reply to message #14750]

Thu, 02 December 2010 07:16

stevem
Messages: 4733
Registered: June 2004
Location: NY

Senior Member

Sorry I lost track of the questions.
Yes you can replace that switch with a on/off switch since you have a grounded cord now.

Use a doubble pole single throw type switch(DPSH for short)rated for atlest 3 amps at 120 volts.

Wire it in so it opens and closes both the white and black wires coming in from the power cord.

On the metal face amps the record output jack taps signal off of the speaker out thru a 10 or 15k resistor if I remember right, and this was the same with the RCA jacks on the 200 and 400 models.

The monitor out jack or power amp out jack took the in coming signal to the driver from the preamp board.

One other thing you might try to trouble shoot the amps problem is to pick up a can of freeze spray from Radio Shack.

With this and a hair dryer you can heat up and rapidly cool down sections of the circuit board and see if the temperature swing effects the sqeals volume and or frequency and in this way pin down a bad soilder joint or component.

Do not go overboard with the heat 120 degrees is about tops in regards to transistors and the 14 pin IC chip, caps and resistors can take a bit more but its hard to keep the heat that concentrated from other componets.

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