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SWR Repair

B

billfoss

Jan 7, 2006
34
1
Az.
#1
I have an SWR Super Redhead (mid 90's) that's "on the blink". It seems to go into low power with no bottom end. I took it to Sam Ash and was told there was some type of module that isn't made/used anymore, so he couldn't fix it. Is there a SWR genius in So. Cal. that might be able to help? It's too good an amp (and spendy) to just let it go.
Thanks,
Bill
 
#6
billfoss said:
I have an SWR Super Redhead (mid 90's) that's "on the blink". It seems to go into low power with no bottom end. I took it to Sam Ash and was told there was some type of module that isn't made/used anymore, so he couldn't fix it. Is there a SWR genius in So. Cal. that might be able to help? It's too good an amp (and spendy) to just let it go.
Thanks,
Bill
Click to expand...
Its an SWR power module 2000. The redhead shares the workingmas 4004. Yes fender discontinued it. I am currently working on one now. most likely need a 2sc3264 transister there are 4 of them. cot about 10.00 each. someone with solder skills can do for you. I recomend chaning all 4 becouse its like puting new wine in old bottles.also change R22 resister as it comonly blows with new pwer transisters installed and change the voltage regulaters on the board there are 3{(2-C4382 and (1-A1668)}. Here is the one im working on now for the local high school. and a schematic. good luck my friend.
board pic.jpg
thumbnail.jpg
 

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#7
Its an SWR power module 2000. The redhead shares the workingmas 4004. Yes fender discontinued it. I am currently working on one now. most likely need a 2sc3264 transister there are 4 of them. cot about 10.00 each. someone with solder skills can do for you. I recomend chaning all 4 becouse its like puting new wine in old bottles.also change R22 resister as it comonly blows with new pwer transisters installed and change the voltage regulaters on the board there are 3{(2-C4382 and (1-A1668)}. Here is the one im working on now for the local high school. and a schematic. good luck my friend.
thumbnail-jpg.jpg
board-pic-jpg.jpg
 
#10
S-Bigbottom said:
Thanks for putting up schematics for this and Welcome to TalkBass.
You need to check the dates before posting as this post is from 2008 and the poster has not been around since 2011.
Hope he had it setup by now.
Click to expand...
Ohhhh geese lol thanks
I was repairing this and googled swr and took me to this site. And thought Ohhh just offer info i had. Thanks
 
#11
I know you are trying to help, but your advice has really missed the mark on this.

Only replace the power transistors that have actually failed. Testing them is the way to identify what has failed. Note that there are more counterfeit power transistors of this style on the market than genuine parts.

The 2SC4382 and 2SA1668 transistors are not voltage regulators, nor do they have anything to do with voltage regulators. One pair is used as emitter followers to drive the output transistors in a Darlington configuration and one is used as a voltage amp in the VAS. Again, these and the emitter resistors in both the drivers and outputs plus R11, R40 and every part in the VI limited must also be tested. This amp should be powered up through a variac as well as the supply being current limited.

Before power up, the bias control should be set for minimum output stage bias. It's helpful to understand how the circuit works before attempting a repair.
 
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#12
agedhorse said:
I know you are trying to help, but your advice has really missed the mark on this.

Only replace the power transistors that have actually failed. Testing them is the way to identify what has failed. Note that there are more counterfeit power transistors of this style on the market than genuine parts.

The 2SC4382 and 2SA1668 transistors are not voltage regulators, nor do they have anything to do with voltage regulators. One pair is used as emitter followers to drive the output transistors in a Darlington configuration and one is used as a voltage amp in the VAS. Again, these and the emitter resistors in both the drivers and outputs plus R11, R40 and every part in the VI limited must also be tested. This amp should be powered up through a variac as well as the supply being current limited.

Before power up, the bias control should be set for minimum output stage bias. It's helpful to understand how the circuit works before attempting a repair.
Click to expand...
Yes they are not voltage regulaters. I miss spoke on that. Bad terminolgy on my part. You can replace only 1 transister but generally they will fail down the road becouse they are not from the same lot. Ive seen this many times. Its what fender, peavey, mackie have told me to do. whenever I get one I replace all of them now. Also yes power up with variac. Mine doesnt have amp control so I have it wired in with a lightbulb. works great and lights up whenever theres a short. thanks for pointing my termanology error i wrote kinda quick
 
#13
Replacing all output transistors is a myth, which started with germanium output devices because they were horribly inconsistent and unstable.

With modern silicon devices and good amp design, it's totally unnecessary.

Some techs insist on doing this for 2 reasons, the first being that they don't understand, thecsecond is that it makes more money. Both reasons are not in the customer's best interest. Much like replacing caps after 10 or 20 years because they might go bad. I've seen more damage caused by this, but it's another DIY favorite.
 
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#16
NTE is great provider of new and hard to find obsolete parts.
They even have very hard to find Germanium transistors

I'm about to build a smoking 10 watt barn buster right out of the 1968 RCA transistor manual. With NTE Germanium parts
 
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#17
BogeyBass said:
NTE is great provider of new and hard to find obsolete parts.
They even have very hard to find Germanium transistors

I'm about to build a smoking 10 watt barn buster right out of the 1968 RCA transistor manual. With NTE Germanium parts
Click to expand...
Should be exciting if nothing else. At least these days we know a lot more about tempco curves.
 
#18
agedhorse said:
Replacing all output transistors is a myth, which started with germanium output devices because they were horribly inconsistent and unstable.

With modern silicon devices and good amp design, it's totally unnecessary.

Some techs insist on doing this for 2 reasons, the first being that they don't understand, thecsecond is that it makes more money. Both reasons are not in the customer's best interest. Much like replacing caps after 10 or 20 years because they might go bad. I've seen more damage caused by this, but it's another DIY favorite.
Click to expand...
 
#19
that is a good point. The manufacturers usually tell me to do this (shotgunning) on mainly older equipment. An instructor has told me the same thing. You want them from the same lot unless not avail. you have a valid point that makes sence. Right or wrong For me for now im more comfortable doing them all while its out. I havent had any come back. Its not my living.Though its getting to be enough work here for it lol. i do it to help musicians in the area as there are no repar shops here and know what they go through. I charge very little sometimes nothing. depends on the person. so its deffinatly not about money. Have a great day I appreciate the input
thank you
 

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