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Post subject: Tube replacement
Posted: Sat Jul 11, 2015 10:36 am
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I'm thinking of replacing the tubes in my Twin Reverb. It currently has some old 6L6GC tubes, one Sylvania, one GE, and two RadioShack tubes. I'm thinking of buying the Groove Tubes matched quads. They have lower power ones for cheap and higher power ones for more money. I don't know tubes much so I don't know which is closer to stock. Other than NOS or good tested originals, what should I look for to compare to original specs for new tubes? Also, should I have the amp biased, if possible? Thanks.


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Post subject: Re: Tube replacement
Posted: Sat Jul 11, 2015 4:01 pm
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Bias is always a must with other ( new ) output tubes.


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Post subject: Re: Tube replacement
Posted: Sat Jul 11, 2015 5:14 pm
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stratele52 wrote:
Bias is always a must with other ( new ) output tubes.


Absolutely.

It's the only method to ensure proper operation, tasty tone, and optimized tube life.

Bias too cold = sterile, clinical, brittle sound
Bias too hot = increased tube fatigue and decreased longevity
Bias way too hot = red-plating and possible catastrophic damage to tubes and other critical amp components

IMO the Electro-Harmonix 6L6EH is the most economical choice, a reasoned balance between tone and durability except for the late-model ultra-linear Twin Reverb (135-watt chassis). In that case, the Tung-Sol STR is recommended.

Arjay

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Post subject: Re: Tube replacement
Posted: Sun Jul 12, 2015 1:09 am
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I agree what Tom Stewart of SpaceMan Music , Ottawa, said about bias :

Under-biased amps will lack punch and the tubes will run noticibly hotter.

Over-biased amps will sound thin and brittle, with the tube running too cool for proper performance.

A correctly-biased amps will sound clean and tight at moderate volume, then at higher volumes break up and distort musicaly."


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Post subject: Re: Tube replacement
Posted: Tue Jul 14, 2015 9:29 pm
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I'll need to take this amp in to have the tubes replaced as well as caps being looked at and power cord replaced. Thanks, I'll find the right tubes after talking with the tech.


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Post subject: Re: Tube replacement
Posted: Wed Jul 15, 2015 1:40 am
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See a qualified and honest one . So many are not qualified .

Ask him to put F & T filter caps ,not cheap one as so many do.


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Post subject: Re: Tube replacement
Posted: Wed Jul 15, 2015 2:01 am
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stratele52 wrote:
Ask him to put F & T filter caps ,not cheap one as so many do.


+1

F&T......the Cadillac of contemporary electrolytics.

Arjay

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Post subject: Re: Tube replacement
Posted: Tue Aug 18, 2015 9:47 pm
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I'm still a bit confused over the ratings for tubes. R1-R10, Low, Medium, High... I'm not too sure what to research. The local amp tech says he uses JJ tubes, which I'm sure will be fine but I like to know what is going on before stuff gets worked on. What would be a good stock replacement tube rating for this amp? Thanks.


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Post subject: Re: Tube replacement
Posted: Tue Aug 18, 2015 10:15 pm
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Codyyy wrote:
What would be a good stock replacement tube rating for this amp?


What version of a Twin Reverb do you have?

AB763 (or some derivative) or the ultra-linear variant (with the 135-watt chassis)?

Arjay

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Post subject: Re: Tube replacement
Posted: Wed Aug 19, 2015 6:48 am
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I have the AB763.


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Post subject: Re: Tube replacement
Posted: Wed Aug 19, 2015 7:03 am
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In that case I stand by my initial recommendation.

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: Tube replacement
Posted: Fri Aug 21, 2015 9:35 am
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These are just my own personal opinions, so please treat them as such.

If you actually have Radio Shack branded tubes in the amp, chances are the amp is gonna sound "better" regardless of whether you use JJ's or GT's, let alone whether the tubes are particularly hot or cold. That said, I suspect that most people base their tube choice mostly on the style of music they play...blues and jazz players for example may favor tubes that break up easily for a more vintage-like tone where as many country players want as much clean headroom as they can get. That said, if memory serves, the AB763 is a silverface twin, so depending on your own tastes, I would start by shooting for "middle of the road". With the "Groove Tube Rating System" for example, I'd probably lean towards a 5 or 6. If you need more clean headroom, go higher. If you prefer a bit of dirt, go lower.

As others have already said, DO make sure to have that amp properly biased! Considering the mish-mash of tubes that were in there, you'll want to have this done REGARDLESS of brand or rating systems. Likewise, as others have also suggested, make sure you have a qualified tech...setting the bias on most Fender amps isn't really that hard, but there's A LOT of folks around these days who honestly don't know the difference between a soldering iron and a screwdriver! Just because "Joe" at your local Guitar Center can change guitar strings does NOT mean he's actually a qualified service technician...ask other players in your area who they go to, then ask that place who THEY go to (a lot of smaller shops will send amps out to someone else).

BTW...I would also suggest checking the speakers as well. I've seen A LOT of Twins over the years where the original speakers have long since been replaced...and very often with really low quality speakers. I had a friend a few years back who forked out some $350 for new tubes and a recap and afterward, the amp still sounded like crap...the tech never bothered to inform him that the amp had an old pair of TV/stereo speakers bolted in. We plugged the amp into my 2 x12 cab and the difference was literally night and day. Very simply, if someone actually put Radio Shark tubes in it at one time, god only knows what else might have been done to that amp...once you choose a tech, have them go over the amp REALLY well and leave some room in your budget for any surprises he/she may find.


Hope this helps...good luck!


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Post subject: Re: Tube replacement
Posted: Fri Aug 21, 2015 4:33 pm
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lomitus wrote:
If you actually have Radio Shack branded tubes in the amp, chances are the amp is gonna sound "better" regardless of whether you use JJ's or GT's...


Lest you be unaware, Radio Shack's "Lifetime Guarantee" tubes were manufactured by Matsushita (nee Panasonic), using GE jigs and tooling. As such, they were considered to be more than adequate for most guitar and bass amps. Today of course, most of them have succumbed to age and "mileage" and are usually no longer serviceable. But back in the day, there was nothing wrong with them. I remember grabbing a few in a pinch from a Radio Shack that happened to be close to a venue I was playing. I've got a quartet of their 6L6GC's in my used-tube caddy that arrived in a Dual Showman head that I purchased some time ago -- one of them was DOA, one was measured by my TV-7A/U as "marginal" but the remaining pair were still showing 85% good.

Arjay

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