Tubes for MM HD150 ?

[Zeaweed]

Hi,
I juz bought Musicman HD150 (the bass version with its RH115 cab).it has 2 channels,Normal1,2 and Bass1,2.it came with EH EL34's inside which is sound OK to me rite now but I juz want a lil more bass response.I know that it was originally 6L6 GC but the local amp tech has changed them to EL34's without any mods as he said its ok.I'm juz not sure that it's safe like he said or not.Should I change those tubes to 6L6GC ?the new model or NOS?

I did searched for the threads talking about it but cant find one.they only discussed about the 6CA7's and EL34's.

So Could anyone give me a suggestion to choose the tubes or school me the differences between these tubes?
a new 6L6GC (any brand?), EH6CA7s big bottle, JJE34L, which is best for my amp?

thank you very much.
,Saras.

[Zeaweed]

ok,now I know I'd better use 6L6GC.been searching through the tube sites coz there's nothing in here talking about the tubes in HD150!!!thanks for nothing!!next time I should post this in MM website.

[timmus]

hi there...just a quick note before I head off to work...6CA7's and EL34's are the same tube....I prefer JJ tubes for the most part and highly recommend them...

I wouldn't put 6L6GC's in the amp if it calls for EL34's. They aren't the same tube and usually aren't interchangeable in an amp without at least some circuit changes...some of the pins are different and also the two of them require a different bias setting...

As far as diffences between brands/internal tube configurations/styles, unfortunately, it's all in the ear of the beholder...much too subjective to pin down actual sonic differences...way too many variables.

Good luck

[MAMMOTHvolume]

6ca7's and el34's aren't the same valve.

you should be fine with el34's though, personally i'd go for the big bottle 6ca7's for bass

[timmus]

Originally Posted by MAMMOTHvolume

6ca7's and el34's aren't the same valve.

Actually they are electrically identical ...

http://www.ampage.org/td/vtd6ca7.html

EL34 is the European designation for the American 6CA7...physically, they may be different as are any other tubes that have the same designator made by different manufacturers...same tube, different sound.

[BassmanPaul]

Originally Posted by timmus

Actually they are electrically identical ...

http://www.ampage.org/td/vtd6ca7.html

EL34 is the European designation for the American 6CA7...physically, they may be different as are any other tubes that have the same designator made by different manufacturers...same tube, different sound.

Wrong again! The 6CA7 is a beam tetrode and the EL34 a true pentode. If Pin 1 (G3 - EL34) of the base is strapped to Pin 8 (cathode) then both tube will work in much the same way.

[timmus]

what can I say? I stand corrected...

I always thought they were identical except for Euro/US designators (except of course for sonic differences between manufacturers).

Color me beet red...

typically, they are interchangeable though in audio applications.

[BassmanPaul]

You are not alone in this. Many people believe the two to be identical. It's the same with the 6550 and KT88. Similar tubes but not interchangeable per se. Another is the 5881 and 6L6GC. Not the same tube at all. The 5881 is equivalent to 6L6WGB and has less plate dissipation, thus output, than its GC cousin.

[jackcheez]

Originally Posted by BassmanPaul

Many people believe the two to be identical.

While we're on the subject, how about the EL34 and KT77 as far as interchangeability ?

[BassmanPaul]

Same thing! EL34: pentode, KT77 Kinkless tetrode. There again modern manufacturers are not following the old specifications so who knows what anymore!!! They seem to be just snagging designations out of thin air or back filling available spaces.

[KramerBassFan]

Get a nice quad of 6CA7's.

Not 6AC7's... i found a drawer full of them in the garage, and i don't even know what i could use them in.

Maybe a radio in a P-38 Lightning? Maybe...

[BassmanPaul]

It's a high gain pentode and were used a lot during WW2. You could actually design a nice pre-amp using them. It would make an interesting project.

[KramerBassFan]

I've had offers from techs on other forums to help me design a nice tube pre amp with them. I have maybe a half dozen, and i don't know if any of them even are good. But if they aren't, nobody wants them, so NOS are about $6 a tube on ebay.

I'm all down for building my own pre amp! Especially a tube that is not a 12ax7 or its variants.

[Zeaweed]

Wowwww..I'm so surprised that my thread is so disputable!!!apologize for my english as I'm from Bangkok,Thailand.really appreciated that u guys argue in here and I wanna give a big thanks to all of you.As I read,I think I agree with BassmanPaul.EL34 and 6CA7 aren't the same but really similar in term of use.it can be interchangeable without any mods.but for 6L6GC,its a different story but somehow interchangeably in some cases .For my amp,the MM HD150,it is a solid pre and tube power.it was originally come with 6L6GC as I read from MM amp website. I don't know why but I can use all of them,6L6GC,El34 and 6CA7,my amp tech guarantees that for me.only thing I should bare in mind is to find any of them that have a high plate voltage as the MM perform high voltage.the EL34s inside rite now getting too hot and hotter.

I found this article that would be really useful to all of you
http://www.vacuumtube.com/FAQ1.htm

thank you guys so much!!!!!now I juz wanna choose between the new model(JJ,winged C)or the NOS (RCA blackplates,GE Fat boy,Sylvania).Can u guys giv me an opinion?I think I might try both of them 6CA7 and 6L6 coz I already got EL34 inside.

[Jim C]

One could argue that using the tubes the manufacturer specified will equal very good results.
I remember these amps to be very reliable back in the day

[Chef]

I had several of these and would highly recommend the stock tubes.
I think mine came with Sylvania.

If you need more bass than the bass knob and deep switch provide, you might think about a different speaker cabinet.
I'd be very surprised if swapping tubes came you lots more bass.

[rickdog]

Originally Posted by BassmanPaul

Wrong again! The 6CA7 is a beam tetrode and the EL34 a true pentode. If Pin 1 (G3 - EL34) of the base is strapped to Pin 8 (cathode) then both tube will work in much the same way.

Are you sure? I just pulled my RCA Receiving Tube Manual off the shelf, and it has one entry for "6CA7/EL34". It's described as a "Power Pentode". Pin 1 is G3. The PDF of a Tung-Sol 6CA7 datasheet I have shows the same thing.

As far as the original question about substituting an EL34 for 6L6GC - generally you don't want to just do this without opening up the amp and checking first. Because the 6L6GC doesn't have any connection to pin 1 (it may not have a pin there), it's possible that pin was used as a convenient wiring point. In fact, I think I've heard of amps where the screen resistor is mounted on the socket connecting pin 4 to pin 1 - not what you'd want to connect the suppressor grid to!

But if your amp tech has looked at it and says it's okay, it may be that pin 1 is strapped to pin 8 so you can use either tube (maybe with a little bias adjustment).

[timmus]

From Wikipedia:

Interestingly, many tubes that are described as pentodes actually turn out to be beam tetrodes. The ubiquitous Mullard EL34 (6CA7), although manufactured by Mullard as a pentode, was also produced by many manufacturers around the world as a beam tetrode instead. Even Philips/Mullard themselves were not immune; several examples of Mullard-marked ECL82s (a signal triode plus low-power pentode intended for single-ended operation) have turned out to contain beam tetrodes.

So it seems it depends on manufacturer

[Chef]

I'm not sure I'd trust wikipedia as a great resource on this.

[KramerBassFan]

Originally Posted by Chef

I'm not sure I'd trust wikipedia as a great resource on this.

+1

I see wrong stuff up there all the time...