10W suitcase amp

famousmockingbird · 19th August 2011, 02:38 AM

I have an ampex 2010 suitcase amp that worked until one day it got real noisey with lots of static so I shut it off and decided to recap it. I replaced the power supply caps and the noise is still present even with just the rectifier in it. I used a dim bulb tester and I don't think there is any shorts because a 40w bulb does not glow. What is my amps ailment?

andrew_k · 19th August 2011, 02:56 AM

coupling capacitors letting DC through?

famousmockingbird · 09:12 PM

correct me if I am wrong but I thought that if the output tubes were removed then it would not matter if there was DC passing to pin 5. I know in tube amps the speaker should always be hooked up when on but what about if the output tubes are removed? I would like to check voltages but the noise is so bad with the speaker hooked up it is pretty much impossible.

http://recordist.com/ampex/schematic...n/ampex612.jpg

andrew_k · 19th August 2011, 10:03 PM

Sorry, i totally missed your point about removing the other valves.
If you don't have output tubes in, you don't need a speaker attached. There will be no current drawn through the OT without output tubes.

famousmockingbird · 19th August 2011, 10:22 PM

Ok so I think I found my problem. With the speaker not connected and just the rectifier tube in I can hear arcing from the output transformer and it smells like its melting! Can I just replace the transformer with any 6v6 output tranny?

famousmockingbird · 19th August 2011, 10:33 PM

The numbers on the OT say 58-0005-C 606013

dcgillespie · 19th August 2011, 10:38 PM

That was surely going to be my suggestion! With no output tube in place, but the rectifier in place, any noise from the speaker must be from an arcing (to ground) output transformer. You will want to make sure that the transformer matches the application (i.e. SE or PP), has the proper primary impedance, secondary impedance, and that it is rated for the power output rating of the amplifier.

Dave

famousmockingbird · 19th August 2011, 11:12 PM

Well I was putting the amp back together and noticed that where the line power comes into the amp the common wire had broken off so only the hot was connected to the amp. I soldered it back on and the problem has been resolved. What are the chances I did some serious damage to the output transformer?

famousmockingbird · 19th August 2011, 11:20 PM

I measured with a multimeter from pin 3 to pin 3 on the output tubes and I get a reading of 8.5k. From the center tap to pin 3 of one tube I get 8.3k and from center tap to pin 3 of the other tube I get 150 ohms. Is it fried or what?

dcgillespie · 19th August 2011, 11:37 PM

The reading of 150 ohms is about normal. The reading of 8.3K is not. Do not operate the amplifier in this condition. I don't know what output tubes you are using, other than since the plate connections are on pin #3 it sounds like a standard octal tube. In any event, operating any output tube with no plate voltage while the screen grid does receive power will damage the tube. Also, the other output tube will be under biased if a common cathode bias resistor scheme is used. There is little doubt that the output transformer needs to be replaced.

Dave

19th August 2011, 02:38 AM	#1
famousmockingbird diyAudio Member Join Date: Dec 2010 Location: Amesbury, MA	10W suitcase amp I have an ampex 2010 suitcase amp that worked until one day it got real noisey with lots of static so I shut it off and decided to recap it. I replaced the power supply caps and the noise is still present even with just the rectifier in it. I used a dim bulb tester and I don't think there is any shorts because a 40w bulb does not glow. What is my amps ailment?

19th August 2011, 09:09 PM	#3
famousmockingbird diyAudio Member Join Date: Dec 2010 Location: Amesbury, MA	correct me if I am wrong but I thought that if the output tubes were removed then it would not matter if there was DC passing to pin 5. I know in tube amps the speaker should always be hooked up when on but what about if the output tubes are removed? I would like to check voltages but the noise is so bad with the speaker hooked up it is pretty much impossible. http://recordist.com/ampex/schematic...n/ampex612.jpg Last edited by famousmockingbird; 19th August 2011 at 09:12 PM.

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19th August 2011, 02:56 AM	#2
andrew_k diyAudio Member Join Date: May 2009	coupling capacitors letting DC through?

19th August 2011, 10:03 PM	#4
andrew_k diyAudio Member Join Date: May 2009	Sorry, i totally missed your point about removing the other valves. If you don't have output tubes in, you don't need a speaker attached. There will be no current drawn through the OT without output tubes.

19th August 2011, 10:22 PM	#5
famousmockingbird diyAudio Member Join Date: Dec 2010 Location: Amesbury, MA	Ok so I think I found my problem. With the speaker not connected and just the rectifier tube in I can hear arcing from the output transformer and it smells like its melting! Can I just replace the transformer with any 6v6 output tranny?

19th August 2011, 10:33 PM	#6
famousmockingbird diyAudio Member Join Date: Dec 2010 Location: Amesbury, MA	The numbers on the OT say 58-0005-C 606013

19th August 2011, 10:38 PM	#7
dcgillespie diyAudio Member Join Date: May 2010 Location: Ball Ground, GA	That was surely going to be my suggestion! With no output tube in place, but the rectifier in place, any noise from the speaker must be from an arcing (to ground) output transformer. You will want to make sure that the transformer matches the application (i.e. SE or PP), has the proper primary impedance, secondary impedance, and that it is rated for the power output rating of the amplifier. Dave

19th August 2011, 11:12 PM	#8
famousmockingbird diyAudio Member Join Date: Dec 2010 Location: Amesbury, MA	Well I was putting the amp back together and noticed that where the line power comes into the amp the common wire had broken off so only the hot was connected to the amp. I soldered it back on and the problem has been resolved. What are the chances I did some serious damage to the output transformer?

19th August 2011, 11:20 PM	#9
famousmockingbird diyAudio Member Join Date: Dec 2010 Location: Amesbury, MA	I measured with a multimeter from pin 3 to pin 3 on the output tubes and I get a reading of 8.5k. From the center tap to pin 3 of one tube I get 8.3k and from center tap to pin 3 of the other tube I get 150 ohms. Is it fried or what?

19th August 2011, 11:37 PM	#10
dcgillespie diyAudio Member Join Date: May 2010 Location: Ball Ground, GA	The reading of 150 ohms is about normal. The reading of 8.3K is not. Do not operate the amplifier in this condition. I don't know what output tubes you are using, other than since the plate connections are on pin #3 it sounds like a standard octal tube. In any event, operating any output tube with no plate voltage while the screen grid does receive power will damage the tube. Also, the other output tube will be under biased if a common cathode bias resistor scheme is used. There is little doubt that the output transformer needs to be replaced. Dave

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