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Tiarnan · January 4th, 2011, 02:45 PM

Just out of Interest would it be possible to use this transformer

http://ampmaker.com/190-0-190v-5w-po...er-1250-0.html

in Vibro Champ circuit and replace the standard 6v6 with an EL84?

Thanks,

Tiarnan

JohnnyCrash · January 4th, 2011, 07:13 PM

Typical Champ PT may be a bit high in the voltage department (it can be reduced easily though), and OTs are about the same for 6V6 or EL84.

You may consider looking at old Gibson Les Paul Jr amp schematics for a single ended EL84 amp - at least for the power section stuff... or the Kalamazoo Model-1... or... you get the idea, there are a lot out there :)

It shouldn't be too hard to "convert" the power section to an EL84 with the same PT/OT.

printer2 · January 4th, 2011, 10:46 PM

http://ax84.com/p1.html

Do a P1 but rather than a TMB tone stack you can use a one knob tone control.

Cliff Schecht · January 4th, 2011, 10:54 PM

The 190-0-190V B+ is a bit on the low-side for EL84's. I'd look for something closer to 230-0-230 @ 50-60 mA minimum for a B+ closer to 330-350V (will sound MUCH better than such a low plate voltage).

marshman · January 5th, 2011, 09:22 AM

Not to second guess anyone, but 190-0-190 is a Push-pull PT spec, innit? Is it a good idea to put 350ishVDC on an SE EL84?

Tiarnan · January 5th, 2011, 01:01 PM

Thanks guys was just wondering because I have a vibro champ circuit and that transformer. I think ill just stick with a 6v6 and order a weber transformer.

Tiarnan

limbe · January 5th, 2011, 03:08 PM

Most manuals list 300 v as max plate voltage for EL84 and 350v for 6V6.

laird · January 5th, 2011, 04:29 PM

A 190-0-190 transformer will give you around 255v B+ (with a solid state rectifier). Although it's not the maximum voltage for an EL84 it's certainly sufficient to power it. Cathode bias should raise the cathode around 10v, leaving 245v for operation. Perfect - The EL84 data sheets have 250v listed as the example operating voltage. Lowering the voltage dropping resistors to 250-470 ohms on the first drop, 4.7k on the next should keep the preamp B+ near 200v.

Another big improvement on the Champ is to add a filter stage before the OT gets its B+ - around 20uf and 50-100 ohms (2-3 watt). It'll cut the AC ripple hum down to practically nothing.

I'm not sure how much the tremolo circuit would be affected by the lower B+. It might be fine, it might not work at all! I'll let someone else answer that one. :)

-Laird

Wally · January 5th, 2011, 05:20 PM

limbe, actually the 6V6 and the EL-84 have very simular voltage specs. In fact, a quick look at Duncan tube data site shows the 6BQ5 max voltage in AB1 exceeding the 6V6's specs.
And....most guitar amp designs exceed these specs. I haven't seen very many guitar amps with plate voltage below 300V.....and both of these tubes have a max of 285 from what I have seen. Deluxe REverbs often run well over 400V on 6V6 plates. There are technical aspects that account for these tubes ability to tolerate this. Maybe someone will clue us in on this aspect. I simply know that these tubes will operate with palte voltages above their design limits.

printer2 · January 5th, 2011, 06:37 PM

A big variable from what I have been reading is the screen voltage and power rather than the plate. The screen is more fragile and in between the cathode and plate so it makes sense it is more the limiting factor.

Playing around with a 6AQ5 in a SE amp the last couple of days, it is the 7 pin smaller version of the 6V6. It has maximum ratings of 275v for the plate and screen. The data sheet give an example of 250v, was running the amp at that (cathode biased so actual voltage about 240) and am now running it with 300v supply. I have it biased for 43mA and it seems to not mind the voltage. It is just under the dissipation limit for the tube but there is no red plating so it seems fine.

6V6's or EL84's are a little beefier so they could take a little more.

Telenut62 · January 5th, 2011, 11:37 PM

Why not ask the Mr. Amp Man himself....barry@ampmaker.com
He's a really nice guy and certainly kows his stuff. One thing about this EL84/6V6 comparison ain't they got diff pin arrangements, so you'd have to swap the socket as well?

printer2 · January 6th, 2011, 07:28 PM

Quote:

Originally Posted by Telenut62

Why not ask the Mr. Amp Man himself....barry@ampmaker.com
He's a really nice guy and certainly kows his stuff. One thing about this EL84/6V6 comparison ain't they got diff pin arrangements, so you'd have to swap the socket as well?

Different tube socket.

xStonr · January 10th, 2011, 09:37 PM

will a THD yellow jacket work with existing PT?

January 4th, 2011, 02:45 PM	#1 (permalink)
Tiarnan Tele-Meister Join Date: Feb 2010 Location: Ireland Age: 20 Posts: 104	EL84 Champ Just out of Interest would it be possible to use this transformer http://ampmaker.com/190-0-190v-5w-po...er-1250-0.html in Vibro Champ circuit and replace the standard 6v6 with an EL84? Thanks, Tiarnan

January 4th, 2011, 07:13 PM	#2 (permalink)
JohnnyCrash Doctor of Teleocity Join Date: Mar 2005 Location: Fullerton, CA Posts: 10,661 1 Photos	Typical Champ PT may be a bit high in the voltage department (it can be reduced easily though), and OTs are about the same for 6V6 or EL84. You may consider looking at old Gibson Les Paul Jr amp schematics for a single ended EL84 amp - at least for the power section stuff... or the Kalamazoo Model-1... or... you get the idea, there are a lot out there :) It shouldn't be too hard to "convert" the power section to an EL84 with the same PT/OT. __________________ - 3 Gibsons, 5 Teles, assorted other guitars, about a dozen amps, about two dozen pedals, a Smith & Wesson SW40VE, & a .40 SIG Sauer P226R = too many toys, no money, carpal tunnel, and a serious hearing problem.

January 5th, 2011, 09:22 AM	#5 (permalink)
marshman Friend of Leo's Join Date: Feb 2007 Location: SE PA Age: 44 Posts: 3,750	Not to second guess anyone, but 190-0-190 is a Push-pull PT spec, innit? Is it a good idea to put 350ishVDC on an SE EL84? __________________ 42

January 5th, 2011, 11:37 PM	#11 (permalink)
Telenut62 Friend of Leo's Join Date: Oct 2008 Location: Eugowra, Australia Age: 52 Posts: 2,819	Why not ask the Mr. Amp Man himself....barry@ampmaker.com He's a really nice guy and certainly kows his stuff. One thing about this EL84/6V6 comparison ain't they got diff pin arrangements, so you'd have to swap the socket as well? __________________ .....I love the sound of distortion in the morning!!

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January 4th, 2011, 10:46 PM	#3 (permalink)
printer2 Friend of Leo's Join Date: May 2010 Location: Canada Age: 52 Posts: 2,841	http://ax84.com/p1.html Do a P1 but rather than a TMB tone stack you can use a one knob tone control.

January 4th, 2011, 10:54 PM	#4 (permalink)
Cliff Schecht Tele-Holic Join Date: Oct 2010 Location: Lubbock, Texas Posts: 602	The 190-0-190V B+ is a bit on the low-side for EL84's. I'd look for something closer to 230-0-230 @ 50-60 mA minimum for a B+ closer to 330-350V (will sound MUCH better than such a low plate voltage).

January 5th, 2011, 01:01 PM	#6 (permalink)
Tiarnan Tele-Meister Join Date: Feb 2010 Location: Ireland Age: 20 Posts: 104	Thanks guys was just wondering because I have a vibro champ circuit and that transformer. I think ill just stick with a 6v6 and order a weber transformer. Tiarnan

January 5th, 2011, 03:08 PM	#7 (permalink)
limbe Tele-Afflicted Join Date: Sep 2009 Location: Stockholm,Sweden Age: 61 Posts: 1,223	Most manuals list 300 v as max plate voltage for EL84 and 350v for 6V6.

January 5th, 2011, 04:29 PM	#8 (permalink)
laird Tele-Meister Join Date: Jul 2009 Location: Palm Harbor, FL Age: 32 Posts: 366 14 Photos	A 190-0-190 transformer will give you around 255v B+ (with a solid state rectifier). Although it's not the maximum voltage for an EL84 it's certainly sufficient to power it. Cathode bias should raise the cathode around 10v, leaving 245v for operation. Perfect - The EL84 data sheets have 250v listed as the example operating voltage. Lowering the voltage dropping resistors to 250-470 ohms on the first drop, 4.7k on the next should keep the preamp B+ near 200v. Another big improvement on the Champ is to add a filter stage before the OT gets its B+ - around 20uf and 50-100 ohms (2-3 watt). It'll cut the AC ripple hum down to practically nothing. I'm not sure how much the tremolo circuit would be affected by the lower B+. It might be fine, it might not work at all! I'll let someone else answer that one. :) -Laird

January 5th, 2011, 05:20 PM	#9 (permalink)
Wally Doctor of Teleocity Join Date: Mar 2003 Location: Lubbock, TX Posts: 13,737	limbe, actually the 6V6 and the EL-84 have very simular voltage specs. In fact, a quick look at Duncan tube data site shows the 6BQ5 max voltage in AB1 exceeding the 6V6's specs. And....most guitar amp designs exceed these specs. I haven't seen very many guitar amps with plate voltage below 300V.....and both of these tubes have a max of 285 from what I have seen. Deluxe REverbs often run well over 400V on 6V6 plates. There are technical aspects that account for these tubes ability to tolerate this. Maybe someone will clue us in on this aspect. I simply know that these tubes will operate with palte voltages above their design limits.

January 5th, 2011, 06:37 PM	#10 (permalink)
printer2 Friend of Leo's Join Date: May 2010 Location: Canada Age: 52 Posts: 2,841	A big variable from what I have been reading is the screen voltage and power rather than the plate. The screen is more fragile and in between the cathode and plate so it makes sense it is more the limiting factor. Playing around with a 6AQ5 in a SE amp the last couple of days, it is the 7 pin smaller version of the 6V6. It has maximum ratings of 275v for the plate and screen. The data sheet give an example of 250v, was running the amp at that (cathode biased so actual voltage about 240) and am now running it with 300v supply. I have it biased for 43mA and it seems to not mind the voltage. It is just under the dissipation limit for the tube but there is no red plating so it seems fine. 6V6's or EL84's are a little beefier so they could take a little more.

January 10th, 2011, 09:37 PM	#13 (permalink)
xStonr Friend of Leo's Join Date: Jun 2005 Location: Lost in the Ozone....again Posts: 2,103 4 Photos	will a THD yellow jacket work with existing PT?

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