Parts for GK 800RB

[froghat]

Hi all - I have an 800RB from 1987 (the 'A' version) that needs some work. At least a full re-cap and then a number of power transistors. I spoke with Lani at GK, and the cost of buying them through GK will be too high to make the overhaul/repair worthwhile. Are there good recommendations for replacement parts? Should I be looking to upgrade the caps? I need:

6 x 1000uF 100V axial electrolytic ($9.10 each)
4 x 470uF 63V axial electrolytic ($3.50 each)
? x MJE15022 ($14.40 each)
? x MJE15023 ($14.40 each)

plus various miscellaneous components (micas, various caps and resistors). The pots are all original too, and are noisy, but seem to be working.

Thanks!
Bill

[Enzo]

Hi Bill, welcome to the forum.

Do you generally service amps? None of these parts are special. General suppliers like MOuser should have most of what you want. Or Digikey or Allied or Newark.

First, those outputs are MJ15022, not MJE15022.

Looking at Mouser:
MJ15022 are in stock at $4.07 ($3.34 each if you want to get 25 of them) MJ15024 is the same part with a bit higher voltage rating. It goes anywhere a 15022 goes.

MJ15023 are also in stock at $4.07. They are the PNP complement to the 15022. And as for the other MJ15025 also works.

I don't know what upgrades you might have in mind, but those plain old vanilla generic caps they built it with lasted 35 years, and I bet most of them still work. But looking at 470uf 63v axial caps, Mouser has seven kinds in stock, from $2 to $6. The dimensions are listed, so make sure none are too long or too wide for your board. Note the $6 ones are actually 150 degree high temp caps. Whee!

They also have two different 1000uf 100v axials in stock for 5 and a half bucks a pop.


get yourself a can of Deoxit D5 spray and clean the noisy pots, I bet they clean up fine.

[Jazz P Bass]

Deoxit D5 spray can be purchased at Radio Shack.

[froghat]

Thanks for the help Enzo and Jazz P. About me - I used to fix amps for Sam Ash (in the 70s) but really haven't done much with them since then. In any case I have no equipment (variac, scope, signal gen, etc) beyond a basic multimeter and my trusty Weller station. I've fixed a few things lately where there were obvious defects (bad solder joints, cracked resistor) and yes, I find Deoxit is like a miracle drug. Anyway, I'm tempted to buy a cheap scope and take this up as a hobby now.

More details on the amp: The LF power amp works but will occasionally give some whooshing transistor noise. The HF amp has no power and is badly distorted. I'm not so concerned with the HF amp though, as I would probably get along just fine without biamping. The idea of re-capping and checking all the output transistors came from a tech who said at 26 years they were beyond their life expectancy. He also said all the micas should be replaced just for good measure. All I originally wanted was to find and replace the source of the whooshing noise.

[Jazz P Bass]

Well, welcome back!
Here is what I believe is the Rev A schematic.
The very first item that I would recommend is to check the power supply voltages.
Sameness between + & - voltages & lack of Vac ripple.
Happy hunting.

[Jazz P Bass]

Came up with the parts layout.

[froghat]

Thanks for the docs, Jazz P. I'll let you know how I'm progressing.

[rbegg]

Hello I am looking for screws for the top metal plate for the 800rb Does anybody have any for sale or at least know the size for me?