Great , this is something I didn't calculate , I basically went to Torres UK and got the power transformer that was recomended to me for running 4 6L6's at 100W. If you guys rekon this is not enough what sort of current do I need. Is it best to just buy a standard fender replacement one for a 100W twin or something.
Could you guys recomend a good place to go to?
p*ssed off now
Jim
Could you guys recomend a good place to go to?
p*ssed off now
Jim
I'll measure the voltage after the choke when I'm playing loud and see if the voltage drops, looking at the tube specs max current draw at volume is about 210mA so the transformer seems very underpowered something I didn't check on. So now I have to look for a different power transformer. Will I also have to keep an eye on the output transformer as the B+ is going into the centre tap of the primary. Don't want to be ordering a new output transformer as well..
HELP.....
Jim
HELP.....
Jim
Hi
Your output tranny is fine dont worry. The screen voltage does seem high at 500V. The datasheet says max 450V . I would have thought around 300-350V would be best. There are many different 6L6 about, which ones do you have?
Your power tranny is too small. by the time you have taken the bias of the output valves plus all the input stages and drops across resistors, rectifier diodes etc then you dont have anything left to actually give you music.
I guess you can get another tranny the same and wire the secondarys in parallel or get a bigger one. All depends on price.
Also you dont show a conection to ground from the centre tap of the power tranny on your diag. I presume you have this conection otherwise some weird stuff would happen.
Cheers
Matt
Your output tranny is fine dont worry. The screen voltage does seem high at 500V. The datasheet says max 450V . I would have thought around 300-350V would be best. There are many different 6L6 about, which ones do you have?
Your power tranny is too small. by the time you have taken the bias of the output valves plus all the input stages and drops across resistors, rectifier diodes etc then you dont have anything left to actually give you music.
I guess you can get another tranny the same and wire the secondarys in parallel or get a bigger one. All depends on price.
Also you dont show a conection to ground from the centre tap of the power tranny on your diag. I presume you have this conection otherwise some weird stuff would happen.
Cheers
Matt
Thanks Matt , thinking of getting a power transformer that'll give me about 500V AC at 250 mA. And yes there is an earth on the power transformer and it is wired up.
I accepted some advice that I shouldn't have.
I was wondering if an undercurrent rated power transformer is a design choice, do output valves distort more at a lower current. Is this why the amp is loud , real loud but the sound gets messed up at volume.
I use different types of 6L6GC type matched quads , mainly the svetlana with this amp , but I do tend to swap for the Electro Harmoix ones its like my backup set.
If you know of anyware good that I can get a suitable transformer from please let me know at the moment I'm looking at the spares for a marshall fender and such like. Just got to find something with a 50V Bias Tap and 6.3 Volt for heaters. Not a problem in the US not so much choice in the UK
Jim
I accepted some advice that I shouldn't have.
I was wondering if an undercurrent rated power transformer is a design choice, do output valves distort more at a lower current. Is this why the amp is loud , real loud but the sound gets messed up at volume.
I use different types of 6L6GC type matched quads , mainly the svetlana with this amp , but I do tend to swap for the Electro Harmoix ones its like my backup set.
If you know of anyware good that I can get a suitable transformer from please let me know at the moment I'm looking at the spares for a marshall fender and such like. Just got to find something with a 50V Bias Tap and 6.3 Volt for heaters. Not a problem in the US not so much choice in the UK
Jim
Just a little more info this is similar to the current power transformer I have except it supplies 750V not 690.
http://www.torresamps.com/images/100w mains.gif
jim
http://www.torresamps.com/images/100w mains.gif
jim
Hello,
Do you mean 500Vac center tapped if so your voltages will be too low. If you were to full wave rectify the full 500V you would have way too much voltage.
I think you need to be looking for something in the 300-0-300 to 350-0-350 range. Your voltages are on the high side at 530V for the output valves. Something around 450 would be better. Also the screens should be at 300-350V.
Bluebell do some of the Hammond range of trannys and these have the required 50V tap for bias.
http://www.bluebellaudio.com/
bit pricey though.
funily enough I am building a pair of push pull paralel 807 amps. The trannys I have are AnTek. They are way over rated at 400VA but it is a HiFi amp.
http://www.antekinc.com/
I am going to wind on an extra winding for bias. I bought these for something like 50 dollars each plus 34 dollars shipping and an 18 quid customs and excise charge. Not bad but the economic situation is very diferent now.
You are right it is a design choice to have a bit of supply droop in a guitar amp but not as much as you have at the moment.
I guess the cheapest route is to buy a transformer the same as the one you have then put them in parallel, this will give you 300mA.
Cheers
Matt.
Do you mean 500Vac center tapped if so your voltages will be too low. If you were to full wave rectify the full 500V you would have way too much voltage.
I think you need to be looking for something in the 300-0-300 to 350-0-350 range. Your voltages are on the high side at 530V for the output valves. Something around 450 would be better. Also the screens should be at 300-350V.
Bluebell do some of the Hammond range of trannys and these have the required 50V tap for bias.
http://www.bluebellaudio.com/
bit pricey though.
funily enough I am building a pair of push pull paralel 807 amps. The trannys I have are AnTek. They are way over rated at 400VA but it is a HiFi amp.
http://www.antekinc.com/
I am going to wind on an extra winding for bias. I bought these for something like 50 dollars each plus 34 dollars shipping and an 18 quid customs and excise charge. Not bad but the economic situation is very diferent now.
You are right it is a design choice to have a bit of supply droop in a guitar amp but not as much as you have at the moment.
I guess the cheapest route is to buy a transformer the same as the one you have then put them in parallel, this will give you 300mA.
Cheers
Matt.
Hi all looking at replacing my Power transformer with a fender Twin reverb/bassman 100 transformer
Technical Specifications:
Primary: Universal (117VAC & 230VAC).
Secondary: 420VDC@450mA FWCT, 320-0-320 VAC, 450mA with 60V bias tap.
Filament Winding: 6.5V, 5.5A
M6 Lamination (0,35mm)
Can anyone see any problems if I replace the power transformer with this one. Currently the resistors in my power supply are 2 Watt types am I gonna have to up the wattage.
Appreciate everyones help
Jim
Technical Specifications:
Primary: Universal (117VAC & 230VAC).
Secondary: 420VDC@450mA FWCT, 320-0-320 VAC, 450mA with 60V bias tap.
Filament Winding: 6.5V, 5.5A
M6 Lamination (0,35mm)
Can anyone see any problems if I replace the power transformer with this one. Currently the resistors in my power supply are 2 Watt types am I gonna have to up the wattage.
Appreciate everyones help
Jim
Hi Matt , had a look at bluebell audio , thinking about this one
372JX 243 300-0-300 @ 250ma 5vct @ 4A 6.3vct @ 8A X14 £77.70
Do you mind casting your eye of this to see if its suitable . I don't really understand the rating on the transformer. the one above is 300V AC yeah , when that gets rectified through the diodes in the power supply won't I be left with about 200V DC which is a bit low. According to your last post I'm a bit lost with this one. Don't want to order the wrong one again!!
There is this one as well
378CX Total Power : 465VA 400-0-400 @ 465ma 6.3vct @ 6A X21 112.20
Both come with 50v Bias Tap
I really appreciate your input
thanks
Jim
372JX 243 300-0-300 @ 250ma 5vct @ 4A 6.3vct @ 8A X14 £77.70
Do you mind casting your eye of this to see if its suitable . I don't really understand the rating on the transformer. the one above is 300V AC yeah , when that gets rectified through the diodes in the power supply won't I be left with about 200V DC which is a bit low. According to your last post I'm a bit lost with this one. Don't want to order the wrong one again!!
There is this one as well
378CX Total Power : 465VA 400-0-400 @ 465ma 6.3vct @ 6A X21 112.20
Both come with 50v Bias Tap
I really appreciate your input
thanks
Jim
Eek! I was going to reply to this thread yesterday but I had pressure of work and already it has moved on.
Most amplifier design processes involve a little bit more consideration than this.
Already you bought some stuff that didn't work out. Now you bought some more stuff. Who really knows whether this stuff will work out?
This is design by trial-and-error.
You need to calm down and do some calculations or at least make some estimates regarding the voltages, currents, gain, power and output impedance of your amplifier. All you other guys need to stop encouraging the idea that you can just throw together a bunch of valves and transformers and expect them to work in harmony.
w
BTW, are these valves matched?
Most amplifier design processes involve a little bit more consideration than this.
Already you bought some stuff that didn't work out. Now you bought some more stuff. Who really knows whether this stuff will work out?
This is design by trial-and-error.
You need to calm down and do some calculations or at least make some estimates regarding the voltages, currents, gain, power and output impedance of your amplifier. All you other guys need to stop encouraging the idea that you can just throw together a bunch of valves and transformers and expect them to work in harmony.
w
BTW, are these valves matched?
Jim5150 said:
That is absolutely classic of blocking distortion. It's probably coming from the power valves (four output valves makes for a lot of grid current!), so I would suggest you increase those 1.5k grid-stoppers to something more substantial, say 10k.
(Your input valve should have a grid stooper too, or it may also block. Don't know if you just missed that out of the drawing).
In your case it looks like you simply have too much bass in that amp, and that makes blocking even worse. I would suggest you reduce the 0.1uF coupling cap to something closer to 1nF to 4.7nF (yes!), just to tighten up the bass and lose the loose 'woofiness' you seem to be describing. Big coupling caps are nearly always a bad idea in guitar amps, unless the bass is very tightly controlled somewhere else (which it isn't in your design).
300Vac @ 250mA is only 75VA, which isn't nearly enough for your amp (four 6L6s right?!).
I replied before really thinking about it. It will give you 400-420V with no load. but when loaded up ie once all the valves are warm you will probably only get 380-390V or so. This could be a bit low.
You really shouldnt have rushed and bought one. The Fender one you mentioned looked to be fine. How much was it?
Matt.
You really shouldnt have rushed and bought one. The Fender one you mentioned looked to be fine. How much was it?
Matt.
Well I've bought it now , thats me get an idea in my head and I just go do it without thinking. It was £77 by the way. and rated at 243VA. Its gotta be better than what I've got. Had a chat with the guy in the workshop and explained what I wanted to do and he said it would be fine and more or less the same spec as a 100W fender. I aint got many tubes to power. Its got 8Amps for the heaters and a 5Vct at 4A which I'm not gonna use so the voltage won't drop that much and give me a bit more headroom, hopefully.... Was looking at some specs for some of the amps I've based my design on and they use simular power.
But basically I'll pop it in and see. If that don't work I'll try some of the other sugestions in the previous posts.
Its all good fun maybe I should have sat down and done some calculations. Which I did for some stuff but most of it was based on the Torres book. I built a 50W based on ideas in that book and its a crackin sounding amp. Maybe didn't take the care to design the 100W properly. But there we go whats done is done.
Just got to try and turn it round.
Thanks everyone for all your suggestions. Gonna modify things 1 buy 1 starting with the power tran see how it affects the sound. But thats the fun of it. Change something see what happens.
Could have just gone out and bought myself a stock boogie or something , nah this is much better !!!
Will let you all know how it goes...
But basically I'll pop it in and see. If that don't work I'll try some of the other sugestions in the previous posts.
Its all good fun maybe I should have sat down and done some calculations. Which I did for some stuff but most of it was based on the Torres book. I built a 50W based on ideas in that book and its a crackin sounding amp. Maybe didn't take the care to design the 100W properly. But there we go whats done is done.
Just got to try and turn it round.
Thanks everyone for all your suggestions. Gonna modify things 1 buy 1 starting with the power tran see how it affects the sound. But thats the fun of it. Change something see what happens.
Could have just gone out and bought myself a stock boogie or something , nah this is much better !!!
Will let you all know how it goes...
Hi all , got the new transformer and put it in , get 440V initially that drops to about 415 when the valves warm up.
The amp seems more powerful and clear and sounds better at full volume. I've also changed the coupling cap to a .1 instead of a .02 and turned the bass down on the POD and yes the sound is definetly getting there. The only problem I have now is volume. The amp doesn't seem to be that loud for a 100W. My 50W is twice as loud.I've got a feeling that the first gain stage isn't producing enough oomph to drive the phase splitter.
There are two output types on the POD Line and amp. If you turn to LINe the sound is louder but messed up. I think its too much for that first gain stage and is overloading it. But if you switch to AMP output the sound is basically what I want very strong very clear but not very loud. I'd like to keep it on the AMP setting (Its what it was made for) the line setting is for plugging straight into a recording mixer. The point of that first gain stage is to raise the level to line level. I have replaced the 12AT7 's for 12AX7 's and this has made a difference to the quality of the sound and the volume , but still not enough for the amp to be useable in a live rock situation.
Does anyone know the ideal signal strength voltage that should be going into that phase splitter?
I'm going to try a few different resistor configurations on that first stage and bring the gain up but not too much so that it distorts.
If anyone has any thoughts on what resistor configs to use for maximum headroom and volume then please let me know.Been looking at schematics for the mesa 290 power amp which uses 100K and a 1K configuration.
I'm also going to experiment with different coupling caps when I can get hold of the right type. I've noticed that the mesa 290 uses a .1 so I'll see how it goes. Gonna try the resistor config first.
If I can nail the volume problem I'll be a very happy man.
But getting happier as this project goes along. Its definetly in a better state than when I first started posting to this forum.
Thanks for everyones help on this its greatly appreciated. If you were all local to me I'd buy you all a pint!!
Jim
The amp seems more powerful and clear and sounds better at full volume. I've also changed the coupling cap to a .1 instead of a .02 and turned the bass down on the POD and yes the sound is definetly getting there. The only problem I have now is volume. The amp doesn't seem to be that loud for a 100W. My 50W is twice as loud.I've got a feeling that the first gain stage isn't producing enough oomph to drive the phase splitter.
There are two output types on the POD Line and amp. If you turn to LINe the sound is louder but messed up. I think its too much for that first gain stage and is overloading it. But if you switch to AMP output the sound is basically what I want very strong very clear but not very loud. I'd like to keep it on the AMP setting (Its what it was made for) the line setting is for plugging straight into a recording mixer. The point of that first gain stage is to raise the level to line level. I have replaced the 12AT7 's for 12AX7 's and this has made a difference to the quality of the sound and the volume , but still not enough for the amp to be useable in a live rock situation.
Does anyone know the ideal signal strength voltage that should be going into that phase splitter?
I'm going to try a few different resistor configurations on that first stage and bring the gain up but not too much so that it distorts.
If anyone has any thoughts on what resistor configs to use for maximum headroom and volume then please let me know.Been looking at schematics for the mesa 290 power amp which uses 100K and a 1K configuration.
I'm also going to experiment with different coupling caps when I can get hold of the right type. I've noticed that the mesa 290 uses a .1 so I'll see how it goes. Gonna try the resistor config first.
If I can nail the volume problem I'll be a very happy man.
But getting happier as this project goes along. Its definetly in a better state than when I first started posting to this forum.
Thanks for everyones help on this its greatly appreciated. If you were all local to me I'd buy you all a pint!!
Jim
Hi all , I've just realised that if I change the plate and cathode resistors to 100K and 1K this will actually lower the gain. Hmm not sure what to do now the actuall schematic I'm looking at is this
http://www.schematicheaven.com/boogieamps/boogie_290.pdf
Don't see that much of a difference between the mesa schematic and my design when you cut out all the "deep" switches etc...
Jim
http://www.schematicheaven.com/boogieamps/boogie_290.pdf
Don't see that much of a difference between the mesa schematic and my design when you cut out all the "deep" switches etc...
Jim
Hello Jim,
Glad it seems to be working. Just ironing out the other problems to do now.
I was looking at the Ampeg schematic you just posted. It has a strange output stage, the outer two valves have an extra small section of the output transformer and a resistor between cathode and grid(the other two dont).
I wonder what the idea of this is. Anyone know?.
Could you tell me what your overall impression is of the Hammond tranny ie. build quality, does it conform to the voltage specs etc? I am thinking of buying a pair of 1650R output transformers and I know this is like comparing chalk and cheese but I would like to know what their modern fair is like as I have only seen old stuff.
Cheers
Matt.
Glad it seems to be working. Just ironing out the other problems to do now.
I was looking at the Ampeg schematic you just posted. It has a strange output stage, the outer two valves have an extra small section of the output transformer and a resistor between cathode and grid(the other two dont).
I wonder what the idea of this is. Anyone know?.
Could you tell me what your overall impression is of the Hammond tranny ie. build quality, does it conform to the voltage specs etc? I am thinking of buying a pair of 1650R output transformers and I know this is like comparing chalk and cheese but I would like to know what their modern fair is like as I have only seen old stuff.
Cheers
Matt.
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