!!!!!It's Alive!!!!!

similost

similost

Rockin and Rollin....
I'm so proud of myself.. My first recap/rebuild ever!!!

I didn't do anything fancy or try and gussy it up any. All I did was replace the caps, the selenuim rectifier, bought all the tubes, replaced some bad wires, and added a bias adjustment, replaced the cord and switch.... AND IT LIVES!!!

OH.. it's one of the Bogen KO-100 amps I bought off Tinkerbelle...

I got the switch and cord replaced tonight, and slowly brought it up on the really nice (damn it.. forgot the name of the gadget that controls the voltage.. DOH!!!) anyway.. that Spartanmanor gave me...

With all the help and advice ya'll gave me, the cool amps Tinkerbelle sold me (and some tubes) and the gadget Spartan gifted me with, I've got one half of my mids ready to rock...

Only one little thing I may need some help with...

I added a bias adjustment per the values of the schematic. The voltage is supposed to read -47v at the test point. I'm getting -43.7v at the test point with the adjustment at the max.. Will this be a problem, or should I do something to get it corrected?

Once again... THANKS ALL!!!!

(I'm too excited to sleep!)
 
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Congrats on your first recap/rebuild!

The name of the thing that controls the voltage is a variac.
 
similost said:
I'm so proud of myself.. My first recap/rebuild ever!!!

I didn't do anything fancy or try and gussy it up any. All I did was replace the caps, the selenuim rectifier, bought all the tubes, replaced some bad wires, and added a bias adjustment, replaced the cord and switch.... AND IT LIVES!!!

OH.. it's one of the Bogen KO-100 amps I bought off Tinkerbelle...

I got the switch and cord replaced tonight, and slowly brought it up on the really nice (damn it.. forgot the name of the gadget that controls the voltage.. DOH!!!) anyway.. that Spartanmanor gave me...

With all the help and advice ya'll gave me, the cool amps Tinkerbelle sold me (and some tubes) and the gadget Spartan gifted me with, I've got one half of my mids ready to rock...

Only one little thing I may need some help with...

I added a bias adjustment per the values of the schematic. The voltage is supposed to read -47v at the test point. I'm getting -43.7v at the test point with the adjustment at the max.. Will this be a problem, or should I do something to get it corrected?

Once again... THANKS ALL!!!!

(I'm too excited to sleep!)
Click to expand...

Awesome, that's great news!

Any pics coming?
 
Thanks.. yes, variac.. I was having a bad brain fart...

Give me a few and I'll snap a few pictures.. and like I said, don't expect anything fancy, all I did was replace what needed to be replaced, and didn't clean up the amp at all.. yet.. I'll repaint the trannys, and wax the chassis, but that's all I'm gonna do.. .
 
Not the greatest, but you get the idea.. .

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I'm very super impressed now...

I got out my small tapco mixer, plugged in my Blackberry Storm into it, hooked the amp up to one of my JBL C36 speakers, and let some front 242 flow...

WOAH!!!! Insanely stupid loud, and just as crazy clear sound.. I can't wait to hear these in the application I have planned for them!

Even my wife was impressed :thmbsp:
 
LOL.. yeah, especially when I'm the one doing it. Had it of not worked, Ya'll would have probably been pretty sick of all my questions trying to troubleshoot it..

Just cross your fingers I have as much luck with the second amp...

I am insanely impressed by the bass this amps puts out. I know the C36's have a good punch to them, but wow.. really clean clear crisp bass.. hits crazy low compared to what I've heard them do with my silverstreak amps..
 
Thanks Tim..

Still waiting to see if anyone can answer the question about the bias. It sounds pretty damn good, and seems to be cranking out the tunes pretty well, so I'm thinking running the bias voltage a little low isn't that big of a deal? Figure it just isn't putting out as much wattage?

OR, should I try and make a change somehow to get the voltage to the correct reading?
 
This is one novice to another so take it with a grain of salt but I think it would be best to have the amp biased correctly.

You'll probably have to change the bias resistor so you can get it into a range where you can make the adjustment with the bias pot you installed.
 
hhhmm.... so I wonder if I can just install another resistor in line with the pot? Anyone know for sure, or would I have to buy different pots?

If I can just make a change and use the pot I have, how would I calculate what I need?
 
Ok I am just going to throw it out there, just looking at the photos. In the second photo it seems to me that the 2 big blue ecaps are connected right, it looks like you have the positive on one of the ecaps running into the negative side of the other, then grounded to the chassis. I may be wrong, but just wanted to throw that out there. Also I can't tell if the old can cap is still in place, if that wasn't replaced it would be a good idea to replace that.
 
Re. the bias - from where are you getting the -47V figure? The schematic you posted shows -43V at the 100KΩ resistor, and -42.5V at pin 5.
 
Well without having a schematic for the thing no one will be able to tell you much.
(I didn't see where you posted the schem)

The way a tech would do it is calculate the plate dissipation.

--------------

What that intails is measuring plate voltage and the cathode voltage of each output
tube, usually in an amp that has a neg voltage applied to the grid there is say 10ohm
resistors on each tubes cathode (if not you should install them) and you measure MV
across them, so say you measure 500mv (millivolts) that equals 50ma (.5 / 10 = .050),
say you have 450v at the plate, equals 22.5w of plate dissipation (450 x .050 = 22.5).

Your running EL34's, they have a rating of 25W, general rule of thumb is no more then
80% of the rating is acceptable, so the 22.5w factor is a touch high at 90%, they will
run just fine at that but may not live as long if they were biased a bit lower. (more neg)

Anyway that is just a test type condition an yours will no doubt be different then that.
 
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Good work!! The underside of those old tube amps without a single copper trace scare the living crap out of me. I don't know how you guys can figure out what to do with those!
 
Kegger said:
Well without having a schematic for the thing no one will be able to tell you much.
(I didn't see where you posted the schem)

The way a tech would do it is calculate the plate dissipation.

--------------

What that intails is measuring plate voltage and the cathode voltage of each output
tube, usually in an amp that has a neg voltage applied to the grid there is say 10ohm
resistors on each tubes cathode (if not you should install them) and you measure MV
across them, so say you measure 500mv (millivolts) that equals 50ma (.5 / 10 = .050),
say you have 450v at the plate, equals 22.5w of plate dissipation (450 x .050 = 22.5).

Your running EL34's, they have a rating of 25W, general rule of thumb is no more then
80% of the rating is acceptable, so the 22.5w factor is a touch high at 90%, they will
run just fine at that but may not live as long if they were biased a bit lower. (more neg)

Anyway that is just a test type condition an yours will no doubt be different then that.
Click to expand...

The schematic was posted in this earlier thread:

http://www.audiokarma.org/forums/showpost.php?p=2617414&postcount=16
 
OOPS.. damn.. I need to get new eyes or something.. Yes, it is -43 volts, SO, I'm right in specs!!! :D Now that makes me really freakin happy. I have NO CLUE where I was getting -47v... I'm sorry all... This is a good reason I shouldn't do projects like this.. LOL..

As far as the two large caps, Yes, they are wired in series, and yes, one side does go to ground...

Also, I did replace the multi-section can. the most single expensive parts this project took.

Here is the schematic too...

http://www.flickr.com/photos/dc-duo/3324673420/sizes/o/
 
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