modding a 15w class A amp

David Atkinson · Post by **David Atkinson** » 8 Mar 2013 2:23 am

Hi All

First post here but avid reader while I await delivery of my first steel.

If anyone has any thoughts or advice on modding a small tube amp, it would be great to hear.

I have a SJB Audio 'Ant' amp kicking around that seems suitable for turning into a flexible home/small club amp for PSG. I don't know much about the builder other than it was a one man operation in Somerset, England, back in the 1990s.

It's Class A, point-to-point wired and has a 5Y3 rectifier (behind PT in pic); a 6N7GT and a pair of 6V6 power valves. It currently has a 75w Fane 12" speaker in it.

Other specs: volume and tone controles, normal & bright inputs, speaker out, ipedance control.

So, would it be possible to speculate on what mods might clean up the tone (it gets crunchy at 50% volume) and what speaker might be a suitable replacement? The Fane sounds boxy with regular guitar...

Sorry for long post, and thanks in advance for your input.

David

Jim Pitman · Post by **Jim Pitman** » 8 Mar 2013 3:23 am

I'm guessing it might be about a 10W amp?
It might be difficult to get by with it in all public situations especially playing with other musicians, namely a drummer.
It's the type of amp used to get a nice over driven sound at lower volumes that a regular electric guitar player would use.
I have a 25W tube amp and just barely get by with it. Some gigs I can compete with the wall of guitar sound.
You could make a mod to move the point where the distortion sets in on the volume control but I really don't think you will increase the clean volume any.
My experience is the output section is over driven not the pre-amp, and this is limited by the output tube/transformer. (albeit that output T looks big)
Perhaps some of the tube amp gurus here can chime in.

David Atkinson · Post by **David Atkinson** » 8 Mar 2013 3:39 am

Thanks for your thoughts.

Yeah it is approx 12 - 15 watts

As it has a DI out I had envisaged using it as a personal monitor on stage and running it through a speaker emulator to the PA - Not sure how that would work but seems to make sense in my head!

Wouldn't be up against a maniacal drummer or loud guitarist in current situation.

Jay Fagerlie · Post by **Jay Fagerlie** » 8 Mar 2013 9:42 am

David-
Does the output transformer that connects to the two 6V6 tubes use two wires or three?

Do you have a schematic?

I can suggest some things for more headroom.

Jay

Donny Hinson · Post by **Donny Hinson** » 9 Mar 2013 6:12 am

Class "A" amps are among the cleanest out there. But like Jim, I think that if it is running class "A", the maximum clean power you'd ever see woulld be about 10 watts...and frankly, you can't expect much for pedal steel from an amp that small. (Pedal steel and straight guitar have vastly different requirements for amplification.) While it might be okay for practice, it would likely fail miserably at a gig, even if you doubled the power.

Rather than hacking up an amp that might be valuable, I'd suggest you find another amp. Or maybe, you could try a super-efficient speaker (like an SRO, Gauss, or EVM) in a closed-back cabinet. (That could effectively double the loudness, but you'd still probably be "under-powered" for most gigs.)

David Atkinson · Post by **David Atkinson** » 11 Mar 2013 12:58 am

Jay Fagerlie wrote:David-
Does the output transformer that connects to the two 6V6 tubes use two wires or three?

Do you have a schematic?

I can suggest some things for more headroom.

Jay

I don't have a schematic and am not close enough to the amp to check the wires at the present time. Will have to look at this later.

Cheers

Lee Holliday · Post by **Lee Holliday** » 27 Jan 2016 12:05 pm

David do you still have the Ant amp???

If so how did you get on with the steel link up.

I have both an Ant and more recently have acquired a Hornet as well I will get some photos up on photoshop to give a better illustration.

Lee

David Atkinson · Post by **David Atkinson** » 28 Jan 2016 1:30 am

Hi Lee

Sorry saw your PM before your post.

I still have the Ant but it's sat unloved in my cupboard since this thread.

I opted for a cheap Mustang III for steel that's so-so, but good enough for the time being. When I'm a bit more flush I'll get the Ant fixed.

Great to see some pics of your SJBs - they are great little amps.

Cheers
David

Lee Holliday · Post by **Lee Holliday** » 28 Jan 2016 5:45 am

David check out Malcolm Hine in North London to get your Amp looked over.

He is also manufacturing his own tube Amps which look quite interesting.

Regards

Lee

ajm · Post by **ajm** » 28 Jan 2016 9:05 am

FWIW, I just noticed that this topic was revived after 3 years since the last post.

Michael Brebes · Post by **Michael Brebes** » 28 Jan 2016 9:52 am

Doing some research, it looks like it is probably based on an early Fender Deluxe schematic, 5A or 5B. Class AB cathode biased push-pull. They are about 14 watts.

Lee Holliday · Post by **Lee Holliday** » 28 Jan 2016 1:39 pm

My three great little Amps, nothing complicated. More suited to Lap steel though as there are little or know effects.
Lee

Lee Holliday · Post by **Lee Holliday** » 28 Jan 2016 1:48 pm

Keep it simple

Jim Pitman · Post by **Jim Pitman** » 28 Jan 2016 3:20 pm

I bulit myself a SE class A 1/4 watt tube amp, output transformer included, that's buffered by a solid state class A/B power amp section. The SS section has no voltage gain just impedance matching. I tell ya , it's got "it".
It sags then blumes a bit if you hammer it hard just like a tube amp does to provied a bit of compression. it's totally clean otherwise up to 70watts. It can fill a room even with the eminence 12" speaker I have in it.
I use if for steel but it's an awesome regular guitar amp too.

David Atkinson · Post by **David Atkinson** » 28 Jan 2016 11:42 pm

Love the pics Lee. I once tried a Hornet and they sounded great too. Shame I didn't buy it at the time.

That Velocette is a great amp too. I remember them from the late 90's. I think they became the tube amps that Gibson produced for a while in the early 2000s after they acquired Trace Elliot.

Good stuff!