6CA7 in a Marshall DSL100HR. Worth Doing?

This thread is not quite dead yet! After running the EHX 6CA7 tubes in my DSL100HR for 2.5 months I unfortunately had one go bad. While I'm waiting for a replacement from my tube guy I popped in a set of EHX EL34 that I had sitting around and rebiased.

They totally sucked! I couldn't stand the sound, so I yanked those out and put the stock Marshall tubes back in it and rebiased again. These sucked just as bad!

Going from the 6CA7 to EL34 the bass got super flubby with a fair amount of overdrive, the mids got grainy and I lost almost all the cool harmonics I was getting. I'm using my 1987 until my new 6CA7 shows up. After using them for a couple of months I won't use anything else in the DSL100HR.
 
Cadorman said:
This thread is not quite dead yet! After running the EHX 6CA7 tubes in my DSL100HR for 2.5 months I unfortunately had one go bad. While I'm waiting for a replacement from my tube guy I popped in a set of EHX EL34 that I had sitting around and rebiased.

They totally sucked! I couldn't stand the sound, so I yanked those out and put the stock Marshall tubes back in it and rebiased again. These sucked just as bad!

Going from the 6CA7 to EL34 the bass got super flubby with a fair amount of overdrive, the mids got grainy and I lost almost all the cool harmonics I was getting. I'm using my 1987 until my new 6CA7 shows up. After using them for a couple of months I won't use anything else in the DSL100HR.
Click to expand...
Ive often wondered if they were worth trying. I got a JCM2000 DSL50 ive considered them in
 
Clockworkmike said:
Ive often wondered if they were worth trying. I got a JCM2000 DSL50 ive considered them in
Click to expand...
It was totally worth it in the new model. After using the 6CA7's for quite awhile you really get spoiled. I regularly run my gain at 7 on the red channel and it sounds fantastic with solid bass, great clarity and harmonics. I can't go over 5 with EL34's or it just mushes out regardless of volume.
 
Amp Mad Scientist said:
The elctro harmonix 6CA7 is not a real 6CA7.
It's a relabeled tube, but who knows which tube it really is.
A real 6CA7 is a pentode.
The EH 6CA7 is a tetrode.
Just a heads up.

Electro-harmonix has been pulling a lot of substitutions and re-labeling of tubes....

Traynor Amps:
DO NOT plug an electro harmonix 6CA7 into a Traynor amp.
You will short out your bias power supply and damage the amp.
Just a word of warning.
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We've been through this before on TTR, where-upon I gave you the definition of;

A "Pentode," contains a "suppressor grid," located between the screen grid & anode (or plate).

A "Beam Tetrode," does not contain a suppressor grid, rather, uses "beam forming plates" to achieve the same suppression of secondary emissions that the suppressor grid does in a Pentode.

Sylvania designed the original fat bottle 6CA7 as a Beam Tetrode. Regardless that US manufacturers that also made this fat bottle tube utilising beam forming plates rather than a suppressor grid INCORRECTLY drew it schematically as a Pentode & called it a Pentode on data sheets, the fact remains that by definition it is a Beam Tetrode.

The EHX 6CA7 is also, by definition a "BEAM TETRODE" as it contains NO SUPPRESSOR GRID & actually incorporates "BEAM FORMING PLATES" & is so a TRUE 6CA7.

One of the problems with the internet is that people make incorrect (aka FAKE) statements that others may unknowingly think is actually gospel.
Cheers
 
Cadorman said:
This thread is not quite dead yet! After running the EHX 6CA7 tubes in my DSL100HR for 2.5 months I unfortunately had one go bad. While I'm waiting for a replacement from my tube guy I popped in a set of EHX EL34 that I had sitting around and rebiased.

They totally sucked! I couldn't stand the sound, so I yanked those out and put the stock Marshall tubes back in it and rebiased again. These sucked just as bad!

Going from the 6CA7 to EL34 the bass got super flubby with a fair amount of overdrive, the mids got grainy and I lost almost all the cool harmonics I was getting. I'm using my 1987 until my new 6CA7 shows up. After using them for a couple of months I won't use anything else in the DSL100HR.
Click to expand...

This interests me greatly, because I've considered 6CA7 in the Origin 50H mod...@syscokid
 
Robert Herndon said:
This interests me greatly, because I've considered 6CA7 in the Origin 50H mod...@syscokid
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You should try them Robert. The bass is much tighter with better overall clarity and harmonics. I know a bunch of guys that have done it. They are a direct replacement for the EL34. Like I said they really didn't do much in my 1987 (it seems to need the harshness of an EL34) but are great in the DSL. I can easily take the gain 3 steps higher on any channel without losing definition.
 
Cadorman said:
You should try them Robert. The bass is much tighter with better overall clarity and harmonics. I know a bunch of guys that have done it. They are a direct replacement for the EL34. Like I said they really didn't do much in my 1987 (it seems to need the harshness of an EL34) but are great in the DSL. I can easily take the gain 3 steps higher on any channel without losing definition.
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I'm excited!!!!
 
Robert Herndon said:
This interests me greatly, because I've considered 6CA7 in the Origin 50H mod...@syscokid
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I agree with @Cadorman. An EL34 amp that generates it's distortion in the preamp will benefit from 6CA7's for the reasons our buddy Cadorman has given.
While I don't know how exactly, Mike Matthews/New Sensor/EHX have stayed true to the original fat bottle 6CA7 design with the EHX 6CA7.
What I find amusing is that tube suppliers list the EHX 6CA7 as a remake of the original "Philips" fat bottle 6CA7, while the reality is that the 6CA7 came about in the quest to make an EL34 Pentode substitute while also avoiding paying Pentode royalties to Philips. Cheers
 
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Cadorman said:
Got the tubes. I didn't get inside the shop as they are being super careful. Probably for the best anyway with me having surgery in a week. Very nice couple (Tyler and Chelsea) specializing in stereo/guitar tube amp and turntable repairs.
View attachment 63869
The Electro Harmonix 6CA7 set was nicely matched. My plate voltages were all within .4 volts and they biased up just fine. Plate voltages ended up right around 436.5 vdc.

I can't crank it up tonight since my wife is home, but I can tell it sounds better. I was having issues with some weird buzzing harmonics that I had been trying to dial out with my eq pedal and amp eq to no avail. It was like the harmonics were out of tune with each other and grating. Totally gone with the new tubes. The harmonics have a very nice kerrang now and I am very happy. I had an old set of EH EL34s in it before that came in a used amp. I had them in the 100 watt 900 and they were fine. I'll have to try them again.

If anyone wants to check out the shop the web address is www.tctubes.com
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The plate voltage changes when you adjust the bias.
If the bias is adjusted colder the plate voltage goes up.
If the bias is adjusted hotter the plate voltage goes down.
The bias adjustment depends on the individual set of tubes.
 
Amp Mad Scientist said:
The plate voltage changes when you adjust the bias.
If the bias is adjusted colder the plate voltage goes up.
If the bias is adjusted hotter the plate voltage goes down.
The bias adjustment depends on the individual set of tubes.
Click to expand...
What's your point? I install the tubes, check the plate voltages on all 4 tubes, calculate and set bias, recheck plate voltages and do what is necessary. Oh! I forgot to put the lotion in the basket. Forgot we were playing lambs...
 
Cadorman said:
What's your point? I install the tubes, check the plate voltages on all 4 tubes, calculate and set bias, recheck plate voltages and do what is necessary. Oh! I forgot to put the lotion in the basket. Forgot we were playing lambs...
Click to expand...
The point is:
Hotter bias puts more load on the power supply and the plate voltage drops.
I'm showing people who read this that the plate voltage is changed by the bias voltage adjustment.
Something that many are not aware of.
 
Amp Mad Scientist said:
The point is:
Hotter bias puts more load on the power supply and the plate voltage drops.
I'm showing people who read this that the plate voltage is changed by the bias voltage adjustment.
Something that many are not aware of.
Click to expand...
What causes the voltage change on the plates with differing current flow is:
Current flows within the tube in the form of electrons. Electrons carry a negative charge.
So, increased current flowing to the plates means more "negatively charged electrons" landing on the positively charged plates. It stands to reason that this causes the positive potential on the plate to fall. Example, +400V plus -50V = +350V.
Conversely, less current flowing to the plates means less negatively charged electrons landing on the positively charged plates. The plates positive potential thus rises.
This is how changes in current flow brought about by applied signal cause voltage swings across the output transformer primary. Cheers
 
Robert Herndon said:
@ivan H - Which 6CA7 would recommend for my Origin 50H????
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If you want a current production "true" 6CA7, the EHX is your only choice.
JJ take large liberties with some of their tube designs, in that their tubes may not bear any resemblance to the "original" tubes of that same designation. One example is the JJ 6V6, another is the JJ 6CA7. Hope this helps. Cheers
 
Amp Mad Scientist said:
The plate voltage changes when you adjust the bias.
If the bias is adjusted colder the plate voltage goes up.
If the bias is adjusted hotter the plate voltage goes down.
The bias adjustment depends on the individual set of tubes.
Click to expand...
The good ol rule of inverse proportion! " As voltage increases, amperage decreases and vice versa"
 
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