Why Not EL34's??

Nuklhed · Post by **Nuklhed** » Thu 09/16/04 2:00 am

Hey all,
why isn't anyone using EL34's in this amp?? Is the power not there to push the 34's??

Thanks for any explanation.

NUKLHED

habitron · Post by **habitron** » Tue 10/26/04 1:27 pm

It takes way more voltage swing to drive EL34s. (I am attempting a build similar to what I think you may be after: 2 EL34s, cathode biased, no NFB, but a slightly different preamp.)

I have heard it said that the PI of the 18w is more along the lines of what you would expect to drive larger octal tubes with, like 6L6s or EL34s. I'm guessing this is how the Jason PI mod came about.

So, has anyone else tried bldg the 18w preamp onto a 2xEL34 power amp that is willing to share tips on how to set up the PI to drive them?

Thanks in advance!

Post by **Plexi** » Tue 10/26/04 1:41 pm

Yes back at the start Ron Ott built an amp that used EL34s..
I think a little part of the magic though is the EL84s..thats why i built the 36 watter with 4xEL84s..
For the EL34s you'd have to change some things,trannys etc..

Richie

habitron · Post by **habitron** » Tue 10/26/04 2:30 pm

Yeah, I've got the right trannies and power supply design to do the job, just unsure about having enough Vg1 p-p to drive.

I do love EL84s, but wanted to do something a little different this time. I'll let you know how it turns out.

Post by **zaphod_phil** » Tue 10/26/04 2:37 pm

habitron wrote:I have heard it said that the PI of the 18w is more along the lines of what you would expect to drive larger octal tubes with, like 6L6s or EL34s.

So have I, but I don't really believe it. At the very least, you will need to change the PI tail resistor to around 20k. You can also experiment with a 470 ohm cathode resistor, as used in the bigger Marshalls and Fenders. You will need a load impedance of around 4k at the OT.Then it should work. However, you will need to run the amp at brain frying volume levels before you get it to overdrive.

habitron · Post by **habitron** » Wed 10/27/04 10:16 am

Phil, I'm pretty confident I can drive them enough with the values I've chosen, but we'll see. It certainly won't drive them as hard as the 18w PI does for EL84s. Some people have mentioned that the last 1/3rd of the 18w volume control doesn't really do much other than add more distortion and splat, but I find that if you use the knob on the guitar or a vol pedal, you can obviate the need for stompbox distortion altogether. If I can accomplish something close with this amp, I'll be happy.

Post by **zaphod_phil** » Wed 10/27/04 2:59 pm

One of the guys on the AX84 board was building a very similar amp using the Matchless Clubman PI and power stage - ie cathode-biased EL34 power stage and the same PI resistor values as yours. I hand-held him through most of his build. He could never get the amp to crank, until he changed the PI resistor values...

habitron · Post by **habitron** » Thu 10/28/04 10:35 am

Hey Phil, you've helped me out before too. Most notably, the PI on the Atlas Tweed (2x6V6 w/Spit front end). You'll have to drop by my little web page when I get the photos of my newest combo up. Just got the Mojo cab last night and installed the chassis & spkrs. It's a beaut and sounds as great as it looks!

Any way, if you were to look at the Orange AD15 preamp in front of a cathode bias EL34 pwr amp (or the VibroKing from the effects return forward) that's pretty much what I'm going to start with. I figure the Vibro King gets enough voltage wing off its phase inverter for 6L6s, and the AD15 preamp has plenty of gain, but I could be wrong. Would not be the 1st time

I will leave an extra spot on the chassis for a presence control if I cannot get what I want this way. As usual, I appreciate your input on the subject.

Craig

DennisF · Post by **DennisF** » Thu 10/28/04 12:48 pm

Hey Craig that sounds like another winner of an amp! I have a 18watt lite variant that may be more of a VT than a VTB with the triodes run individually and a tone control between the triodes. It sounds really good.
Did you have a board layout for your Orange clone you would be willing to share?
I'll be watching your site for this next build.
-Dennis

habitron · Post by **habitron** » Thu 10/28/04 2:19 pm

Dennis how are you? Yes i made my own layout which is handdrawn, but can I make something up and email a gif to you (is it still the same earthlink address?), or photocopy snail-mail? Might be a few days though.

Also, I'll be adding pictures of my latest *under-construction* project to the website, which features an AD15-ish circuit in a 2x10 tweed combo cab. Just got the cabinet from Mojo and put it all together last night after work. Stay tuned for that.

Aharon · Post by **Aharon** » Thu 10/28/04 6:13 pm

zaphod_phil wrote:One of the guys on the AX84 board was building a very similar amp using the Matchless Clubman PI and power stage - ie cathode-biased EL34 power stage and the same PI resistor values as yours. I hand-held him through most of his build. He could never get the amp to crank, until he changed the PI resistor values...

I built a Spitfire on steroids at Ax84 and Phil Rowley helped me through the process.The amp was loud and very clean untill the volume was earshattering.Good learning experience.
Hey..... zaphod_phil=Phil Rowley?

Aharon

habitron · Post by **habitron** » Thu 10/28/04 6:25 pm

Hey I know you

Just out of curiosity, what was your ballpark voltage off the rectifier on the Steroidal-Spit?

Aharon · Post by **Aharon** » Thu 10/28/04 6:36 pm

habitron wrote:Hey I know you

Just out of curiosity, what was your ballpark voltage off the rectifier on the Steroidal-Spit?

Hey habitron.........
Let's see 'cuz this was a while back and the amp " is no mo".....
it was probably 430/440V after recto if I'm not mistaken.
Used individual cathode cap/resistors.
Aharon

Post by **zaphod_phil** » Thu 10/28/04 6:49 pm

Aharon wrote:I built a Spitfire on steroids at AX84 and Phil Rowley helped me through the process. The amp was loud and very clean untill the volume was earshattering.Good learning experience. Hey..... zaphod_phil=Phil Rowley?

Looks like this is turning into a happy re-union, but I deny everything!

Anyway, this particular episode is what taught me about how PI tail resistors need to be chosen to suit power tube gain. So it was a learning experience for me too.

BTW, if you read Hitch Hikers' Guide to the Galaxy, Phil is the name Zaphod used when he showed up at this party on Earth, and took Trillian away with him, when Arthur Dent was trying to get to know her. So Phil = Zaphod

Aharon · Post by **Aharon** » Fri 10/29/04 8:39 am

Deniability!
Small world indeed.....
Aharon

habitron · Post by **habitron** » Mon 11/01/04 1:09 pm

http://www.geocities.com/craigbbbb/index.html

Slightly off topic, but click on the SuperTweed if you wanna see pictures of my new amp.

The EL34 amp is coming along, so I'll return to this thread and let you know how it turns out...

habitron · Post by **habitron** » Wed 11/17/04 1:22 pm

Hi ya'll, I'd be happy to give some honest unbiased impressions of how my TMB EL34 amp turned out, if anyone is still interested. (I guess this should really be in the "By the BBQ" section, since this is not the 36w EL84 design.)

Post by **zaphod_phil** » Wed 11/17/04 5:05 pm

We're waiting....

habitron · Post by **habitron** » Wed 11/17/04 7:22 pm

Well, first, my two biggest worries turned out to be no problem at all. 1.) The preamp and PI with stock values gives plenty of drive to the EL34s. 2.) It is not farty sounding, even full blast, with no NFB cicrcuit.

I tested using my standard US tele, and my hecho-in-mexico thinline tele with duncan nashville p'ups. For speakers I used an old openback GT 1x12 with a celestion, and a laney 4x12.

With the gain WAY down and the master full up, it gives up a wonderful classic rock tone that is plenty loud, but not ear-splitting, and it segues from clean to breakup in a way that a 50w won't. Using the MV to attenuate while bringing up the gain to varying degrees gives loads of varying rock tones. It's not until you get to low volume on the power amp that it ranges from uninspiring clean to decent breakup to that wonky preamp-only distortion that you get with those silly MV-modded Marshalls. The TMB controls work well. It is fairly quiet even with everything full-up.

In conclusion, the chime and great clean tones the EL84 amp produces gets traded away for that cool Marshally wooly-mid thing. This is not a bedroom or apartment dweller amp. As much as I like it, I still prefer the EL84s for my playing style.

Tonebender · Post by **Tonebender** » Tue 12/07/04 7:05 pm

Hi, Is there a layout posted somewhere for the 36 watter with El34's?

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