Citation 12 failure...

[lasse]

Hello,

I have to admit it- I have made a partial mess out of my recapping of my old Citation 12 amp.

Probably, the recapping is quite OK but I must have touched something on the board when adjusting the bias, so that when I connected the amp to the speakers, DC of probably quite a lot of amps, Went right into the woofer and destroyed it (Not a very big thing, a few hours work to replace it, but still....)

Now the issue at hand: What shall I do with the amp? I have invested like 200 USD in new caps and one thing could be to replace all transistors. If so, the trouble would be to find adequate replacements (does anyone know that have done this?) Perhaps the transistors are getting oldish after 40+ years??

Another would be to find and replace the one/few that is malfunctioning and that will be a challenge (advice on how to take the first steps in this would be greatly appreciated..)

I NEVER give up! I will have that Cit12 operational att ANY cost in time or dineros!

Best regards//lasse

[fastbike1]

Re: Citation 12 failure...

The bias pots may have been bad/dirty. I burned a channel on a 70's Pioneer Integrated when the bias made a big swing for a very small movement of the pot. In that case I know that nothing got shorted. Since then my practice has been to fully rotate the pot several times with no power, then return to the original position before starting adjustment.


I can't find the links, but there are complete rebuild kits for Citation 12 available. Also check Nelson Pass' site for his mods to the Citation 12.

[Pete Basel]

Re: Citation 12 failure...

I cloned that amp when I was a young kid and have made lots of comments on it
over at DIY Audio. A modern replacement
for the outputs would be the 2N3773, however what you really want is a single
diffused type and I'm fairly certain that the 2N3773 is triple diffused. There is
often smoke when the outputs go, so hope for the best.
I believe that the outputs are socketed, pull them and test them as back to back
diodes with an ohm meter - look it up if you don't know how.
Let us know what you find.

I always suggest putting in current limiting resistors in the rail paths when
working on SS amps.

Which rail is it stuck at? You might have just blown the small VAS transistor.
A blown amp is like a crime scene, make as few changes as possible and save
all the old parts.

[lasse]

Re: Citation 12 failure...

The bias pots may have been bad/dirty. I burned a channel on a 70's Pioneer Integrated when the bias made a big swing for a very small movement of the pot. In that case I know that nothing got shorted. Since then my practice has been to fully rotate the pot several times with no power, then return to the original position before starting adjustment.


I can't find the links, but there are complete rebuild kits for Citation 12 available. Also check Nelson Pass' site for his mods to the Citation 12.

[fastbike1]

Re: Citation 12 failure...

Here's a couple of links.

http://www.analogmetric.com/goods.php?id=993

www.firstwatt.com/pdf/art_mos_citation.pdf

Note I have no additional knowledge about the analogmetric kit. I think it claims to be based on Nelson Pass' mosfet design.

[robertcottiers]

Re: Citation 12 failure...

Pick up a few Dummy load resistors with your next capacitor order.....sorry for your troubles.

[johnhenry]

Re: Citation 12 failure...

safety first

never use your speaker as a tester or a dummy load

use current limiter either
using lamp in series @ the ac voltage supply (simpler)
or (100R) resistor in series at dc supply replacing the fuse

always check your amp o/p for d/c voltage more than 100mV is unacceptable

I think if you've time and ready to learn plus money to burn you can repair electronic stuff
but probably not the newer swicthing and smd stuff

[Pete Basel]

Re: Citation 12 failure...

[ATTACH=CONFIG]51760[/ATTACH][ATTACH=CONFIG]51761[/ATTACH][ATTACH=CONFIG]51762[/ATTACH]

Do you have the schematic?
You can pull out the driver boards and that might isolate the output transistors so
that you can test them.
Which rail does it go to when you power it up?

[Pete Basel]

Re: Citation 12 failure...

I am PB2 here and there are many other Citation 12 threads there:
http://www.diyaudio.com/forums/solid...ansistors.html

That was some time ago, I would not use the 243/253 drivers since I found out that their
SOA is not very good. I'd probably go with BD139/140s instead.

[fastbike1]

Re: Citation 12 failure...

I know how you feel. The Pioneer was an SA-7800 in pristine condition.

[lasse]

Re: Citation 12 failure...

safety first

never use your speaker as a tester or a dummy load

use current limiter either
using lamp in series @ the ac voltage supply (simpler)
or (100R) resistor in series at dc supply replacing the fuse

always check your amp o/p for d/c voltage more than 100mV is unacceptable

I think if you've time and ready to learn plus money to burn you can repair electronic stuff
but probably not the newer swicthing and smd stuff