Peavey Classic 50 help

Telebuckers · 09-02-2009, 11:32 PM

Hello all- I'm working on a Peavey Classic 50- and the resistor in r58 is burnt out. On the schematic it reads 400W 5FP. I'm guessing this means 400ohm 5W Flame Proof? Here is a link to the schematic:

http://www.schematicheaven.com/newam..._classic50.pdf

Any help on sourcing this part and/or hints on why it could've blown would be much appreciated.

Thanks

Enzo · 09-03-2009, 12:34 AM

That is exactly what it is. Just use the common ordinary everyday rectangular cement power resistor. 400 ohm 5 watt. if you don;t see 400 ohm, use the standard value 390 ohm instead. Peavey did that themselves often enough.

That resistor failed for a reason, and the most likely one is a failed power tube.

oc disorder · 09-03-2009, 12:34 AM

Hi Telebuckers
Firstly either you will have to replace it with the nearest prefered value ie 390 ohms or 430 ohms or order the exact part from Peavey.
Its the main HT feed to the screens of the output tubes and later is stepped down for the pre-amp tubes supply.
Most likely there is an issue with the output valves - some kind of internal short.
A filter cap C40,C38 & C39 could be faulty.
Unlikely but a possible issue with a pre-amp valve.
Maybe it just died from old age !
If you pull out the output tubes you could try soldering across the 400ohm 2 x 1k 1 watt resistors as a temp measure to see if they burn out.
BE CAREFUL as you no doubt know this is the high voltage area and can kill to put it bluntly!
Just check if there is any short to ground of that HT rail after the standby switch.

Telebuckers · 09-03-2009, 01:26 AM

Thanks a lot guys- I figured the power tubes were most likely involved with that because they were toast. This guy's had the amp over 10 years and all this time he thought it was solid state- so you can figure the tubes were never changed.

Gtr_tech · 09-03-2009, 03:42 AM

Quote:

Originally Posted by Telebuckers

This guy's had the amp over 10 years and all this time he thought it was solid state- so you can figure the tubes were never changed.

Enzo · 09-03-2009, 03:52 AM

Yeah, and a lot of teenagers still think you can;t get pregnant the first time you screw.

Telebuckers · 11-02-2009, 09:00 PM

Well I finally got the ceramic resistors in from Peavey and installed one and it burnt out immediately with all of the tubes pulled. Could this be from bad filter caps?

52 Bill · 11-02-2009, 09:19 PM

Quote:

Originally Posted by Telebuckers

Could this be from bad filter caps?

Yes C40 in particular, or could be a bad power tube socket.

Telebuckers · 11-02-2009, 09:22 PM

Ok thanks I'll look into that.

Telebuckers · 11-05-2009, 06:42 PM

Thanks for the help guys- amp is up and running now. One of the 47uf filter caps turned out to be bad.

09-02-2009, 11:32 PM	#1
Telebuckers Member Join Date: Sep 2007 Posts: 41	Peavey Classic 50 help Hello all- I'm working on a Peavey Classic 50- and the resistor in r58 is burnt out. On the schematic it reads 400W 5FP. I'm guessing this means 400ohm 5W Flame Proof? Here is a link to the schematic: http://www.schematicheaven.com/newam..._classic50.pdf Any help on sourcing this part and/or hints on why it could've blown would be much appreciated. Thanks

09-03-2009, 12:34 AM	#2
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,287	That is exactly what it is. Just use the common ordinary everyday rectangular cement power resistor. 400 ohm 5 watt. if you don;t see 400 ohm, use the standard value 390 ohm instead. Peavey did that themselves often enough. That resistor failed for a reason, and the most likely one is a failed power tube. __________________ Education is what you're left with after you have forgotten what you have learned.

09-03-2009, 03:52 AM	#6
Enzo Senior Member Join Date: May 2006 Location: Lansing, Michigan, USA Posts: 10,287	Yeah, and a lot of teenagers still think you can;t get pregnant the first time you screw. __________________ Education is what you're left with after you have forgotten what you have learned.

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09-03-2009, 12:34 AM	#3
oc disorder Senior Member Join Date: Jul 2006 Posts: 417	Hi Telebuckers Firstly either you will have to replace it with the nearest prefered value ie 390 ohms or 430 ohms or order the exact part from Peavey. Its the main HT feed to the screens of the output tubes and later is stepped down for the pre-amp tubes supply. Most likely there is an issue with the output valves - some kind of internal short. A filter cap C40,C38 & C39 could be faulty. Unlikely but a possible issue with a pre-amp valve. Maybe it just died from old age ! If you pull out the output tubes you could try soldering across the 400ohm 2 x 1k 1 watt resistors as a temp measure to see if they burn out. BE CAREFUL as you no doubt know this is the high voltage area and can kill to put it bluntly! Just check if there is any short to ground of that HT rail after the standby switch.

09-03-2009, 01:26 AM	#4
Telebuckers Member Join Date: Sep 2007 Posts: 41	Thanks a lot guys- I figured the power tubes were most likely involved with that because they were toast. This guy's had the amp over 10 years and all this time he thought it was solid state- so you can figure the tubes were never changed.

11-02-2009, 09:00 PM	#7
Telebuckers Member Join Date: Sep 2007 Posts: 41	Well I finally got the ceramic resistors in from Peavey and installed one and it burnt out immediately with all of the tubes pulled. Could this be from bad filter caps?

11-02-2009, 09:22 PM	#9
Telebuckers Member Join Date: Sep 2007 Posts: 41	Ok thanks I'll look into that.

11-05-2009, 06:42 PM	#10
Telebuckers Member Join Date: Sep 2007 Posts: 41	Thanks for the help guys- amp is up and running now. One of the 47uf filter caps turned out to be bad.

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