Heathkit AA-81 What fuse does it take?

5/4/2009 3:57:02 PMDave Froehlich

Hello All,
Somehow this message got deleted. Does anyone know what fuse went in this amp? Does anyone know where I can find the service data for it? I have checked with several places and there is only one picture of it on one website. There is no mention of service data anywhere. It has 4 tubes in it: GZ34, EL34, EL34 and a 6AN8. Inside there are two 50µf capacitors @ 450v, two 150µf capacitors at 350 volts (wired in series). There is a bias diode (selenium) with a 20µf capacitor as the filter for the bias supply. There are two 100µf capacitors at 50 volts, and a 50µf at 50 volts. There are 5 other paper capacitors. All paper and electrolytic capacitors have been replaced.
When I first tried it out after replacing the capacitors, the rectifier tube sparked a little inside and the fuse opened. The fuse that was in the holder was open. I do not know what fuse should be in the holder.
Does anyone know?

Thanks,

Dave

5/4/2009 4:26:57 PMWarren

The specs are saying 120VAC at 130 Watts ,,

I would say a 2 Amp. Slow Blow should be right.

5/4/2009 4:39:07 PMBob B

:Hello All,
: Somehow this message got deleted. Does anyone know what fuse went in this amp? Does anyone know where I can find the service data for it? I have checked with several places and there is only one picture of it on one website. There is no mention of service data anywhere. It has 4 tubes in it: GZ34, EL34, EL34 and a 6AN8. Inside there are two 50µf capacitors @ 450v, two 150µf capacitors at 350 volts (wired in series). There is a bias diode (selenium) with a 20µf capacitor as the filter for the bias supply. There are two 100µf capacitors at 50 volts, and a 50µf at 50 volts. There are 5 other paper capacitors. All paper and electrolytic capacitors have been replaced.
: When I first tried it out after replacing the capacitors, the rectifier tube sparked a little inside and the fuse opened. The fuse that was in the holder was open. I do not know what fuse should be in the holder.
: Does anyone know?
:
:Thanks,
:
:Dave

Dave, here is some info i found for you. Your amp is labeled to consume about 117 v, 100-130 watts, which in today's standards of 125v, and hitting a peak of 130 watts is 1.18 amps. That should be the size of the fuze for you system. Keep in mind that it needs to be a slo-blow fuse otherwise the amp will always burn out the fuse as it hits the peak. Here is the website i got the power info from: http://www.heathkit-museum.com/hifi/hvmaa-81.shtml Hope that helps. Bob B

5/4/2009 8:07:59 PMDave Froehlich

Bob,
That's where they have the picture but no service data. I guess I'll have to make my own service data from the tube information and what's inside the chassis.
Yes, that makes sense. If it's taking out a 4 amp fuse something's not right.

Thanks,

Dave
::Hello All,
:: Somehow this message got deleted. Does anyone know what fuse went in this amp? Does anyone know where I can find the service data for it? I have checked with several places and there is only one picture of it on one website. There is no mention of service data anywhere. It has 4 tubes in it: GZ34, EL34, EL34 and a 6AN8. Inside there are two 50µf capacitors @ 450v, two 150µf capacitors at 350 volts (wired in series). There is a bias diode (selenium) with a 20µf capacitor as the filter for the bias supply. There are two 100µf capacitors at 50 volts, and a 50µf at 50 volts. There are 5 other paper capacitors. All paper and electrolytic capacitors have been replaced.
:: When I first tried it out after replacing the capacitors, the rectifier tube sparked a little inside and the fuse opened. The fuse that was in the holder was open. I do not know what fuse should be in the holder.
:: Does anyone know?
::
::Thanks,
::
::Dave
:
:Dave, here is some info i found for you. Your amp is labeled to consume about 117 v, 100-130 watts, which in today's standards of 125v, and hitting a peak of 130 watts is 1.18 amps. That should be the size of the fuze for you system. Keep in mind that it needs to be a slo-blow fuse otherwise the amp will always burn out the fuse as it hits the peak. Here is the website i got the power info from: http://www.heathkit-museum.com/hifi/hvmaa-81.shtml Hope that helps. Bob B

5/5/2009 11:27:12 PMDave Froehlich

Bob, Norm, All,
I cannot find anything wrong anywhere inside the set. There are no short circuits. The positive end of the filter capacitor is connected to the cathode of the rectifier. I did test the rectifier. There is some good emission for about a second after it warms up but then the emission drops, when either plate is checked. I'm not sure it it's the tube or the circuitry. This is a brand new tube. When I have it in the amplifier, it takes a rather long time to "warm up", then I can hear amplifier hiss. When I turn the volume control up and down I hear the noise of a dirty control. Then the fuse opens and the amplifier shuts off. This is a 4 amp fuse, not a slow-blow. I do not want to risk another expensive 5AR4. Maybe I can use a cheaper tube, and just hook it up. Will a 5U4 work just for testing? I see that a 5AR4 is the sub for a 5U4 but not the other way around. But will it work just for testing so I don't damage an expensive 5AR4?

Thanks,

Dave
:Bob,
: That's where they have the picture but no service data. I guess I'll have to make my own service data from the tube information and what's inside the chassis.
: Yes, that makes sense. If it's taking out a 4 amp fuse something's not right.
:
:Thanks,
:
:Dave
:::Hello All,
::: Somehow this message got deleted. Does anyone know what fuse went in this amp? Does anyone know where I can find the service data for it? I have checked with several places and there is only one picture of it on one website. There is no mention of service data anywhere. It has 4 tubes in it: GZ34, EL34, EL34 and a 6AN8. Inside there are two 50µf capacitors @ 450v, two 150µf capacitors at 350 volts (wired in series). There is a bias diode (selenium) with a 20µf capacitor as the filter for the bias supply. There are two 100µf capacitors at 50 volts, and a 50µf at 50 volts. There are 5 other paper capacitors. All paper and electrolytic capacitors have been replaced.
::: When I first tried it out after replacing the capacitors, the rectifier tube sparked a little inside and the fuse opened. The fuse that was in the holder was open. I do not know what fuse should be in the holder.
::: Does anyone know?
:::
:::Thanks,
:::
:::Dave
::
::Dave, here is some info i found for you. Your amp is labeled to consume about 117 v, 100-130 watts, which in today's standards of 125v, and hitting a peak of 130 watts is 1.18 amps. That should be the size of the fuze for you system. Keep in mind that it needs to be a slo-blow fuse otherwise the amp will always burn out the fuse as it hits the peak. Here is the website i got the power info from: http://www.heathkit-museum.com/hifi/hvmaa-81.shtml Hope that helps. Bob B

5/6/2009 12:12:59 AMDave Froehlich

Hello Again All,
Last night when I was checking things I noticed that the filter capacitor negative connection was somehow connected to the chassis. I didn't think it should be because it's mounted in an insulator and it's negative connection doesn't connect to the chassis. So I checked every wire and finally noticed that power supply negative is connected to the input phono jack. So that was what was connecting it to the chassis.
So today, after I discovered that a 5U4 could be used temporarily, so as not to damage another expensive 5AR4 (GZ34), that when I removed this negative connection to the phono jack, suddenly the neon pilot lamp started to work. Suddenly the fuse didn't open almost immediately after warm-up. Then I connected some audio to it for a test. Since the "ground" was disconnected, there was a very noticeable AC hum because the shield was disconnected. So I had to unbolt the jack completely and re-connect power supply negative to it. Now that it was no longer attached to the chassis there was no danger of causing any problems. This time the sound was excellent. Crystal clear. The EL34s have a little gas inside the metal (plate), I could see it through the holes. Is this normal or do I have gassy EL34s?
So my conclusion is that whoever built this Heathkit, didn't put the insulator on the jack before tightening the screws. What should I make the insulator out of? This jack has two ears on it for mounting on a chassis with nuts and bolts. The face that goes against the chassis is metal. The screws go through a phenolic plastic insulator. I I assume that an insulator, that also extends through the hole the jack goes through so the chassis is covered around the edge of the hole is covered as well and so that the shield part of the phono plug can never touch the chassis.
So I have solved the problem. A 5U4 seems to work fine. Can I use it or do I have to put a 5AR4 back into the socket?

Thanks,

Dave
:Bob, Norm, All,
: I cannot find anything wrong anywhere inside the set. There are no short circuits. The positive end of the filter capacitor is connected to the cathode of the rectifier. I did test the rectifier. There is some good emission for about a second after it warms up but then the emission drops, when either plate is checked. I'm not sure it it's the tube or the circuitry. This is a brand new tube. When I have it in the amplifier, it takes a rather long time to "warm up", then I can hear amplifier hiss. When I turn the volume control up and down I hear the noise of a dirty control. Then the fuse opens and the amplifier shuts off. This is a 4 amp fuse, not a slow-blow. I do not want to risk another expensive 5AR4. Maybe I can use a cheaper tube, and just hook it up. Will a 5U4 work just for testing? I see that a 5AR4 is the sub for a 5U4 but not the other way around. But will it work just for testing so I don't damage an expensive 5AR4?
:
:Thanks,
:
:Dave
::Bob,
:: That's where they have the picture but no service data. I guess I'll have to make my own service data from the tube information and what's inside the chassis.
:: Yes, that makes sense. If it's taking out a 4 amp fuse something's not right.
::
::Thanks,
::
::Dave
::::Hello All,
:::: Somehow this message got deleted. Does anyone know what fuse went in this amp? Does anyone know where I can find the service data for it? I have checked with several places and there is only one picture of it on one website. There is no mention of service data anywhere. It has 4 tubes in it: GZ34, EL34, EL34 and a 6AN8. Inside there are two 50µf capacitors @ 450v, two 150µf capacitors at 350 volts (wired in series). There is a bias diode (selenium) with a 20µf capacitor as the filter for the bias supply. There are two 100µf capacitors at 50 volts, and a 50µf at 50 volts. There are 5 other paper capacitors. All paper and electrolytic capacitors have been replaced.
:::: When I first tried it out after replacing the capacitors, the rectifier tube sparked a little inside and the fuse opened. The fuse that was in the holder was open. I do not know what fuse should be in the holder.
:::: Does anyone know?
::::
::::Thanks,
::::
::::Dave
:::
:::Dave, here is some info i found for you. Your amp is labeled to consume about 117 v, 100-130 watts, which in today's standards of 125v, and hitting a peak of 130 watts is 1.18 amps. That should be the size of the fuze for you system. Keep in mind that it needs to be a slo-blow fuse otherwise the amp will always burn out the fuse as it hits the peak. Here is the website i got the power info from: http://www.heathkit-museum.com/hifi/hvmaa-81.shtml Hope that helps. Bob B

5/6/2009 12:21:07 AMBob B

:Bob, Norm, All,
: I cannot find anything wrong anywhere inside the set. There are no short circuits. The positive end of the filter capacitor is connected to the cathode of the rectifier. I did test the rectifier. There is some good emission for about a second after it warms up but then the emission drops, when either plate is checked. I'm not sure it it's the tube or the circuitry. This is a brand new tube. When I have it in the amplifier, it takes a rather long time to "warm up", then I can hear amplifier hiss. When I turn the volume control up and down I hear the noise of a dirty control. Then the fuse opens and the amplifier shuts off. This is a 4 amp fuse, not a slow-blow. I do not want to risk another expensive 5AR4. Maybe I can use a cheaper tube, and just hook it up. Will a 5U4 work just for testing? I see that a 5AR4 is the sub for a 5U4 but not the other way around. But will it work just for testing so I don't damage an expensive 5AR4?
:
:Thanks,
:
:Dave
::Bob,
:: That's where they have the picture but no service data. I guess I'll have to make my own service data from the tube information and what's inside the chassis.
:: Yes, that makes sense. If it's taking out a 4 amp fuse something's not right.
::
::Thanks,
::
::Dave
::::Hello All,
:::: Somehow this message got deleted. Does anyone know what fuse went in this amp? Does anyone know where I can find the service data for it? I have checked with several places and there is only one picture of it on one website. There is no mention of service data anywhere. It has 4 tubes in it: GZ34, EL34, EL34 and a 6AN8. Inside there are two 50µf capacitors @ 450v, two 150µf capacitors at 350 volts (wired in series). There is a bias diode (selenium) with a 20µf capacitor as the filter for the bias supply. There are two 100µf capacitors at 50 volts, and a 50µf at 50 volts. There are 5 other paper capacitors. All paper and electrolytic capacitors have been replaced.
:::: When I first tried it out after replacing the capacitors, the rectifier tube sparked a little inside and the fuse opened. The fuse that was in the holder was open. I do not know what fuse should be in the holder.
:::: Does anyone know?
::::
::::Thanks,
::::
::::Dave
:::
:::Dave, here is some info i found for you. Your amp is labeled to consume about 117 v, 100-130 watts, which in today's standards of 125v, and hitting a peak of 130 watts is 1.18 amps. That should be the size of the fuze for you system. Keep in mind that it needs to be a slo-blow fuse otherwise the amp will always burn out the fuse as it hits the peak. Here is the website i got the power info from: http://www.heathkit-museum.com/hifi/hvmaa-81.shtml Hope that helps. Bob B

Dave, The American designation 5AR4, European GZ34 are one and the same tubes, and there is no proper substitute for this unique, indirectly heated cathode type. Definitely do not sub 5R4, 5U4 or any filamentary cathode type as they produce DC almost immediately which could cause cathode stripping on your amplifier tubes. Back to your fuse issue, brother I think you are going to have to break down and buy the schematic for this Heathkit. 4 amps is way to much fuse for this amp especially since its a mono-block amp. I had a simular issue with a knight KG-250 amp. I have a schematic of a Heathkit AA-181. I believe the power section is the same. There is a difference of 10 watts amp power but htat wouldn't matter as you need to fix your power. Give me your email and i will send it to you. Bob

5/6/2009 1:03:49 AMDave Froehlich

Bob,
My e-mail address is above and to the left. When you click on my name it should bring up a mail window.
I solved the problem. The shield on the phono jack is not supposed to be connected to the chassis. So originally there must have been an insulator on the jack. Now that the problem is solved I can replace the GZ34.

Thanks,

Dave
::Bob, Norm, All,
:: I cannot find anything wrong anywhere inside the set. There are no short circuits. The positive end of the filter capacitor is connected to the cathode of the rectifier. I did test the rectifier. There is some good emission for about a second after it warms up but then the emission drops, when either plate is checked. I'm not sure it it's the tube or the circuitry. This is a brand new tube. When I have it in the amplifier, it takes a rather long time to "warm up", then I can hear amplifier hiss. When I turn the volume control up and down I hear the noise of a dirty control. Then the fuse opens and the amplifier shuts off. This is a 4 amp fuse, not a slow-blow. I do not want to risk another expensive 5AR4. Maybe I can use a cheaper tube, and just hook it up. Will a 5U4 work just for testing? I see that a 5AR4 is the sub for a 5U4 but not the other way around. But will it work just for testing so I don't damage an expensive 5AR4?
::
::Thanks,
::
::Dave
:::Bob,
::: That's where they have the picture but no service data. I guess I'll have to make my own service data from the tube information and what's inside the chassis.
::: Yes, that makes sense. If it's taking out a 4 amp fuse something's not right.
:::
:::Thanks,
:::
:::Dave
:::::Hello All,
::::: Somehow this message got deleted. Does anyone know what fuse went in this amp? Does anyone know where I can find the service data for it? I have checked with several places and there is only one picture of it on one website. There is no mention of service data anywhere. It has 4 tubes in it: GZ34, EL34, EL34 and a 6AN8. Inside there are two 50µf capacitors @ 450v, two 150µf capacitors at 350 volts (wired in series). There is a bias diode (selenium) with a 20µf capacitor as the filter for the bias supply. There are two 100µf capacitors at 50 volts, and a 50µf at 50 volts. There are 5 other paper capacitors. All paper and electrolytic capacitors have been replaced.
::::: When I first tried it out after replacing the capacitors, the rectifier tube sparked a little inside and the fuse opened. The fuse that was in the holder was open. I do not know what fuse should be in the holder.
::::: Does anyone know?
:::::
:::::Thanks,
:::::
:::::Dave
::::
::::Dave, here is some info i found for you. Your amp is labeled to consume about 117 v, 100-130 watts, which in today's standards of 125v, and hitting a peak of 130 watts is 1.18 amps. That should be the size of the fuze for you system. Keep in mind that it needs to be a slo-blow fuse otherwise the amp will always burn out the fuse as it hits the peak. Here is the website i got the power info from: http://www.heathkit-museum.com/hifi/hvmaa-81.shtml Hope that helps. Bob B
:
:Dave, The American designation 5AR4, European GZ34 are one and the same tubes, and there is no proper substitute for this unique, indirectly heated cathode type. Definitely do not sub 5R4, 5U4 or any filamentary cathode type as they produce DC almost immediately which could cause cathode stripping on your amplifier tubes. Back to your fuse issue, brother I think you are going to have to break down and buy the schematic for this Heathkit. 4 amps is way to much fuse for this amp especially since its a mono-block amp. I had a simular issue with a knight KG-250 amp. I have a schematic of a Heathkit AA-181. I believe the power section is the same. There is a difference of 10 watts amp power but htat wouldn't matter as you need to fix your power. Give me your email and i will send it to you. Bob