5F2-A Question for a first build

[Scott S]

Originally Posted by limbe

6AU6 is a vacuum tube,actually a RF Pentode normally used in tuners but if you wire it as a triode it can be used to drive an output stage in an audio amplifier.I assume that Scott is building an amplifier using 6AU6 as a driver. Limbe

Nope, I built a push-pull amp using two pentode-wired 6AU6's in the output stage. Kind of an outside-the-box project. http://www.tdpri.com/forum/shock-bro...g-verbose.html

Get better, Pete!!

- Scott

[big-daddy-59]

Pete , sorry to here that you've got to put your project on hold. Hoping you and your family can all get well soon. Sucks having to give up your fun money to pay doctors bills.

[PeteG45]

Thanks big-daddy. It's only on hold and I'm not in any hurry. I am going to take this as a chance to learn more about what I'm about to do. I found another error in my layout, the left most lug of my volume pot was not connected to ground.

Speaking of grounds, I was planning to run a star grounding scheme splitting the amp into three stages. The first stage would be: input jacks, V1 bias, volume and tone. The second would be: OT-speaker jack, cathode bias V2 and V3 and presence control. The third would be the main filter caps. These would each connect to a common wire located near their respective components that would all lead back to one of the PT mounting nuts.

I have a few questions about this. How do I handle the grounds for the power tubes? Do I run a common wire from the tubes back to the PT or would it be better to run the OT and the power tube grounds together and then back to the PT (instead of running the OT ground back up under the board)? Am I correct that this would mean that I have to isolate my jacks from the chassis? Would the pots also need to be isolated from the chassis?

[big-daddy-59]

Pete I have a question for you. Are you participating in any other amp building forums? I like to suggest that you check out the Ampage forum http://music-electronics-forum.com/f10/ and the Weber forums as well. You will have to register for that one. But there is an extensive thread on grounding there started by Lbusters that you should really check out. I didn't isolate any of my jacks or pots and used a two point grounding setup with PT center taps connected to a PT bolt along with the first three filter caps. the fourth one is the preamp supply and it was grounded to a buss along with everything else pots jacks preamp cathode etc. that buss was terminated by forming a loop in the end and bolting it down to the chassis behind the the input jacks AWAY from the transformers. my amp is very quiet, no hum or hiss at all until it's dimed and even then its very slight. The power and rectifier tube don't need grounded. the power tube is grounded at the cathode and the rectifier grounds at the filament windings center tap of the PT.

[PeteG45]

I was thinking about doing something like that but I wasn't sure how to connect the end of the bus and where. Where did you ground your output jacks and OT?

I'll definitely check out the Ampage forum. I have read a little in the Weber forum I guess I'll do some more. Thanks.

[limbe]

Originally Posted by Scott S

Nope, I built a push-pull amp using two pentode-wired 6AU6's in the output stage. Kind of an outside-the-box project. http://www.tdpri.com/forum/shock-bro...g-verbose.html

Get better, Pete!!

- Scott

Calling your amplifier an outside-the-box project is really an understatement.I hope that you have an isolation transformer and/or a ground fault breaker.No,I didn´t think that you would use 6AU6,s in the output stage but it looks like an interesting experiment.I´m following your thread to see where it ends up.Good luck!Limbe

[PeteG45]

Well I spent a lot of time on the Ampage forum over the last couple of days and I think that I have a pretty good understanding of what I need to do to ground this thing. I may even be able to order some more parts in the not too distant future and maybe get this thing done before Christmas.

[PeteG45]

Believe it or not the circuit is changing again. I've added a voicing switch like the two stroke and changed the connection point for the NFB to the 8 ohm tap of the OT (suggested as something to try).

I'm waiting on the board and some wire, they should be here next week and I'll be able to start in again. The sooner I start the sooner I'll stop making changes. Here it is:

[Cap'n Kier]

Are you going to be making your own board or modifying a stock 5F2-A board? or getting one custom made?

Looking good so far! I'm hoping to make a two-stroke soonish so will be good to see how your mods work out :)

[Dr.Ow!]

This is a fun thread to follow. Like you I have been pondering,learning , and reading to gather up enough infos to do a scratch build. Either 5f2a if I can get a good SE OT @ Ebaycheap $, or a 5E3ish thing using a 8kpp ot I already have. I got a potted Stancor 70mA PT same as these use @Ebay recently.

Anyway something I have considered due to my own 'Scope Creep'(great term) malady/syndrome Is when I do my first build I'll do my darnedest to K.I.S. by building first true to a proven layout and spec, and then step by step add in the alternates. That way you can get fired up with minimal hassle, and then too really be able to hear any worthwhile effect/impact of your mod ideas. I think I heard this suggested in my early reads @ MEF or Hoffmans.

Hope you and yours are feeling well now, and warming the iron, look forward to hearing if you like the presence/reso circ.

John

[limbe]

Yes!It is a good idea to build the basic amp,see that it is working properly and then add the other things one by one.I work that way myself even though I´ve built more than a few amps.Limbe.

[PeteG45]

Yeah that would probably be a better way to build it but then I couldn't call it "Scope Creep". :O)

I started a new thread to document the slow build process here.

[Dr.Ow!]

That's a good point. Where I tend to get pulled is into complicated tone stack designs. I want to keep to a simple build, but a tweed T just aint enough(even though it is)...so i get sucked down into the D***le ts thing and lay in 3 switches, or tmb w/ selectable slope and fat, or or...

Nice work your doing on yours. The really cool thing about building these is once you have it and know what's happening you can change it up whenever you want to. or go back to the original.