36 Watter Roaring like a lion !!
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36 Watter Roaring like a lion !!
Fixed it
Took a leaf out of Graydon's book (or was it more like half the book) and studied the Vox AC30 circuit more closely. I added two more 100 ohm 5W grid resistors giving each EL84 it's own. I have left the cathode resistors as they were, two 150 ohms, one to each pair of EL84s.
Cured all the screeching and tizzing.
It's based on the MV/TMB and has none of the high pitched whistling you can sometimes get, that's down to following Jersey Aarons earthing layout to the letter.
Graydon is right, loads more clean headroom, the ordinary channel is very powerful. Literally power you can feel in your body. The MV channel doesn't break up easily, perhaps a few more value tweaks there. It is not possible to turn it up full in the house, it is just too damned loud. I will wait until it rains hard, lock the beast in a room and take the guitar outside the door to see how loud it will go. At the moment I wouldn't be able to stay in the room with it turned up full.
I would say it is fuller, with more body and just feels and sounds more ' powerful ' not just louder, but almost startling in it's power.
Not suprisingly you can still hear the 18 watt character in there. I will build another with a 30 watt Vox AC30 OT to see if it breaks up quicker. At the moment I have a Hammond 60 watt OT in there as it is the only Hammond around 4K primary impedance.
Steve UK
Took a leaf out of Graydon's book (or was it more like half the book) and studied the Vox AC30 circuit more closely. I added two more 100 ohm 5W grid resistors giving each EL84 it's own. I have left the cathode resistors as they were, two 150 ohms, one to each pair of EL84s.
Cured all the screeching and tizzing.
It's based on the MV/TMB and has none of the high pitched whistling you can sometimes get, that's down to following Jersey Aarons earthing layout to the letter.
Graydon is right, loads more clean headroom, the ordinary channel is very powerful. Literally power you can feel in your body. The MV channel doesn't break up easily, perhaps a few more value tweaks there. It is not possible to turn it up full in the house, it is just too damned loud. I will wait until it rains hard, lock the beast in a room and take the guitar outside the door to see how loud it will go. At the moment I wouldn't be able to stay in the room with it turned up full.
I would say it is fuller, with more body and just feels and sounds more ' powerful ' not just louder, but almost startling in it's power.
Not suprisingly you can still hear the 18 watt character in there. I will build another with a 30 watt Vox AC30 OT to see if it breaks up quicker. At the moment I have a Hammond 60 watt OT in there as it is the only Hammond around 4K primary impedance.
Steve UK
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Yeah! And tells us your voltages too.
Mine has the twin 18W OTs and it breaks up exacgtly like the 18W - at around 2 on the volume it starts to break up and around 5 it is roaring. However, 2 on the 36W is a "little louder" than 2 on the 18W so there is a significant difference bewteeen the two.
Congratulations Steve. That is a great feeling isn't it!
Who's next? Richie, are you there?
Mine has the twin 18W OTs and it breaks up exacgtly like the 18W - at around 2 on the volume it starts to break up and around 5 it is roaring. However, 2 on the 36W is a "little louder" than 2 on the 18W so there is a significant difference bewteeen the two.
Congratulations Steve. That is a great feeling isn't it!
Who's next? Richie, are you there?
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Phil, Graydon,
Yes it is a great feeling after the initial frustrations.
I have the 10 Henry Hammond choke temporarily lashed in for now, across the 32 + 32 Cap taking full B+. I am going to take it out and see if there is a discernible difference.
It seems the key was giving each EL84 it's own 100 ohm grid resistor. Originally, I had two sharing two EL84s each.
I still have two seperate 150 ohm cathode resistors connected to two EL84s each.
I would like a bit more crunch at less ear shattering volumes, but then I suppose I have my other amps if I want that. This is for bigger venues. There isn't as great a difference between the normal and MV channel as the 18 watt MV TMB, and that is pretty loud. I suppose you could compare it to a V6 and a V8. The V6 is sweet, but the V8 rumbles your soul.
Now my acceptance speech.
Thanks to Richie, Graydon, Phil and Jersey Aaron and anybody else I know I couldn't have done it without you,
Steve UK
Yes it is a great feeling after the initial frustrations.
I have the 10 Henry Hammond choke temporarily lashed in for now, across the 32 + 32 Cap taking full B+. I am going to take it out and see if there is a discernible difference.
It seems the key was giving each EL84 it's own 100 ohm grid resistor. Originally, I had two sharing two EL84s each.
I still have two seperate 150 ohm cathode resistors connected to two EL84s each.
I would like a bit more crunch at less ear shattering volumes, but then I suppose I have my other amps if I want that. This is for bigger venues. There isn't as great a difference between the normal and MV channel as the 18 watt MV TMB, and that is pretty loud. I suppose you could compare it to a V6 and a V8. The V6 is sweet, but the V8 rumbles your soul.
Now my acceptance speech.
Thanks to Richie, Graydon, Phil and Jersey Aaron and anybody else I know I couldn't have done it without you,
Steve UK
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That choke will nullify the effect of having a valve rectifier. The separate screen grid resistors are a very good idea, as that helps reduce interaction between the valves. Note that "Jason's Mods" use a 1k screen voltage dropper resistor, with individual 100 ohm resistors then going to each EL84. You could try that with your amp - with either a 470 ohm supplying four individual 100 ohm resistors going to each screen grid, or have a 1k for each pair. Having the separate 150 ohm cathode resistors is a nice idea because it makes it easy to pull a couple of EL84s if you ever want to run the amp at half power. BTW, what grid leak resistors have you got on the EL84s?
Last edited by zaphod_phil on Fri 03/26/04 5:23 am, edited 1 time in total.
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- MatthewShadwick
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Steve,
Well done. I have been watching the 36watt posts and monitoring your progress. I am thinking a 36watt head would be great to complement my 18watt combo. I would love to see some photos of the inside of your amp if possible.
Graydon,
Are you very far away from testing your 36W transformer?
Cheers
Matthew Shadwick
Well done. I have been watching the 36watt posts and monitoring your progress. I am thinking a 36watt head would be great to complement my 18watt combo. I would love to see some photos of the inside of your amp if possible.
Graydon,
Are you very far away from testing your 36W transformer?
Cheers
Matthew Shadwick
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Mathew,
Yes, as soon as I have verified all functionality of the 36W PT and OT, they will be available.
Also, I will post photos soon. My layout is basically the same as a regular 18W. All of my additional parts for the power section fit on the normal locations on the eyelet board or on the pins of the tube sockets. It is really a fairly easy swap. I think I could change any 18W head into a 36W without being completely unreasonable.
Yes, as soon as I have verified all functionality of the 36W PT and OT, they will be available.
Also, I will post photos soon. My layout is basically the same as a regular 18W. All of my additional parts for the power section fit on the normal locations on the eyelet board or on the pins of the tube sockets. It is really a fairly easy swap. I think I could change any 18W head into a 36W without being completely unreasonable.
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Steve,Graydon,JA.. sorry i've been out of the loop here a few days. You sure miss alot in just a couple days.. I've been down and out with the flu or something.. Just now getting able to get caught up some.
Steve glad to hear your amp is blastin.. So far what i've read is what i was hoping this amp would turn out like. more volume..but with same character of the 18,but still you'll have more clean volume that is usefull for people who might need that. Or for people that just was on the verge of not enough with just an 18.. the 36 should step them up into being able to play with a louder rock bad situation.
I see Graydon is useing the 2x OTs. I'll be watching to see how his one OT sounds. Mine is coming along slowly. its a little different,And as far as i know,i don't think its ever been done or tried. Just have to wait and see if i can make it work. Most of the hard work is done, just have to throw it together,and wire it up.. I also talked to my friend about useing his pro tools to record some clips when its done.
As for a layout..all i have is a hand drawn pic i made,and its just of the board layout. It may sound goofy, but it took me a while, till i got everything in the spot i wanted it.
Maybe after Steve has more time to play his amp and check it out,he can give us more details.. what all was changed etc.. Maybe post some voltages. Maybe after some of this medication clears out,i can answer some questions on the forum..lol
Richie
Steve glad to hear your amp is blastin.. So far what i've read is what i was hoping this amp would turn out like. more volume..but with same character of the 18,but still you'll have more clean volume that is usefull for people who might need that. Or for people that just was on the verge of not enough with just an 18.. the 36 should step them up into being able to play with a louder rock bad situation.
I see Graydon is useing the 2x OTs. I'll be watching to see how his one OT sounds. Mine is coming along slowly. its a little different,And as far as i know,i don't think its ever been done or tried. Just have to wait and see if i can make it work. Most of the hard work is done, just have to throw it together,and wire it up.. I also talked to my friend about useing his pro tools to record some clips when its done.
As for a layout..all i have is a hand drawn pic i made,and its just of the board layout. It may sound goofy, but it took me a while, till i got everything in the spot i wanted it.
Maybe after Steve has more time to play his amp and check it out,he can give us more details.. what all was changed etc.. Maybe post some voltages. Maybe after some of this medication clears out,i can answer some questions on the forum..lol
Richie
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The way chokes store energy means they tend to regulate/stabilize the voltage of the current passing through them, so you loose some of the sag effect you gain from having a vacuum rectifier. How much you loose depends on what kind of rectifier you're using vs how big the choke is. Of course, this is one of the reaons chokes were used in some vintage amps, when they didn't want much sag, and the only realistiv alternative was selenium rectifiers.
FYI, this is also why in some amps they use chokes to provide a "stiff" screen grid voltage, when they want to get the most power out of the amp.
FYI, this is also why in some amps they use chokes to provide a "stiff" screen grid voltage, when they want to get the most power out of the amp.
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