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Post subject: 65 fender twin replacing 6l6 tubes
Posted: Mon Jul 06, 2015 1:59 am
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I have a fender 65 twin reverb reissue. I need to replace the output tubes (one is defective). The tubes are svetlana 6l6gc tubes and I was thinking of buying some jj 6l6 tubes. Do I have to rebias when swapping them out? I have no idea how to do that so I guess I'd have to take it to an amp tech.
What if I get the svetlana 6l6gc's (the ones pictured on the internet look different to mine... mine are red and the ones I've seen are black)?


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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Mon Jul 06, 2015 2:53 am
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Output tubes should be matched for balanced trans-conductance then biased for optimum tone and maximum service life. If you are not familiar with fundamental electronics or comfortable working around high-voltage (470 VDC) circuits, tube replacement is a task best left to a trained professional. Theoretically, it might be possible to locate a match for your three surviving Svetlana bottles but that's a problematic exercise that will likely end in frustration.

Arjay

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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Mon Jul 06, 2015 3:17 am
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Bias is a must if you want the best tone and save your tubes .

Matched quartet ; since few years I never bought matched set and they are always matched when received .

Up to 10 milliamp unmatched is more musical than perfected matched.
-Gerald Weber books


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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Mon Jul 06, 2015 4:45 am
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Not a fan of svetlana 6l6GC tubes. Put a quad in my 65 twin reverb and they just sound waay flat and lifeless.
Tons of other 6L6GC's to choose from.


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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Mon Jul 06, 2015 5:05 am
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cool thanks ill take to an amp tech.
also, I run my twin with two tubes and one speaker (to cut the volume). I assume running the twin like this doesn't put extra stress on the 2 tubes.


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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Mon Jul 06, 2015 9:44 am
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anth202 wrote:
also, I run my twin with two tubes and one speaker (to cut the volume). I assume running the twin like this doesn't put extra stress on the 2 tubes.


A number of people run their Twin Reverbs in this configuration but it's not something that I would ever recommend. The better option is to choose a less-powerful amp.

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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Mon Jul 06, 2015 8:03 pm
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yeah I get that. But I haven't found a less powerful fender amp that I like (tried deluxe and Princeton). The twin is the tone for me.

Also, there is a popping noise with the amp (hence why I thought it was a tube problem) but it goes away when you get to 3 and above on the volume knob...?


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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Tue Jul 07, 2015 1:50 am
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anth202 wrote:
y
Also, there is a popping noise with the amp (hence why I thought it was a tube problem) but it goes away when you get to 3 and above on the volume knob...?


Popping noise ;
Check tubes ( all )
Clean tubes socket pins and tensionning
Check solders in power


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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Tue Jul 07, 2015 2:14 am
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I would look for a marginal cathode bypass cap in one of the pre-amp stages. If the issue is limited only to the normal channel, check V1 and its surrounding components. If the problem occurs solely in the vibrato channel, that would be the circuitry associated with V2 through V5. If both channels exhibit the same symptom, take a look at V6. It may be a defective part but more likely, it's a poor solder joint that needs to be re-heated and re-flowed.

Arjay

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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Tue Jul 07, 2015 7:15 am
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the popping noise is only heard when running the twin with two tubes and one speaker (and only with a volume of below 3)? When everything is connected normally, there is no popping noise?


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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Tue Jul 07, 2015 9:53 am
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You have claimed that you now have a defective output tube and you want to purchase another set?.....I use the JJ's and they have been consistently performing well for me; But before you place any new tubes in your amp, perhaps you may ask yourself why a tube failed. Did it glow red prior to failure? Is the glass coated with a white powder inside? Did the tube glass crack, etc. That tube may have reached its life expectancy and failed or there may have been something else influencing the failure......the new tubes you put in may also find a shortened life unless you insure through inspection there are no other problems; The popping sounds you note can be from tubes, and many times from resistors, especially HT, load, or screen resistors. If you didn't re-bias after you removed half the tubes on your output, then you're probably running excessive current through the output tubes at quiescent - they will run much hotter....to the point of destruction when you push them. You might consider an another output xformer with tapped Z leads for an optional 4 or 8 ohm load that you could manually switch, in order to match the speaker load you're wanting to use; I suggest you see a professional amp tech and have them go over the amp.....that popping noise is not a volume pot cause and effect

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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Tue Jul 07, 2015 1:33 pm
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I like JJ tubes and I get lots of help and advice from Eurotubes which sells JJ's exclusively, he also posts video's of how to BIAS the power tubes on most popular amps.

http://www.eurotubes.com/store/pc/how%2 ... videos.htm

Disclaimer I have no business interests with Eurotubes I am simply pleased with the service and support I get from doing business with them......

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Post subject: Re: 65 fender twin replacing 6l6 tubes
Posted: Thu Jul 09, 2015 11:09 am
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[quote="anth202"]yeah I get that. But I haven't found a less powerful fender amp that I like (tried deluxe and Princeton). The twin is the tone for me.

Man I agree with that, My fav Amp is a Pro-Reverb. I also have a 212 Hot Rod Deville III that I really like, but those take a good 3 months time to get the speakers broken in


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