KT88 vs EL34 vs 6L6 Substitution In Vacuum Tube Amplifier.wmv

This video was inspired by a question I was asked about swapping KT88's in place of EL34/6CA7's. I have used a couple of amps in the video and made cathode current and power output measurements on three types of tubes -- 6L6GC, KT88 and EL34. This video is not meant to encourage anyone to swap the output tubes in their amplifier out for other types but in the case of musicians, I know they are always looking for a unique sound that they may be able to get through vacuum tube substitution. Remember also, swapping around the 12AX7, with a 12AU7 or 12AT7, etc. may also change the sound and no over current conditions are going to exist with these tubes. In rare cases I have seen instabilities introduced by substituting these tubes resulting in oscillations. In any case, I hope the video does provide some (safe) ideas on tube substitution and helps prevent destruction of equipment.

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Автор Alan Torrance ( назад)
At 1% distortion -- this is NOT good. The old Quad Amplifier (from UK)
using KT66's (mind you only 15 Watts max) had less than 0.1% total

The sound with 1% or more distortion must have been terrible. No good
whatsoever for classical music, but perfect for Pop, Metal, etc and other
modern "noise".

Автор Don Molenda ( назад)
soo?? this second amp has a B+ of around 350v when the 88s load it
down...in order to qualify 70ma each. i am looking to convert a marshall
superlead (34s) to 88s.. could you verify the needed change in splitter
resistors and screen resistors...?

Автор R. Weaver ( назад)
I too am contemplating a KT88/6550 tube change in a older marshall 1988 for
more clean headroom, none of the new amps have the tone i’m after and I
can’t afford a Dumble or Bludotone!

Автор GraffitiPhysical ( назад)
In a nutshell, you have to re bias your amp if you change the tubes. Some
amps have switching on the back, others the bias has to be manually done.
So, the rule of thumb is just use the recommended tubes. My experience is
the better the tubes the better your amp will sound. New tubes have to be
broken into, they will sound very clean. I was upset when I put new tubes
into my amp, it didn't have the same distortion and sounded too clean.
Well, a lot to be said about old tubes and good distortion.

Автор Christopher Rowe ( назад)
hit a power chord with each of'em.

Автор Giuseppe Loriga ( назад)
Can i Replace in a Marshall 1986 or 1987 the EL34 with the KT88-94 for More
clean Headroom ?
The Heater current of the KT88 is about the same of the EL34 ....I know i
have to lower the bias feed resistor from 220k to 100k to avoid tube
problems ..the question is : the transformer can handle the bias current
draw with the KT88... i have read that the tube should be biased like a
EL34...but if bias this way they should be biased too cold !!!!! Can i bias
at 60% with a plate voltage of 470v-480v without overheating the
transformer ?

Автор Greg Graham ( назад)
This seems to be a very informative video -- thank you for posting it!
In the spirit of improving things, I must say that I did find it difficult
to watch because of the head-mounted camera, and had to stop watching
part-way through. Perhaps a tripod would help, and as would arranging
your test equipment so that the DVM and scope are both near the amp can be
seen with minimal camera movement. Not trying to be mean-spirited, just a
suggestion for your consideration that might get you more viewers.

Автор Jacksonkellyfreak ( назад)
One of the more interesting videos I've seen in a long time. Excellent.

Автор koubou kankyu ( назад)
I like EL34

Автор erwin flores ( назад)
you just change your - voltage ex: KT88 or 6550 -55, KT77 or 6CA7 -38, KT66
or 6L6 -44.

Автор erwin flores ( назад)
fix bias amp

Автор József Horváth ( назад)

Автор AL theDoctorWho ( назад)
Those 6CA7s tubes are very dependable and they sound great I have a Quid
set in my plush amp we tinkered with they are GEs however so the tone is
there. EL34s were very unstable in the plush. I did put in a presence pot
in the circuit. so the amp sound like a fender on steroids a cross between
English & American. I like the math of it but I am not a tech. Thank you
for posting this video. c];-D

Автор Crobular I (1283 года назад)
I don`t know if you are using grid or cathode bias but check the
manufacturers tube spec. Also remember that with EL34`s (6CA7) you must
earth the screen pin (G3) seperately.

Автор Hector J (984 года назад)

Автор Mike Muratagic ( назад)
Thankyou soo much for your input on that, as that is one of the most common
questions people ask me when buying used amps is how can they make sure
they are getting what they are paying for, or if there is less output then
what the amp should be putting out.. In your experiences have you ever come
across amps that should put out more power, but for some reason don't? Or
are all manufacturers honost when they publish rms power output? (I know
the peak power output of some amps are a farce,) haha I've seen computer
speakers that say 1500watts pmpo output! hahaha... Maybe they are like
10watts at most probably less i'm guessing and yet no one does anything
about them putting those crazy numbers as far as i'm concerned they should
get sued for putting that crap.. - I've bookmarked you and subscribed, you
are very knowledgable in your field as I can see and your definately my new
mentor, please keep making your videos they are very informative. If you
wouldn't mind I would like to keep in contact and probe you for knowledge
now and then if thats okay with you..? I think i'm going to start with tube
amps, as their circuts seem so simplistic compared to solid state.
Always look forward to your reply. - Mike.

Автор Mike Muratagic ( назад)
question, when your figuring out the wattage output of an amp, i know you
use voltage squared divided by the ohms gives you the wattage, but when
your checking the voltage do you have to have to use a true rms meter, or
is there a way to do it with a regular multi meter?also, do you know of any
cheap devices that I can get to verify the actual output of an amp before
clipping? or do you basically have to have a osciloscope, frequency driver,
rms volt meter, resistive load(to emulate speaker), and distortion
analyzer? or can i not use an osciliscope and just get away using
a distortion analyzer?(somehow i have a feeling a dist analyzer is more
expensive then a scope)

sorry for my igrorance but i'm relatively new at electronics repair and am
trying to set myself up for working on tube/ss power amps. 

Автор vargasmongo3435 ( назад)
hello sir this video is really teaching a lot and it does help me a lot I
still reading and comprehending more about tube amplifiers, I have a
question if you don't mind, I still in the process of making a KT88 push
pull ultra linear hi fi amp "not for guitar" home use on the cathode of the
KT88 what resistor should I use 10R 3W is fine or should I get a 5W ? many
people have use 5W and 3W what is correct ?

the B+ will be around 460V DC from a Edcor transformer model XPWR247-120
330 - 0 - 330 you mention already "long time ago" that I should use 4.2K
output transformer one more question about output transformer, should I get
one that can go up to 100W or one that supply about 60W ? I was thinking
about the B+ and I'm not sure what transformer should I get because of the
460V DC B+ I'm a bit confuse to be honest


Автор Nikos Damigos ( назад)
Hi my friend thanks for your videos
i have one old 70's Sound City-50plus amp, with JJ EL34 power tubes
I want to make his headroom bigger and stop the break up with bigger
volumes (i have allready check my preamps and i find the right for me)
could i change them with KT 88. KT66 or other powertubes.
How this could change the sound with the KT88 or other set?.
Thanks a lot again

Автор orange70383 ( назад)
Tubes are great, there's honesty in them, you get what you get.

Автор Jyme Bale ( назад)
Yes, Tim, your question will work with a JTM 45, you can use a dozen
different tubes, you do have to change the bias resistor though.

Автор Tim Stanley ( назад)
Do you think this will work with any Kt88-6550 Amp? I have a 50 watt Ampeg
VL502 and I wanna try a set of 5881"s or Kt66"s. I cant get a good yes or
no from any one... the amp has the switch to run either EL34"s or KT88"s

Автор jamesterry51 ( назад)
thats what is guitar players love is the distortion on a tube amp when you
crank it

Автор Bernard Mahoney ( назад)
i had an 80 watt valve amc power amplifier using kt88 it was awesome a
great sound for the money .

Автор AeroKitsune ( назад)
So you could potentially run a pair of 6L6GC's with a pair of KT88's? Or am
I mistaken?

Автор Alexander Shibilski ( назад)
What is that piece of equipment that tells you the voltage and percentage
of distortion?
I've got a scope and would love something like that!!

Автор lukefenderrhodes ( назад)
hello boss on a line balance potentiometer i dont have a 27 ohm resistor
but i hve a thirty ohm resistor, how would that effect the line balance on
the plate, or could i take a twenty ohm and a 8 ohm put them in parrallel
together? thanks for listing to my nonsense

Автор Mark70609 ( назад)
Could you list the equipment you used?

Автор Tomii S Sonic ( назад)
This was a great video, articulated very well! Thank you!

Автор Bobby Dhal ( назад)
you are awesome !!!!!! thank you thank you 

Автор munja2111 ( назад)
Great video Sir! Please advise me, I have HiFi amplifier Cayin A55T which
have 4 KT88 in output in push pull configuration. Anode voltage B+ is about
400 V, Cathode is connected to 10 ohm resistor to GND. Bias is adjusted by
negative voltage on grid and can go from -70V to -10V. I biased KT88 of
about 45 mA (0.45 V across cathode resistor). Can I put EL34 valve in my
amp and rebias it to about 40mA cathode current (voltage on grid can go up
to -10 V)? Pin 1 and 8 are connected together in valve socket. I know that
I will lose some power but I love EL34 tube a lot. Thanks :)

Автор wqpeb ( назад)
Wonder what this MK III would actually sound like? 

Автор A Colin Flood ( назад)
shared on my Audio Tube Amp page on Facebook

Автор wreckoningday ( назад)
I have a Sunn TC-50 50/25 watts w 6L6's and it has a bias adjustment so
could I swap those w EL34's? Sorry if you already answered this roundabout
in ur video, I'm just learning about all this and find it fascinating.
Thanks for any help u can provide

Автор jpalberthoward9 ( назад)
You got that right. I sold my '66 Marshall plexi 50w years ago because if I
turned it up to where it sounded good, everybody in the world hated my
guts. These days, I use an old Tweed Fender Princeton and everybody's
happy, including me. That's it in the little picture to your left. It works

Автор ElPaso TubeAmps ( назад)
have a bias supply with enough range to be able to make the bias supply
negative enough to move from 6L6's to KT88's. 6L6's need bias something in
the -40 volt range whereas the KT88's need bias voltage in the -50 volt
range. I don't know about your Mesa Boogie Triple Rectifier - some Mesa
Boogie's don't have adjustable bias voltage - you will just have to
investigate the schematic carefully to determine if it will work and not

Автор ElPaso TubeAmps ( назад)
I can't remember the tube layout for every amp so I make mistakes. I have
done mods for clients whereas I have swapped out 6L6's for KT88 and the
client is happy just as you are. The potential problem is the 6L6's draw
0.9 amps each for the filaments and the KT88's draw 1.6 amps each so, most
likely the filament voltage is low and the power transformer filament
winding is overly stressed. It may last years or it may not. If it works
and you are happy with it then all is good. Not all amps (next)

Автор decadepast decadepast ( назад)
Yea but like I said I replaced the 6L6s in my Marshall JCM 900 with KT88s
years ago and it still play perfectly. Do you know anything about guitar
amplifiers? When I switched out the 6L6s with KT88s I had the amplifier
re-biased and the thing plays better now than it ever has before. I'm just
wondering If it is possible to do the same thing with a Mesa Boogie Triple

Автор ElPaso TubeAmps ( назад)
A pair of 6L6's is good for 50 watts and a pair of KT88's are good to 100
watts - that's just the way it is. You cannot put KT88/6550 in place of
6L6's - It will "work" but not very well and not very long. Hope this

Автор decadepast decadepast ( назад)
I use a Marshall JCM 900 with KT88s and it destroys my guitar player's Mesa
boogie triple rectifier which has 6L6s in it. We can't put KT88s inside the
Mesa so is there anyway that we can get the Mesa as powerful, clear and
have anywhere near the same headroom my Marshall has? Please help! 

Автор thescubacult ( назад)
I love this guy. 

Автор ElPaso TubeAmps ( назад)
For a RPN calculator it is 1 (enter) 1 (+) to get the display of 2

Автор ElPaso TubeAmps ( назад)
Is that where the stainless McIntosh (repos) are coming from? I haven't
seen them on Ebay yet but I have seen the "redone/rechassis" amps that look
great. If someone starts making repo Mc transformers I have serious
concerns that they will be the quality of a Mc transformer which is the
heart and soul of the Mc performance. Thank for bring this up.

Автор ElPaso TubeAmps ( назад)
That is correct about the 7027 - pin 1 is tied to pin 4 internally which is
the screen - which also means depending on how the socket is wired, if a
6550 with its metal ring is plugged into a 7027 socket you could end up
with screen voltage on the metal ring (because of pin 1). Also, pin 5 and 6
are tied together on the 7027 which means on the 6L6, etc group of tubes,
often times pin 6 is used as a tie point. Thanks for the post and bringing
this to light for all viewers.

Автор Lefty McStinky ( назад)
EL34 has a slightly different pinout because the suppressor is brought out.
This is little problem except that on units wired for 34s putting in 7027s
you will have fireworks if I remember right.

Автор Lefty McStinky ( назад)
Anyone with a reasonable IQ can learn electronics. The yuppies and
biggerdickers just don't want to. 

Автор Lefty McStinky ( назад)
KT120 is a bowdlerized version of the EL156 used in Neumann cutter head

Автор Lefty McStinky ( назад)
No one wants high power guitar amps anymore because everyone has caught on
to micing them. 

Автор Lefty McStinky ( назад)
The chassis rusted very easily so you would have had to store in inert dry
gas. Cosmetics are everything because the orientals set the market and they
are buying a totem. Someone is selling repro chassis complete with original
silkscreen and Mc refuses to do anything which will bite them in the ass
when repro xfmrs become available. 

Автор gbtayc ( назад)
What guitar are you rockin

Автор ElPaso TubeAmps ( назад)
I have only experienced the KT120 in some Dynaco spin-offs - can't remember
the brand - impressive tube, very healthy bottle. I think their cathode
current is a bit higher than the KT88 and KT90 so. some care should be
taken before switching them.

Автор ronnieparfait ( назад)
Great Video, you must be an O'l TV repair man with all the knowledge you
have, thanks for taking the time to educate some of the students of
electronics out there., and please keep up the good work, I myself is can't
thank you enough for the free teachings that I'm sure you had to pay for
through out life. Thanks again and people out there if you don't like the
video don't watch it,, it's that simple.

Автор Hayves Yong ( назад)
Have you try to use KT120 as well?? It seems like this tube relatively
quite new to market...

Автор ElPaso TubeAmps ( назад)
I have never personally had any KT77's but they are sold as replacements
for EL34. The KT66 is sold as a replacement for the 6L6. KT88's and 6550's
are interchangeable. All, of course, with attention to bias and plate
current when initially setup.

Автор Danyrd P. ( назад)
So you can use KT 77s instead of 6LS? KT77 would be fine for 6l6? This
video kicks ass. 

Автор Justin Franks ( назад)
+1 (or should it be 1+ ?) for using an RPN calculator :)

Автор littlegoobie ( назад)
today, all i can say is thank goodness i did not buy one because i i would
need to go buy cassette tapes in the clearance shops beside VHS/Beta tape
display, which is behind the film camera aisle, around the corner from the
wooden wagon wheels. I still like my vinyl but it's pretty much impossible
to find new stuff these days and besides that, the analog edge is gone now
that mastering is pretty much all digital so tapes and vinyl makes less
sense to me every day. I enjoyed the video.thanks

Автор littlegoobie ( назад)
20/20 hindsight. I can only hope my retirement funds start moving soon
because, according to their growth the past 2 years, i've been in some sort
of time stopping bubble where nothing gains value. I also remember
nakamichi dragon tape decks in the pawn shops and i was drooling all over
those too, given the choice, i could see myself getting that instead of the
power amps because i was looking at all kinds of amps. There was so much to
choose from compared to top shelf tape decks. 

Автор ElPaso TubeAmps ( назад)
I wish I had bought every Mac amp I saw even at retail price back in the
early 60's - the MC275 was $444.00 new - a NIB one now from that era would
be worth an easy $10K+ - better than the stock market. I love this stuff
and now that I am retired I get to play with it a lot - I don't have any
vids on mods - I have done mods for musicians around my area but it seems
many turn out disappointing as they don't get the sound they thought they
were going to get - good luck.

Автор littlegoobie ( назад)
jibber jabber volts amps jibber. I wish i had the background to understand
what you're doing. looks like really cool stuff. I used to see mcintosh
amps in pawn shops 25 yrs ago. I wish i grabbed a few when they were there.
Oh well. I got here while watching vids on adjusting/modifying tube guitar

Автор Rocknrollthor ( назад)
Brilliant video man! 

Автор Lawrence Hudlin ( назад)
God I wish I knew valve technology like you do. Fantastic video and

Автор ElPaso TubeAmps ( назад)
6L6's run at about 40 mA each (80 mA per pair) and it is customary to put
in a fuse at twice the normal current rating. KT88's are about 70 mA per
tube (140 mA per pair) so,l with that approach you would need 280 mA fuses
- It would be wise to stick with the 6L6's - there are many brands out
there, and 6L6's are about half price of KT88's. Hope this helps.

Автор Noillacspart ( назад)
Well my ENGL's 60 watt's per side and spec's say that each power amp tube
gives has a fuse of 160mAM, is that enough to power it? Will i have to look
at other 6L6GC's?

Автор ElPaso TubeAmps ( назад)
KT88's draw 1.6 amps per tube filament current to a 6L6 of only 0.9 amps
per tube so, that is one concern. The bias on the KT88 will need to be made
considerable more negative to reduce the cathode current to an acceptable
value. There is likely not enough adjustment in the bias pot to accomplish
this. You will need to change bias divider resistors and even then, you may
not be able to attain a proper negative voltage setting for your KT88's.
You may find more help in some of my other videos.

Автор Noillacspart ( назад)
Hi, i have an Engl 930/60 watt power amp and was looking into changing the
6L6's inside to KT88's. Will i be able to do this or will they have to be
biased for them to work?

Автор Anthony Brown (919 лет назад)
this is so cool. I am a worship pastor and I use tube amps with my electric
gutiars and I love how all this works. I hope to have the understanding and
some of the testing equipment you have someday. Glad that there are people
doing this kind of stuff still, no one my age seems to be (Im in my mid
20's). The only tube thing Ive built so far is a 12ax7 powered overdrive

Автор Doogie Lindsay ( назад)
Those EL34's are filament pigs too...

Автор ElPaso TubeAmps ( назад)
Thank you for your comments. There are may reasons we can't permamently
swap 6550's into a 6L6 amp and one of the most fundamental reasons we can't
is because of the filament current required for the 6550's. A pair of
6550's require 3.2 amps to light the filament whereas a pair of 6L6's only
require 1.8 amps. The filament winding on the power transformer will be
damaged over a period of time if it is overloaded by that amount.

Автор fiream773 ( назад)
I am brand new to the world of tube amps. I have a '55 AMi G-120 Jukebox
with a mono 6L6 amp that a knowledgble friend helped me rebuild. I've been
bugging him about modifying the amp to clean up the sound and improve the
headroom with 6550's. He's an excellent engineer, but not good at
explaining why I can't just drop in 6550's and make 1 billion gigawatts.
This video showed very clearly the pitfalls of tuning an amp "by ear". Best
15 minutes I've ever spent on YT. Thank you 4 posting!

Автор KyleCarrington ( назад)
Interesting. Makes perfect sense, really.

Автор pseudokowski ( назад)
Unfortunately it does, on most Audio Amps all the vibration is isolated
from the speakers unless it's a console unit.

Автор KyleCarrington ( назад)
Interesting point. Does that same ideology apply, then, to a combo -
wherein the tubes are in the same box, that the speakers rattle? 

Автор ElPaso TubeAmps ( назад)
I understand what you are saying but I came to realize that the creation of
music and the playback of music is two different worlds and the fact that
tubes are electro-mechanical devices and are affected by the vibrations of
the cabinets is what allows musicians to create the music we love. Then, we
try to playback at ultra-low distortion the music they created a 10% THD
and above. Holding the guitar in front of the speakers may create a
desirable tube related mechanical feedback that we like.

Автор pseudokowski ( назад)
It's all about the pre amp section, also I don't get why Guitar players
insist having the Amp head on top of the speaker stack. Man all the 12AX7's
will go microphonic so fast compared to a Audio system that isn't going
through a Earth Quake of vibration.. Kills me seeing nice OLD Tubes going
into Guitar Amps sitting on the stacks!

Автор Bob Hope ( назад)
Would you build a 6V6 6SL7 stereo amp with good power reserve and clean
output in return for a pair of diy 2-way audiophile speakers? You can
listen to my audio skills at youtube.com/watch?v=UaNeqOT95ck I have some
other speaker projects going too.

Автор ElPaso TubeAmps (1242 года назад)
I have noticed that the vintage amps deliver a lot of power with low
distortion and no clipping up to full power - example - Ampeg SVT. And I
agree with you on the Fenders (6L6) - usually run at a lower distortion
(overdrive) level and cleaner tone and the Marshall's (EL34) run at high
power and lots of overdrive/crunch (which is clipping at 10% THD or better)
They all have their purpose in making the music we love.

Автор Jonathan Justin ( назад)
i have come to realise most amps and most tones require the power section
to not clip. ie deriving their tone via the preamp section. the only tone i
can recall off hand would be like a marshall crunch a la acdc that would
benifit from a clipping power section. namley EL34s. for instance a fender
mostly needs the 6l6's to not distort. my engl savage 120 has only 2 kt88
tubes getting about 60 watts per tube or 120watt amp total. all the tone is
comming from the 6 12ax7 tubes

Автор BixLives32 ( назад)
EXCELLENT. Once again a sober, well researched test based on science,
repeatable measurement and not some air-head's "killer ears". All it takes
is some reading and LEARNING from text books. The ARRL handbook is a great
primer. The math is simple, but verbal hype from the guy at the bar or the
salesman at the snobby hi-fi shop will NOT teach you about this technology.
Most people hate having to learn even simple science. Lazy brains I

Автор BarchettaValveAmp ( назад)
Always use the tubes recommended for the correct voltage, bias, and primary
impedance of the output transformer. Period.

Автор ElPaso TubeAmps ( назад)
Speakers being connected is only important if you are driving the amp with
a signal. You can safely measure voltages with no speakers attached. High
voltage is a rattle snake so connect your leads before you plug it in to
the wall. Work with one hand in your pocket and never lean on the equipment
and don't use both hands when measuring high voltage as you want to avoid
any current flowing from arm to arm through your heart. Getting across the
plate voltage is a bad experience :-(

Автор ElPaso TubeAmps ( назад)
If you check plate voltage with no tubes the power supply will be operating
with no load and it will be abnormally high and not the voltage that will
be on the plates of the tubes when they are plugged in. The bias voltage
will not be affected with or without the tubes being in.

Автор marmuguk ( назад)
I am a beginner, this is likely based on a marshal major 200, modified at
some point with tag strip. possibly modified to drive four EL34/6CA7 as
hard as possible. I need to check the voltages delivered to the power
valves as safely as possible, if I run the amp to test the plate and bias
voltages without tubes installed I am guessing the main danger is the
capacitors. Is it safe to run the amp without power valves as long as I
connect a speaker? I have a variac and a digital multi meter. thanks

Автор ElPaso TubeAmps ( назад)
Pin 1 on the metal based 6550's is connected to the metal base and should
be grounded for safety. Pin 1 on EL34's is the third grid and must be
connected to ground or the cathode (pin 8). G2 at 1Kohm sounds like a
smaller tube than the 6550. G1 at 55Kohm is pretty high. Glowing hot EL34's
- not good - make sure the bias voltage is adjustable to at least -60 and
there is no AC ripple on it. My guess at a distance is bias supply issues.
Hope this helps.

Автор marmuguk ( назад)
Hi, a 1965/7 amplifier 4 octal and five 9 pins, I think it showed 800V on
the plates, blew a capacitor and stopped fiddling! I am guessing a KT88
amp. I have EL34's but they quickly glowed very orange! G2's go through 1
KOhm 5W resistors to the PT output, and G1's go through 55KOhm 1W resistors
to the preamp section. Kathodes are tied to pin1's (G3) could this be the
main cause of the orange glow along with 650V on g2 ? Is it safe to check
delivered voltage with no power tubes or speaker? cut@1 

Автор Dean ( назад)
oh, i missed the point. so it's 'safer' to run kt-88's if you are already
set up for el-34's? interesting.

Автор Dean ( назад)
the marshall jtm 45 head is basically the same as the fender bassman, which
is the original westinghouse design that fender bought the license to back
in the 1950's. marshall used the kt-88 in this amp for a time. all 3 tubes
have been used in various models of the same circuit. the typical marshall
tube today is assumed the el 34, but the kt-88 was in the marshall amp eric
clapton used way back. but best to have a pro set it up.

Автор Fionn Mac Cumhaill ( назад)
This is interesting. Nice Vid!

Автор ElPaso TubeAmps ( назад)
Best to tube it for what it was designed for. KT88 and EL34 draw about the
same amount of filament current (1.6A and 1.5A respectfully) 6L6 is only
0.9A so if you put the bigger tubes in a 6L6 amp, you will overload the
filament winding of your power transformer. 6L6 and EL34 are close in power
output. You can get a little more out of the EL34 as it can take 800 volts
on the plate, 500 max for the 6L6. KT88/6550 is twice the power tube of a

Автор ElPaso TubeAmps ( назад)
With correct cathode current of 40 mA on the 6L6 raised to 80-100 mA, I
would say less than an hour. I used to have a McIntosh MC240 that would
ruin 5881's within the day. 6L6GC would last years. If you look up the old
specs of tubes you will see that a 5881 has less plate dissipation than the
6L6GC - and plate dissipation matters very much. If you can measure cathode
current, just simply multiply that times plate voltage and you will get
idling plate dissipation. It will increase under drive.

Автор Dean ( назад)
what does 'not very long' equal???

Автор Dean ( назад)
ok, so all three tubes are pinned the same then? i'm no expert and i
suspected as much. but i don't want to blow anything up. 2 6l6's get around
35 watts, i take 'clean' because all class ab amps that are touted as 50
watts use two el34's or 6l6's. people tell me i need to tube my 50 w.
marshall head with kt 88's. will all i need is have the bias set? btw, i
suspect the bias adjust on my marshall head is NOT very wide at all

Автор ElPaso TubeAmps ( назад)
Yes, 420 - 450 is a healthy plate voltage for 6L6's although 490 or so is
not uncommon and I believe that is what the Dynaco and MA230 cloan is
running at in this video.

Автор JR ( назад)
how much voltage do these amps run on the plates? I'm guessing around

Автор ElPaso TubeAmps ( назад)
Yes, I have always heard that the 6L6 is a better bass amp tube than the
EL34. Not sure how to measure that. Again, got to think about it. Thanks
for your comments.

Автор ElPaso TubeAmps ( назад)
Fortunately my wife has stayed with me 35 years, so far. The first one
didn't though :-) As for 3 main types of distortion I assume you mean
amplitude, harmonic, and frequency? And the old amps often times specified
phase distortion. I will have to think about it and see if I can come up
with something real. Thanks for your comments.

Автор ElPaso TubeAmps ( назад)
I will have to think about this one. It will be a challenge. Some of my
first videos are comparing KT88/6550's from vintage to modern Chinese and
Russian in a Dynaco amp. You might find some of them interesting.

Автор BixLives32 ( назад)
The extra power sure helps with bass and transients. Frequencies below
200Hz use most of your current. You speaker is 8 Ohms @ 1000Hz (NOMINAL
impedance). At 80 Hz where the deep bass of the kick drum or string bass
resides, most speakers go down to 1-2 Ohms -or less! -That's where all that
great KT88 current goes! Now they even make a KT120. But if you get up to
that power range, Why not experiement with 811s or 572Bs (they're not
expensive) -You might like class A at 50 watts! 

Автор BixLives32 ( назад)
PS: I'd love to see a proper show-down of the 6L6 vs. EL 34 (for hi-fi
purposes). Do a sweep through all extreme freqs, IM, HD, clipping,
headroom, periodic harmonics, etc. E.g. do the 6L6s really have better
bass? Which valve has better transients? @ which freqs? Using the same amp
(output & power x-formers) with reasonable bias, cathode current & B+
adjustments makes this a 1st class objective test, Next, I'd love to see
tube brands tested with no tears. -GREAT STUFF!

Автор BixLives32 ( назад)
Excellent presententation. You, um, have a few more test toys than I do.
You are either a serious pro or your wife has left you. Seriously, This
shows that there is not much difference in the desgin for push-pull amps
using the popular valves. However, it also shows that there is a more than
simple grid bias to good tube life, low distortion & high efficiency. Could
you do a test on power vs. 3 main types of distortion with the 4-5 main
power tubes?

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