Repair [message #28494] |
Wed, 06 April 2022 10:12 ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
stevem
Messages: 4763 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.
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Re: Repair [message #28497 is a reply to message #28494] |
Thu, 07 April 2022 07:27 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
stevem
Messages: 4763 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] Report message to a moderator
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Re: Repair [message #28511 is a reply to message #28510] |
Sat, 09 April 2022 11:14 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
NLKustom
Messages: 50 Registered: March 2022
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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] Report message to a moderator
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Re: Repair [message #28514 is a reply to message #28494] |
Mon, 11 April 2022 12:57 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
NLKustom
Messages: 50 Registered: March 2022
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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] Report message to a moderator
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Re: Repair [message #28521 is a reply to message #28494] |
Tue, 12 April 2022 10:30 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
chicagobill
Messages: 2005 Registered: April 2003
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Senior Member |
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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.
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Re: Repair [message #28644 is a reply to message #28643] |
Sun, 26 June 2022 14:51 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
rodak
Messages: 514 Registered: October 2001 Location: Georgia
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Senior Member |
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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
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Re: Repair [message #28684 is a reply to message #28494] |
Thu, 21 July 2022 22:32 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
NLKustom
Messages: 50 Registered: March 2022
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Steve
After playing this amp for a bit, the reverb starts to make a buzzing noise. If you turn the reverb off it goes away, but if you give the amp a slight tap or hit, it starts to make an awful rumble noise and the buzzing goes away also. Then after 5 minutes or so the buzzing is back again.
Any ideas? It seems to be a reverb issue, the amp is pretty quiet otherwise.
Also when you turn on the trem-vib effect, the overall volume decreases and gets a little muffled.
[Updated on: Thu, 21 July 2022 22:34] Report message to a moderator
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Re: Repair [message #28778 is a reply to message #28777] |
Thu, 29 September 2022 22:03 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
NLKustom
Messages: 50 Registered: March 2022
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Yes, turning off the reverb stops the noise/roar.
The sound is not the normal hiss you hear from the power being on. It's hard to describe. It's like the reverb starts acting up and begins to roar. If you shake or hit the amp you hear the springs in the tank rattle and make a loud noise, then the "roar/echo hiss" stops. The reverb goes back to normal, then it will happen again. Almost like some electrical interference brings it on. I really don't know how else to explain it.
I never tried unplugging both connections from the tank, because the unit is all put together when it happened.
And, no the sound is not like an AM radio in between stations. The AM sound is there as soon as you turn on the power. When this noise is happening you can't hear the reverb effect while playing guitar. It's like a thunder and lightning storm. Give the amp a tap so you shake the reverb springs and the noise goes away and you can hear the reverb effect with the guitar again.
[Updated on: Thu, 29 September 2022 22:15] Report message to a moderator
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Re: Repair [message #28780 is a reply to message #28779] |
Fri, 30 September 2022 16:00 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
NLKustom
Messages: 50 Registered: March 2022
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I've looked inside the tank. the sponge was been peeled back before I bought it. The springs are attached and everything looks fine inside.
Obviously something is weak somewhere in the reverb system.
[Updated on: Fri, 30 September 2022 16:02] Report message to a moderator
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Re: Repair [message #28790 is a reply to message #28783] |
Fri, 07 October 2022 08:57 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
NLKustom
Messages: 50 Registered: March 2022
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Steve:
I haven't tried it with the tank unplugged, but with the reverb turned off, most of the noise isn't there.
With just the amp powered on, you can hear a low frequency "hiss", the thing is not quiet by no means. and every now and then you hear what I can only describe as low distant rolling thunder, and it still pops when the de-humidifier cuts in, but not as loud. But that might be a grounding issue with my electrical system.
I want to take it to my local dealer for a check up , but don't know if those young guys know much about these old amps and their inner workings. I don't want to be replacing things un-necessarily.
Also sometimes the reverb won't work at all until you give the amp a tap, then it makes a little roar and kicks in.
There is a loose connection there somewhere. Taking it to my music shop tomorrow, gotta leave it. Will let you know what I find out.
[Updated on: Fri, 07 October 2022 18:33] Report message to a moderator
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Re: Repair [message #28961 is a reply to message #28494] |
Sat, 04 March 2023 17:18 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to next message](/FUDforum/theme/vk30/images/down.png) |
NLKustom
Messages: 50 Registered: March 2022
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Hi Steve,
Update on the amp.
Took it back from the shop after 4 months. The guy said there was no input going to the reverb tank, he replaced two resisters or something, now there's input going to the tank, but nothing coming out. He's saying a transducer is gone in the tank and I need a new tank. So I took the amp, everything works but no reverb.
So I need to get a new tank, the one in there is 4FB2A1A, which is "input grounded, output grounded", don't know if that's the right one, or should it be 4FB2C1A, which is "input insulated, output grounded".?
Which tank is right for the K150-8?
I just bought the schematics online and sent the pdf to him, but there is no mention of what is the proper tank for that unit.
Help please!!!
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Re: Repair [message #28970 is a reply to message #28969] |
Thu, 09 March 2023 14:35 ![Go to previous message Go to previous message](/FUDforum/theme/vk30/images/up.png) ![Go to next message Go to previous message](/FUDforum/theme/vk30/images/down.png) |
rodak
Messages: 514 Registered: October 2001 Location: Georgia
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Senior Member |
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Where did you buy the schematics at? Was it a PDF or an actual physical copy? I have a PDF, but would love to have a nice, full size foldout copy.
Always happy to support anyone selling these old schematics (as long as it's not horribly over-priced)
www.combo-organ.com
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