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broken bass pot on my 1971 150-2 [message #14026]

Sun, 11 July 2010 04:00

drjymmiphreak
Messages: 6
Registered: July 2010

Junior Member

I traded a guy a computer for this amp almost 10 years ago now. used it for everything from vocals, to guitar, bass, and even used it as a pa! It always had a bit of crackle in it. At first, it was the cables, then the pots. I took the cover off only to discover I'm probably the first person to open it up since 1971! After a little WD-40, everything came apart nicely, exept the bass pot on the first channel... The nut froze and spun the pot in its case, shredding the internals... Can any one help me get a replacement? I'm not worried about period correctness, just functionality. I love this amp! The good news is that it plays like new again, except I cant adjust the bass on channel 1... Any help appreciated. I'm not an electrician, just a fix it all kinda guy. I can probably solder the new one in if I can find one...

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Re: broken bass pot on my 1971 150-2 [message #14034 is a reply to message #14026]

Sun, 11 July 2010 12:03

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

Senior Member

That seems to a common problem with the slant metal face amps. Frozen nuts on the pre amp boards will destroy the pot. I don't have any place to direct you to find a replacement pot but I do have a K150-2 head for sale on Craigslist in grand rapids, michigan posted it for 125.00 I thought about parting it out. Everything works great, Power and polarity switches work, just needs bulbs, I've seen these go for 30.00 each or more on ebay. Pre amp boards and the power amp boards will work in the SS series amps, so I know I could make more on selling just the parts than the whole amp would bring on ebay. Make me an offer and I'll let you part it out, or keep it for spare parts for your amp.
pleat

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Re: broken bass pot on my 1971 150-2 [message #14035 is a reply to message #14034]

Sun, 11 July 2010 23:38

drjymmiphreak
Messages: 6
Registered: July 2010

Junior Member

There were bulbs that light up in the power and polarity switches?!? they never worked in the one I have. I always thaught they should've had them, makes it difficult to tell when it's on or off. I can't afford to buy your head all at once. I could possibly buy it in pieces for around 100, 20 bucks at a time. (that doesn't include the shipping cost. I will pay the extra to ship it myself if you are willing.) let me know if that sounds good to you and we'll get the details together.

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Re: broken bass pot on my 1971 150-2 [message #14037 is a reply to message #14026]

Mon, 12 July 2010 06:02

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

I can help you find a pot, but which channel is the pot in, also have you got the remains of the old pot out yet?

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Re: broken bass pot on my 1971 150-2 [message #14039 is a reply to message #14037]

Mon, 12 July 2010 09:27

drjymmiphreak
Messages: 6
Registered: July 2010

Junior Member

the pot is from the 1 channel. it is the bass pot. i have done everything but remove the part of the pot that is soldered to the board. i was going to wait until i got a rplacement to mess with the soldering part. where would i find the bulbs for the power and polarity switches?

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Re: broken bass pot on my 1971 150-2 [message #14051 is a reply to message #14026]

Tue, 13 July 2010 06:14

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Hi. these type of 50K pc mount pots are getting very hard to come by in a drop in replacement form, so give me a while longer to continue my search.
It may come down to piecing componets of two different pots together as I have done in the past.

In regards to getting nut off the pot and the board dismounted from the face of the amp there are two different ways to do it, and you are down to the last choise of how to get it off.

What you have to do at this point is use a dremel loaded with a cut off disc to cut thru opposite sides of the pots hold down nut, but the cut off disc must be reduced in diameter some by waring them down first on stone,brick concret or another section of metal
.
In this way it will be small enough to not cut up the cast contorl ring on the face plate of the amp, but yet be big enought to cut most of the way thru the nut and then let you just snap it off.

The job is not as bad as it sounds and the whole thing takes about 15 minutes and be sure to ware eye and nose protection.

The lamp/bulb number A GE 335.

Be very carefull when prying off the blue lamp cover or doing any work on these two switches as the plastic mounting section of them as got very brittle with age and snaps off easy.

When you load the blue lens/cover back in place be sure to hold/support the ass ned of the switch from inside the amp.

It helps at times to use a section of automotive or fish tank vacume tubing to remove and install the lamp.

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Re: broken bass pot on my 1971 150-2 [message #14056 is a reply to message #14051]

Tue, 13 July 2010 08:54

drjymmiphreak
Messages: 6
Registered: July 2010

Junior Member

how exactly does the bulb cover come off? I don't want to screw it up any worse, so i'd like to know exactly what the hell i'm doing this time. i never even knew it took bulbs and want to install them correctly. does the cover come off from outside the amp, or do i need to pull the switch out from inside before it will come off? I appreciate all the help. hell, i've had this thing for nearly 10 years now and only found out what the hell exactly it is less than a week ago. i was under the impression it was a guitar amp lol! i also had no idea how old it was...

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Re: broken bass pot on my 1971 150-2 [message #14058 is a reply to message #14035]

Tue, 13 July 2010 09:33

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

Senior Member

If you wanted the K150-2 head, I'd let it go for 100.00 and actual shipping cost.
Replacing the bulbs, since the switches haven't been made since 1975, I remove the amp from the case. Remove the lid, and I remove all the screws holding the face plate so I can tilt the face plate and get some room to remove the screws holding the switches to the face plate. The blue lens cover has a white plastic part that goes into the switch. I gently push on the white part to remove it from the switch. You will then see the burned out bulb and it unscrews like a regular light bulb. Install the new bulbs and put everything back together. You may have to unplug the wires that connect the pre amp boards to get enough room to tilt the face plate. A little more work than just trying to push out the lens assembly, but I've never broken a switch doing bulb replacements.
pleat

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Re: broken bass pot on my 1971 150-2 [message #14060 is a reply to message #14058]

Wed, 14 July 2010 01:20

drjymmiphreak
Messages: 6
Registered: July 2010

Junior Member

what about just the baord for the first channel? would you let go of just that? I can't squeeze 100+ at the moment, but i may be able to swing like 35 for the board sans shipping. would u go for that?

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Re: broken bass pot on my 1971 150-2 [message #14061 is a reply to message #14026]

Wed, 14 July 2010 01:21

drjymmiphreak
Messages: 6
Registered: July 2010

Junior Member

and thanks for the info on the light bulb. i really appreciate it

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Re: broken bass pot on my 1971 150-2 [message #14065 is a reply to message #14026]

Thu, 15 July 2010 05:59

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

A bass pot that will work can be had from Mouser electronics on line, part number 31VQ405-F. Cost is less than twp dollars, I do not know if they have a dollar amount minimum on orders.

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Re: broken bass pot on my 1971 150-2 [message #14253 is a reply to message #14026]

Tue, 31 August 2010 21:05

charles
Messages: 1
Registered: August 2010
Location: home nearby computing in ...

Junior Member

guys you seem like the right bunch to ask .. i am new here and this is first post

i got a k150-2 amp that hasn't woorked in ten years
i had it repaired to only have it last an hour.

this kustom provides loads of fun ,

i just want it repaired
and i am technically able

so my question is

board per board in this thing ,
the one with the metal sheilded
three pronged cf's

who has one of those?

and

who has those inverted flat rca/ic's which come up in its own main body alcove?

i know confusing , lets talk cause i mean business
need pointers, can tell i have a knowledgable bunch

i live in canada

thanks
charles

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Re: broken bass pot on my 1971 150-2 [message #14257 is a reply to message #14026]

Wed, 01 September 2010 10:00

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Hello and welcome!
I will guess that the board you are speaking of is the #5033 board on the floor of the amp.

This is the driver board with the two box mounted/heat sinked driver transistors.

If your amp is blowing fuses and or producing a 120 hz hum like mad out of the sepaker(s) then your problem may be on this 5033 board with one of those two driver transistors and or one, may be both of the output transistors mounted on the bottom of the amp.

It is possible to have a bad driver transistor and not have a shorted output transistor, but most times not the other way around.

also on the driver board are two 5 watt box type resistors of under 1 ohm in value,if you have a dead output transistor than one those resistors may be open also.

Keep us informed on your progess.

New transistors to replace these driver transistors will not have the boxed heat sink, so what I do is reinstall the box on the new one and also add a slip on metal star type heat sink also as once you unload the original from the box you never get the good metal to metal contack/grip that the orignals had, and poor cooling will fry these transistors if you drive the amp hard.

The orignal numbers on these transistors where 38736 and 38737, replacements for these are NTE brand NTE 128 and NTE129 respectivly.

The output transistors are both the same type.
A commom replacement will be a 2N3055, or a NTE131, or the better built NTE181.

If one of your outputs is toast I would replace them both with NTE131MP which is a matched pair of the 131`s.

Also note that the smaller transistors on the driver board should be checked as well, although if they are toast the amp will not alway blow the fuse.

The small round recitifer bridge mounted on the floor of the amp near the power transformer with the two black and one red and one green wire coming off of its tower should be checked for shorts also, as some times a blown output stage that kills the fuse may creat enough of a currnet draw to short that out also.
Also

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