Conference napalm::guitar

My guess would be the the resistor tied between the Cathodes and
ground.  This resistor value provides the proper grid bias to make
the tubes operate in the in the correct parametric range. If the
tubes are biased wrong you may get distortion, reduced power, or
reduced life.  Any radio and tv guy could do this for you once you
explain what you want to do.

The only other part I would suspect might be the output transformer
(I doubt that's an issue, there pretty crude and robust). 

Frank (tubes! yuk!)


 

    Thanks Frank,
    	That seems to sound remotely familiar.
    
    		joe (simple technology for a simple mind)

	Kt66's?


	How about El 34's or Kt88's which are english amp type tubes,
the kt88's are used in the 200 watt marshalls. If kt 66's are the english
equivalent of a 6l6 I'm sure some one can crossreference it to a possible
replacement.

	If you make these type of changes to other power tubes you do
need to change the before mentioned resistors and your impedance matching
(output) transformer. You will also be taxing the power supply more and
might find you will need to beef up the supply. Longterm effects on wear
and tear could be castrophic.(like expensive replacement transformers and
excessive labor/repair bills) It's really what tradeoff's you want to make.


						Rick


						

                                                   
	I looked up a Kt66 for a cross reference last night and found that the
tube is an English version of a 5881 which was originally a miltary tube. 
	Fender replaced the 5881 with a 6L6 due to availability,so a Kt66
will be very hard to find and really is an older style 6L6. If you want that
older funky sound you might try a Groove Tube 5881.
						
							Good Luck,

								Rick

    Thanks, all:
    	Your tips are really appreciated.  I think I'm going to play
    it safe and just go for a pair of good quality, matched 6L6s.
    						joe
    

    5881s are way cool substitutes for 6L6s.  You can still get them
    too, without paying the inflated Groove Tube prices.  The 5881s
    I've seen are slightly smaller than your average 6L6.  They've got
    a nice sweet sound and they break up smooth and early.

    /rick

    Thanks rick,
    	How about other changes, like those suggested for KT66s?  I
    Don't want to wind up having to do any expensive mods/repairs on
    my amp (if I could afford that I'd just buy a Marshal).
    					joe
    

    Aren't the EL34s essentially the English equivalent of the 6L6?
    Do these two tubes produce a substantially different sound?  I have
    a Hiwatt with the EL34s (it's been broken for awhile, so I don't
    really remember how it sounds...).
    
    Thanks,
    Greg

    5881s are direct replacements for 6L6, so you don't have to make
    any modifications to install them in your Bandmaster.  Adjusting
    the bias is recommended, but this is always true whenever you replace
    power tubes, even when using the exact same type.

    EL34s are supposed to be similar to 6L6s; I've heard they have a
    "softer" sound, maybe similar to 5881s.  You cannot replace 6L6s
    with EL34s without doing some modification, as there are slight
    differences in the pinout and bias requirements.  I have a copy
    of a procedure for modifying Fender amps to use EL34s (from the
    "Groove Tubes" book) if anyone's interested.

    /rick

	El 34's can be put in a Fender amp which has 6l6's for power tubes
fairly easily. The work involves taking out a resistor which is soldered
directly to the power tube sockets and inserting another one. And disconnect-
ing another and running a wire and rebiasing the tubes. It doesn't increase 
volume or output of the amp,but will change tonality. Any competant knowledge-
able repair person which does modifications should be able to do this in an 
hour or two. Whether or not it will give you the sound you want is up to you.
	In my spare time I've been playing around with this stuff,but it's
time consuming as opposed to doing music unfortunately. 

	Kt 66's are the English equivalent of a 6L6 and 5881 and my opinion is
that they all have there own tonal characteristics as does the sound of a Fender
Marshall,Hiwatt,and old Marshall amp's.

	The Groove Tube book that is mentioned has some good modification info
in it.

							       	Rick

	So I tried the 6L6 to El34 conversion last night in my spare
Fender and found that it seemed to increased power.(or my 6l6's were beat?)
	Since it was kinda of late I really didn't care to wake up the neigh-
borhood and will give it the acid test on Wednesday night. I did not notice
a significant change in tonality of the amp. I also didn't notice that it 
sounded similiar to my marshall(which I sold :^( ! ) This could change dras-
tically with the right volume. 
	The acid test/road test was defined by WJB as: 

			"Vol 10 treble 10 middle 10 bass 10" 

	I guess my next step is to beef up the power supply. Btw I installed
a bias pot so I could adjust the power tube bias from the -45v to -20 if needed.


							We'll see...

								Rick

                                                                          

    see note 396.18
    
    might help...
    
    Paul

    Hi gang!
    	I visited my old friend Harvey (come on Fred, let me Hot Rod your
    amp) over the weekend. As hard as it was to keep the screwdriver out
    of his hand, I talked him into letting me try some new power tubes in
    my reissue VibroVerb (actually it's Andy Fraser's old amp). I left the
    (what looked to be) original Chinese 6L6's to get a baseline on the
    volume and tone. We plugged in some older (but hardly used) Sylvania's
    and they brought up the headroom alittle, and the tone stayed about the
    same. We then plugged in a pair of those new RUBY tubes we've heard
    great things about in the music rags. We were both very disappointed
    in the sound. The headroom increased (clipping seemed to start around
    a vol. of 5.5), BUT lost most of the midrange tones. The RUBY's were 
    brighter and harder sounding...  basically sounded terrible. We both 
    started scratching our heads in disbelief...  then I asked Harvey if 
    he had any new Sovtek 5881's around. He had a few new tubes in a box, 
    so we plugged two in. WOW! Alot better!!!! The Sovtek 5881's had a 
    much FATTER sound than any of the tubes we tried. The amp started 
    clipping at a volume of 5.5 (compared to a volume of 4.5 using the 
    original tubes.
    	I thought that the amp sounded good with the original Chinese
    6l6's, but this amp sounds REALLY cool with the 5881's in it!
    
    			One very happy camper!
    
    	Rock on,
    		 Fred (who thought he should have chosen 5881's from
    		       the beginning).