Kustom K150-5 PA no reverb

[jessadr]

I have a metal face K150-5 PA amp. The Reverb doesn't work.
The reverb tank in it is a 4FB2A1D part# 031-0005-01
Is this the right tank ? It was mounted with out any cables
attached. Looks like a new tank mounted with rubber standfoffs.
I put new cables on it, no reverb I changed cables around
to see it that was the problem. No reverb. Every thing else works great.I
would like to ask if the input and output are
grounded to the tank or not. The schematic looks like the input is grounded and the output is not. Both of the contactors on this tank are grounded.
input about 1400 output about 2200

[Enzo]

What is the circuit board number for the board supporting the reverb.

[jessadr]

pc5034

[Enzo]

Damn, my files skip right over 5034. But looking through other boards of that era, if the board is all transistors, then both input and output of the pan are grounded. Later boards in the 5100 or later, and that had ICs to drive the pan, at least some wanted non-grounded pan INPUT. Any ICs on that board? Or only transistors?

[Chuckl]

Check those transducer leads in the reverb tank. The black & green wires are ALWAYS breaking!

[jessadr]

the leads are ok. what is the correct reverb pan number for a K150-5. ? It has an IC on the board 4558

[jessadr]

here are the schematics

[jessadr]

is the input or output that is insulated ?

[52 Bill]

According to your schematic the output should be isolated from ground at the tank. The cable should be shielded.

[jessadr]

thanks Bill will try it tonight and let you know. Still wish I knew the factory tank number.

[jessadr]

I insulated the output on the 4FB2A1D tank . Still no reverb. The tank will bong when rapped. The output rca jack makes normal noise when touched on the end. It changes in volume along with the reverb master control.
I changed out the 2500/50v caps with 10,000/50v caps. That was the problem with the amp when I got it. It was blowing fuses. I also by passed the power switch and fuse, and installed an off/on switch and normal fuse holder in the rear of the amp. The factory switches were bad. I still use the lights , they are cool.
The amp works fine except when it first comes on there is a little squeal that vary's with the master volume control, for maybe 30 seconds. Guess there is a weak cap somewhere. Amp hasn't be used in years so I guess that is normal

The amp sounds great on all 4 channels and the eq's all work. Very little noise in the amp at all. All pots and jacks were cleaned and are noise less. Amp in very loud and clean with a 4x12 cab.

I wonder can I move the reverb jacks to the rear of the amp and use them as an effects loop. I have an Digitech DSP256xl effect unit. This has been a fun project if the reverb never works.
Check out my picture album on this site and you can see some other things I work on.

[52 Bill]

Have you tried taking the drive signal from the board and sending it to a small speaker? The schematic shows basically a small push pull transistor output stage that should be able to drive a small speaker. Try it and see if there is any signal getting to that jack.

Also with that transistor drive stage, I would think that the tank input transducer would be a low impedance type, unlike the usual Kustom tank.

[jessadr]

I made up a cable to plug the rca jack into. With the out put jack the little speaker cone can be touched and it makes a sound threw the amp. The input cable does nothing.
I still have the little squeal in channel 3 when I turn the amp on. If I turn up the volume on that channel as I flip the power switch it is real loud. But after about 30 seconds it is quiet as a mouse. Works normal. I noticed there was a NTE725 chip in that channel The other 3 channells have
RCA4739DP's in them. Looks like Channel 3 has been worked on in the past
Here are the cross list of ICs
007-7015-00 / uA739 / XR4739/nte725 / 14 pin DIP Dual Op-Amp
Looks like the right chip

[52 Bill]

I made up a cable to plug the rca jack into. With the out put jack the little speaker cone can be touched and it makes a sound threw the amp. The input cable does nothing.

What you need to test is the signal coming out of the amp that would drive the reverb tank.

With the speaker hooked up to what you are calling the input cable, turn up the reverb and play something through the amp and listen to see if there is a signal getting to the speaker.

[Chuckl]

Check to see you have about 200 ohms dc on both the tank rca jacks (nothing plugged into em.