I have an old 75 watt Bell Tube PA that I just got up and running again. ! . I just re-did it a few weeks ago for guitar use with a Sunn model T pre-amp and after 2 hours it stopped working and it started Oscillating real bad so this time I decided to gut it all except for the power section and to use a known pre-amp and splitter wiring .
I copied a Sovtek Mig 50 guitar amp with 6L6 tubes to see what it would sound like with the 6L6 ! .
I got it working again and all of the loud humming problems are gone now and it works but I have no bass or mid controls and the wiring diagram that I used is a little confusing to me on the bass pot because it shows the ground wire on # 1 one and nothing on # 2 and on # 3 the cap and out wire both on pin 3 - it has to be wrong is what I am thinking ? ! Should I move the cap or wire out on pin # 3 to use pin # 2 ? .
I cannot alter the pictures right under here so I will post the new ones down lower !
The amp is real dirty sounding now on low notes and I am guessing this pot wire problem is why ? ! .
If any one can help me - Thank You , Gary !
Skip the other posts and Go SEE Pictures at the bottom post # 10 of ; Amp re-build as Mig 50 Thanks !
I copied a Sovtek Mig 50 guitar amp with 6L6 tubes to see what it would sound like with the 6L6 ! .
I got it working again and all of the loud humming problems are gone now and it works but I have no bass or mid controls and the wiring diagram that I used is a little confusing to me on the bass pot because it shows the ground wire on # 1 one and nothing on # 2 and on # 3 the cap and out wire both on pin 3 - it has to be wrong is what I am thinking ? ! Should I move the cap or wire out on pin # 3 to use pin # 2 ? .
I cannot alter the pictures right under here so I will post the new ones down lower !
The amp is real dirty sounding now on low notes and I am guessing this pot wire problem is why ? ! .
If any one can help me - Thank You , Gary !
Skip the other posts and Go SEE Pictures at the bottom post # 10 of ; Amp re-build as Mig 50 Thanks !
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Pictures of amp !
Here are a few pictures !
Here are a few pictures !
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Conventional punctuation (including paragraphs) would make your post easier to read, and thus more likely to attract good advice. A circuit diagram might help too.
I worked on it all day today and I got the pre-amp section design figured out and working great !
I made it so I can blend the sound of the 12AV6 with the First Half of the 12AX7 together and 50 % with the second half of the 12AX7 , I'm not sure what I did is called but I used half the capacitance and a 100 K resistor to accomplish it across two1 meg pots ! , worked out real good though ! . Then 2 Volumes and two more 12AX7's . Bias set is at ; neg .048 with 525 Plate volts , Idle is very quiet ! . This amplifier was a worthy project in my opinion ! , It's pretty loud if you turn it up ! . I need to decide on my speakers and ohms now and what brand is best and what ohns is best for guitar ! , I have been using 8 ohms so far for testing this amp it's Just a peavy stage monitor speaker with one 12 and a tiny horn .
I like the sound of The Eminence 12 inch instrument speakers.
I made it so I can blend the sound of the 12AV6 with the First Half of the 12AX7 together and 50 % with the second half of the 12AX7 , I'm not sure what I did is called but I used half the capacitance and a 100 K resistor to accomplish it across two1 meg pots ! , worked out real good though ! . Then 2 Volumes and two more 12AX7's . Bias set is at ; neg .048 with 525 Plate volts , Idle is very quiet ! . This amplifier was a worthy project in my opinion ! , It's pretty loud if you turn it up ! . I need to decide on my speakers and ohms now and what brand is best and what ohns is best for guitar ! , I have been using 8 ohms so far for testing this amp it's Just a peavy stage monitor speaker with one 12 and a tiny horn .
I like the sound of The Eminence 12 inch instrument speakers.
Great find! My first real guitar amp project was an old Bogen PA that I got from a church yard sale for next to nothing. Made a great clean tone to add on top of. I eventually ended up building it into a Marshall Plexi clone. One man's trash really is another man's treasure!
As for speakers, that really depends on the application, and even more on personal preference. How much power are you going to be pumping into it, how many speakers are you using, what kind of configuration, etc. There are a lot of good brands out there for guitar speakers, the big 3 probably being Eminence, Celestion, and Jensen. They all have pretty wide product lines, so you'll have to do some research into trying to find what sounds right for you. What kind of sound are you going for?
As for speakers, that really depends on the application, and even more on personal preference. How much power are you going to be pumping into it, how many speakers are you using, what kind of configuration, etc. There are a lot of good brands out there for guitar speakers, the big 3 probably being Eminence, Celestion, and Jensen. They all have pretty wide product lines, so you'll have to do some research into trying to find what sounds right for you. What kind of sound are you going for?
Thanks Amp Killer 66 ! , I paid 80 for it without any tubes and it had a shorted bias pot and a burned up wire , he also messed up input section , I fixed it and put in new tubes ,
I'm up around the 150 mark now and a few days work but I guess it was still a good deal now that I have it working ? , Hard to find these big Transformer things for cheap any more ! .
I have been experimenting with the coupling caps this evening and working on the tone .
I put .02 in and .01 , I like the .02 better and I put a .0068 on the bias resistor of the second pre-amp tube and it got the lows more under control . I want to try .022 and .025 and .027 caps also for the tone . I think I have .03 but think I will need to order some of the other sizes . Maybe I will try a 0047 on the bias resistor also ? . I Have those . I'm tired now and it's too late to crank it up again , so I guess I am about done for tonight ! . The tone sounds good over all but I want to get it as sweet as I can get it without it making all of those nasty piggy noises when I turn it on and off ! .
I'm up around the 150 mark now and a few days work but I guess it was still a good deal now that I have it working ? , Hard to find these big Transformer things for cheap any more ! .
I have been experimenting with the coupling caps this evening and working on the tone .
I put .02 in and .01 , I like the .02 better and I put a .0068 on the bias resistor of the second pre-amp tube and it got the lows more under control . I want to try .022 and .025 and .027 caps also for the tone . I think I have .03 but think I will need to order some of the other sizes . Maybe I will try a 0047 on the bias resistor also ? . I Have those . I'm tired now and it's too late to crank it up again , so I guess I am about done for tonight ! . The tone sounds good over all but I want to get it as sweet as I can get it without it making all of those nasty piggy noises when I turn it on and off ! .
Guitar amplifier threads belong in Instruments And Amplifiers where this thread will now be moved. Going forward please note the forum Tubes / Valve forum subheader: AND
RE - Bell PA Amplifier Modification to Guitar Questions ?
I Re-did the pre-amp section last night and removed 2 of the tubes and just decided to go with a splitter 12AX7 and a Pre-amp 12AX7 instead of using all 4 pre-amp tubes . I also decided to use the second wiring section from a SUNN ( Model T Super ) amplifier . I played the amp today through one 12" Peavy Monitor Speaker at around 4 volume and it sounds good on rhythm guitar but I know that it can sound better because I have a Mig 100 with EL 34's that has a beautiful tone. I have a few thoughts and Questions I have build audio but I am relatively new to modifying tube guitar amps. My affordable tech got old and He died on me so now I am on my own again , like most musicians my pockets are not very deep . But I don't mind spending money in the right places ! . My first question is this ; would adding a tube rectifier help me any to remove some of the sharpness ? and could I use a 5U4 because I have some of those already ? . My Second question is a little deeper about the pre amp section and what value resistor should I use on the first cathode coming out of the splitter ? There were a few things in the Model T Super wiring that I just did not understand there so I left the old resistor there in place ? . The in on of the first half of the pre-amp tube grid is through a 66K resistor with a 1 meg to ground into a 1 meg pot . I have .02 (#203) Capacitors for coupling ? . My high notes seem cut off some when I play lead and they are somewhat compressed , this is especially true on the high E string . My Tone seems just a little bit flat but it's not real bad over all when playing a rhythm . It does have some pretty good sound quality also and it know it will be worth the effort to get it right ! . I tested the 2 watt power tube resistors and one is reading 1.5 and the other is reading 1.3 - I'm guessing this is a little too far out of spec and that I should replace the lower one ? . I tried both new tubes and NOS vintage tubes and both sound about the same in this amp so the tubes are not to blame for the amps tone problems. My neg bias is at ; -.38 and the tubes are matched pairs. The splitter phase is all stock as it was as an original PA amp ? . Can a splitter effect the amps over all tone any ? I have noticed in some guitar amps that box plates perform very well as splitters for some reason ? .
I Re-did the pre-amp section last night and removed 2 of the tubes and just decided to go with a splitter 12AX7 and a Pre-amp 12AX7 instead of using all 4 pre-amp tubes . I also decided to use the second wiring section from a SUNN ( Model T Super ) amplifier . I played the amp today through one 12" Peavy Monitor Speaker at around 4 volume and it sounds good on rhythm guitar but I know that it can sound better because I have a Mig 100 with EL 34's that has a beautiful tone. I have a few thoughts and Questions I have build audio but I am relatively new to modifying tube guitar amps. My affordable tech got old and He died on me so now I am on my own again , like most musicians my pockets are not very deep . But I don't mind spending money in the right places ! . My first question is this ; would adding a tube rectifier help me any to remove some of the sharpness ? and could I use a 5U4 because I have some of those already ? . My Second question is a little deeper about the pre amp section and what value resistor should I use on the first cathode coming out of the splitter ? There were a few things in the Model T Super wiring that I just did not understand there so I left the old resistor there in place ? . The in on of the first half of the pre-amp tube grid is through a 66K resistor with a 1 meg to ground into a 1 meg pot . I have .02 (#203) Capacitors for coupling ? . My high notes seem cut off some when I play lead and they are somewhat compressed , this is especially true on the high E string . My Tone seems just a little bit flat but it's not real bad over all when playing a rhythm . It does have some pretty good sound quality also and it know it will be worth the effort to get it right ! . I tested the 2 watt power tube resistors and one is reading 1.5 and the other is reading 1.3 - I'm guessing this is a little too far out of spec and that I should replace the lower one ? . I tried both new tubes and NOS vintage tubes and both sound about the same in this amp so the tubes are not to blame for the amps tone problems. My neg bias is at ; -.38 and the tubes are matched pairs. The splitter phase is all stock as it was as an original PA amp ? . Can a splitter effect the amps over all tone any ? I have noticed in some guitar amps that box plates perform very well as splitters for some reason ? .
My Pictures of The Re-Build as Mig 50 with 6L6's
Here are the pictures on the amp after gutting it and re-doing it as a Mig 50 with 6L6 tubes ! . Have a pot problem with the bass and mid controls I am trying to figure out on pin # 2 and # of bass pot ? . And I have a adapter I made and I was wondering if I can make it into a mA tester ?.
I was also wondering what the 5 K pot is for on the splitter ? . I used a 223 and a .0015 to make a 250 for the treble control at about 245 or so ? I don't know if that is Ok to do or not but it seems to work the treble part ! .
I'm not really a Tech I'm just a home amp hobby builder ! .
I was hoping to make me a vintage Mig 50 out of this amplifier ! . Need a little help getting things right in it ! .
I have - 50 on the grid negative bias not sure about the mA but the tubes are pretty cool running right now .
Here are the pictures on the amp after gutting it and re-doing it as a Mig 50 with 6L6 tubes ! . Have a pot problem with the bass and mid controls I am trying to figure out on pin # 2 and # of bass pot ? . And I have a adapter I made and I was wondering if I can make it into a mA tester ?.
I was also wondering what the 5 K pot is for on the splitter ? . I used a 223 and a .0015 to make a 250 for the treble control at about 245 or so ? I don't know if that is Ok to do or not but it seems to work the treble part ! .
I'm not really a Tech I'm just a home amp hobby builder ! .
I was hoping to make me a vintage Mig 50 out of this amplifier ! . Need a little help getting things right in it ! .
I have - 50 on the grid negative bias not sure about the mA but the tubes are pretty cool running right now .
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