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Topic: twin tube questions |
Cody Russell
From:
Arkansas, now in Denver
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Posted 20 Feb 2011 4:56 pm |
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I just bought a 77 twin and it only had 2 power tubes in it.I've heard different opinions on this but I'm wondering if I can just buy 2 new tubes to put in there or if I need to buy a matched set of 4? and also what kind of 6L6's sound good for steel in a twin? Thanks
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carter pro, 66 twin revrerb, steel king, tut taylor dobro, gibson rb 250 |
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Cliff Kane
From:
the late great golden state
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Posted 20 Feb 2011 5:18 pm
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| You should take it to an amp tech or someone who can check the tubes to get a match for the two tubes that are missing, or get a matched set of four tubes and have the bias set to where the amp sounds good to you. If you are getting a set of four tubes you could try KT88's or 6550's instead of 6L6's if you want more power for playing steel guitar. A Fender Twin Reverb is a great steel guitar amp. |
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James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 20 Feb 2011 7:32 pm
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6550 tubes are not drop in replacements for 6L6 tubes, with out some proper internal upgrades to handle 6550's.
_________________
"Good judgement comes from experience, and a lot of that comes from bad judgement"~old cowboy proverb.
shobud@windstream.net |
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Tony Prior
From:
Charlotte NC
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Posted 21 Feb 2011 3:29 am
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For the first few decades of Fender amps, aka Twins, matched tubes were not even invented yet. Sure, purists will tell you that your amp will be at tip top performance with matched tubes,..I say maybe...I have never used matched power tube sets in my Fender amps over the past 40 years. New tubes ? sure...I personally think it is a marketing scam that began with Groove Tubes. For the longest time Fender was using Sovtek 6L6's before Groove tubes got the gig..
Why doesn't the amp have 4 6L6's in it now ? Is there a problem ? Did you swap the positions to be sure the plates are not glowing red ?
here's a good TUBE read
http://www.audiotubes.com/6l6.htm
As stated, matched sets are typically within a 5% tolerance, I would hope that two tubes purchased UN matched are pretty close to that number as well and it is all relative to the amp DC supply and bias anyway . I think the tube hardness rating is more important than the matched set specs.
Twins require 6L6GC as they have a DC circuit exceeding +450...
great amp, enjoy it...
t
_________________
Emmons L-II , Fender Telecasters, B-Benders , Eastman Mandolin ,
Pro Tools 12 on WIN 7 !
jobless- but not homeless- now retired 9 years
CURRENT MUSIC TRACKS AT > https://tprior2241.wixsite.com/website |
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Cliff Kane
From:
the late great golden state
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Posted 21 Feb 2011 10:16 am
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| James Morehead wrote: |
| 6550 tubes are not drop in replacements for 6L6 tubes, with out some proper internal upgrades to handle 6550's. |
James, other than adjusting bias, what needs to be done? I thought they were interchangable with a rebias. I've been thinking of trying them in my '68 Twin.
Thanks,
Cliff |
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James Morehead
From:
Prague, Oklahoma, USA - R.I.P.
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Posted 21 Feb 2011 10:57 am
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Maybe Ken Fox will chime in. I'm not a tech, but rather an owner who enjoys this amp like you do. 
_________________
"Good judgement comes from experience, and a lot of that comes from bad judgement"~old cowboy proverb.
shobud@windstream.net |
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Blake Hawkins
From:
Florida
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Posted 21 Feb 2011 1:06 pm
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James is correct. The 6550 requires 6.3 volts at
1.6 Amperes for heater current.
The 6L6 GC requires 6.3 volts at .9 Amperes.
The higher current demand will cause the heater winding of the transformer to run much hotter than
normal. Perhaps causing a premature failure of that
expensive power transformer.
Also the increased load will cause a reduction in
the other voltages supplied by the transformer.
Total heater current draw for 4 6L6GC is 3.6 amps.
Total heater current draw for 4 6550 is 6.4 amps.
To do it correctly, you need to add an additional
transformer to just supply the heaters of the 6550.
There is also a difference in the load resistance
of the two tubes. Optmization would mean changing
the output transformer and perhaps some additional
power supply changes.
While the actual power output is dependent on circuit design and testing methods, here are some
numbers from the tube manual.
RCA says a pair of 6L6GCs will give 55 watts @ 1.8%
distortion.
Sylvanis says a pair of 6550s will give you 100 watts
@2.5% distortion.
That being said, there are people who have "dropped
them in" to the Fender amps. Perhaps some of those
players will chime in with their experience.
There is good engineering practice, then, there is
"what you can get away with."
James and Cliff, I owe you both an apology, I got the names mixed up at the beginning. I've now corrected that.
Blake
Last edited by Blake Hawkins on 21 Feb 2011 8:47 pm; edited 1 time in total |
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Ken Fox
From:
Nashville GA USA
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Posted 21 Feb 2011 3:45 pm
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| Well put! |
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Cliff Kane
From:
the late great golden state
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Posted 21 Feb 2011 4:11 pm
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Blake,
thanks very much for that info. It sounds scary. I like the way my amp sounds with its old low output transformer. I wouldn't want to change it and I certainly wouldn't want to push it to failure.
Thanks,
Cliff |
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