Hello this is my first posting on this forum, ever!
I thinking of building a 100w bass guitar amp. Really haven't nailed down
a design yet but I'm thinking the most typical would be four 6l6's
in a push pull configuration.
I know there are tons of kits out there. And there are off the shelf transformers available.
That doesn't stop me from wanting to "do it myself" !!!
Now I know there is a thread on this forum that is exactly what I need. But there is so much info on this forum that I can't seem to find it.
So I thought I would start with the most complicated part (at least to me) first.
The output transformer. Now from reading here and other places I've figured out that two 6l6's in push pull are needing a 4k primary. Now does that mean that four in push pull need 2k????
And is that impedance on either side of the center tap? Or is it the entire winding?
I would like 4 and 8 ohm taps on the secondary also.
I think I will leave it there because I don't have a clue. I've been reading about interleaving, bifilar windings and I pretty confused as you can tell. So feel free to post your designs or point me to other threads and links.
Thanks in advance.
Dennis
I thinking of building a 100w bass guitar amp. Really haven't nailed down
a design yet but I'm thinking the most typical would be four 6l6's
in a push pull configuration.
I know there are tons of kits out there. And there are off the shelf transformers available.
That doesn't stop me from wanting to "do it myself" !!!
Now I know there is a thread on this forum that is exactly what I need. But there is so much info on this forum that I can't seem to find it.
So I thought I would start with the most complicated part (at least to me) first.
The output transformer. Now from reading here and other places I've figured out that two 6l6's in push pull are needing a 4k primary. Now does that mean that four in push pull need 2k????
And is that impedance on either side of the center tap? Or is it the entire winding?
I would like 4 and 8 ohm taps on the secondary also.
I think I will leave it there because I don't have a clue. I've been reading about interleaving, bifilar windings and I pretty confused as you can tell. So feel free to post your designs or point me to other threads and links.
Thanks in advance.
Dennis
Its OK if the OPT is slightly higher impedance than the tubes,
slight reduction in power out in exchange for greater control.
Maximum power is transferred when "impedances match",
but that equation doesn't tell about steady state losses.
And loudspeaker impedance varies with frequency, xmax,
and cone breakup...
Remember that DC resistance of your plates will not be the
same as impedance (slope of the plate curve at that point),
though both are measured in Ohms.
What would be bad is OPT lower impedance than the tubes.
Just don't go lower and you will be fine. Throw some extra
turns on your primaries for insurance.
slight reduction in power out in exchange for greater control.
Maximum power is transferred when "impedances match",
but that equation doesn't tell about steady state losses.
And loudspeaker impedance varies with frequency, xmax,
and cone breakup...
Remember that DC resistance of your plates will not be the
same as impedance (slope of the plate curve at that point),
though both are measured in Ohms.
What would be bad is OPT lower impedance than the tubes.
Just don't go lower and you will be fine. Throw some extra
turns on your primaries for insurance.
Fender Bassman 100W complete project with opt details:
http://www.audiyofan.org/wiki/index...e_du_FENDER_Bassman-100#Transfo_de_sortie_DIY
I doubt you will find anything better.
http://www.audiyofan.org/wiki/index...e_du_FENDER_Bassman-100#Transfo_de_sortie_DIY
I doubt you will find anything better.
For BASS amp 100W would be minimum.... Since bass needs more power due to lower frequencies....
I prefer using the JJ KT88 valves or 6550A valves.....
You can push the Plate B+ to about 700V safely and then make sure the screens are about 350V , no greater.....this is IDLE VOLTAGES....
Figure you will get roughly 100W per pair at those voltages with a 5K plate load in Class AB1..... So 4 tubes would be about 2.5K plate load, which to answer your question is refered to as Plate-to-Plate when talking push-pull...
Impedance matching for maximum power transfer only works in transmission lines and RF applications when using for example S-parameters 50 ohm or 75 ohm line matching , or when you are dealing with 600 ohm balanced lines ect ..... For pentode tubes you want the biggest plate load that will stay in the "SATURATION REGION"...this will give you the most power output for the lowest distortion, also refered to as the "optimum plate load".....
The saturation region of a pentode is the section of the curves that go almost flat approaching constant current, of course they don't go perfectly flat but almost, that represents the plate resistance of the pentode tube and is quite high... The region to the left that is almost vertical is refered to as the DIODE region and has a very low plate resistance...you don't want your load-line to intersect this region for your application...For starters you need the correct curves....by making sure you have ones for 300V screen since your 350V screen voltage at idle will droop down under full load... Also assume for now your 700V plate voltage supply will droop to 600V , which is not that far off what will really happen... So with 300V screen voltage selected curves, draw your load-line from 600V up to where you intersect the 0-BIAS curve , making sure you stay to the RIGHT of the knee of the curve, since this will make sure you stay in SATURATION region...
It's judgement call when the plate resistance drops by more than 25% as you move to the LEFT of the 0-BIAS curve, don't go that far... Then multiply this Load-Line by 4 and you get roughly 5K plate-to-plate load....
So you need a transformer to handle 200W at 2.5K load for 4 KT88 valves this will produce about 707V of AC signal across the full winding at full power output... I can tell you right now it will be roughly a 3" stack of EI-150 using M6 core material.... You will want to keep the flux density about 13,000 at 20Hz at 700 volts AC for an acceptable bass OPT..... This 3" satck of EI# 150 would be 26.7 cm^2 of effective area......this would equate to roughly 2271 turns on the primary.... You have roughly 280mA of RMS AC current so a safe wire gauge for the primary would be #26 or #27 AWG...... Modest amount of interleaving is OK, keep in mind this is a bass amp not a MacIntosh Bi-filar wound OPT....
You can figure the rest out I am sure....
Best Regards
Chris
I prefer using the JJ KT88 valves or 6550A valves.....
You can push the Plate B+ to about 700V safely and then make sure the screens are about 350V , no greater.....this is IDLE VOLTAGES....
Figure you will get roughly 100W per pair at those voltages with a 5K plate load in Class AB1..... So 4 tubes would be about 2.5K plate load, which to answer your question is refered to as Plate-to-Plate when talking push-pull...
Impedance matching for maximum power transfer only works in transmission lines and RF applications when using for example S-parameters 50 ohm or 75 ohm line matching , or when you are dealing with 600 ohm balanced lines ect ..... For pentode tubes you want the biggest plate load that will stay in the "SATURATION REGION"...this will give you the most power output for the lowest distortion, also refered to as the "optimum plate load".....
The saturation region of a pentode is the section of the curves that go almost flat approaching constant current, of course they don't go perfectly flat but almost, that represents the plate resistance of the pentode tube and is quite high... The region to the left that is almost vertical is refered to as the DIODE region and has a very low plate resistance...you don't want your load-line to intersect this region for your application...For starters you need the correct curves....by making sure you have ones for 300V screen since your 350V screen voltage at idle will droop down under full load... Also assume for now your 700V plate voltage supply will droop to 600V , which is not that far off what will really happen... So with 300V screen voltage selected curves, draw your load-line from 600V up to where you intersect the 0-BIAS curve , making sure you stay to the RIGHT of the knee of the curve, since this will make sure you stay in SATURATION region...
It's judgement call when the plate resistance drops by more than 25% as you move to the LEFT of the 0-BIAS curve, don't go that far... Then multiply this Load-Line by 4 and you get roughly 5K plate-to-plate load....
So you need a transformer to handle 200W at 2.5K load for 4 KT88 valves this will produce about 707V of AC signal across the full winding at full power output... I can tell you right now it will be roughly a 3" stack of EI-150 using M6 core material.... You will want to keep the flux density about 13,000 at 20Hz at 700 volts AC for an acceptable bass OPT..... This 3" satck of EI# 150 would be 26.7 cm^2 of effective area......this would equate to roughly 2271 turns on the primary.... You have roughly 280mA of RMS AC current so a safe wire gauge for the primary would be #26 or #27 AWG...... Modest amount of interleaving is OK, keep in mind this is a bass amp not a MacIntosh Bi-filar wound OPT....
You can figure the rest out I am sure....
Best Regards
Chris
bass output transformer
Thanks everyone for your replies. I actually was considering the bassman circuit.
cerrem
Is that 2271 turns of #27 the entire winding with a center tap? This would be good for the 4 tubes with a plate load of 2.5k?
I calculate a winding radio of about 17:1 if you use 8 ohm speaker.
That would be roughly 147 turn on the secondary. Any Idea of the secondary wire size?
Thanks everyone for your replies. I actually was considering the bassman circuit.
cerrem
Is that 2271 turns of #27 the entire winding with a center tap? This would be good for the 4 tubes with a plate load of 2.5k?
I calculate a winding radio of about 17:1 if you use 8 ohm speaker.
That would be roughly 147 turn on the secondary. Any Idea of the secondary wire size?
I'm still searching the forum for info. Still no detailed winding info to be found for the lowly push pull transformer.
There is a lot of info on winding SE transformers.
I guess what I need is detailed instructions from someone who has actually done this.
100 watt bass guitar push pull output transformer. Using 4 6l6 tubes.
It would be nice to have 4 and 8 ohm outputs.
thanks
There is a lot of info on winding SE transformers.
I guess what I need is detailed instructions from someone who has actually done this.
100 watt bass guitar push pull output transformer. Using 4 6l6 tubes.
It would be nice to have 4 and 8 ohm outputs.
thanks
audiojerk said:
If you want to wind one...you need a winding machine, even if it is small, with a counter.... Then you need to cut the insulating sheets by hand for the proper widths, these need to be applied for each layer... Solder the lead-out wires..Then stack the steel laminations, VACUUM impregnate with varnish to now make the insulations electricaly sound, then bake... the biggest problem nowadays with making transformers is nowing what materials to use and what and where to get them.....
First get a transformer book...Like by " Ruben Lee" then you will have the basic equations that you can design with...
Chris
Hi Chris Thanks for the reply, again.
This is what I found in my junk box. It's an old 10 hy 250ma. choke.
I think it might make a good donor core. Here are some dimensions.
2 x 3 1/4 x 4 inches. The laminations appear to be aprox .014 thick.
The thing weights about 7 pounds with the copper still on it.
Let me know what you think about it. What kind of watts is it good for?
Sorry about the delayed responses. They still have me on moderation.
How long is this going to go on for?
thanks
Dennis
This is what I found in my junk box. It's an old 10 hy 250ma. choke.
I think it might make a good donor core. Here are some dimensions.
2 x 3 1/4 x 4 inches. The laminations appear to be aprox .014 thick.
The thing weights about 7 pounds with the copper still on it.
Let me know what you think about it. What kind of watts is it good for?
Sorry about the delayed responses. They still have me on moderation.
How long is this going to go on for?
thanks
Dennis
Chris do you have plans for a winding machine you describe? I think I saw one or two on this forum but I can't find them.
How elaborate does this have to be?
I have rewound a few power transformers with nothing more than a hand cranked apparatus.
Oh the winding window on that core is about 2" x .75"
Chris does this core have an official EI number?
How elaborate does this have to be?
I have rewound a few power transformers with nothing more than a hand cranked apparatus.
Oh the winding window on that core is about 2" x .75"
Chris does this core have an official EI number?
That's it Chris. Exactly.
Is this usable? For what wattage?
I've been playing around with " OPT Design Assistant" by Yves Monmagnon ??
I was using EI106-36 I wonder how close that is?
It recommends #29 for primary and #25 for secondary.
Have you heard of this calculator? Can you recommend numbers to plug in?
Is this usable? For what wattage?
I've been playing around with " OPT Design Assistant" by Yves Monmagnon ??
I was using EI106-36 I wonder how close that is?
It recommends #29 for primary and #25 for secondary.
Have you heard of this calculator? Can you recommend numbers to plug in?
Dennis,
A quick look at US supplier here:
http://www.tubesandmore.com/
2 options immediately suggest themselves.
100W Bassman replacement tranny $67.95 - 4 Ohms out ONLY
Hammond 1650T 4/8/16 Ohms out good for about 150W Bass or 200W Lead (120W for HiFi) $95.50 (Could run 3 pairs of 6L6 into this one if you wanted, 2 pairs will be fine).
S you are looking at US$70 to $100 typically to buy something off the shelf.
Cheers,
Ian
A quick look at US supplier here:
http://www.tubesandmore.com/
2 options immediately suggest themselves.
100W Bassman replacement tranny $67.95 - 4 Ohms out ONLY
Hammond 1650T 4/8/16 Ohms out good for about 150W Bass or 200W Lead (120W for HiFi) $95.50 (Could run 3 pairs of 6L6 into this one if you wanted, 2 pairs will be fine).
S you are looking at US$70 to $100 typically to buy something off the shelf.
Cheers,
Ian
Thanks Ian for the post. That's kind of what I though they would be.
I found this link to weber: https://taweber.powweb.com/store/magnetic.htm
They have a couple replacements for bassman. One is about $58.
It mentions something about 2 ohm output. Never heard anything like that for a guitar amp.
If anyone else has any links feel free to post them.
By the way Chris. I started to open up that choke. Guess what it has #27 wire in it
Wonder if the wire is usable. Doesn't look like it's been too hot.
I measure the choke at 13 hy. And it's full of wire. Wouldn't be any room for a secondary without less primary turns.
I found this link to weber: https://taweber.powweb.com/store/magnetic.htm
They have a couple replacements for bassman. One is about $58.
It mentions something about 2 ohm output. Never heard anything like that for a guitar amp.
If anyone else has any links feel free to post them.
By the way Chris. I started to open up that choke. Guess what it has #27 wire in it
Wonder if the wire is usable. Doesn't look like it's been too hot.
I measure the choke at 13 hy. And it's full of wire. Wouldn't be any room for a secondary without less primary turns.
Dennis,
A home build bass amp project for possible interest.
http://home.triad.rr.com/scottvicki/150BassAmpProject.htm
and another similar:
http://diytube.com/phpBB2/viewtopic.php?t=1436
scan down the thread - he has posted schematics.
Both of these projects use a Hammond 1650T - both borrow heavilly from Ampeg amps rather than Fender.
Cheers,
Ian
A home build bass amp project for possible interest.
http://home.triad.rr.com/scottvicki/150BassAmpProject.htm
and another similar:
http://diytube.com/phpBB2/viewtopic.php?t=1436
scan down the thread - he has posted schematics.
Both of these projects use a Hammond 1650T - both borrow heavilly from Ampeg amps rather than Fender.
Cheers,
Ian
audiojerk said:
"Bassman" can refer to a whole family of bass / guitar amps. The "Tweed" Bassman (5F6, 5F6-A) was a combo amp with 4x10" speakers wired in parallel for a 2 ohm load. If one speaker blew, the other 3 would still work, unlike a series-parallel circuit where you'd lose two speakers if one opens up.
The high power '70s Bassman 100 and Bassman 135 use a different topology, more like a blackface Fender (separate preamp channels and no cathode follower around the tone stack,) and ultralinear output xformers. I had one and it was just enough power for bass, but it was always a little fuzzy sounding. I had to run another amp in larger venues to get the kind of clean power I wanted.
The next step up would be something like the Ampeg V4B, which used 7027A's for about 120W. Then you can go up another notch like some of the Sunn amps, which were typically 2 or 4 KT88's for ~100W up to about 200W.
The next step up from _that_ is an SVT, which is in the 280-320W neighborhood. Those are 6x6550.
My fave is the Boogie Bass 400+, which is 12x6L6GC, although it doesn't run them nearly hard enough to really get full power. The main deal with the Boogie is that it has a lower-gain Fender-type front end rather than the midrangey-sounding Ampeg preamp. The Ampegs have a kind of funny sound if you're used to Fenders. I like 'em both.
I really wouldn't bother trying to wind my own output OR power trans. The amount of work to do it right is too much hassle for one piece.
I've built BIG rackmount bass power amps with these:
http://www.tubesandmore.com/scripts...evclients/cemirror/ELEVATOR.FXP?item=P-T1650W
Hammond 1650w. 280W output iron, with 6x6146B tubes. I build one in a 2U rackmount chassis, although it was almost 5U high once I put in the tubes (6146's have plate caps so they're pretty tall bottles.) I used the 378CX power transformer, 400-0-400 at 465 mA. I didn't measure output but the math says it was 344W. I'll never do one of those again!
100W is a nice size / power range for a tube bass amp. Smart money says tap off the output trans for a line-out, and then you can slave another amp to it if you need more power. You might never need it but it's nice to have and the extra jack only costs a buck.
Matt Farrow
Thanks Matt there is some very useful information there. Thank you everybody for the posts.
I know that the transformers are reasonably priced and I wouldn't be doing this except for the learning experience and I have most of the parts.
Has anyone used the OPT Design Assistant by Yves Monmagnon ?
I'm trying to use it and I'm having lots of trouble. Probably because I not familiar with all the terminology and that it's metric.
If someone has knowledge of this calculator or has another one to share please post it.
Also if someone has wound a pp output transformer or any OPT please post your experience. It will be greatly appreciated.
Thanks
Dennis
I know that the transformers are reasonably priced and I wouldn't be doing this except for the learning experience and I have most of the parts.
Has anyone used the OPT Design Assistant by Yves Monmagnon ?
I'm trying to use it and I'm having lots of trouble. Probably because I not familiar with all the terminology and that it's metric.
If someone has knowledge of this calculator or has another one to share please post it.
Also if someone has wound a pp output transformer or any OPT please post your experience. It will be greatly appreciated.
Thanks
Dennis
Here is a very interesting site if you want to learn about transformer winding. Both some theory and the actual winding techinque:
http://www.turneraudio.com.au/education+diy.html
This is HiFi oriented and you don't need to use 14Hz as lowest freq so some recalcualtion is needed here and there.
/Olof
http://www.turneraudio.com.au/education+diy.html
This is HiFi oriented and you don't need to use 14Hz as lowest freq so some recalcualtion is needed here and there.
/Olof
Thank you very much hemgjord.
I wish I had found that site a lot earlier.
A very informative site. It really tells you everything you need to know.
http://www.turneraudio.com.au/education+diy.html
I wish I had found that site a lot earlier.
A very informative site. It really tells you everything you need to know.
http://www.turneraudio.com.au/education+diy.html
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