Grommes 50PG into a Guitar Amp?

[Cygnus X1]

http://cgi.ebay.com/ws/eBayISAPI.dll...MEWN:IT&ih=005

Edit: This link does not seem to work.
It is a Precision Audio Grommes Little Jewel.
Some of you may be familiar with it.

A friend sent this one to me.
He wants it gutted, and built into a "guitar amp".

It has 6 octal sockets. It was a 10 watt monoblock.
I have no idea what the primary impedance of the output transformer is.

I was thinking 5C3, Tweed Deluxe...with 6SC7 preamps,
2x6V6, 5Y3 rectifier. I would leave that 6th octal slot empty.

One issue is I want to use those bass/treble controls as-is.
I don't know how to wire a tweed "tone" control into "bass/treble". I glanced at the Pro-Amp, the Bassmans, but it looks like using the combination of the octal 6SC7's is just something they didn't do.

The phono/radio switch on the far left could be an internal jumper for a single jack system. I plan on using just one jack, one volume control.

Any ideas here?

And any clue how I could use the existing output transformer?
I think the PT would be sufficient.

Thanks, and have at it!

[Structo]

I just added a tone stack to a version of a Deluxe.
I made it so it only had one input as I wanted to use both halves of the first tube rather than have dual inputs.

Here is what I did.
I used 250KA pots.

The 100K resistor is the slope resistor and this sets the frequency knee for the stack.

This really gave me a range of sweep on the volume control where as before with just a 1M tone control it was almost off and on.

This diagram isn't exactly what I used but similar.
If I recall, I don't have a resistor going from the bass pot to ground.

[Cygnus X1]

Thank you, structo!
I not only have this one to plan...I have one I have built that is really too loud to tame.

I ought to try it on that one first.

Wait.
I was browsing the Tweed vs. Blackface.
AA763 is Blackface, right?

I ought to dig further before asking.
My understanding was that a BF circuit is vastly different than the 5X3 circuits. I have built the 5E3 tweed, but never the BF.

[Structo]

Yeah, pretty much totally different between tweed and blackface circuits.
The BF circuit has a long tailed pair PI for one thing.

[Cygnus X1]

Oh...fudge.
The 5C3 schematic calls for 16uf on the filter caps.

I have a bucketload of 10uf/500V.
Do you suppose that is close enough?

[Structo]

You could put a couple in parallel for 20uf.

[Cygnus X1]

On the other hand-the original Grommes are 40uf.

Given the assumption that the PT isn't exactly what Leo called for...then maybe I ought to stay with the 40's and check B+ to see what shows up.

Hmmm?

[Structo]

Although I just built my first tube rectified amp, I became aware that tube rectifiers have a limit on how much first stage filtering they can take.

On my 5U4GB it is 40uf.

On a 5Y3 it seems to be 32uf?

Another data sheet said 10uf so I'm not sure which is correct or why it matters.

[Cygnus X1]

I cleaned up the chassis, and built the basic board for the 5C3. Wired up the heaters and pilot lamp.
It takes more time converting than building from scratch!

I'm lazy-how do I throw in a basic Treble/Bass control circuit instead of a "tone" control?
In the absence of an answer, I'll start looking at tweed bassman circuits.

[Cygnus X1]

Arf. Arg. My brain hurts.
Help me out please...

I want to use that bass/treble control on the Grommes and incorporate it into the "tone" control for the 5C3 tweed.
So I looked at the 5F4 schem, and came up with this:

Treble lug 1 runs to 6SC7 #2, pin 2.
Treble lug 2 runs to 6SC7 # 2, pin 4.
Bass essentially goes to ground through a tone cap.

One of the issues I'm dealing with is one is a 12AX setup, and I'm using 6SC7's for preamp tubes.

Check the 5C3 schem, and see if that seems correct before I Kurt Cobain myself here.


https://taweber.powweb.com/store/5c3_layout.jpg

5F4:
https://taweber.powweb.com/store/5f4_layout.jpg

[Cygnus X1]

Bump.

Anyone have any ideas about this?

[Wayne]

The 5C3 is a one-knob tone control; the 5F4 is a Bax. It's not clear to me from your posts which one you are trying to implement.

There are a few different ideas on this page:

http://amps.zugster.net/articles/tone-stacks

including layouts for building them right on the backs of the pots. Hopefully this will help.

As far as which tube is being used, it shouldn't matter as long as you pay attention to which element of the tube connects where.

W

[Cygnus X1]

I am attempting to put in a bass control and a treble control in place of a tone control.

In a 5C3 circuit.

[Cygnus X1]

I went by the schem to get it built, just a tone control for now.

It is in break-in right now. It has tone very similar to my other Tweed Deluxe project, the 5E3.
But two things I have noticed right away. Lower overall volume, and less headroom. So I think I am going to play with the dropping resistors on the preamp tubes, and look closely at the bias on the power tubes. Correct me if I'm wrong about what to do with the preamp tubes. I'm not going for high volume with it.

I tried some 6V6 GTA's, and it likes older Sylvania GT's the best.
The GTA's seem to run too hot and break up, but not in a good way. (fizzy). I tried a few different 6SC7's, and it didn't change the tone much at all. The Fisher 5Y3 recto is solid. I also swapped in and out RCA, GE, Tung-Sol. No difference in "sag", and didn't show any significant drop on the meter under load, so it stays.

I never did get a primary impedance value on the output transformer, but I suspect it is a soft, conservative value for hi fi use. It warms the amp up quite a bit (sonically-it "runs" cool).

It is very quiet, hum free.
I haven't learned much, but I know how to run grounds, and not rely on the chassis. I could build these things in a cardboard box!

I'll spend some more time on it this weekend. It promises to be really sweet!

[M Fowler]

I have another version of this 5C3 schematic to see if the differences may better suit you. Filter caps are 30, 20, 20 at 350v.

Mark

Argh can't get it load up right on my end. Okay here we go.