new build/pics with 6AU6A pentode preamp

[Alexander]

Hey Gents-

Just finishing up a new build with a pentode (7-pin) preamp; replaced the microphonic 6SJ7WGT's I had been using. Here's the page I tossed together:

http://www.retrodyne1.com/29Wamp.html

Rock on,
Alexander
Retrodyne Amplification

[JWK]

Very cool. After being absent for a few years due to extremely significant and unpleasant life events, I'm looking forward to resuming my build that also uses a 6au6 for the first input/gain stage.

Interesting that you found this tube to be more quiet than an ef86. I've often wondered about the noise issue, but I've never tried anything else and the 6au6 sounds great, so what the hey? NOS are plentiful and cheap. I'm going to try having everything after the 6au6 to be either NOS 12au7s or 6n1ps. My previous amp had one 12ax7 in the preamp section. I'm done with those for now.

Very nice job. I'm envious. And you beat Mark! A HA HA HA HA HA!!! That was funny. We should start our own 6au6 club.

[Alexander]

Thanks, JWK for the kind words! A few years back Dr.KT88 Pierre Debs hisself and me traded some tubes back 'n forth, he sent me some Euro EF86's. I had a few Svetlanas but found them just like the 6SJ7WGT's from Angela Instruments; great-sounding but the internal structure prone to rattling no matter how suspended/mounted. Nobody will stand for setting your amp head on a pillow on the speaker cab, but that would be the only way to isolate it enough! Pierre did include one Valvo EF86 that's dead quiet and super sweet!
But that was out of 14 others...no thanks! Supposedly JJ is re-issuing one eventually, the NA distributor told me they were trying for 2006 NAMM show.
Guess that didn't happen! But in the end I want a musical pentode that's durable, that's all!

6AU6's are an NOS bargain and very durable. Triode Electronics has 7-pin ceramic sockets with shields and base pin-shields which I ALWAYS use now to help reduce noise. You can build an amp with 6AU6 input, 6AU6 tone-stack driver, 6AU6 as phase inverter...Lavelle would use them as the power section too!

I have to get back to the 'hi gain' channel and post a full schemo shortly.

Rock on,
Alexander

[Alexander]

Sound Sample has been added plus link to custom guitar builder

Here's what she sounds like-

http://www.retrodyne1.com/29Wamp.html

Rock on,
Alexander
Retrodyne Amplification

[bulldogguitars]

Alexander, I have to tell ya that amp sounds very good. Ill have to look I think I have some of those pentodes that I got from an auction a year or so ago. Now maybe I can do something with them. But anyway awesome sounding amp. Danny

[JWK]

Alexander, I grew up in WNY. In which town do you live?

[Alexander]

Figures, SUCH a small world...
I have an industrial building in Niagara Falls where I paint & bake my chassis finishes, my electronics/assembly shop is in Lockport, and I have a duplex in Churchville. I do combustion engineering for a firm out of the Rochester area.
I drive about 1000 miles a week- thank God for company cars!

Alexander

[dai h.]

sounds good! (and nice work on the amp too!)

[JWK]

Alexander, did you use a Hammond OPT? If so, was it the 1620 or 1650G? There is no 25 watt with a 6600 primary listed on Angela's site. Just wondering. I'm looking at that 15 watt with a 5000 primary for a lower power amp. So many ideas, so little time...

[hasserl]

SSHHHHHH!!!!!! Don't tell anyone!

I built an amp based obn the Clubman circuit several years ago using a 6AU6 as the pentode. I made several posts about how good it was, but no one seemed interested. Over the years, on different amp bbs's, as people complain about microphonic EF86's I've posted numerous times about 6AU6's, no one responds. Finally I decided screw it, I'll keep the good news to myself and scarf up 6AU6's whenever I can and build my own amps using them.

I really don't know why this tube has not become more popular, I guess people don't like to try new things.

Now you come along and let the good news out. Ouch!

Just kidding. Nice looking amp, and the clip sounds great. Congrats on a great build.

Maybe you could help me out understanding the 12DW7 pi. I remember reading several posts on the old Ampage about how this would make a great pi tube for amps w/ a cathodyne pi where the AU section is used for the pi. But I've not grasped why this lower gain triode makes for a better pi. Evidently it has higher current capacity, but doesn't the lower gain result in a lower voltage out to the power tubes? And since we need voltage swing from the pi to push the power tubes out of their linear range if we're going to get them to break up, doesn't this defeat the goal? If were not running in AB2, why is higher current an advantage?

Sorry if the q's are primary, but this is just something I haven't grasped yet.

Thanks,
Hasse

[Alexander]

JWK- Output transformer is from Triode Electronics, Chicago IL. They sell through ebay too. It's their 'Deluxe' model, also now available with paper interleave- the older unit in my amp is something else...plastic bobbin? You heard the clip- who cares!?!!? it screams, and the clean sound is nice & sweet. Hey it's a 39.00 unit, way cool bargain to MY ears! This is just a knockaround R&D chassis anyway.

What part of WNY were you from?

Hasserl-

Hey I hear ya about getting ignored for using something other than 12AX7's!!!
I raved about 6SJ7WGT's (before realizing 70% are microphonic!) and ho-hum, nobody is adventurous enough to try anything else. Heck, some guys ask about changing a couple resistor values and what do you think? In the damn time it takes to post/ask the question they could have DONE IT and LEARNED something in the process!! Go figure...

Rock 'n roll,
Alexander

[JWK]

SSHHHHHH!!!!!! Don't tell anyone!



Maybe you could help me out understanding the 12DW7 pi. I remember reading several posts on the old Ampage about how this would make a great pi tube for amps w/ a cathodyne pi where the AU section is used for the pi. But I've not grasped why this lower gain triode makes for a better pi. Evidently it has higher current capacity, but doesn't the lower gain result in a lower voltage out to the power tubes? And since we need voltage swing from the pi to push the power tubes out of their linear range if we're going to get them to break up, doesn't this defeat the goal? If were not running in AB2, why is higher current an advantage?

Sorry if the q's are primary, but this is just something I haven't grasped yet.

Thanks,
Hasse

My understanding from the help on this board and messing around with TubeCad is that the lower mu tubes with much lower plate resistance and higher current capabilities will indeed have less gain but be capable of a higher output voltage swing, if that makes any sense. IOW, the input voltage swing capability of the 12AU7 will be higher and the resulting output swing is further enhanced with low impedance and high current drive.

This is my limited understanding. If Ray Ivers or Ken Gilbert show up I'm sure you will get a much better explanation. There are others of course who are perfectly capable. I'm just mentioning these two since they have given me such detailed help in the past.

Note that a ECC99 tube (JJ) is used as a driver for high voltage SE triode amps, the most demanding for driving the output tube(s). Same mu as a 12AU7 (close, anyway) but much higher current and much lower plate resistance resulting in even higher voltage swing output than a 12AU7 given the proper operating parameters.

If I got something wrong, I hope someone can jump in and lend a better understanding.

HTH.

John

[Richard]

Are you saying that the lower gain tubes can ultimately have more output voltage swing but that they need a stronger signal to achieve this? And that a signal that may cause a 12ax7 to distort will be cleanly reproduced with a 12au7? I've actually been wondering about that sort of thing, how to get the maximum clean signal.