Musicman HD130 Head, bought it off ebay for parts or repair. Both channels output was extremely low and distorted. Noticed the rectifier board(I think) was bowed up in the middle so I removed the two screw on each end of it and tried to flatten it out somehow. After reinstalling the screws I noticed that the resistor on the bottom left of the rectifier board(facing back of head) was loose. It has a white wire going to the rectifier tube and a purple wire going to the impedance switch. Resoldered the resistor and know I got an extremely loud hum that is not affected by any of the control knobs. Any ideas would be appreciated. Thanks.
Musicman Hd130 Head Repairs
- Thread starter ca7922303
- Start date
Re: Musicman Hd130 Head Repairs
Do you have any experience working an amps.?
You are going to need a schem and a decent meter.
When you say hum, with an amp of that age, filter caps come to mind.
But it could also be 60Hz coming from a power tube heater.
Is this a SS preamp btw.?
Anyway...it could be all kinds of things.
If you can get it on a dummy load, it will help you to take some voltage measurements without driving yourself insane.
good luck
Do you have any experience working an amps.?
You are going to need a schem and a decent meter.
When you say hum, with an amp of that age, filter caps come to mind.
But it could also be 60Hz coming from a power tube heater.
Is this a SS preamp btw.?
Anyway...it could be all kinds of things.
If you can get it on a dummy load, it will help you to take some voltage measurements without driving yourself insane.
good luck
Chickenwings
Alnico 6/8
Re: Musicman Hd130 Head Repairs
this is the place for you:
http://www.pacair.com/cgi-bin/discus/discus.cgi?pg=topics
it was a great help and resource when i was restoring my music man.
this is the place for you:
http://www.pacair.com/cgi-bin/discus/discus.cgi?pg=topics
it was a great help and resource when i was restoring my music man.
Re: Musicman Hd130 Head Repairs
All Music Man amps had SS preamps with tube power sections.
Al
Do you have any experience working an amps.?
You are going to need a schem and a decent meter.
When you say hum, with an amp of that age, filter caps come to mind.
But it could also be 60Hz coming from a power tube heater.
Is this a SS preamp btw.?
Anyway...it could be all kinds of things.
If you can get it on a dummy load, it will help you to take some voltage measurements without driving yourself insane.
good luck
All Music Man amps had SS preamps with tube power sections.
Al
Re: Musicman Hd130 Head Repairs
Appreciate the help. I've got a schematic(not a very good one), a mutimeter, a usb oscilloscope/frequency generator/counter, but need direction on this. Not enough experience. When I first tested this amp, it was having low output on both channels and distorted. It is marked outside the chassis as chassis no. 2100-130. It is a hd130 w/o reverb. Has a 12ax7 as the rectifier. If anyone could maybe show pictures of a step by step description of how to test this amp or how it should be correctly wired if it is a wiring issue, I would very much appreciate it. I'm in a learning process. Can't find any picture tutorials on this at all. Thanks.
Appreciate the help. I've got a schematic(not a very good one), a mutimeter, a usb oscilloscope/frequency generator/counter, but need direction on this. Not enough experience. When I first tested this amp, it was having low output on both channels and distorted. It is marked outside the chassis as chassis no. 2100-130. It is a hd130 w/o reverb. Has a 12ax7 as the rectifier. If anyone could maybe show pictures of a step by step description of how to test this amp or how it should be correctly wired if it is a wiring issue, I would very much appreciate it. I'm in a learning process. Can't find any picture tutorials on this at all. Thanks.
Re: Musicman Hd130 Head Repairs
You definitely have the desire and a good attitude.
You probably mean you have a tube phase inverter, and THAT is a 12AX7.?...not a rectifier.?
If you have never done this before...I don't know...there is A LOT going on in that amp.
There is High Voltage for the EL34 or 6CA7, and regulated 16VDC for the Solid State stuff...and all kinds of "things" to check.
Looks like there is a "death cap" ground switch to abandon, before it abandons you.
I am not the right person to lead you through this, not via The Internet.
There is plenty of info on the net about basic tube function...you especially need to know What/Why is going on with all the different Pin Numbers.
You just need a lot of basic skills, including with your meter. Do you know how to check a diode/transistor...even if your meter does not have a dedicated function on it, for that.?
http://www.pacair.com/mmamps3/forum
This is the link for the "new" forum. They probably updated their software...or maybe they got "hacked" on the old sight...it happens all the time.
The link to the old sight, that gibson175 provided, is a Great Place to start.
Anyway...take some time to read about tubes, so you are familiar with a Cathode, Grid, Screen, and Plate...all their corresponding numbers and what kind of voltage to expect at each node. When somebody on the internet asks you the voltage on the power tube plates...you need to be able to get that number, without asking how...know what I mean.?
Otherwise, assisting you with this, will be a daunting task.
Make sure you have one Clip-On connector for your meter probes...so you can clamp onto ground, and just poke around with One Hand. It does not matter what color it is...just so you can establish a hands free ground connection.
Or maybe another member here will want to help you with this...kind of over my head.
Do you happen to live near me.?
good luck
You definitely have the desire and a good attitude.
You probably mean you have a tube phase inverter, and THAT is a 12AX7.?...not a rectifier.?
If you have never done this before...I don't know...there is A LOT going on in that amp.
There is High Voltage for the EL34 or 6CA7, and regulated 16VDC for the Solid State stuff...and all kinds of "things" to check.
Looks like there is a "death cap" ground switch to abandon, before it abandons you.
I am not the right person to lead you through this, not via The Internet.
There is plenty of info on the net about basic tube function...you especially need to know What/Why is going on with all the different Pin Numbers.
You just need a lot of basic skills, including with your meter. Do you know how to check a diode/transistor...even if your meter does not have a dedicated function on it, for that.?
http://www.pacair.com/mmamps3/forum
This is the link for the "new" forum. They probably updated their software...or maybe they got "hacked" on the old sight...it happens all the time.
The link to the old sight, that gibson175 provided, is a Great Place to start.
Anyway...take some time to read about tubes, so you are familiar with a Cathode, Grid, Screen, and Plate...all their corresponding numbers and what kind of voltage to expect at each node. When somebody on the internet asks you the voltage on the power tube plates...you need to be able to get that number, without asking how...know what I mean.?
Otherwise, assisting you with this, will be a daunting task.
Make sure you have one Clip-On connector for your meter probes...so you can clamp onto ground, and just poke around with One Hand. It does not matter what color it is...just so you can establish a hands free ground connection.
Or maybe another member here will want to help you with this...kind of over my head.
Do you happen to live near me.?
good luck
Last edited:
guitfiddle
firstlessonologist
Re: Musicman Hd130 Head Repairs
Anything you need to know is somewhere on this archived site....
http://www.pacair.com/cgi-bin/discus/discus.cgi?pg=topics
Anything you need to know is somewhere on this archived site....
http://www.pacair.com/cgi-bin/discus/discus.cgi?pg=topics
Re: Musicman Hd130 Head Repairs
The 12AX7 is a phase inverter tube, they had those in some early amps, later ones didn't. Still part of the power section.
Al
The 12AX7 is a phase inverter tube, they had those in some early amps, later ones didn't. Still part of the power section.
Al
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