Triple Rectifier blowing fuses
Moderators: pompeiisneaks, Colossal
Re: Triple Rectifier blowing fuses
I’m sure everyone is tired of this post by now but I put the amp back together, put in the preamp and 4 brand new power tubes. I did not have a 4A slow blow so I put in a 3A. I plugged into the lightbulb limiter with the 100 watt bulb and turned on power and turned off standby. The lightbulb stayed reasonably dim. With no bright bulb, I decided to check voltages to see if anything was out of wack. Everything I checked was lower than what’s written on the schematic but all readings were similar in proportion if that makes sense. I’m still scared to take this amp off the lightbulb limiter. Can anyone think of anything else I should check before pulling the trigger?
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Stevem
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Re: Triple Rectifier blowing fuses
With the amp in standby other then the filiment’s you only have the low current drawing parts of the amp fired up.
1) the dc to the heater of the first preamp tube.
2) the bias to the output tubes .
3) the dc to the solid state parts of the amp.
In short nothing that will blow a 3 amp fuse.
If it where me,I would leave in only one output tube on each end of the OT and then throw the switch and see if the smoke says in the amp.
In terms of the bias voltage make sure before you take the amp out of standby that you do have atleast -45 volts on pin 5 of each output tube socket.
1) the dc to the heater of the first preamp tube.
2) the bias to the output tubes .
3) the dc to the solid state parts of the amp.
In short nothing that will blow a 3 amp fuse.
If it where me,I would leave in only one output tube on each end of the OT and then throw the switch and see if the smoke says in the amp.
In terms of the bias voltage make sure before you take the amp out of standby that you do have atleast -45 volts on pin 5 of each output tube socket.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Triple Rectifier blowing fuses
Ok, so I fired it up but have only turned standby off for a few seconds to take quick voltage measurements. So far everything seems to be running about 6-8V high. Not sure if that’s an issue. Also, there is a low hum from OT when in standby that goes away when standby is switched off and then a different frequency low level hum emanates from the PT. I’m still a little too gun shy to leave the amp on for very long without more input of what I should be checking to be absolutely sure everything is good again.
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Triple Rectifier blowing fuses
If you gave it that quick fire up with two output tubes out then that’s why your V + voltage and maybe even the filiment voltage was reading a big high.
Concerning to me, especially if this test you did was with two output tubes out is that you report a low frequency hum from the pt, because that indicates a high current draw like there still may be a short in the amp, or now that pt has a internal short on the secondary side.
Concerning to me, especially if this test you did was with two output tubes out is that you report a low frequency hum from the pt, because that indicates a high current draw like there still may be a short in the amp, or now that pt has a internal short on the secondary side.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Triple Rectifier blowing fuses
It's pretty faint but I can hear it. I'm pretty sure it's 120 HZ. According to the nets, it could be plate vibration at twice the fundamental frequency, which would be 60 HZ. With all voltages ready for the most part correct, is it possible for there to be a short in the PT?
Re: Triple Rectifier blowing fuses
So I fired it up and it seems to be running as it should. Sounds good for a $200 amp. So for anyone else who comes across this thread because their triple rectifier is blowing fuses, it’s always the tubes. I replaced all the power and the preamp tubes and switched to solid start recrifiers and this amp works fine.
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
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Re: Triple Rectifier blowing fuses
I don't know why with this amp and its many output tubes and expensive OT that they did not do what Ampeg did and have blow out resistors in the plate circuit of each output tube that simply goes open if a tube shorts!
This same thing should have been done with Highwatt and Marshall 200s especially considering how much those amps cost back then.
These days 400 bucks without shipping for a Marshall 200 output trans is hard to swallow!
Note that output tubes short/ fail many times from fatigue.
This is seeing when the amp was playing fine and you turn it off and the next time you go to use it and take it out of standby a fuse blows on you.
The cause of this is repeated machcanical thermal stress.
The heat up and fast cool down can weaken the grid and screen windings, and when one of these windings breaks off they short out to the heater and then it's blown fuse time.
The way to limit this is to allow the output tubes to both heat up and cool down slow, or atleast the cool down slow part.
When your done playing the amp wait 2 minutes before you place the amp in standby, after that wait another 4 minutes before you turn the amp off completely.
This will reward you with long lived output tubes and is why folks that call for no need for a standby switch in a amp that gets played hard are just flat out dead wrong if you want my 2 cents worth.
There looking purely on the electronic side of the equation, not the electro mechanical side as it should be viewed!
This same thing should have been done with Highwatt and Marshall 200s especially considering how much those amps cost back then.
These days 400 bucks without shipping for a Marshall 200 output trans is hard to swallow!
Note that output tubes short/ fail many times from fatigue.
This is seeing when the amp was playing fine and you turn it off and the next time you go to use it and take it out of standby a fuse blows on you.
The cause of this is repeated machcanical thermal stress.
The heat up and fast cool down can weaken the grid and screen windings, and when one of these windings breaks off they short out to the heater and then it's blown fuse time.
The way to limit this is to allow the output tubes to both heat up and cool down slow, or atleast the cool down slow part.
When your done playing the amp wait 2 minutes before you place the amp in standby, after that wait another 4 minutes before you turn the amp off completely.
This will reward you with long lived output tubes and is why folks that call for no need for a standby switch in a amp that gets played hard are just flat out dead wrong if you want my 2 cents worth.
There looking purely on the electronic side of the equation, not the electro mechanical side as it should be viewed!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!