Kustom 300

[stingray_65]

I just came upon a Kustom 300 with silver sparkle tuck and roll

are these worth rebuilding?

I've heard they are problematic

not much into the SS thing, I was gonna use it for parts, looks to have a reverb pan and a dozen jack on it.

Ray

[Gtr_tech]

I'd rebuild it and flip it. They're getting collectable these days. If it wasn't the colored covering type (a black tuck/roll) it might be a good chassis to build a tube amp in, but the collectors go for the sparkley colored ones.

[stingray_65]

LOL I thought so too

I offered it up on a Kustom website either parts or whole and no takers yet.

It's white with silver sparkles

I'm not so sure about building a tube amp in it as I'm afraid of melting the vinyl tuck and roll.

I'm not sure what is wrong with it and I havent really put the meter to it except to see that there is 38VDC going every where

it looks to have been repaired numerous times. that is to say I see burns on different boards and found the component ontop of the burns to be good

man, if some one had a use for a MONSTER power supply...

the tranformer is about 6" x 7" x 6"
the choke is 5" x 4" x 5"
and two huge caps that look like beer cans sitting in there

the guy that gave it to me had suggested that the 6 seperate preamps boards are probably not the culprit, no matter wich channel you plug into still no sound comes out.

so I got to thinking I might make 6 "kustom" preamps

I'd have to find a few small enclosures and maybe power them off a wall wart

I dunno, for now its collecting space and looking Kool in my shop

if you're interested in it, Owosso, Mi is about 2 hrs north of me on rt23
offer me a trade or cash and I'd surely get rid of it if you picked it up.

Ray

[Gtr_tech]

Heat wouldn't be an issue if you put a small fan in there to circulate the air.

I'd make an interesting chassis/cab to build on, but I have way too many similar things waiting around in my attic/basement/shop for that kind of treatment. I just had a 70s Kustom "1 Lead" donated to science about a week ago. The speaker terminal board broke and it burned up the output section (and some of the front end as well) when the leads shorted together.

[stingray_65]

GRRRR!

now you did it!

this cab is WAY to big for me to build an amp in,

but I been looking at puttin together a stand alone reverb unit (6G15)

and the Joanns fabric has some blue sparkle vinyl.

I can do tuck and roll......

nice shiny throw back cab for a throw back reverb unit

think I'll break out the digital embroidery machine and throw on a few period correct designs

Keep on truckin'
Ray

[Gtr_tech]

Oh I see what that is now....its a PA head and its FRIGGIN' EEUGE!! Not sure about the collectability of one....maybe a "Kustom Kompletist" will just have to have it. CAn't build anything in it 'cause the back is all solid/closed off. Too big anyway....maybe someone would want to build an analog synth in it? That'd be pretty sweet.

[olddawg]

If it wasn't a PA head I would say fix it. Old SS discrete amps are usually not that difficult. Just use a block diagram approach. If the outputs are good and the power supply comes up it would probably come down to a handfull of dry caps. A Kustom 300 guitar amp would be a good bass amp for someone. The PA head is kind of a boat anchor. You could just use it for a mono power amp if you have the need. If you want to restore it take your time, get one channel working, and go from there.

[stingray_65]

the layout of this thing breaks itself down into blocks as you said.

there are 6 seperate preamps each with its own board, 5 pots for volume, bass, mid, teble and reverb, 2 wires for power green and red, 1 input from 2 jacks blue and black, a purple wire that is the reverb signal out and that leaves a brown and black twisted pair to be the output and 1 14 pin chip in the center of that

the PS is in a corner by iteslf with a dozen green and red wires coming of it to the various boards

two board on the chassis floor I'm assuming are the pwer amp and a power amp driver with a brown and black wire going in, a red and green power supply and a blue and black going to the speaker jacks

the driver has 6 big transistors on heat sinks and identical circutry surrounding each transistor and has 3 leads going to BIG transistors mounted on a HUGE heat sink rail

it's the mess in the middle that I'm pretty sure is where the trouble is
all the outs from the 6 preamps, the reverb tank driver, 3 pots with push pull switches that when the pots are pulled they kick in anti feed back circuitry, 3 more pots for overall tone, 3 pots for the reverb and 1 master gain

from what I've read these were pretty advanced circuits for thier time

DAMN! I just went out to the shop to make sure what I was describing was acurate and I looked at it again and think I might try a fix on it.

I just wonder how available some of those 14 pin chips are. they pretty much have to be just opamps.

HMMMMmm.....

Ray

[olddawg]

Are you sure those ICs aren't LM4558s. They were as common and cheap as dirt for that era. They also rarely fail. Check your power supply rail symmetry. Should be around +/-15v within .6v of each other with no ripple. If it has been setting all the electrolytics are suspect just like a tube amp.

[52 Bill]

Are you sure those ICs aren't LM4558s. They were as common and cheap as dirt for that era. They also rarely fail. Check your power supply rail symmetry. Should be around +/-15v within .6v of each other with no ripple. If it has been setting all the electrolytics are suspect just like a tube amp.

No, they're obsolete 14 pin 4739 dual op amps. There are adapter boards that allow the use of 8 pin dips available.

Does this amp have a single power amp or is it one of the ones that have two power amp circuits?

[olddawg]

No, they're obsolete 14 pin 4739 dual op amps. There are adapter boards that allow the use of 8 pin dips available.

Does this amp have a single power amp or is it one of the ones that have two power amp circuits?

I would guess that it is mono but I don't have a print. I don't remember any old Kustoms being stereo. A 4558 op amp is a dual 741. I don't have the spec sheet in front of me but I believe I have subbed one for the other in the past. I think the 739 isn't compensated. Here's another approach:

You can replace it with a TL072 (it's dual, isn't it?) if you note which pins on the 4739 have the (+), (-) and output designations on them, and connect those points to the corresponding *symbol* on the TL07x parts; this will be on a different pin number. Also, you have to connect the most positive voltage to the + power pin on the TL07x and the most negative voltage to the - power pin on the TL. The easiest way to do this is to glue the replacement part upside down, legs up (a process known as "dead bugging") and run wire wrapping or other fine wires to the pins from the appropriate holes on the PCB. This is a simple way to rescramble pinouts.

Generally an op amp is an op amp but the 4739s are still around too with a little searching. NTE725 (at $6 apiece!) if nothing else is convenient. Some are cleaner than others. In any event I doubt if they are your major issues. One 1 of 6 channels is bound to have a working one for a base line. Seriously, if it powers up and isn't blowing fuses check for DC offset on the output and measure your rail voltages. I would bet that you have a regulation or filtration problem with the power supplies because of its age. BTW what is the problem?

[stingray_65]

Sorry about the poor pics.

I havent fired this up at my place as the highest rated speaker I have is 30 watts

but at my buddies we did fire it up and I cant remember if it had no sound out or very quiet

I'm sure that would make all the difference.

I've only been reluctant to fix this because it's SS and a crowded board. That has always intimidated me.

I would LOVE to hear this thing, but unless I could fix it for cheap ( $20 every couple weeks) I would have to let it sit, or scrap it for parts.

OH it has a Gibbs reverb tank that is out so that I can repair the lock and the rubber mounts.


Ray

I just hate to see vintage equipment relinquished to the scrap bin, I've recently discovered Johnny Cash used this same model for years , execept his was black (go figure)

[52 Bill]

I havent fired this up at my place as the highest rated speaker I have is 30 watts

Any speaker will work to test the unit out. The 300 watt rating is peak - 150 rms. As long as you don't have any dc on the output and you keep the volume down the 30 watt speaker will be fine.

I've only been reluctant to fix this because it's SS and a crowded board. That has always intimidated me.

These amps are probably one of the simplest and most reliable of all the old SS stuff out there. If you break it down into individual circuit sections repair should be a snap.

The output transistors are basic 2N3055's. The driver transistors (the ones with the built in heat sink) are RCA 40409 and 40410's.

Olddawg: This one is mono, they all were. Some of the big ones had two power amps running a mono signal to double the power output.