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 Post subject: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Sun Aug 18, 2013 8:22 am 
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Will swapping out the stock 6v6 tubes in my Excelsior with GT 6l6 tubes damage my amp in any way?


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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Sun Aug 18, 2013 8:29 am 
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I don't know if the Excelsior is fixed or cathode biased. In either case, a 6L6GC is going to require different idle bias settings which may not be possible to achieve in the Excelsior without modifications.

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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Sun Aug 18, 2013 11:39 am 
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Thanks for the reply - I'm pretty sure it's fixed bias.


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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Sun Aug 18, 2013 12:29 pm 
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The Excelsior is Cathode biased. Heater current draw is also a consideration. One 6L6 draws approx 1 amp for the heater, and a 6V6 about .6 amp for the heater. So, if you try a pair of 6L6 in an amp designed for 6V6, you will be using approx .8 amp more current from the PT. Try them at your own risk, the PT might be able to handle the extra current, or it might not.

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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Sun Aug 18, 2013 1:44 pm 
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shimmilou wrote:
The Excelsior is Cathode biased. Heater current draw is also a consideration. One 6L6 draws approx 1 amp for the heater, and a 6V6 about .6 amp for the heater. So, if you try a pair of 6L6 in an amp designed for 6V6, you will be using approx .8 amp more current from the PT. Try them at your own risk, the PT might be able to handle the extra current, or it might not.


In which case the cathode resistor may require changing in order to properly bias the 6L6GCs.

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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Sun Aug 18, 2013 11:58 pm 
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If you are looking for a "bigger" tone --- albeit with a more scooped out midrange than the standard 6V6GT --- may want to try the JJ 6V6S. It'll be pull-&-play in your amp.


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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Mon Aug 19, 2013 12:01 am 
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BMW2002Ti wrote:
If you are looking for a "bigger" tone --- albeit with a more scooped out midrange than the standard 6V6GT --- may want to try the JJ 6V6S. It'll be pull-&-play in your amp.


+1

And a far safer procedure than whistling past the grave yard by subbing in a pair of 6L6's.

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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Tue Aug 20, 2013 4:43 pm 
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I put the JJ6v6s in mine just because I had some around. I was very happy with the result. That and adding the tone knob made it really nice sounding.


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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Tue Aug 20, 2013 8:18 pm 
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emailed GrooveTubes tech support and received this reply:

"Thanks for your inquiry. You should contact a qualified tech before you replace 6V6 tubes with 6L6 tubes. You could damage your power transformer. The amp may need some modifications for it to work properly. You would definitely need to get the bias set for the new tubes.

Hope this helps,
-GT"


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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Tue Aug 20, 2013 8:22 pm 
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And finally, forwarded the GT email to my local music store, who replied:

"Although a 6V6 and 6L6 will replace each other and work, the amp would need to be re-biased and in the case of the Excelsior it is a fixed bias and cannot be adjusted. I suppose it is something they did with that one to keep that vintage, pawnshop sort of vibe. So with some amps no problem but shouldn’t be done with this one."

The manager offered to swap back the 6l6s I had bought for a set of 6v6s - and threw in a set of strings to make up for the confusion.

So it's been another educational trip for me. I appreciate all the feedback - I should note there is a lot of valuable info on the GT website.

thanks, guys!


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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Tue Aug 20, 2013 8:56 pm 
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lvaughan wrote:
emailed GrooveTubes tech support and received this reply:

"Thanks for your inquiry. You should contact a qualified tech before you replace 6V6 tubes with 6L6 tubes. You could damage your power transformer. The amp may need some modifications for it to work properly. You would definitely need to get the bias set for the new tubes.

Hope this helps,
-GT"


lvaughan wrote:
And finally, forwarded the GT email to my local music store, who replied:

"Although a 6V6 and 6L6 will replace each other and work, the amp would need to be re-biased and in the case of the Excelsior it is a fixed bias and cannot be adjusted. I suppose it is something they did with that one to keep that vintage, pawnshop sort of vibe. So with some amps no problem but shouldn’t be done with this one."

The manager offered to swap back the 6l6s I had bought for a set of 6v6s - and threw in a set of strings to make up for the confusion.

So it's been another educational trip for me. I appreciate all the feedback - I should note there is a lot of valuable info on the GT website.

thanks, guys!


Isn't that what we all told you?

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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Tue Aug 20, 2013 9:17 pm 
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Yes, more or less - So fixed bias is different than cathode bias? I wasn't clear on that point.


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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Tue Aug 20, 2013 9:19 pm 
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Yeah, except for the part about the Excelsior being "fixed bias and can not be adjusted", it's not fixed bias, it's Cathode biased, and you could certainly adjust it (as bluesky636 pointed out), although it would be unusual to do so.

Fixed bias means that a negative voltage is applied to the tube control grid through a series of resistors, while the Cathode of the tube is connected to ground. Fixed bias amps require a bias adjust when changing output tubes. Some fixed bias amps have an adjustment pot, and some have a resistor that would have to be changed to adjust the bias.

Cathode biased means that ground is connected to the tube control grid through a series of resistors, while the Cathode of the tube has a parallel resistor and capacitor, connected in series between the Cathode and ground. Cathode biased amps are known as plug-and-play, since typically no bias adjustment is necessary when changing output tubes. However, changing from 6V6 to 6L6, or vice-versa, is not a typical tube swap.

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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Sat Aug 30, 2014 7:57 am 
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The Excelsior is cathode biassed! Fixed bias does not mean the bias can't be adjusted, it means the bias is set by applying some (fixed!) Voltage on the control grid. The older blackface Fender amps had a fixed bias circuit with adjustable bias. Later they switched to fixed bias that was not adjustable but had a "balance" control so they didn't have to use matched output tubes.

Now to your question. First of all, the tubes themselves will not draw any more current from the power transformer as resistor that is connected to the tube of the cathode to ground determines the amount of current. Bear in mind that if you put a 6L6 in a 6V6 cathode biassed socket, it's running on the same current, probably around 25 - 30 mA including grid current. This is relative cold for a 6L6 but they will last a lifetime!

6V6's will draw around 0.45A heater current, 6L6's will the draw double (0.9) Amps. For two tubes, that's 0.9A more. Power tubes will draw 1.8A instead of 0.9A. The two 12AX7's will draw around 300 mA each. Total filament current wil be around 2.4A instead of 1.5A. As the transformer transforms high AC Voltage to lower AC Voltage, the secundary 6.3 filament Voltage side of the trannie will have (much) less windings than the primary (110VAC or 240VAC) side. Mostly, these windings are made of relatively thick wire that can handle at least 2A easily.

The dimensions of the Excelsior's power transformer are similar to the Hammond 290AX series but the package of iron lamelles is thicker, about 1.6" instead of 1.25. The 290AX can handle 2A @ 6.3VAC. Bear in mind many manufacturers keep their specs within a marigin of around 10% so the smaller 290AX should probably be OK with 2.2A draw. Giving the fact that Excelsior's power transformer is thicker than the Hammond 290AX series, I reckon (this is my personal opinion and not an advise!!) the 2.4A draw heat current won't be that mucht of a problem.

So yeah, I've got Russian 5881's (6L6GB's) in my Excelsior for some time and it's holding up FINE. Power transformer does not get hot (just warm), no indication of overloading by excessive current draw whatsoever. If you would bias the 6L6's to their specifications by replacing the cathode resistors on the powertube sockets to half their values, it would stress the power transformer (it would require thicker wire on the B+ winding). One more pitfall: the output impedance of the 6L6's is lower. Yes, when biassed to 6L6 specs, they would draw more current so would require an output transformer with lower input impedance. But while the 6L6's are running on relatively low current, the mismatch is very little and the 6V6 output trannie will be fine.

6L6's will give you a little more "oomphfff..", slightly fuller tone and because they're drawing relative low current, they will last a lifetime. When you push the 6V6's (as I do), they burn like candles. That was my main consideration to swap the 6V6's to 6L6's.

Again: I do not advise anyone to swap their 6V6's to 6L6's. I'm just stating that I did, and tried to explain why I think it shouldn't be that much of a problem in this particular case with this particular (cathode biassed!) amp.


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 Post subject: Re: Replacing 6v6 in Excelsior with 6l6?
PostPosted: Sat Aug 30, 2014 4:50 pm 
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Good job of summarizing what we've already posted. And, you're only a year late. :lol:

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