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Post subject: Strange noises from a late 70s ultralinear 135w Twin Reverb
Posted: Sat Jan 12, 2013 12:58 pm
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Howdy!

I got this amp in fall of 2011 off eBay; the previous owner claimed to have retubed it right before selling it, so as far as I know the tubes were pretty much out of the box. I didn't like how my SG sounded through it so it mostly sat in a closet for six months. I tried running my Stingray through it into a 4x10 bass cab on a whim and it sounded fantastic so I started using it for that in spring of 2012. Not too long after that the amp started to gurgle, especially when I'd play lower frequencies. I took it to a shop in summer 2012 and they retubed it again. It sounded fine for about six months and now the gurgle is creeping back in.

My questions are:

-- Should I expect more than a six-month lifespan out of the tubes in this kind of amp, or do the ultralinear Twin Reverbs tend to burn through tubes quickly?

-- Is a bass with an active pickup likely to be frying the preamp tubes, and is there a relatively inexpensive way I could replace them with something more durable without completely changing the amp's sound?

Any help/suggestions/insight will be highly appreciated. Thanks for reading!


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Post subject: Re: Strange noises from a late 70s ultralinear 135w Twin Rev
Posted: Sat Jan 12, 2013 9:11 pm
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10cat, I believe Arjay recommended Phillips 7581 power tubes for these amps. Don't see a problem if you use quality power tubes and phase inverter. Of course, you'll want to have healthy filter and bias caps, but your tech should have already addressed this issue. I don't see an inherent problem with the input section. I think the noise will have to be isolated to a particular section of the amp(diagnosed) before making any further investment. JMO, Art

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Post subject: Re: Strange noises from a late 70s ultralinear 135w Twin Rev
Posted: Sat Jan 12, 2013 10:36 pm
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No, it was BMW2002ti who recommended the Philips 7581, which are now as rare as Element 115 (aka "Unobtainium"). A good contemporary match for an STR415-type output tube is the new Tung-Sol re-issue 6L6GC-STR. I installed a quartet into my Bassman 135 and they're performing quite well.

However, I don't think the issue at hand is power tubes. Likely, it's the result of driving the amp with an active pickup system which is probably overloading the input stages. The amp was never designed for signals of that amplitude. A temporary solution might be to use the number 2 input (attenuated by 6dB).

Arjay

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Post subject: Re: Strange noises from a late 70s ultralinear 135w Twin Rev
Posted: Sun Jan 13, 2013 1:04 am
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10Cat, Did you reform the filter caps after buying the amp? Old filter caps sometimes start to fail and allow oddball harmonics on top of notes, a few months into heavy use (after sitting for awhile --- like months or years).

You may need new filter caps. FYI... to properly re-form caps:

http://www.angelfire.com/electronic/fun ... e_cap.html

If you want to go the 7581 route ($$$ route --- :lol: ). Use th 7581A. It's rated for much higher plate voltage and idle bias. If you have the money, this is way to go. This puppies last and are toneful --- if you get good ones.

As far as I know, only GE and Philips ECG/Sylvania made the 7581A. Sylvania made the first STR-415, for Mesa-Boogie. GE's Owensboro plant then came out with the Holy pink based 7581A, also meeting STR-415 specs. Both were also made to US mil spec qualifications.

http://www.ebay.com/sch/i.html?_trksid= ... &_from=R40


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Post subject: Re: Strange noises from a late 70s ultralinear 135w Twin Rev
Posted: Sun Jan 13, 2013 3:01 am
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10Cat wrote:

My questions are:

-- Should I expect more than a six-month lifespan out of the tubes in this kind of amp, or do the ultralinear Twin Reverbs tend to burn through tubes quickly?



Two retubing and 6 months after same problem.

Look retubing cure the problem ....for 6 months each time ?

Better to ask your tech why . It is not normal, is he qualified ? Which tubes he replace ? Probably output tubes ? You did not tell us. Put wrong ones ?
He could forget to do some check up on the amp or is not qualified ?


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Post subject: Re: Strange noises from a late 70s ultralinear 135w Twin Rev
Posted: Mon Jan 14, 2013 12:50 am
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stratele52 wrote:
10Cat wrote:

My questions are:

-- Should I expect more than a six-month lifespan out of the tubes in this kind of amp, or do the ultralinear Twin Reverbs tend to burn through tubes quickly?



Two retubing and 6 months after same problem.

Look retubing cure the problem ....for 6 months each time ?

Better to ask your tech why . It is not normal, is he qualified ? Which tubes he replace ? Probably output tubes ? You did not tell us. Put wrong ones ?
He could forget to do some check up on the amp or is not qualified ?


+1

There's a lot of information missing or sketchy at best. Unless the OP can provide it, this thread is at a standstill.

Arjay

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Post subject: Re: Strange noises from a late 70s ultralinear 135w Twin Rev
Posted: Mon Jan 14, 2013 5:35 pm
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Yeah Arjay, the input may be suspect. The Twin is looking for 100mv from the guitar, but the Stringray may be as high as 1volt. As far as I can see the use of the #2 input jack would help, to some degree. Ultimately, I'd go with a local feedback circuit with a sensitivity adjustment control after the first gain stage(via London Power Bass Preamp). Now, I'm not really up to speed with bass amps. But, I do know that our bass player switches between a P Bass and a 5-string active pup bass, without messing with his amp. The amp is somekind of solid state Acoustic. So I don,t know if this applies to the tube amp???? Beemer, neat link to the cap forming procedure!!! I'm gonna try the current trickle method the next time I mess with one of my amps. I have to look up that site, since I had this computer scrubbed and lost all past files. Art

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Post subject: Re: Strange noises from a late 70s ultralinear 135w Twin Rev
Posted: Mon Jan 14, 2013 7:30 pm
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aclempoppi wrote:
Yeah Arjay, the input may be suspect. The Twin is looking for 100mv from the guitar, but the Stringray may be as high as 1volt.


The hottest passive pickup I've ever seen was the bass humbucker that Gibson used on their EB0 and EB3L models. "Back in the day" we measured one at close to 750 millivolts. And those Gibson basses would tear the livin' crap out of a Fender amp (think the fuzzed-out vibe of Jack Bruce and Felix Pappalardi).

Arjay

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