| Author | Message | ||
     ogdave |
I posted this in another thread but realized it was under the wrong topic. Any one know if this tool will work with my 1974 MM 112-sixt five. I was told it has fixed bias but from what i read here that is not true.http://www.groovetubes.com/product.cfm?P roduct_ID=1711 | ||
| mike kaus |
It will work just fine, IF you amp has a 12ax7 phase inverter tube. The later amps used a SS driver/inverter that you had to measure a voltage across a couple of cathode driver resistors. | ||
| ogdave |
Thanks Mike. I do have the 12AX7 . Is the pre amp the only section that needs biased ? What about the power tubes ? Is mine fixed or adjustable? Thanks,Dave | ||
| ogdave |
with this tool would I be looking for a voltage of .25 per tube? Thanks , Dave | ||
| mike kaus |
You'll have to determine(from the instructions) whether or not the GT unit directly reads voltage or current. Some of the interupters have 1 ohm resistors in them that allow you to read the VOLTAGE, others interupt the current flow and you are reading the CURRENT flow directly. You are biasing the powere amp section only with the bias control. The 12ax7 does NOT need biasing. I would say though that 23mA is PLENTY high and if you are using GT, even lower. You amp is what they call adjustable bias. If it had no pot and needed a resistor change to alter bias voltage, it's fixed/adj. Mike. | ||
| ogdave |
Thanks Mike ! Like a lot of other folks on here I want to be able to do my own bias adjustment. And for me it is not about saving money ,though I do like saving money.I just like to work on things I own and to be able to understand how things work. Plus the fact that the only time in 30+ years that I took my amp to have it serviced it came back with about 6 new scuffs and gouges in the tolex . This amp was almost like new. Anyway I decided that this amp was not the best amp for me to start learning on and took it in this morning to be serviced. Got the name of a tech in my area (Nashville) recomended by Guitar Amplfier Blue Printing as one of "the wolds best". Gave them a call and they said they new how to work on MM amps. Took it over and gave them an informal quiz (unknown to them) about MM amps and made sure they new it wasn't like a Fender.When I mentioned tubes they said that MM amps had very high plate voltage and needed tubes that would not burn out quickly.They had some they were using in MM that had held up well. I knew (thanks to this web board)that this tech did at least know the difference between MM and Fender. He said Rodney Crowell had been in recently to have his Music Man serviced .Tried to find a pic of him with it. http://www.rodneycrowell.com/index.html | ||
| mike kaus |
Don't know Rodney but a friend of mine lives in N'ville and has been making his living down there doing the music thing since "79(yeah, he's old like me). Unfortunately, he does the mixer, pod, EON thing and now does a single only. No accounting for taste but you have to eat! Anyway, if your <tech> doesn't work out, we'll be more than glad to give you any assistance you need. Mike. | ||
| Clayton Choate |
Check out Artists Using MM section. Post regarding Rodney Crowell from his days backing Emmylou Harris. |