SuperBass EL34 to 6550 bias circuit INFO need PLEASE

David_Well · 10-31-2009, 10:07 PM

Yep , this question again....
My Goal is to target the Most perfect BIAS as possible.
I need to know witch value of resistor i need to Swap for Winged"C" 6550
It for a SuperBass 73 PCB (you know how is to mod on PCB...All tweek in same time)
I Really whant to get fix before open it....
I still Asking the question cause so many people say different thing's about the cercuit.
Now my bias is way too mutch...
What do I need....

Split 82K,220K or 150K
NFB 4 or 8 ohm
In line with the diode, 47K,56k or 100K
down the board 15K or 27K
8Uf or 10Uf twin cap....

What I whant is to get Headroom And Kick when crank-up and for shure , Elephant Ball's TONE !

Thanks and best regards to All
Dave

Wilder Amplification · 11-01-2009, 01:04 PM

Quote:

Originally Posted by David_Well

Yep , this question again....
My Goal is to target the Most perfect BIAS as possible.
I need to know witch value of resistor i need to Swap for Winged"C" 6550
It for a SuperBass 73 PCB (you know how is to mod on PCB...All tweek in same time)
I Really whant to get fix before open it....
I still Asking the question cause so many people say different thing's about the cercuit.
Now my bias is way too mutch...
What do I need....

Split 82K,220K or 150K
NFB 4 or 8 ohm
In line with the diode, 47K,56k or 100K
down the board 15K or 27K
8Uf or 10Uf twin cap....

What I whant is to get Headroom And Kick when crank-up and for shure , Elephant Ball's TONE !

Thanks and best regards to All
Dave

Hey Dave. Most Marshalls I've seen that are set up for 6550s usually have a 56K resistor (green/blue/orange) in place of the 47K range resistor (yellow/purple/orange) that's right above the bias adjustment pot in the bias supply. If you post up some pics of the area around the bias pot I can show you exactly which one to change out. You shouldn't need to change out any other resistors in the amp except for that resistor.

David_Well · 11-01-2009, 09:35 PM

Thanks jon, I know witch one is....
What it's cofuzed me is the twin resistor.
Some say to let the 220K, other put 82K...
I will chanke the 47K for a 56K , the one in line with the Bies trim pot.
For the NFB tap I will put the 8ohm output Tap.

I just whant to be shure cause lift the PCB is quoite a job...
So change all in the same time , and after I redone Great nice Wiering arrangement.

Thanks

Wilder Amplification · 11-01-2009, 09:39 PM

Quote:

Originally Posted by David_Well

Thanks jon, I know witch one is....
What it's cofuzed me is the twin resistor.
Some say to let the 220K, other put 82K...
I will chanke the 47K for a 56K , the one in line with the Bies trim pot.
For the NFB tap I will put the 8ohm output Tap.

I just whant to be shure cause lift the PCB is quoite a job...
So change all in the same time , and after I redone Great nice Wiering arrangement.

Thanks

Yeah the 220K resistors are called the grid load resistors. Most every guitar amp regardless of valve type uses 220K resistors here. Some people may say to lower them for tone reasons. But it's not an electrical requirement that they be changed.

Not sure how much you're willing to spend on that amp, but if you plan on poking around that amp quite a bit I highly suggest getting a board kit to convert that thing to a point to point board. This will make everything so much easier on you since everything on a point to point board is top soldered and you won't have to keep removing the board everytime you change out a part.

MajorNut1967 · 11-01-2009, 09:55 PM

Quote:

Originally Posted by Wilder Amplification

Yeah the 220K resistors are called the grid load resistors. Most every guitar amp regardless of valve type uses 220K resistors here. Some people may say to lower them for tone reasons. But it's not an electrical requirement that they be changed.
.

If you lower the grid split resistors you also keep the tubes on a shorter leash, less likely to have a power tube super nova. I lower them down to 150k on 6550's; some guys go as low as 100k

David_Well · 11-04-2009, 06:45 PM

Thank's guy's...
Yes Jon, Switch for a Point-toPoint make things easyer...But, The Original thing got a point got a PCB original and All coponent are original except 2 resistor and the V1 cathode Bypass cap. What I should do is to use the PCB as a template if I whant to install PTP.
I think doing this gonna decrese the original value....

For the 220K, I Whant to lower them to 150K. Some people even put 82K...
I Don't have old 150 Res, Value, Only have Piher 120K ½W and 180K 1W Beyschlag and 82K 1W Beyschlag.
I think My best Deal is the 120K I think.
I got around 130 Piher,ISKRA and Beyschlag of 24 different value.

I'm Also Thinking to buy a 50K trim pot for Bias....I not shure if is a good Idea,
I know that CeriaTone use them in their SuperBass Copie.

For The Bias Point... -42 is OK???

Thanks for All to All of You Helping me In My first BIG restoration Project...
Really Appreciate.

Dave

Wilder Amplification · 11-04-2009, 07:07 PM

Quote:

Originally Posted by David_Well

I'm Also Thinking to buy a 50K trim pot for Bias....I not shure if is a good Idea,

NO! Increasing the value of the bias pot may give you more adjustment range, but it also makes it too sensitive, which is not a good idea.

Quote:

Originally Posted by David_Well

For The Bias Point... -42 is OK???

Again...NO! That's for EL34s. 6550s need much more than that, which is why you have to change the 47K resistor out to a 56K. If the 56K still isn't enough, go with a 68K.

It's actually a better idea if you try the 68K first, then if you don't have enough bias current with that, then reduce it to a 56K.

David_Well · 11-04-2009, 07:39 PM

OK...I try out the 68K first!
So..So the Bias point may be between between Witch value?...
Between -25 and -32 ?

My Quad 6550 are Match and ther's a 118 hand wright on the top...
What this 118 mean ?

Should I target this 118 with a bias Prob?

Wilder Amplification · 11-04-2009, 07:44 PM

Quote:

Originally Posted by David_Well

OK...I try out the 68K first!
So..So the Bias point may be between between Witch value?...
Between -25 and -32 ?

My Quad 6550 are Match and ther's a 118 hand wright on the top...
What this 118 mean ?

Should I target this 118 with a bias Prob?

No...go the other way. More like around -50 to -60ish. The voltage has to be MORE negative.

David_Well · 11-04-2009, 09:11 PM

Ok...Good...LOL...
I finally understand...
I will try to not kill myself with modifing amp !
As soon as I receive my parts, I will send picture...
I fing a vintage trimmer pot so, I will replace the new one.
I also need to find a vintage original Impedance Switch .
If I use The 240V insted of the 120V tap on the PT....Is I have something else to change to drop it at 50W???

Wilder Amplification · 11-04-2009, 09:56 PM

Quote:

Originally Posted by David_Well

Ok...Good...LOL...
I finally understand...
I will try to not kill myself with modifing amp !
As soon as I receive my parts, I will send picture...
I fing a vintage trimmer pot so, I will replace the new one.
I also need to find a vintage original Impedance Switch .
If I use The 240V insted of the 120V tap on the PT....Is I have something else to change to drop it at 50W???

DO NOT drop the mains voltage setting! Keep it on 120!!!

To drop the power down to 50 watts, you pull either V5 & 6 or V4 & 7. Then you drop the impedance selector down one setting from your cab's impedance. Example, for a 16 ohm load you set it to 8 and for an 8 ohm load you set it to 4 ohms. You can't do it at all on a 4 ohm cab and you'll have to rewire the 4 ohm cab to 16 ohms. The mains voltage ALWAYS stays on 120V.

David_Well · 11-05-2009, 12:15 PM

Some People actually do it, a switch between the 120 and 240.
Other use a variac to drop voltage but not less then 70VAC.(Van Halen)
Older Marshall like the 67 plexi have a power selector.
And like you suggest, taking off 2 valve reduce the output Wattage at 50W
Some use Yellow jacket and use EL84....

Seem's to me thet is many way to do it...Is just to find the one that not going to damage the and and no need to rebias....

Wilder Amplification · 11-05-2009, 12:46 PM

Quote:

Originally Posted by David_Well

Some People actually do it, a switch between the 120 and 240.
Other use a variac to drop voltage but not less then 70VAC.(Van Halen)
Older Marshall like the 67 plexi have a power selector.
And like you suggest, taking off 2 valve reduce the output Wattage at 50W
Some use Yellow jacket and use EL84....

Seem's to me thet is many way to do it...Is just to find the one that not going to damage the and and no need to rebias....

I know some people actually do it, but some people fail to stop for red lights too. Just because people actually do it doesn't mean it's a smart thing to do.

Dropping mains voltage (unless the mains voltage is too high for whatever reason) via a variac or changing the voltage selector is a bad thing and something I will always preach against. This runs the amp out of its design limits and can fry shit. There are other ways of dropping the HT supply voltage and compensating the bias for such without altering the heater voltage, such as using a MetroAmp dual voltage secondary with their 3Pole double throw center off Standby switch with a compensating bias pot on the switch.

If you read the EVH interviews, you'll also see that Eddie's amp was constantly in the shop because of this.

David_Well · 11-05-2009, 05:56 PM

That really make sence to me....
The amp is build like this so ,use it this way....simple
I give you all credit on what you saying.
Right now i have a really nice Collection Amp, but with the 6550 it's more then 100W ( I suppose ) and it's F%&king LOUD !!!! Cé fort en Tabarnak !!!
I'm not Playing in a stadium men !!!
Just to Make this monster well calibrate ane Great sounding is a Great achivement for me....and with forum member's and specially you'r help , I am a big step further.
I don't have the AH1N1 but a critical amp building disease !!!!

I'll give you some new's when I make the Mod for Bias and other...
For now I'm searching a vintage impedance switch...Male and Female parts.

Best Regards

Dave

Wilder Amplification · 11-05-2009, 06:36 PM

Quote:

Originally Posted by David_Well

That really make sence to me....
The amp is build like this so ,use it this way....simple
I give you all credit on what you saying.
Right now i have a really nice Collection Amp, but with the 6550 it's more then 100W ( I suppose ) and it's F%&king LOUD !!!! Cé fort en Tabarnak !!!
I'm not Playing in a stadium men !!!
Just to Make this monster well calibrate ane Great sounding is a Great achivement for me....and with forum member's and specially you'r help , I am a big step further.
I don't have the AH1N1 but a critical amp building disease !!!!

I'll give you some new's when I make the Mod for Bias and other...
For now I'm searching a vintage impedance switch...Male and Female parts.

Best Regards

Dave

I doubt it's more than 100 watts simply due to the current draw limit of the power supply. And even if it were, it wouldn't be noticeable except on an oscilloscope and it would be WAY less than 200 watts, which would be required to get 3dB more than 100 watts, hence why it wouldn't be noticeable.

The increase in bass response/low end is probably what you're hearing as "louder = more power". This just means that the amp has a "more powerful sound"...not that the amp is putting out more power.

10-31-2009, 10:07 PM	#1 (permalink)
David_Well Member Join Date: Mar 2009 Posts: 67	SuperBass EL34 to 6550 bias circuit INFO need PLEASE Yep , this question again.... My Goal is to target the Most perfect BIAS as possible. I need to know witch value of resistor i need to Swap for Winged"C" 6550 It for a SuperBass 73 PCB (you know how is to mod on PCB...All tweek in same time) I Really whant to get fix before open it.... I still Asking the question cause so many people say different thing's about the cercuit. Now my bias is way too mutch... What do I need.... Split 82K,220K or 150K NFB 4 or 8 ohm In line with the diode, 47K,56k or 100K down the board 15K or 27K 8Uf or 10Uf twin cap.... What I whant is to get Headroom And Kick when crank-up and for shure , Elephant Ball's TONE ! Thanks and best regards to All Dave Last edited by David_Well; 10-31-2009 at 11:10 PM.

11-01-2009, 09:35 PM	#3 (permalink)
David_Well Member Join Date: Mar 2009 Posts: 67	Re: SuperBass EL34 to 6550 bias circuit INFO need PLEASE Thanks jon, I know witch one is.... What it's cofuzed me is the twin resistor. Some say to let the 220K, other put 82K... I will chanke the 47K for a 56K , the one in line with the Bies trim pot. For the NFB tap I will put the 8ohm output Tap. I just whant to be shure cause lift the PCB is quoite a job... So change all in the same time , and after I redone Great nice Wiering arrangement. Thanks

11-04-2009, 06:45 PM	#6 (permalink)
David_Well Member Join Date: Mar 2009 Posts: 67	Re: SuperBass EL34 to 6550 bias circuit INFO need PLEASE Thank's guy's... Yes Jon, Switch for a Point-toPoint make things easyer...But, The Original thing got a point got a PCB original and All coponent are original except 2 resistor and the V1 cathode Bypass cap. What I should do is to use the PCB as a template if I whant to install PTP. I think doing this gonna decrese the original value.... For the 220K, I Whant to lower them to 150K. Some people even put 82K... I Don't have old 150 Res, Value, Only have Piher 120K ½W and 180K 1W Beyschlag and 82K 1W Beyschlag. I think My best Deal is the 120K I think. I got around 130 Piher,ISKRA and Beyschlag of 24 different value. I'm Also Thinking to buy a 50K trim pot for Bias....I not shure if is a good Idea, I know that CeriaTone use them in their SuperBass Copie. For The Bias Point... -42 is OK??? Thanks for All to All of You Helping me In My first BIG restoration Project... Really Appreciate. Dave

11-04-2009, 07:39 PM	#8 (permalink)
David_Well Member Join Date: Mar 2009 Posts: 67	Re: SuperBass EL34 to 6550 bias circuit INFO need PLEASE OK...I try out the 68K first! So..So the Bias point may be between between Witch value?... Between -25 and -32 ? My Quad 6550 are Match and ther's a 118 hand wright on the top... What this 118 mean ? Should I target this 118 with a bias Prob?

11-04-2009, 09:11 PM	#10 (permalink)
David_Well Member Join Date: Mar 2009 Posts: 67	Re: SuperBass EL34 to 6550 bias circuit INFO need PLEASE Ok...Good...LOL... I finally understand... I will try to not kill myself with modifing amp ! As soon as I receive my parts, I will send picture... I fing a vintage trimmer pot so, I will replace the new one. I also need to find a vintage original Impedance Switch . If I use The 240V insted of the 120V tap on the PT....Is I have something else to change to drop it at 50W???

11-05-2009, 12:15 PM	#12 (permalink)
David_Well Member Join Date: Mar 2009 Posts: 67	Re: SuperBass EL34 to 6550 bias circuit INFO need PLEASE Some People actually do it, a switch between the 120 and 240. Other use a variac to drop voltage but not less then 70VAC.(Van Halen) Older Marshall like the 67 plexi have a power selector. And like you suggest, taking off 2 valve reduce the output Wattage at 50W Some use Yellow jacket and use EL84.... Seem's to me thet is many way to do it...Is just to find the one that not going to damage the and and no need to rebias....

11-05-2009, 05:56 PM	#14 (permalink)
David_Well Member Join Date: Mar 2009 Posts: 67	Re: SuperBass EL34 to 6550 bias circuit INFO need PLEASE That really make sence to me.... The amp is build like this so ,use it this way....simple I give you all credit on what you saying. Right now i have a really nice Collection Amp, but with the 6550 it's more then 100W ( I suppose ) and it's F%&king LOUD !!!! Cé fort en Tabarnak !!! I'm not Playing in a stadium men !!! Just to Make this monster well calibrate ane Great sounding is a Great achivement for me....and with forum member's and specially you'r help , I am a big step further. I don't have the AH1N1 but a critical amp building disease !!!! I'll give you some new's when I make the Mod for Bias and other... For now I'm searching a vintage impedance switch...Male and Female parts. Best Regards Dave

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