HOFFMAN AC30

[geoffmulberry]

Hello,
I am planning on building a HOFFMAN AC30, I have a few questions...

1- How am I supposed to hook up the input jacks?
2- Are the 2 volume pots for each channel?
3- Is there any way to put on a master volume pot?
4- I am thinking on using tube depot transformers, are they any good?
5- Any ideas for speakers... that aren't 300 dollars a piece?

That should be all for now
Thanks for the help..
-Geoff

[tubeswell]

1. See the note about common hookup info at the bottom of the layout diagram

http://www.el34world.com/charts/CommonHookups.htm

2. Yup. You will see that the input of each pot is connected to the .047uF and 500pF coupling caps accordingly (from the respective halves of V1)

3. Most common methods are either before the PI (but after the PI input cap) or (a dual ganged pot) after the PI output coupling caps

4. Depends on whereabouts in the world you are. Some Xformer manufacturers still apparently don't understand the implications of a 230V @ 50Hz mains supply, and therefore don't put enough iron in their PTs, and they meltdown just as the warranty period expires. (Doesn't apply if you are in the US).

5. Weber speakers are good and very reasonably priced

2CW

[fyl]

- Is there any way to put on a master volume pot?

Most MV's work well in this design : crossline, PPIMV, bootstrapped PIMV... You may also consider adding a VRM/VVR/Power Scaling module, which will give you much more flexibility.

- I am thinking on using tube depot transformers, are they any good?

Tube Depot resells Mojo xformers OEM'ed from Heyboer. Excellent iron.

- Any ideas for speakers... that aren't 300 dollars a piece?

I really like a pair of Red Fang's in a Voxish cab. But there are many other options.

[Regis]

Geoff,

I don't want to hurt your feelings, but if you don't know how to hook up the input jacks and deduce what the two volume pots are for then you shouldn't be attempting this amp for a first build.

[Gaz]

Geoff,

I don't want to hurt your feelings, but if you don't know how to hook up the input jacks and deduce what the two volume pots are for then you shouldn't be attempting this amp for a first build.

Ah, whatever. way to make someone self-concious about asking a question

i built amps more complex than this one, and I still am confused by input jacks. I also have a lot of seemingly naive questions.

As long as you're safe, patient, and willing to put in a good amount of research (it seems like you're trying here), then you can definitely build a vintage amp like an AC30.

And I really don't get why some folks insist that a SE is soooooo much easier to build than a PP. There are way more factors that contribute to a build's difficulty than it's output stage.

Respectfully,


Alex

[geoffmulberry]

Would this make a functioning master volume?

[fyl]

The MV should be inserted between the coupling caps and the 220K grid resistors.

Check for instance https://taweber.powweb.com/store/smokeII_schem.jpg for a possible implementation.

[geoffmulberry]

I took a look at that schematic and I revised mine...
I think this would work...
my only issue is: will the cut pot still function properly?

[fyl]

my only issue is: will the cut pot still function properly?

Both pots will be quite interactive but the cut function will still work.

[geoffmulberry]

Just finished the amp this morning...

It sounds good overall, but you kind of have to tweak the pots for it to sound right.

[J M Fahey]

Hey !! This one *is* a VOX !!
At least it says so.