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reverb howl on 1145pa [message #15281]

Tue, 22 February 2011 10:42

bbird
Messages: 13
Registered: July 2007
Location: MICHIGAN

Junior Member

I have a 4 channel pa head that the reverb hadn't worked for years. It didn't work when I bought it 15 years ago. I finally tore it down and found a broken wire at the connection in the tank and fixed it. Now the reverb works great but occationally gets a runaway feedback loop even with nothing attached. Would this be a tank issue or component issue? Adjusting the amount of reverb doesn't stop it. Disabling the reverb with the foot switch cures it. Any suggestions?

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Re: reverb howl on 1145pa [message #15282 is a reply to message #15281]

Tue, 22 February 2011 13:35

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Your description makes me want to think Frankenstein head, but I'm gonna guess that you have an early K200A style head? Does your amp have 4 separate channels with volume and tone controls for each channel, or 4 inputs with two sets of controls?

If it's what I think it is, a 4 channel amp, the reverb control changes how much signal goes into the reverb circuit and now how much comes out of the circuit. Because of this fact, the reverb tank is always fully "on". So I would think that the problem is acoustic in nature and not electronic.

If you cover the amp with a blanket will it stop the feedback?

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Re: reverb howl on 1145pa [message #15283 is a reply to message #15282]

Tue, 22 February 2011 15:10

bbird
Messages: 13
Registered: July 2007
Location: MICHIGAN

Junior Member

it has 4 seperate inputs with individual controls for each channel. The reverb tank is mounted upside down on the top rail crossbraces. I have seen a lot of posts on different reverb issues but most don't reference this model type so wasn't sure quite what I was dealing with. Right now I have it attached to a newer Kustom 2 12 horizontal cabinet.

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Re: reverb howl on 1145pa [message #15284 is a reply to message #15283]

Tue, 22 February 2011 15:12

bbird
Messages: 13
Registered: July 2007
Location: MICHIGAN

Junior Member

One other thing, it seems to do it more with the amp inside of the tuck and roll cabinet than when it's just the bare chassis if that helps?

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Re: reverb howl on 1145pa [message #15288 is a reply to message #15284]

Wed, 23 February 2011 09:05

cassent5150
Messages: 341
Registered: August 2009

Senior Member

I have had that problem before and dealing with one at the moment on a challenger model. Have you got the reverb wires in the correct jacks? You should have a PC-803 reverb board mounted on the bottom of the amp chassis right behind channel 1 where the reverb wires plug in. On that circuit board there are 2 RCA jacks, the one towards the back wall is the input from the output of the reverb tank and the one towards the front of the amp is the output to the input of the tank. Is that the correct reverb tank? Check to see what kind of readings you get from the input and output jacks on the reverb tank, it should be around 180 ohms on each (I think some were around 200 ohms as well) and the ground of each jack should be ground to the tank at the rivots on each jack and the tank should have a ground wire grounding it to the chassis. Sometimes all it takes is remounting the reverb tank 180 degrees so the output of the tank is away from the power transformer. I do know on some models they even shielded the reverb tank with metal over the spring opening. Hope that helps. Steve C

Steve C

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Re: reverb howl on 1145pa [message #15289 is a reply to message #15284]

Wed, 23 February 2011 09:48

bbird
Messages: 13
Registered: July 2007
Location: MICHIGAN

Junior Member

Thanks for the info. I was curious if I had it connected correctly. I thought I marked the wires when I removed the tank to resolder a broken wire on the connector but it's not like I've never made a mistake. On closer inspection last night, the connections look like they could use a little more cleaning etc. so I'll get some cleaner today. The board info will definately help determine if I screwed up.

I'll update the post with what I find tonight

Thanks again for the help.

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Re: reverb howl on 1145pa [message #15290 is a reply to message #15281]

Wed, 23 February 2011 11:57

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

The simplest way to check if the tank is connected correctly is to turn on the amp and touch each one of the RCA plug ends that go to the tank. The return line will cause the amp to buzz, just like a guitar cord plugged into the front of the amp.

The return line goes to the tank output connector. Also be sure that the tank is mounted so that the output side is furthest from the power transformer.

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Re: reverb howl on 1145pa [message #15291 is a reply to message #15290]

Wed, 23 February 2011 13:07

pleat
Messages: 1454
Registered: June 2004
Location: Belding, Mi

Senior Member

The 1145 model number is a early K200A series amp before they changed to the K200A. There is dealer memo for the K200A-5 pa heads. Changes to PC803 are change R834 to 1K ohms, R835 to 100ohms and R846 to 22K ohms. I don't know if your PA has had the changes made. the memo was dated 12-27-1968.
pleat

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Re: reverb howl on 1145pa [message #15292 is a reply to message #15291]

Wed, 23 February 2011 13:42

bbird
Messages: 13
Registered: July 2007
Location: MICHIGAN

Junior Member

I will look to see if it had the changes. Did the memo state what the changes were to fix?

Thanks for the verification on the type of unit. Most info doesn't include the 1145 model although I did find the mfg date on this site awhile back. I stuck it on the back of the amp for reference. Seems to me it was built in 1967 so probably doesn't have the mod. The unit looks all original with the exception of the 3 prong power cord.

Thanks for the info

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Re: reverb howl on 1145pa [message #15293 is a reply to message #15292]

Wed, 23 February 2011 15:52

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Hello.
That dealer memo the Pleat told you about IS for the problem you are having with the reverb.
Also make sure that both springs in the pan and not sagging due to transportation vibration and age, as this can make them very sensivtive to vibrations from the speaker cabinet it is near or sitting on.
Also the two connection points ( male and female) on both on ens of the RCA connectors need to be shinny clean, not a dull aluminum as most times they are due to age. This problem will create a feedback type problem also in the Reverb circuit.

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Re: reverb howl on 1145pa [message #15296 is a reply to message #15293]

Wed, 23 February 2011 16:54

bbird
Messages: 13
Registered: July 2007
Location: MICHIGAN

Junior Member

Thanks to all. I will make the suggested mods and clean the jacks. Hopefully get another 40 years out of it!

- Brian

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Re: reverb howl on 1145pa [message #15298 is a reply to message #15281]

Thu, 24 February 2011 10:41

bbird
Messages: 13
Registered: July 2007
Location: MICHIGAN

Junior Member

I pulled the unit down last night and realized a parts layout on the PC803 board would save me alot of time trying to figure out where the specified resistors are located. I had hoped it might be screened onto the board. Does anyone have a layout? I did find a schematic on the PC-803 board from a link at this site which will be a great help but not the component layout.

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