Has anyone built a stand-alone power amp?

[markmalin]

I'd like to build something small, maybe even a single ended 6V6 stand-alone power amp.  Before I go down this road, wondering if anyone else has done something like this?  One idea was to use Doug's 5F2A Princeton schematic, but to be honest, I'm not sure about a few things.  For example, would I just have the signal from the preamp output enter at the R10/R11 divider?   If so, what about the feedback resistor (R14)?


https://el34world.com/Hoffman/files/Hoffman_5F2A.pdf


In any case, if someone already has a simple single-ended poweramp build, i'd like to learn more about what you did (or get ideas!)


As always, gentlemen, thank you for your help and support.

Mark

[labb]

https://ax84.com/archive/ax84.com/static/corepoweramps/5W_SE/AX84_5W_SE_Poweramp_Schematic.pdf


https://ax84.com/archive/ax84.com/static/corepoweramps/5W_SE/AX84_5W_SE_Poweramp_Chassis_Layout.pdf

[shooter]

done a few, mostly as a "base" for testing preamps
my2C;
go with a 6L6 or KT88, they are harder (need more signal) to drive to max
but they will give you more "choices".  you can play them as quiet as you like, or when it's home alone, you can reach into gigging range.

the only "tricky" part, MV and coupling cap.  we "assume" the pre has a coupler at the output, but if it don't......
also we "assume" there is a way to control the amount of pre out, but if it don't....

[markmalin]

done a few, mostly as a "base" for testing preamps
my2C;
go with a 6L6 or KT88, they are harder (need more signal) to drive to max
but they will give you more "choices".  you can play them as quiet as you like, or when it's home alone, you can reach into gigging range.

the only "tricky" part, MV and coupling cap.  we "assume" the pre has a coupler at the output, but if it don't......
also we "assume" there is a way to control the amount of pre out, but if it don't....

Thanks for the input.  I do need as much headroom as possible.  I'm looking for a test bed, just like you mentioned.  A base for testing preamps. 


So my preamp will have a master volume, but for a coupling cap, I may put one in the input of the power amp.


You built a single ended 6L6, then?  Would you be OK with sharing the schematic?


Thanks.  Mark

[sluckey]

the only "tricky" part, MV and coupling cap.  we "assume" the pre has a coupler at the output, but if it don't......
also we "assume" there is a way to control the amount of pre out, but if it don't....

Probably a good idea to not assume anything. 

[markmalin]

the only "tricky" part, MV and coupling cap.  we "assume" the pre has a coupler at the output, but if it don't......
also we "assume" there is a way to control the amount of pre out, but if it don't....

Probably a good idea to not assume anything. 

Adding a 1M audio pot to the input as a precaution probably would be fine.
It's only ever me that's going to be using this.   Of course....I've been known to do stupid things :P

[sluckey]

Putting a coupling cap between the input jack and the pot is also a good idea.

[shooter]

Would you be OK with sharing the schematic

it was before my documenting days!
Look at the AX84 page, there was a "universal", could pick between PA tubes.
If you go "big bottle", aim for a plate vdc = or >400vdc.  have a PT that can just chill when 100mA is being sucked up.
I personally like UL OT 40% tap, self biased. NO sag PS.  I want the PA to just amplify whatever I give it "clean" (without adding flavor) up til ~~ 7 on volume/drive, then maybe add some nice bark and color 

[markmalin]

Would you be OK with sharing the schematic

it was before my documenting days!
Look at the AX84 page, there was a "universal", could pick between PA tubes.
If you go "big bottle", aim for a plate vdc = or >400vdc.  have a PT that can just chill when 100mA is being sucked up.
I personally like UL OT 40% tap, self biased. NO sag PS.  I want the PA to just amplify whatever I give it "clean" (without adding flavor) up til ~~ 7 on volume/drive, then maybe add some nice bark and color 

D'oh!   
I'll check out the AX84 page.
I have a few 6L6's, EL34's and KT66's laying around. I'm looking for exactly what you did - something that won't color the PA at all but just amplify what's put into it.


So you went self biased single ended?  That seems nice and easy.  Also, solid state rectifier?

[shooter]

 
when I showed up here there weren't many SE threads, so I took it upon myself 

Yes, SS rectifier, big Ecaps
here's my last SE build, look over the PS, and PA, look over the AX stuff, sharpen the crayons 

[markmalin]

Thanks, shooter.  This is a good place to start.  I'll look closer at the AX site as well. 

Mark

[labb]

If you go to the AX84 site, go to building blocks and you will find SE power amps up to 20 watts. I would modify their schematics to fit what I wanted...

[markmalin]

If you go to the AX84 site, go to building blocks and you will find SE power amps up to 20 watts. I would modify their schematics to fit what I wanted...

Thanks.  I saw the 20W one, which I figured I'd start with.  It's kind of uncharted territory for me.  I was confused at first by the 20W SE schematic because it showed filament wiring for other tubes (preamp tubes) and the additional B+ sections, but I figure I can just take what I need from the schematic.  I also see it has notes for EL34, which is good - I have a couple in the spares drawer.

[kagliostro]

Just my 2c

as you want a small PA to be used to test preamps .......

why don't build it with 2 tubes, a 6V6 & one EL84, swappable

6V6 tubes are way less sensible to imput signal than EL84 tubes

if you can swap between them you'll have a larger test ability on testing preamps

Franco

[markmalin]

Just my 2c

as you want a small PA to be used to test preamps .......

why don't build it with 2 tubes, a 6V6 & one EL84, swappable

6V6 tubes are way less sensible to imput signal than EL84 tubes

if you can swap between them you'll have a larger test ability on testing preamps

Franco

Thanks, Franco.  I'll have to give that some thought...  I'd like to do something very simple to start with.  I still need to buy a set of transformers, so am still open to options at this point!  :)
Mark

[DummyLoad]

.

--pete

[kagliostro]

This Ampmaker kit is only an example





it was planned to use Octal & Noval Tubes (EL84 - 6V6 - 6L6 - EL34 and other tubes)

V2 is a Noval - V3 is an Octal

The part of the circuit you need for the PA is that in the red rectangle (plus the involved Power Supply nodes)

Note that you don't really need to have the VVR on the circuit if you don't want it

as you can see the PA circuit is very simple

the project is planned to have on the circuit only one tube at the time, an Octal Tube or a Noval Tube

you must pull the Octal to insert the Noval on his socket

May be someone will be able to give you council about how to have both the kind of tubes (Octal & Noval) at the same time installed and swap betheen it using a switch

Franco


p.s.: If you are interested to plagiarize, I can post documentation (Layout etc. etc.) of the amp and you can cut out the parts you don't require

[Willabe]

I still need to buy a set of transformers, so am still open to options at this point!

That's gonna be the rub.

SE iron is more $$ than PP iron. Especially when you start going for more power in SE.

 

[shooter]

If it's mostly "your personal build";
these are pretty competitive with PP;

https://www.edcorusa.com/xseseries#/specFilters=7m!#-!40

the downside, they will bite you if you don't take some precautions

[p2pAmps]

Does this count?  It's a cool ST120 Dynaco kit.  Fun to build and man she sounds amazing - KT120s just because

[Willabe]

Nice!

How much power a side? 

[silverfox]

I built one using Weber schematices of an S100. Output section only, It is essentially a Dynaco Stereo PA with no UL output. Just built two channels. Rather than, use the UL transformers I went with a typical PP output. I still use this amp from time to time. If you were to build based on the schematics on the thread, be sure to revise the bias supply as if the power is rapidly cycled, it blows the rectifier diodes due to a surge in the output tubes being unbiased. i.e. there should be a slow drain on the bias when the power is shut off.


btw. It totally cranks and I used Trainwreck speced Iron. 35 watts = 50/ chan.

https://el34world.com/Forum/index.php?topic=19662.msg205011#msg205011