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Repair [message #28494] Wed, 06 April 2022 10:12 Go to next message
stevem is currently offline  stevem
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Registered: June 2004
Location: NY
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These amps always have a certain level of noise / gain hiss to them at around 2khz.
Does the volume control in either channel make a difference in the level of hiss being heard?

In terms of the reverb hum that is most likely due to the pan having been taken out of the amp and reinstalled the wrong way .
The end of the tank with the connection marked output can not be the end closest to the power transformer which is on the right side when viewing the open chassis from the front of the amp.
Re: Repair [message #28495 is a reply to message #28494] Wed, 06 April 2022 17:29 Go to previous messageGo to next message
NLKustom is currently offline  NLKustom
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Registered: March 2022
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stevem wrote on Wed, 06 April 2022 10:12
These amps always have a certain level of noise / gain hiss to them at around 2khz.
Does the volume control in either channel make a difference in the level of hiss being heard?

In terms of the reverb hum that is most likely due to the pan having been taken out of the amp and reinstalled the wrong way .
The end of the tank with the connection marked output can not be the end closest to the power transformer which is on the right side when viewing the open chassis from the front of the amp.
Stevem, is this a reply to my question?. if so, the volume control doesn't make a difference to the power hiss you hear, only if you turn them to max it increases a bit.
As for the reverb, I changed one RCA chord because it failed the ohm test on the shield side. The tank is in the right way with the output plug farthest away from the transformer. Actually it wont fit the other way, the rca outputs would hit the back of the amp making it impossible to install. Still think it's a ground issue though. When you turn up the reverb knob, you hear a loud hum, and the volume decreases. The volume also decreases a bit when you turn on the intensity knob.
Re: Repair [message #28497 is a reply to message #28494] Thu, 07 April 2022 07:27 Go to previous messageGo to next message
stevem is currently offline  stevem
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Registered: June 2004
Location: NY
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In this model amp( and many other Kustom's ) only the rca cable used on the output side of the tank should have its outer cable shield making a connection from end to end.

If the cable used on the input side is the same then you will have a problem making ground loop taking place.
The input cable should not show a connection being made from the outside of the preamp board mounted rca jack to the pan's rca jack.

If you look in this sites schematic section at PC1000 you will see how it needs to be wired.

The condition your having of the volume decreasing leads me to think that your tank has a problem, or it's a replacement tank of the wrong type .

Is there a date code on the tank?

With the output cable plugged in and the reverb turned up if you bang on the tank hard do you hear the reverb springs crash?

Let's get this issue ironed out before we go back and look at what may be a hiss problem.

[Updated on: Thu, 07 April 2022 07:31]

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Re: Repair [message #28499 is a reply to message #28494] Thu, 07 April 2022 16:25 Go to previous messageGo to next message
NLKustom is currently offline  NLKustom
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Registered: March 2022
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Thanks for the help Steve.
So I checked the tank again, the RCA chord going to the "input" jack is not showing 0 on the ohm meter on the shield connectors.
The RCA chord going to the "output" jack is showing 0 on the ohm meter, so I'm assuming it's shielded.
The reverb tank has the "input" jack farthest away from the power transformers, looking at it from the front of the amp., and the "output" jack is closest to the transformers, or in the middle of the amp.
The tank is an Accutronics, these are the numbers stamped on it. 031-005-00. 25-75-301. 23572-0. 4FB2A1A. It looks like someone has peeled back the foam on both ends of the tank for some reason, to look inside I suppose. Everything looks fine in there, the foam is still in place.
When I shake the amp I can hear the reverb springs through the speakers.
Re: Repair [message #28500 is a reply to message #28494] Thu, 07 April 2022 18:35 Go to previous messageGo to next message
NLKustom is currently offline  NLKustom
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Update:
So it turns out the reverb tank was put in backwards with the output by the power transformer. Switched it around all the reverb hum disappeared. With no loss of volume. Thanks for the valuable info Steve.
But I am getting a bit of loss in volume and a bit less clearer tone when I turn on the intensity effect.
Re: Repair [message #28504 is a reply to message #28494] Thu, 07 April 2022 19:12 Go to previous messageGo to next message
NLKustom is currently offline  NLKustom
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Steve, another question.
I installed a 3 prong power chord to this amp, so should both RCA tank reverb cables be shielded?
Re: Repair [message #28506 is a reply to message #28494] Fri, 08 April 2022 11:27 Go to previous messageGo to next message
stevem is currently offline  stevem
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The up grade to a 3 prong power cable has no impact on the reverb circuit .
Re: Repair [message #28508 is a reply to message #28506] Fri, 08 April 2022 18:45 Go to previous messageGo to next message
NLKustom is currently offline  NLKustom
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Where can you get those short RCA cables with a 90 degree on one end?
From the numbers I gave you from the reverb tank, Is it the right one?
Thanks again.
Re: Repair [message #28509 is a reply to message #28494] Fri, 08 April 2022 21:19 Go to previous messageGo to next message
rodak
Messages: 470
Registered: October 2001
Location: Georgia
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I checked my two favorite cable sources, but neither had right-angle plug cables.
One did have a right-angle adapter:
https://www.mycablemart.com/store/cart.php?m=product_detail& amp;p=6001

They're cheap, anyway.


www.combo-organ.com
Re: Repair [message #28510 is a reply to message #28494] Sat, 09 April 2022 10:11 Go to previous messageGo to next message
stevem is currently offline  stevem
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If I had to guess at the volume drop off issue your having it would be the two electrolytic caps at each end of the intensity control .
One is a 10 uf and if I recall right the other is a 33 Uf.
This circuit board is a good bit of a pain in the Ass to get out, so if you go thru the work to do that then replace all off the electrolytic type caps and get it done in one shot.

Is your reverb working right now?
Re: Repair [message #28511 is a reply to message #28510] Sat, 09 April 2022 11:14 Go to previous messageGo to next message
NLKustom is currently offline  NLKustom
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Steve, the reverb is working with no volume drop, but it doesn't seem overly strong. I can live with it.
Turns out the volume drop is only when I used the effects, when I turn on the intensity and use trem-vib.
I thought it was the reverb but I had both effects on at the same time.
I have pedals that do trem and vib so I won't be tearing it down for that either I guess.

[Updated on: Sat, 09 April 2022 11:17]

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Re: Repair [message #28512 is a reply to message #28494] Sat, 09 April 2022 16:57 Go to previous messageGo to next message
NLKustom is currently offline  NLKustom
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Should the reverb tank have a case ground to the amp chassis?
I've seen pictures of tanks in Kustom amps with a case ground. Just wondering.
Re: Repair [message #28513 is a reply to message #28494] Sat, 09 April 2022 17:14 Go to previous messageGo to next message
stevem is currently offline  stevem
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That ground wire was only in the early amps.
Re: Repair [message #28514 is a reply to message #28494] Mon, 11 April 2022 12:57 Go to previous messageGo to next message
NLKustom is currently offline  NLKustom
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Steve, this is info I found on the reverb tank.
Type 4FB2A1A, Accutronics, Geneva Ill.
4 = Long 2 springs
F = 1475 ohms input impedance
B = 2250 ohms output impedance
2 = 1.75-3 sec decay rate(medium)
A = grounded input, grounded output
1 = no lock
A = open side up.

Is this the right tank for my K150-8?
Concerned about the first "A" part, grounded input grounded output.

Other numbers on the tank are:031-0005-00, 25-75-301 & 23572-0.

[Updated on: Mon, 11 April 2022 12:58]

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Re: Repair [message #28516 is a reply to message #28494] Mon, 11 April 2022 15:37 Go to previous messageGo to next message
NLKustom is currently offline  NLKustom
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Registered: March 2022
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Here's more info from amprepairparts.com
There are 3 different replacement reverb tanks listed for Kustom amps.
4FB2A1A replacement for K200-A (that's the one in my amp)
4FB2C1A replacement for K100-2,K100-5,K150-2,K200B5,K250-2,K250-4,K400-B5
4FB3D1A replacement for most Kustom amps from the 60's & 70's.

Which tank is the right one for the K150-8?

Thanks,
Greg.
Re: Repair [message #28518 is a reply to message #28494] Mon, 11 April 2022 19:52 Go to previous messageGo to next message
stevem is currently offline  stevem
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Registered: June 2004
Location: NY
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The impeadence of your each end of your tank is right I can tell that.
Tomorrow evening I will take a look in my k100-8 to see how input is set up and I will let you know.
Re: Repair [message #28519 is a reply to message #28518] Mon, 11 April 2022 20:52 Go to previous messageGo to next message
NLKustom is currently offline  NLKustom
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Registered: March 2022
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stevem wrote on Mon, 11 April 2022 19:52
The impeadence of your each end of your tank is right I can tell that.
Tomorrow evening I will take a look in my k100-8 to see how input is set up and I will let you know.
Steve, the main difference in those three tanks is the 5th letter "A, C or D", which is:
A = input grounded, output grounded
B = input grounded, output insulated
C = input insulated, output insulated

Just need to figure which one goes with the K150-8
Re: Repair [message #28521 is a reply to message #28494] Tue, 12 April 2022 10:30 Go to previous messageGo to next message
chicagobill
Messages: 1989
Registered: April 2003
Senior Member
Most Kustom amps used a tank with the input and output grounded. The correct way to test to see which tank should be used in your amp, would be to test the ground connections on the RCA jacks mounted to the pc board.

There are two jacks, one for send and one for the return. Normally the return jack has a connected ground circuit, meaning that the shell part of the jack is directly connected to the ground trace on the pc board. Usually the send jack is not directly connected to the ground circuit and therefore needs to be connected to the circuit by the ground connection inside the reverb tank.

Unplug the tank from the PC board. Take your ohmmeter and read the resistance from both RCA jacks shell connections and see if one or both are connected to the ground (chassis) circuit. If both are connected to ground, then your tank should be insulated input grounded output. If only the return jack is connected to ground, then both jacks should be be grounded.

All of this information is only for the older plexifront amps. The slant metal front amps of the 70's used an IC chip to drive the tank as part of its feedback loop, and therefore need an isolated input jack.

So long story short, in my opinion you have the correct tank.
Re: Repair [message #28643 is a reply to message #28494] Sat, 25 June 2022 21:22 Go to previous messageGo to next message
NLKustom is currently offline  NLKustom
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On this amp, Can the "monitor output" jack, be used to plug in a external speaker or is it just a feed to the mixing board?
Re: Repair [message #28644 is a reply to message #28643] Sun, 26 June 2022 14:51 Go to previous messageGo to next message
rodak
Messages: 470
Registered: October 2001
Location: Georgia
Senior Member
I'm sure it's line-level, meant for input into a mixing board or power amp. You wouldn't get anything plugged into a speaker - way too small a signal there to drive a speaker.

www.combo-organ.com
Re: Repair [message #28645 is a reply to message #28494] Mon, 27 June 2022 05:38 Go to previous message
stevem is currently offline  stevem
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Registered: June 2004
Location: NY
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This monitor jack is set up to feed another power amp.
While it has close to 4 volts of output it does not have the needed current to drive a speaker.

This level of voltage outout is dependent on how loud you play the amp and with 3 to 4 volts of potential outout you will need to pad it down if you pump it into a mixing board.

Even 3 volts is hotter then zero DB line level input.
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