Newbie vacuum tube questions?

[George60]

I am assembling a Ceriatone 36W EF86 and I need to buy tubes for it but I am not sure what to get, there are a lot of choices. I have been using tube amps for about 45 years now but I never payed much attention to the tubes. In the 70's I just went to the local electronics store and got Sylvania tubes. About 25 years ago I got my first Mesa Boogie and I always used Mesa tubes.

Bear in mind that I am going for maximum clean headroom.

There is an article at the Tube Store on Marshall amplifiers and it states that one should use a low-noise type with a coiled heater because of the AC filament voltage.

JJ tubes seem to be popular so I was going to get JJ EC883-S for the 'Marshall preamp'. The EF86 appears to be critcal so I was going to get a Tung-Sol EF806-S Gold. JJ EL84 for the power amp and a JJ GZ34 for the rectifier. I am considering a JAN-Philips NOS (Nicely Oxidised Stock) 5751 with matched sections right off of the bat for the phase inverter. Do these seem to be half decent choices?

I do not have a lot of money and can't afford 'tube rolling'.

Any help will be greatly appreciated,
George Sullenberger

[krx]

The JJs are a good choice for all of the tubes except the EF86. I personally wouldn't bother with the 5751. If you want less drive to the power section, you could change a couple 10 cent resistors instead.

Unfortunately, new production EF86s are not very good. If you pick through them, you can find a good one every now and then, but they're mostly crap. They just don't sound like EF86s plus they're still microphonic. It's the ONLY tube I will pay NOS money for. Different NOS brands will sound pretty different since they were made differently.

My general impressions of various EF86s I've tried in the same amp:
Amperex -- very clear, treblier than most
Mullard, Telefunken -- darker and thicker than most (but still clear on the highs)
Tungsram, Winged C (Soviet surplus) -- balanced

I would either spend the money to buy one from a dealer who will guarantee a non-microphonic tube, or buy a lot of the Soviet tubes on eBay. Probably half of them will be microphonic but half will be good and the total cost will be a lot less.

[George60]

Thanks to krx for replying. I found a Brimar EF86 for $45.00 and a Telefunken EF86 for $55.00 at a place called Upscale Audio. I will email them to see if there is any guarantees. If not, I will try a new Tung-Sol from the Tube Store.

By a couple of 10 cent resisotors are you referring to the 470K grid leak resistors?

[krx]

Thanks to krx for replying. I found a Brimar EF86 for $45.00 and a Telefunken EF86 for $55.00 at a place called Upscale Audio. I will email them to see if there is any guarantees. If not, I will try a new Tung-Sol from the Tube Store.

By a couple of 10 cent resisotors are you referring to the 470K grid leak resistors?

For how much the new Tung Sols cost, I would go NOS. Those are reasonable prices if they can deliver a non-microphonic tube. There are some things you can do to control the microphonics but some tubes are just plain unusable.

And yep, the grid leaks are what I was referring to. I'd try it stock first. The great thing about a good EF86 is you can turn the amp up pretty high and then roll down your guitar's volume knob and get great clean tones with no loss of treble like you get with a triode input.

[vibroluxious]

JJ has had an issue lately with the gz34 tubes. May want to look into an NOS tube for that as well.

I personally run a JAN/Phillips 12AT7 in the phase inverter. I have customer who does the same. Cleans the amp up and it stays very snappy and responsive.

I have tried a G.E. 5751 in the phase inverter and the amp does stay cleaner but personally I find it sounds a bit dull and grainy.

[krx]

I personally run a JAN/Phillips 12AT7 in the phase inverter. I have customer who does the same. Cleans the amp up and it stays very snappy and responsive.

The 12AT7 actually has slightly more voltage gain than a 12AX7 in the 18W PI circuit. The particular tube you used may have been slightly lower gain or simply a more transparent tube (maybe some scoop in the mids) or you could just be hearing things .

Calculate away: http://www.pentodepress.com/home/amplif ... iled-pair/

[George60]

I have read some complaints about the JJ GZ34 so maybe I will try a Sovtek. I could use a $2.78 Fairchild 35A 800V bridge rectifier. Just kidding.

I will try the amp dead stock before I start tinkering. I may be going into this project with the wrong attitude. I am not expecting that much out of this Ceriatone amp but I may be surprised. If I can get a clean, bright, chime tone, reminiscent of the mid 60's British Invasion or American electric-folk groups, I will be in hog heaven. I have not heard any sound clips of an 18W or 36W that is the sound I am looking for but that may be more a statement of modern guitar playing as to the ability of the amps.

[krx]

I have read some complaints about the JJ GZ34 so maybe I will try a Sovtek. I could use a $2.78 Fairchild 35A 800V bridge rectifier. Just kidding.

Actually, I, and a lot of other people who have built more than a few amps, prefer to use UF diodes plus a "sag resistor."

If I can get a clean, bright, chime tone, reminiscent of the mid 60's British Invasion or American electric-folk groups

The TMB channel is basically like a Plexi... The EF86 channel though can get you there with the right speaker and guitar. Be prepared to roll down the volume on your guitar. You won't have the inherent mid-scoop of a 60s Fender or top-boost AC30 though. You might also like the amp better with a choke, but, like you said, I suggest you try it stock first.

[vibroluxious]

I personally run a JAN/Phillips 12AT7 in the phase inverter. I have customer who does the same. Cleans the amp up and it stays very snappy and responsive.

The 12AT7 actually has slightly more voltage gain than a 12AX7 in the 18W PI circuit. The particular tube you used may have been slightly lower gain or simply a more transparent tube (maybe some scoop in the mids) or you could just be hearing things .

Calculate away: http://www.pentodepress.com/home/amplif ... iled-pair/

You are absolutly correct on the calculations part, however I have a bunch of the JAN/Phillips 12AT7 tubes and they all behave the same way in the amp. I would suspect the mid scoop part is true.
Math and calculations are a great tool for design and to predict behaviour.
Ears however still should be the final determining factor.

The tubes are I suspect from the late 70's to early 80's and are pretty cheap to buy. I use them in other amps as reverb driver tubes.

I am hearing things and yes they defy the logical math part in this case.

[George60]

The EF86 channel though can get you there with the right speaker and guitar

I have the wrong guitars and will have the wrong speakers.

I use two Jackson guitars. One is a Soloist with a single-single-hum setup, alnico humbucker. The second one is a Jackson Dinky with two medium output Dimarzio alnico humbuckind pickups, an Air Zone (bridge) and an Air Norton (neck). I like the Dinky better.

I have a Stage Craft Diagonal 2x12 cabinet on order but I got a closed back. The project is running low on money so I will be putting the EVM-12L's that I have in the cabinet at first.

I eventually plan on getting either Celestion Alnico Gold's or 50W Weber Alnico Blue Dog drivers. Bring lots of money.

I can get a very pseudo 60's sound, that people like, out of my Mesa Boogie Mark III combo by switching in the graphic eq on the clean channel and using just a hint of digital phase. The graphic eq is scooped big time for the lead channel. Actually I can get very close to the guitar sound on 'It Don't Come Easy' by Ringo Starr.

[George60]

It's later now and the amp is done and has some hours on it. It's fairly close to what I am after except for the bass, which is boomy, mushy, muddy, just not very distinct. This is my first amp project and a 'Learn from your mistakes' endeavor.

The first thing I thought I might try is a solid state rectifier. I believe I want to use UF4007 diodes and know how to build the rectifier but I don't anything about the sag resistor. What value would I use and how is it wired into the circuit? Will the sag resistor pull the voltage down to where it needs to be?

I also believe I can try changing the cathode capacitor. The amp has single capacitor for all four tubes and it is 100uF. I was going to try 2200uF.

I shot myself in the foot with the speaker cabinet and the speakers. The cabinet is a slant top diagonal 2 12" cabinet with a closed back. The speakers are a 100W Scumback M75 and a 100W Scumback H75. It's a tight sound but not very lively. I thought the first thing I might try is to take the back off and see what I think of that. I can make a different back if I can figure out what I might need.

Any help will be greatly appreciated.

[zaphod_phil]

The 12AT7 actually has slightly more voltage gain than a 12AX7 in the 18W PI circuit. The particular tube you used may have been slightly lower gain or simply a more transparent tube (maybe some scoop in the mids) or you could just be hearing things .

Calculate away: http://www.pentodepress.com/home/amplif ... iled-pair/

That's the theory. But in real life I've often found it not to hold true, even with power amps that have lower grid reference resistors than the 18W.

[Brewmaster]

I also believe I can try changing the cathode capacitor. The amp has single capacitor for all four tubes and it is 100uF. I was going to try 2200uF.



Any help will be greatly appreciated.

I have reworked a Ceritone 36 watter and that is one of things I did. I also changed the bass pot and the "MV" pot to 500k. It got rid of the howling I was getting with both the mV and vol dimed. There were several other things I did such as changing the 68ohm and 62ohm cathode resistors to 150 ohm 10watt resistors. I don't recall what else I did off the top of my head but I have the notes somewhere.
BTW, I have given up on the JJ GZ34 until I hear they have improved the QC. I have had much better luck with the Sovteks.