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Post subject: EC Vibro-Champ problem and bias question
Posted: Thu Jun 21, 2012 5:52 pm
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Hello everyone,

first, i just want to say i'm a musician/producer, not a gear tech.

My brand new EC Vibro-Champ has just died in the studio after a loooong session. I've had the amp for a couple of months and it worked great, until today. I suspect the 5Y3 tube is the problem, as it does not "light" up at all, and rattled when i took it out and shook it.

So i'll order some new tubes from tubestore.com, probably to replace them all to make the shipping costs worthwhile (TungSols and a JJ 5y3). Guess the time has come to try out my recently aquired bias kit!

My questions are:
Where is the bias control!!!
What should i bias the 6V6 and the 5Y3 at to start with?

Any pro tips and info will be much appreciated, thank you.

K.


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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Thu Jun 21, 2012 7:11 pm
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It's a single-ended amp. One power tube. There is no adjustable bias control.

Arjay

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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Thu Jun 21, 2012 7:18 pm
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I would use an NOS or good pull US made 5Y3GT. Chinese and Russian made ones are somewhat noted for shaking apart in combo guitar amps.

Arjay is correct. As long as the plate voltages haven't drifted more than 15-20% off and the cathode-tied resistor is within 10-20% tolerance (and its bypass cap is good)--- the 6V6GT will self-bias to a set idle range. This is typical of ALL Class "A," cathode-biased amps. SE or push-pull.

This is why you never need to re-bias most input/gain/EFX stage tubes. Even when swapping from an OEM 12AX7 to a 5751 or 12AT7 or whatever.

http://www.ebay.com/sch/i.html?_trksid= ... T&_sacat=0


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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Thu Jun 21, 2012 10:02 pm
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thanks for the info, didn't know single power tube amps didn t need biasing after changing tubes.


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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Jun 22, 2012 2:37 am
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Hi nordiquemusic

Sorry to jump in on your query but I was wondering if I could ask you a question on the vibro-champ amp?

I am looking at getting a vintage champ or vibro-champ but I also had my eye on one of the earlier 57 champ tweed reissue but the UK has none of these in the shops and ebay (From my searches anyway).

The Clapton range has since replaced these so I guess my question is how do you find the amp (Not including the problem you are experiencing)?

Is it worth the bucks and are lots of your recording artists using it?

Sorry again and thanks in advance.

Tom

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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Jun 22, 2012 8:15 am
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Hi Tom,

I love the amp.

I don't know how it compares to the previous 57 reissue, but this one accomplishes what I wanted, which is sounding great and breaking up at a manageable volume.

BassettsAllSorts wrote:
Hi nordiquemusic

The Clapton range has since replaced these so I guess my question is how do you find the amp (Not including the problem you are experiencing)?

Sorry again and thanks in advance.

Tom


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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Jun 22, 2012 8:40 am
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nordiquemusic wrote:
Hi Tom,

I love the amp.

I don't know how it compares to the previous 57 reissue, but this one accomplishes what I wanted, which is sounding great and breaking up at a manageable volume.

BassettsAllSorts wrote:
Hi nordiquemusic

The Clapton range has since replaced these so I guess my question is how do you find the amp (Not including the problem you are experiencing)?

Sorry again and thanks in advance.

Tom


Thanks very much that sounds like it will be up my alley.

I'm getting a replacement deluxe telecaster on Monday and there are a few vintage amps to try out but I might try out the champ if they have it and see how I get on.

Thanks again.

Tom

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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Jun 22, 2012 8:50 am
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It's a brand new $1000 amp. take it back to where you got it and have them diagnose and retube it. It should be under warranty.

More importantly, if there's a component issue, changing the tubes fixes the symptoms, not the problem.

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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Jun 22, 2012 10:24 am
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" if there's a component issue, changing the tubes fixes the symptoms, not the problem. "


Neo, absolutely 100% true, except the rectifier in most Fender amps. Since Fender tends to use very good PT's. If rectifiers fails, it's usually the rectifier. Only time I've seen rectifier go bad and not be the issue is when there is catastrophic failure in the filtering cap circuitry (like a short).

And this usually leads to all kinds of other failures in the amp. Since the OP states only rectifier failure, prolly this is a single issue problem.

FWIW in my experience, tube rectifiers are one of the most critical parts in any amp. Esp in combo amps. It pays to buy a good one. I've seen so many old amps with original or 40-50 year old replacement Mullard GZ34 or US made 5U4GB or 5Y3GT still working well in these amps, it's quite a testimony to the quality of these tubes.

" thanks for the info, didn't know single power tube amps didn t need biasing after changing tubes. "

ONLY in cathode biased amps. ALL fixed biased (like 99% of Fender push-pulls) need bias adjustment (despite the poor nom-de-plume of "fixed bias.")


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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Fri Jun 22, 2012 9:19 pm
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i bought it online.

i just bought new tubes, not just the rectifier.

so, to be sure, will the new 6v6 need rebiasing?


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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Sat Jun 23, 2012 2:41 am
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No sir! Cathode-biasing offers that luxury. A wide range of self-leveling even with various recitifiers and output tubes.


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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Sat Jun 23, 2012 8:30 am
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Can someone explain how this amp has the advertised "bias wiggle" tremolo? My thinking is that this type of tremolo typically only modulates the output tube bias, and only on a fixed-bias amp. How would you modulate the bias in a Cathode-biased amp, tremolo tied to output tube Cathode, or...?.

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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Sat Jun 23, 2012 8:40 am
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Well, if the circuit is like the AB764 VC, it doesn't "waggle" the bias. It waggles the 2nd half of the 12AX7 feeding the 6V6GT. Which make for a distinctly different tremolo/vibrato than the PR or DR (for instance).

I can't find an EC VC schemo, online to compare.

http://www.webphix.com/schematic%20heav ... _ab764.pdf


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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Sat Jun 23, 2012 9:23 am
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Yeah, that's the thing. There are various references to a Late '50s Champ, '57 Champ, and 5F1 circuit (no tremolo in any), but they also say that they used a "’50s-era output tube bias tremolo (which produced a more throbbing pulse than later Fender tremolo circuits)", as per EC request. The other EC amps could use the bias wiggle, but the VC? It must be a mistake, or they think that no one would know the difference, and they are just saying that. :?

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Post subject: Re: EC Vibro-Champ problem and bias question
Posted: Sat Jun 23, 2012 10:59 am
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shimmilou wrote:
Yeah, that's the thing. There are various references to a Late '50s Champ, '57 Champ, and 5F1 circuit (no tremolo in any), but they also say that they used a "’50s-era output tube bias tremolo (which produced a more throbbing pulse than later Fender tremolo circuits)", as per EC request. The other EC amps could use the bias wiggle, but the VC? It must be a mistake, or they think that no one would know the difference, and they are just saying that. :?


I can't find it right now (I'll search more later), but I would swear that I read that the EC Vibrochamp was fixed bias as opposed to cathode bias. I cannot think of any technical reason that a single ended or cathode biased amp couldn't be set up as fixed biased. As a matter of fact, Weber offers an option for their 5E3 clone to change from cathode biased to fixed bias.

https://taweber.powweb.com/store/5e3_schem.jpg

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