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Post subject: Re: brand new Champion 600
Posted: Sat Oct 08, 2011 12:48 pm
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BMW2002Ti wrote:
Actually, looking at the schemo. The 470-ohm/22mfd bypass cap combo in the Champion 600 RI is around the same as the combo used in the original BF and SF Champs. Both have 220k-ohm grid to ground resistors---so the idle bias is probably close, as long as the plate voltages are about the same (my bet is the older Champs have higher plate voltages).

And the RI has grid stopper (1.5k-ohms) and screen resistor (470-ohms) that the original Champ did not.

So, what that may mean is the TUBE is the difference. A lot of today's 6V6GT just can't handle being dimed or "12" for great lengths of time. Like the older NOS RCA or Sylvania. I've had four TungSol 6V6GT RI runaway, at idle. If you are having issues, you may want to opt for TAD 6V6GT-STR or NOS 6V6GT's.

Champion 600 RI:

http://support.fender.com/schematics/gu ... ematic.pdf

BF Champ:

http://www.webphix.com/schematic%20heav ... _schem.pdf


Looks like the AA764 you posted has a plate voltage of 350 VDC. This one from Ampwares shows 342 VDC.

http://ampwares.com/schematics/champ_vibro_aa764.pdf

The Champ 600 RI looks to be in the 360 - 366 VDC range.

I believe the Specialty Guitars mod uses a JJ 6V6S which can handle the higher plate voltage and higher bias. Rebiasing with that tube may not be necessary from a tube life standpoint, but it may be useful from a tone standpoint.

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Post subject: Re: brand new Champion 600
Posted: Sat Oct 08, 2011 1:15 pm
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bluesky636 wrote:
nopedal wrote:
So what are you trying to sell me?


No ones trying to sell you jack. I posted a link to something that Champ 600 RI owner's might be interested in. You came in accusing me of of claiming it was a "good mod" when I said no such thing. You didn't like it? Fine. I really don't care. I'm glad that you have been lucky enough in the last two years with your amps. I hope your luck holds out.



Damn! I am really needing some jack.

You presented a mod that I installed and found usless. Then I stated I don't think it's a good mod so you said something about common knowlege that I must be lacking. Then someone warned me that my amps were going to melt down. I guess I shouldn't warn about things that sponser this site. I didn't mean to offend you I was just trying to save some grief.


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Post subject: Re: brand new Champion 600
Posted: Sat Oct 08, 2011 1:32 pm
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nopedal wrote:
It is true that I have no degree in electronics or tube amps. It is also true that I don't have any meltdowns ia any of my Fender set biased amps for the 2 years that I have used them and I can't ignore that irreutable fact.

So what are you trying to sell me?


I'm not selling you jack-fooking-chit, pal.

Two years, huh?

You come back here after ten or twelve years and let us all know how your MLSB's are faring. The odds are, they'll all hit your local landfill around 2016 and you'll be crying the blues about some other POFS wunderamp you own whose theory of operation and practical aspects of usage you're also clueless about.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: brand new Champion 600
Posted: Sat Oct 08, 2011 1:42 pm
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Retroverbial wrote:
nopedal wrote:
It is true that I have no degree in electronics or tube amps. It is also true that I don't have any meltdowns ia any of my Fender set biased amps for the 2 years that I have used them and I can't ignore that irreutable fact.

So what are you trying to sell me?


I'm not selling you jack-fooking-chit, pal.

Two years, huh?

You come back here after ten or twelve years and let us all know how your MLSB's are faring. The odds are, they'll all hit your local landfill around 2016 and you'll be crying the blues about some other POFS wunderamp you own whose theory of operation and practical aspects of usage you're also clueless about.

Arjay



So what. You pitch a lot of woe. Do I know you? You got something against me?


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Post subject: Re: brand new Champion 600
Posted: Sat Oct 08, 2011 2:45 pm
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nopedal wrote:
So what. You pitch a lot of woe. Do I know you? You got something against me?


Lest you've forgotten......

nopedal wrote:
I genuinley loath vintage tube amps. I can't bring myself to even give them a chance. CBS really did a number on Fender.


After you've played a couple of thousand professional gigs and owned a hundred amps over four or five decades of a productive musical career, maybe somebody will actually take what you have to say seriously.

Maybe.

You want forum "congeniality", try Harmony Central.

I "pitch" nothing but the truth, pal.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: brand new Champion 600
Posted: Sat Oct 08, 2011 3:07 pm
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Retroverbial wrote:
nopedal wrote:
So what. You pitch a lot of woe. Do I know you? You got something against me?


Lest you've forgotten......

nopedal wrote:
I genuinley loath vintage tube amps. I can't bring myself to even give them a chance. CBS really did a number on Fender.


After you've played a couple of thousand professional gigs and owned a hundred amps over four or five decades of a productive musical career, maybe somebody will actually take what you have to say seriously.

Maybe.

You want forum "congeniality", try Harmony Central.

I "pitch" nothing but the truth, pal.

Arjay


Sorry I didn't mean to hurt your feelings.


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Post subject: Re: brand new Champion 600
Posted: Sat Oct 08, 2011 8:31 pm
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" The Champ 600 RI looks to be in the 360 - 366 VDC range. "

" I believe the Specialty Guitars mod uses a JJ 6V6S which can handle the higher plate voltage and higher bias. Rebiasing with that tube may not be necessary from a tube life standpoint, but it may be useful from a tone standpoint. "



Bluesky, 360 VDC is a lot for a single-ended, Class "A" 6V6GT amp. Remember, that tube is nearly "on" all the time. It doesn't benefit from a push-pull topology, where one tube is sitting at idle, half the time. I can't believe the suggestion that one site said to increase the cathode resistor to around 600-ohms (by adding resistors in series to the 470-ohm stock unit). That may drop the amp into Class AB1 mode. And it's going to sound not too good for an SE amp. Makes one wonder about the ears of that site's owner.

Class "A" amps push their tubes. So you need good ones. JJ 6V6S is really a 5881 gut in a taller bottle than the 6V6GT. So, I believe you when you say that it may last longer than whatever Fender put into the amp. The TAD 6V6GT-STR has done well in my Princeton. TAD really picks and tests Chinese made 6V6GT's to meet their specs. So, I believe that the tubes maybe a bit tougher and more reliable. Time will tell.

I haven't used the TAD in any of my Champs. I rely on NOS. The best luck I've had is the 1950's mil spec (JAN) gray glass 6V6GTY (brown, micanol base) tubes. They are tough as nails. And sound very good. You can still get some very good Canadian made JAN GE 6V6GTY's every now and then. Keep an eye on EBay.


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Post subject: Re: brand new Champion 600
Posted: Sat Oct 08, 2011 9:49 pm
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Location: Natural Bridge, Virginia
BMW2002Ti wrote:
" The Champ 600 RI looks to be in the 360 - 366 VDC range. "

" I believe the Specialty Guitars mod uses a JJ 6V6S which can handle the higher plate voltage and higher bias. Rebiasing with that tube may not be necessary from a tube life standpoint, but it may be useful from a tone standpoint. "



Bluesky, 360 VDC is a lot for a single-ended, Class "A" 6V6GT amp. Remember, that tube is nearly "on" all the time. It doesn't benefit from a push-pull topology, where one tube is sitting at idle, half the time. I can't believe the suggestion that one site said to increase the cathode resistor to around 600-ohms (by adding resistors in series to the 470-ohm stock unit). That may drop the amp into Class AB1 mode. And it's going to sound not too good for an SE amp. Makes one wonder about the ears of that site's owner.

Class "A" amps push their tubes. So you need good ones. JJ 6V6S is really a 5881 gut in a taller bottle than the 6V6GT. So, I believe you when you say that it may last longer than whatever Fender put into the amp. The TAD 6V6GT-STR has done well in my Princeton. TAD really picks and tests Chinese made 6V6GT's to meet their specs. So, I believe that the tubes maybe a bit tougher and more reliable. Time will tell.

I haven't used the TAD in any of my Champs. I rely on NOS. The best luck I've had is the 1950's mil spec (JAN) gray glass 6V6GTY (brown, micanol base) tubes. They are tough as nails. And sound very good. You can still get some very good Canadian made JAN GE 6V6GTY's every now and then. Keep an eye on EBay.


Correct me if I am wrong, but increasing the cathode resistor will decrease the cathode current, which may be desirable, right? I don't own a Champ 600 (though I have considered getting one for travel/vacation use), so I can't vouch for the validity of this mod. I was merely passing it on as an item of potential interest.

The JJ 6V6S is rated to handle a plate voltage up to 450 volts.

http://www.jj-electronic.com/pdf/6V6.pdf

Here is an interesting thread on TDPRI:

http://www.tdpri.com/forum/amp-central- ... meter.html

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Last edited by bluesky636 on Sun Oct 09, 2011 7:44 am, edited 1 time in total.

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Post subject: Re: brand new Champion 600
Posted: Sat Oct 08, 2011 10:49 pm
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Bluesky, Yes increasing the cathode resistor will lower the bias point. But, it may drop the operating point from Class "A"----which is what you want in most SE amps, to Class AB1 or Class B, which does not sound too good with single-ended amps.

Try this trick, which is easy. Try biasing a 12AX7 (which is biased Class "A" single-ended style) to Class AB1 by increasing the cathode resistor from say 1500 ohms to 3K-ohms and see what it sounds like. Or simply remove the bypass cap (25mfd/25VDC). And see what the amp sounds likes.


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Post subject: Re: brand new Champion 600
Posted: Sun Oct 09, 2011 8:10 am
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BMW2002Ti wrote:
Bluesky, Yes increasing the cathode resistor will lower the bias point. But, it may drop the operating point from Class "A"----which is what you want in most SE amps, to Class AB1 or Class B, which does not sound too good with single-ended amps.

Try this trick, which is easy. Try biasing a 12AX7 (which is biased Class "A" single-ended style) to Class AB1 by increasing the cathode resistor from say 1500 ohms to 3K-ohms and see what it sounds like. Or simply remove the bypass cap (25mfd/25VDC). And see what the amp sounds likes.


Since we have both used the word "may" in our posts, neither one of us obviously knows what the effect of increasing the cathode resistor in the Champ 600 will do. I'll take the view that Specialty Guitars did it and it worked, otherwise I hope that they would not recommend doing it. Maybe someone who has done it will see this thread and chime in.

Unfortunately, I don't have a circuit with a 12AX7 lying around that I can experiement on and I'm not really inclined to hack up my Blues Deluxe Reissue. :D

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Post subject: Re: brand new Champion 600
Posted: Sun Oct 09, 2011 9:50 am
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Blue... I've worked on quite a few single-ended amps. Not just VC or Champs. Some high-end Audio Note 300B and 2A3 amps. And you have to bias them so that they are in Class "A." For 6V6GT at around 350 VDC plate voltage---you need around 470-ohms with a 20mfd bypass cap to keep the tube in Class "A." This will give you the earlier & slower onset of OD and compression you want out of a SE-amp.

Now, dropping the bias will change the tone. And Class AB1 will not have that creamy onset of OD as Class "A." It would be better to drop the plate voltage and maybe alter the cathode resistance or bypass cap to keep the tube in Class "A"-- if the tube can't handle the 350-360 VDC volts. But, if you like this tone, it's ok.

Really, it's like biasing a push-pull into Class B to "save" the tube. The tone is going to be a lot different.

Class "A" is hot. By definition, the tube is "on" almost all of the time. No crossover. You need good power tubes to keep the amp happy. Altering the settings around the tube is not the answer. Unless, you know how to keep the tube in that mode.

I find the best way to keep a 6V6GT or EL84 happy is to use non-inductive cathode resistor (good wire-wound types), use a 1% precision resistor on the grid-to-ground. And 100+ VDC rated bypass caps. I usually put 470ohm screen and 1k-ohm grid stoppers on older Champs, to keep the amp from parasitic oscillations or other instabilities and destroying the power tube.

And I use mil spec or good NOS (read: RCA, GE, Raytheon, original Tungsol,or Sylvania) power tubes. They will last forever, under the worst abuse. 6V6GTY and Reflector (1970-80's vintage) 6pi14pi-EV (or -EB) or Tungsram for EL84 amps work well.

http://www.seielect.com/products/produc ... =wirewound


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Post subject: Re: brand new Champion 600
Posted: Sun Oct 09, 2011 10:43 am
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Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
BMW2002Ti wrote:
Blue... I've worked on quite a few single-ended amps. Not just VC or Champs. Some high-end Audio Note 300B and 2A3 amps. And you have to bias them so that they are in Class "A." For 6V6GT at around 350 VDC plate voltage---you need around 470-ohms with a 20mfd bypass cap to keep the tube in Class "A." This will give you the earlier & slower onset of OD and compression you want out of a SE-amp.

Now, dropping the bias will change the tone. And Class AB1 will not have that creamy onset of OD as Class "A." It would be better to drop the plate voltage and maybe alter the cathode resistance or bypass cap to keep the tube in Class "A"-- if the tube can't handle the 350-360 VDC volts. But, if you like this tone, it's ok.

Really, it's like biasing a push-pull into Class B to "save" the tube. The tone is going to be a lot different.

Class "A" is hot. By definition, the tube is "on" almost all of the time. No crossover. You need good power tubes to keep the amp happy. Altering the settings around the tube is not the answer. Unless, you know how to keep the tube in that mode.

I find the best way to keep a 6V6GT or EL84 happy is to use non-inductive cathode resistor (good wire-wound types), use a 1% precision resistor on the grid-to-ground. And 100+ VDC rated bypass caps. I usually put 470ohm screen and 1k-ohm grid stoppers on older Champs, to keep the amp from parasitic oscillations or other instabilities and destroying the power tube.

And I use mil spec or good NOS (read: RCA, GE, Raytheon, original Tungsol,or Sylvania) power tubes. They will last forever, under the worst abuse. 6V6GTY and Reflector (1970-80's vintage) 6pi14pi-EV (or -EB) or Tungsram for EL84 amps work well.

http://www.seielect.com/products/produc ... =wirewound


I'm not disagreeing with you, I'm just saying I don't know. Heck, I've been looking for a Reissue on E-Bay and if I find one at the right price I may snap it up and replace the 470 ohm cathode resistor with a 1K trim pot and play around with the settings. Certainly wouldn't hurt and the amp is cheap enough that if it does, its no great loss.

I agree that more important point is the fact that the Reissue appears to have a plate voltage 20 to 25 VDC great than the originals. I would assume that this is due to the use of a solid state vice a tube rectifier as well as the slightly higher modern day line voltages. As noted in the TDPRI thread I posted earlier, reducing the plate voltage instead of just playing with the cathode resistor would probably be the best way to get performance and tone similar to the older amps.

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