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Post subject: Champion 600 upgrade tone is bad
Posted: Sat Apr 08, 2017 9:00 am
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I upgraded my reissue champion 600 with a new grill cloth, a new speaker (Jensen Mod 6-15 4 ohm) and new tubes:

JJ 12AX7/ECC803S preamp
Tung Sol 6v6 GT poweramp

I am using a Les Paul bridge PU into the LOW input with the amp volume around 4-5.

It sounds fine when played clean, but if I hit it with a Blues driver in front, it sounds buzzy and raspy and generally offensive

Have I done something wrong, or are my expectations to high as to what this amp should sound like?


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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Sat Apr 08, 2017 9:09 am
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1- How does it sound with Blues Driver before mods ?

2- Put back the original tubes.

3- I'll check 6V6 bias


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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Sat Apr 08, 2017 10:42 am
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stratele52 wrote:
1- How does it sound with Blues Driver before mods ?

2- Put back the original tubes.

3- I'll check 6V6 bias

There is only one 6v6 power tube, how do you check the bias on that?


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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Sat Apr 08, 2017 11:28 am
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You must open the amp and read voltage at TP28 .
Fender adjust bias to 22 volts DC at TP28
Tube amp = lethal voltage.
IMO it is a very very hot bias

You did not answer of all my questions

A correctly biased amp will run efficiently and maximizes the life of your tubes.

Under - biased ( hot ) amps will lack of punch and tubes will run hotter , shorter tube's life .
Overbiased ( cold ) amps will sound thin and brittle. with tubes running too cool for proper performance .
A correctly biased amps will sound clean and tight a moderate volumes, than at higher volumes breakup and distort musically .


Last edited by stratele52 on Sat Apr 08, 2017 12:50 pm, edited 1 time in total.

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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Sat Apr 08, 2017 11:43 am
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stratele52 wrote:
Fender adjust bias to 22 volts DC at TP28


Twenty-two VOLTS?

Perhaps you meant twenty-two milliamps......?

Arjay

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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Sat Apr 08, 2017 12:49 pm
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Retroverbial wrote:
stratele52 wrote:
Fender adjust bias to 22 volts DC at TP28


Twenty-two VOLTS?

Perhaps you meant twenty-two milliamps......?
Arjay


No.

Schematic show 22 volts at the 470 ohms cathode resistor . B+ is 366 Volts DC
22 v /470 ohms = 46 ma for the original tube.


If I'm right ; for 6V6GT
Class A amp bias at 366 b+ = must be close to 34 ma
Class AB = close to 26 ma


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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Sat Apr 08, 2017 1:30 pm
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stratele52 wrote:
46 ma for the original tube.


That's the quickest way I know to a 6V6GTA barbecue.

Pass the coleslaw.

:lol:

Arjay

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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Sat Apr 08, 2017 3:32 pm
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Retroverbial wrote:
stratele52 wrote:
46 ma for the original tube.


That's the quickest way I know to a 6V6GTA barbecue.

Pass the coleslaw.

:lol:

:lol:

Arjay


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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Sat Apr 08, 2017 6:16 pm
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I think we went through this, with the red plating of early reissued Tungsol 6V6GT tubes. The BF and SF Champ and Princeton amps are setup to use US made 6V6GT. They run their tubes HOT. And that is much of where the tone comes from. I like the GTA and GTY mil spec tubes, for this reason.

If you try to lower the bias, by going to a 600 or 800-ohm range cathode resistor. And/or changing the G2G resistor from OEM 220k-ohm to say 180k or even 120k-ohm... the amp starts to sound sterile and lifeless.

Prolly the reason the Champion 600 RI initially came with the last iteration of 6V6GTA tubes.

Those crazy GTA and GTY will last forever, running at the 46-50mA idle bias. I like putting a 470 ohm, 2 or 3-watt metal oxide resistor on the screen grid (not stock in the Champ). Just to keep the screen voltage below the anode. Even under full blast situations.

As for new 6V6GT types in my opinion, there are none that match the long life of the original standard RCA gray glass 6V6GT. One comes close, the JJ 6V6S. But, its tone is nowhere near the US made ones. The JJ internal structure is similar to a 6L6. Tougher construction. But, sacrifice midrange tone.

I don't know how many old Champs and Princeton amps I've seen with original RCA tubes in them. All caked with dust and smoke grime. Yet, still play well.

:)


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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Sun Apr 09, 2017 8:31 am
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I fried the original 6v6 tube that was in my 600 Champion.

Repaired under warranty at the time, with a colder bias (..as I was told...) and replaced with an Russian Electro-Harmonics 6v6GT, and a new Sovtek 12ax7.

Sound was minimally different... More "harsh or brittle" maybe

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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Mon Apr 10, 2017 3:15 am
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BasementBob wrote:
I fried the original 6v6 tube that was in my 600 Champion.

Repaired under warranty at the time, with a colder bias (..as I was told...) and replaced with an Russian Electro-Harmonics 6v6GT, and a new Sovtek 12ax7.

Sound was minimally different... More "harsh or brittle" maybe



There are colder bias and ..colder bias. How much colder ?

Tube amps sound always good just before tubes blow out :lol:


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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Tue Apr 11, 2017 11:17 am
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Sorry it took me a while to get back to this thread.

I didn't have the Blues Driver before the mods, so I don't know how it sounded.

I put the original tubes back in and it didn't make much difference.

I do notice a slight burning smell around the power amp tube - is this normal?


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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Tue Apr 11, 2017 11:35 am
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bill0287 wrote:


I do notice a slight burning smell around the power amp tube - is this normal?


It is not normal
6V6 Power tubes may have finger grease on the glass and when hot it could smell, clean them.

If it smell after cleaning, it is not normal
Resitor burning ; return on warranty.


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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Tue Apr 11, 2017 6:01 pm
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Just pulled my amp apart to see what was done a few years back to satisfy my curiosity regarding the colder bias.

R10 (pin8) was upped to 980-ohm, and R26 (pin 4) was upped to 1000-ohm,
which gives 22 v /1000 ohm = 0.022 Amp = 22 mA

I don't have a multi-meter...so I am not checking the actual values...those are the resistor code values...so take it for what it is.

I don't play the amp much...but it sounds fine to me...and has been for going on 4-years. :D

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Post subject: Re: Champion 600 upgrade tone is bad
Posted: Tue Apr 11, 2017 9:38 pm
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Is this for a Champion 600 reissued amp? At 360VDC plate voltage, 22mA would only be 8 watts idle dissipation. This is not Class "A." IME, single ended amps like this do not sound too good, running in cold Class "A" or Class AB.

However, if this is a Princeton or Deluxe, 22mA would be fine.


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