Sunn Coliseum Salve Help/Ideas

[TigerAmps]

I have a Sunn coliseum slave. The prior owner went in and replaced the drivers (2N3441's) with NTE's and a few other things with NTE.
The schematic I found does not match the board (20-0026 D) exactly. For example: The schematic shows 2 variable resistors yet the board only
has one. The amp dates to 1971. Also, anyone every replace the 2N3441's with anything else? It came to me DOA and I'm trying to bring
it back to life. I have attach a picture of a similar board and the diagram I currently have which is close, but not exact.

One of the BC107's was replaced with an NTE and a few other transistors.
As for the power section, one of the .33 ohm 10W resistors was open and all the output transistors meter out fine.
Also, one of the TO-66 transistor sockets needs to be replaced (one of the connection leads is broken off).

Any ideas or info is greatly appreciated!

[52 Bill]

What do you mean by DOA, no power on, power but no sound?

This is really just a basic power amp so it shouldn't be that hard to fix. As for the 2N3441 replacements, are the ones in there bad now? Have you looked at TO-220 case transistors?

[TigerAmps]

Thanks for responding Bill!

The previous owner said it "blew the fuse" (despite the fact it has a circuit breaker).

Upon inspection:
1) the meter was physically broken.
2) One of the to-66 transistors was not in the socket
3) one of the to-66 sockets connections was broken off.
4) One of the .33 10W resistors was open.
5) the wires to the board were all removed and some were cut (wanker!)

I attached pictures of the actual board!

So far I did the following:
1) replaced the bridge rectifier
2) checked the main caps and they were "good" (not open nor shorted)
3) replaced the .047 caps in the power supply (primary side)
4) replaced the .33 10W resistors that was open.
5) disconnected the +/- 50V from the 2 power caps going to the amp circuitry
6) disconnected the wire feeding the meter circuit
7) fired it up and tested the power supply which measured +/- 52V on the caps. (at least the PS works!)
8) tested the output transistors (all RCA 2n3055) and they all checked out with the diode test

Finally pulled the board and started looking it over.
I noticed half the transistors were replaced with NTE stuff (which always scares my - especially around Halloween!)

So I need to:
1) go over the board (and was looking for the 20-0026 board schematic)
2) order to-66 sockets and the 2N3441's

If I can not get the to-66 sockets, considering the to-220 type transistors.




I hope that sheds some light on what the state of the amps is ...

[loudthud]

Does the board have the number 20-0026 on the back?

The resistor that is soldered to the diode legs in the middle of the board seems to be the bias adjustment. I have a Coliseum Bass dated December 1970 that has no pots on the board. It's layout is slightly different.

Attached is the layout for the 20-0026.

[TigerAmps]

"Does the board have the number 20-0026 on the back?"

Yes it does ... It is different from the image posted above (post #4).
I posted a picture of the actual board from the amp above in post #3.
I think I'm just going to have to go thru the board and mark up a copy of the schematic with the changes.

I was hoping that someone who used to service Sunn amps back in the day may have the full set of schematics
including the changes over the years.

I will measure the resistors/caps and test all the transistors over the next couple of days to see what the damage is.

[Enzo]

I think I may have TO66 sockets in stock, I'll check. But really, I think I would fish the broken contact out of the socket, and just solder a wire to the transistor pin where it sticks through.

[52 Bill]

I'd want to clean up that board a little, there is a burn mark, but because of all of the soot, I can't see how bad the burn is.

NTE stuff is not inherently bad, as long as it is used correctly. I've seen the wrong parts used to replace stuff before, so I'd double check the previous work before trusting it to be correct.

In case you didn't know it, TO-66 cases can be replaced with TO-220 case parts. The pin order and spacing is the same, all you have to do is to bend the base and emitter leads down in the correct spot. Cut off the collector lead and use the metal tab to make the collector contact.

[TigerAmps]

Quick Update:

I checked over the board and there were minor difference such as
1) a few components were in different locations
2) the bias pot was replaced with a 1K resistor
3) One of the C206 or C207 had a different value (I don't remember which)

The resistor that burned was R221 (one of the 150 ohm resistors). The board currently has a 1.5K 1/2 watt resistor (which is wrong)
in it's place (if you look at the picture of the board). However - R220 is a 150 ohm 1 watt resistor on the board and it looks original so
I was going to replace R221 with a 150 Ohm 1 watt resistor as well.

Also, Q204, Q205, Q206 and Q207 all appear to be blown (at least one is shorted, one is open). I plan to replace them all as the BC107 or shorted and the others are questionable (NTE); I need to pull them and check them all; At this point think of replacing them anyway to make sure we start off on a solid foundation.

I was thinking of the following replacements:

BC107B -> Still available (Fairchild BC107B)
2N4250 -> 2N3906 or 2N5401
2N3440 -> Still Available (Central Semiconductor 2N3440)
2N4888 -> 2N5401

If anyone has any better suggestions or recommendations for the transistor substitutions, please let me know ...
Also, someone please confirm these choices make sense (especially the 2N4250).

Thanks!

[R.G.]

Given the degree of damage you noted, I think you would be wise to count on substantially remanufacturing it: either replace or measure and verify every component. The hours you save will probably more than pay for component costs.

[TigerAmps]

That is pretty much where I am; not taking anything for granted!

I am checking all the resistors, diodes, replacing the burnt/charred components and the orientation of the transistors.

Question:
If I start this up on a variac, what do I look for?
Any recommendation for a procedure to follow?

I only ask because this would be the first "near complete" rebuild I have attempted.

Thanks ...

[loudthud]

If you start up the amp with a Variac, don't connect any kind of load. The output will go to the negative rail until the incoming line Voltage reaches about half the intended value. It's best to use a Variac that had some kind of current meter. Watch the current and stop if the current goes too high. There will be some current required to charge up the filter caps so it's hard to say what too much is. A light bulb limiter is really a better idea because it automatically limits current, or use both.

The light should flash bright then dim to a dull orange. Check the Voltage at the output for near zero Volts.

[TigerAmps]

Will Do! Thanks ...

[R.G.]

Don't start it up on a variac. Start it up on a light bulb limiter. Very different kinds of protection.

[TigerAmps]

Update -finally got back to this amp ...

Re-furbished the board and checked the output transistors!
I finally connected the board and fired it up today with the meter circuit disconnected and it works - yeee - haaa!

The meter is damaged beyond repair.

This is going to be a long shot but: Has anyone found replacement meter for the Sunn Coliseum Slave?
Newark.com lists VU meters, I was wondering if anyone in the forum has used any of them or have another source for something that would fit (from experience)?

If not I will pull the meter, measure it and start searching ...

Thanks in advance!

[shiner555]

Oh man!!! This thread may very well save me. I had my 70's coliseum bass go up in flames at a gig this past Sunday. When I compared the driver PCB 20-0026D to the avail schematics, it didn't match and had me really worried I wasn't going to be able to figure out the correct parts to put back in. TigerAmps, did you ever verify the resistor values you replaced?