Feel free to ask Myles

[Caevan O’Shite]

Stewart-MacDonald is another good place to look for such parts.

[Bluesape]

Hey Myles,

 

There's a Marshal JTM60 1x12 for insanely cheap money locally, but I'm reading scary reviews. I read that it has the identical circuit as the JCM600. Are these amps miss-steps for Marshall, or did I read particularly scathing reviews? The reviewers universally loved the sound, but loathed the reliability issues. Apparently, overheating is a huge concern with these, and a cooling fan is advised by several people.

[myles_rose]

If it the Marshall is cheap and it is working it could be fun. They do have a tone that a lot of folks love and if you don't take it on the road much you might be pretty lucky between times of breakages.

[Bluesape]

Well, it sounds good, but it dropped in power in the store on the drive channel, without pushing it hard at all... The clean channel stayed loud n' proud.

[myles_rose]

If level dropped in the store on one of the channels that is probably indicitive of a pending problem.

[Bluesape]

Any guess as to what that problem might be? I ask cuz a few cheap fixes are listed on various forums....

[myles_rose]

It could be many many many things. Like I said, these amps are not exactly reliable and are very interesting to work on to say the least.

[Bluesape]

I think I should back away, then....not being a tech....

[myles_rose]

Most techs would also pick something else if they had to use it and rely on it.

[Bluesape]

Thanks, Myles!

[Caevan O’Shite]

Say, Myles-

 

I've got an old Traynor YBA-1 Bassmaster head, the one with the "Range Expander" controls.

 

It runs a duet of 6CA7's; for use as a bass amp, what would you recommend out of current production tubes for the output and phase-inverter tubes?

 

For bass use, should I stick with 6CA7s, or would some EL34 types be suitable?

 

Thanks for your time and effort!

[myles_rose]

There are no real 6CA7s being made at the moment. Tubes labelled as such as nothing more than big bottle EL34 tubes. You can go the pricy NOS route and find real 6CA7s (they will sound different than an EL34) which have different construction and a much higher internal vacuum than an EL34 or ... you can use a good EL34 such as the real Svetlana winged C =C= which will work pretty nicely although it will not sound like the original 6CA7. Not worse, just different. As a side note, any tube marked 6CA7 from Europe was just an EL34 and not a 6CA7. Since the tubes are interchangable Mullard and some other companies marked some of their softer vaccuum / lighter construction tubes EL34 / 6CA7. There was a GE tube marked "made in Britian" that was sold in both contries that is a Mullard EL34 and not a GE 6CA7. ( http://www.tubedepot.com/nos-6ca7-mullard.html )

[Caevan O’Shite]

THANK-YOU, MYLES!

 

Great, solid info.

[myles_rose]

You are quite welcome

[Caevan O’Shite]

Say, Myles, what do you think of the following tube in a "late distortion"-rated matched-pair for a budget-minded bass player's selection for that Traynor YBA-1?

 

Should they be able to be biased correctly in my stock YBA-1?

 

EH 6CA7

 

"This tube was designed to the same specs as the Sylvania large bottle 6CA7 with lots of detail and nice bottom end"

 

http://www.dougstubes.com/images/eh6ca7.jpg

[myles_rose]

"designed" in the same way they put names on tubes for types that were never made by those folks in the first place. These are not a 6CA7 with crossed grids and other real 6CA7 traits but will probably be a choice.

[Caevan O’Shite]

OK, so long as they'd work well enough for bass, and that particular bass amp without needing any modification to the bias supply or anything.

 

The bass player who'll be using the amp tends to like thick, dark, fudgey, somewhat overdriven/distorted classic retro-bass tones from time to time, as well, so I'm thinking that these tubes might serve him plenty well enough if they're OK to be used with that amp.

 

Plus, sorry to say, cheap cost is a bonus right now!

 

Thanks again, again!

[myles_rose]

I would bet that they will work quite nicely. Mike Matthews (Sovtek, EH, etc) does great stuff and these days it is better than ever in many cases. He puts names on tubes that have nothing to do with the original design but I tend to care less as the tubes are great ones in a number of cases regardless of the label. The Tung Sol 12AX7 they produce is currently the nicest 12AX7 out there when it comes to specs, QA and pretty curve traces that look proper. The tube is clear and articulate and quite neutral in tone. It is not very prone to physical microphonics which is also very nice.

[pinkjimiphoton]

hey myles,

just outta curiosity, and cuz i need one, do you perchance have any leads on a schematic for a ps systems power tool from the early 90's?

mine crapped out last nite at the gig, i was lucky...cold solder joint on a 32,000mfd filter cap...couple minute fix, but made life a leeeeeeeeeeeeeeetle weird last nite, playing thru the PA..which i actually LIKED. i must be weird, yo...

but anyways, a couple minutes of soldering and a new fuse and it's back in business...

but next time, i may not be so lucky!

if you can help, thanks, mate...if not, well, still, thanks, mate!

peace

pink

[myles_rose]

Pink - on my GAB website and on my L.A. Blog there are links to some great schematic folks.

[pinkjimiphoton]

thanks myles, i'll scope 'em out...

but i don't think i'll find it out there in the wild...

ps systems came and went faster than a ....ummm...

but i appreciate the response!

peace!

[myles_rose]

Working on things without prints is a bit of a pain but can be done if push comes to shove.

[Caevan O’Shite]

Hey, Myles-

 

Would running two of the four EL84's in my Carvin Vintage 33- "half the tubes, set at half the impedance"- result in more/earlier output-section overdrive, or less?

[myles_rose]

Hey, Myles-

 

Would running two of the four EL84's in my Carvin Vintage 33- "half the tubes, set at half the impedance"- result in more/earlier output-section overdrive, or less?

 

You can do this is grid biased amps but not in your Carvin cathode biased amp. Cathode biased amps expect all the output tubes to be there as the bias is self adjusting and one of the factors is the tube load.

 

Bottom line - never do this on a cathode biased amp. Or, other than a handful of EL84 amps, never do this on an EL84 amp.

[Caevan O’Shite]

Aaaah, I should have realized that to begin with, d'oh! I COMPLETELY forgot about the cathode-biasing being a factor here... THANKS, Myles!!

 

Hey, Myles-

 

Would running two of the four EL84's in my Carvin Vintage 33- "half the tubes, set at half the impedance"- result in more/earlier output-section overdrive, or less?

 

You can do this is grid biased amps but not in your Carvin cathode biased amp. Cathode biased amps expect all the output tubes to be there as the bias is self adjusting and one of the factors is the tube load.

 

Bottom line - never do this on a cathode biased amp. Or, other than a handful of EL84 amps, never do this on an EL84 amp.

[myles_rose]

You are welcome

[CraigT]

Myles,

 

Wondering if you can give some tube recommendations on my Rivera Quiana 2x12 combo w/ vintage 30's circa 1999? I picked it up used earlier this year and have been struggling to get it sounding like I want. It's pretty bright and nasally and I find the B and high E strings lack meat unless I turn the mid up high which makes it even brighter. I'm looking for a nice balance between the Fender channel and marshall channel and I like a creamy distortion.

 

current setup:

V1 - GT Mullard 12AX7 Reissue

V2 - TungSol 2AX7

V3 - GT 12AX7-R

V4 - GE 12AU7

V5 - GT 12AX7

 

Power Tubes are Svetlana Winged C 6L6 biased to around 80mA.

 

For now I'm hoping for recommendation for preamp tubes and bias current for the Winged C's. The Winged C's are supposed to be good in this amp. The preamp tubes are mostly ones I had available and I'm willing to get a complete new set. I was thinking about trying new speakers but I want the tubes ironed out before I go down that road.

 

Thanks!

Craig

[myles_rose]

Craig - great amp.

 

Get rid of the (V3) GT-12AX7R which is a very dull and low gain Sovtek 12AX7WA or WC. Get rid of the GT-12AX7M in V1, this is the weak link in your entire front end. This tube is the lowest gain 12AX7 ever made, the most dark, the most unreliable. Stick the Tung Sol Reissue in V1 as a start.

In V5 grab a Sovtek 12AX7LP or LPS and have it balanced from www.dougstubes.com and stick it in there.

 

Drop your bias to 34-36mA. You are running too hot. Paul Rivera and I used to debate this point when I had my Fandango head. Your amp will sound less harsh and run much cooler.

 

Hope that helps a bit.

 

[CraigT]

Myles,

 

That helps alot. I've been chasing my tale with adjusting bias and swapping preamp tubes with limited success.

 

So, looks like I can keep the 12AU7 in V4 and put a balanced 12AXLP in V5. The TungSol has alot of hours on it so I'd like replace it. So, what would be your recommendations for me to purchase for V1, V2, and V3?

 

BTW, checked out your website. So much great info on there!

 

Craig

[myles_rose]

Craig,

 

The hours on the preamp tubes are not important if you go NOS as they will last decades. As far as whay to use - totally personal taste and preference. What should I have for dinner? Same sort of quandry.

 

Side note - I do not recall the Quiana using an AU7 but perhaps Paul made changes over the original amp.