Restoring an old Garnet amp

[mayfly]

Ladies and Gentlemen,

I present to you my latest project.  I'm going to restore an old Garnet amp.  But not just any old Garnet amp.  I'm referring to the Garnet that for many years was the test mule for Mayfly amps.  Yep, this was the amp that I tried all my experiments in.  You name the experiment, and it was done up in this amp.  Two channel high gain shred machine?  yep.  Master volume?  Every single type.  Sophisticated switching?  As many relays as I could fit.  DC heaters?  sure thing.  Triode mode?  oh yeas.  Cathode bias?  Pick your tube.  tremolo?  several preamp and bias circuits.  Reverb?  uh-huh - including separate dwell and wetness controls.  You can hear this very amp on EFARM's first album "Doomed anyway"  http://www.cdbaby.com/cd/EFARM.  Just don't ask me what circuitry was in the box at the time...

And this brings us to the amp as it is today:  It's set up as an acoustic guitar amp.  Yes, this was what I was working on back in the day: an all tube acoustic guitar machine.  This included special pre-amp circuits for bridge pickups, variable feedback gain control, an ultra-linear output stage with a heavy duty transformer, baxandall tone circuit, a direct XLR output with gain control, and

are you ready?

a TWEETER!  :headbang:

I don't do any tube amp experimenting any more, preferring to play around with my AxeFX instead. So it's time to put her back the way she was - a straight up guitar amp.

More on this, and Garnet in a bit, but here's some photos of how she is right now.  The tweeter is in the third picture:

 

[fdesalvo]

Gut shot or it never happend!  :headbang:

 

[mayfly]

Gut shot or it never happend!  :headbang:

Well, it hasn't happened yet...

 

[mayfly]

alright!  Let's get down to business.  The goal is to undo all the butchering that the amp underwent during the 15 odd years that I was experimenting on it.  First things first - let's yank out that tweeter:

There it is - all snug and nicely installed.  Turns out I had to take the thing apart to get it out of there!  I have no idea how I put it in in the first place.  Here it is yanked out:

and here's the hole it left:

Don't know what I'm gonna do about it yet, if anything. I figure that I can cut a nice hole out of 3/4 birch plywood using a hole saw and then just glue it in there.  A little paint and no one's gonna know  :icon_jokercolor:

 

[fdesalvo]

Gut shot or it never happend!  :headbang:

Well, it hasn't happened yet...

As stated in your intial post, my good sir.  Just wanted a "before" shot.

 

[mayfly]

Speaking of guts, the thing has the original tubes!

I'll hang on to those thankyouverymuch.

and here's that gut shot:

Lots of crap here.  perhaps about 1% of the original amp remains - the power transformer!

 

[fdesalvo]

Ah, look at all that room!  Can't wait to see your progress!

 

[mayfly]

There are the remains of many experiments in this here amp.  For example, here's a dual bias supply:

and apparently I was really big on filter caps:

on the lower part of this shot you can see the XLR balanced output.  Tube driven no less!

and here's the holes left from the regulator when I had a regulated DC heater supply in the amp:

There are many many other holes, abandoned bits of circuitry, and other evidence of the many experiments done on this amp over the years.

 

[mayfly]

ok - let's gut this sucker!

here's the beginning....

 

[mayfly]

and here's the end!

:evil4:

You can see that at some point I added another preamp tube for something or another.  I pulled that out.  Only the stock power transformer and the stock sockets remain.  Oh - and I left in the output jacks - those are the original wires there and I didn't want to de-value the worth of the amp by disturbing stock circuitry  :icon_jokercolor:

 

[mayfly]

Onto the next phase - the original circuit. 

I got this amp so long ago I have no idea what the circuitry is supposed to be.  There is a clue from the model number:

so it's a G100TR.  What the heck does that mean?

Looking up information on Garnets is a little tricky.  They are not like Traynors where there is a lot of information available from the manufacturer (which still is cranking out gear).  Garnet stopped producing back in the 1980s and the founder has since passed away.  In addition they made a HUGE variety of models - over 58 different ones with the Garnet name and probably that many or more re-branded models that they made for other vendors like Sears Canada.  And you thought that fender made a lot of different amp models - Leo has nothing on Garnet baby!

According to one Garnet website, a G100TR is a "Revolution II" combo.  According to another it's a "Revolution III" combo.  Poking around a little, the Revolution II is a two channel amp with tremolo, reverb, and a master volume.  The Revolution III is similar, but only a single channel amp.  But hold it - some Revolution III heads are two channel as well.  Then there is the pro which is kinda similar, and then the famous session man - which is similar again but with two 12" speakers.  Where to start?

What we know about this example is that it is a two channel amp, with vol, treble and bass in one channel, and volume, treble, mid, and bass in the other.  There is a tremolo with speed and intensity, and a reverb circuit.  there is a master volume, and - get this - a "solo" volume boost control with footswitch!.  It's a 1x12 combo with two 6L6 tubes, fairly low B+ voltage, and a fairly small power transformer.  I kept a lot of the original parts in a box, and included among them are several push-pull pots and a three pin mosfet.  Interesting.....

So what I'm gonna do is start diving into the Garnet schematics that are available out there and try to get a match. 

Here we go...

 

[Mor Paul]

This is gonna be good.

 

[thebutcher85]

Man that's awesome!!!

 

[mayfly]

Gentlemen,

The plot thickens.  Much of the circuitry does not match the G100TR schematics that are out there.  Instead, because of the number and type of caps and the lack of a choke in the amp, the power supply seems to be more like a GS100R.  In addition, the "solo" circuit is kind of like the one in the GS100R, but because of the existence of the tell-tale mosfet and the bunch of push/pull pots, the rest of the preamp seems to be from the G250TR session man.  Also, the GS100R has a cascaded gain section, which is absent from the G250TR.  The power amp could be from the GS100R or from the G100TR, but both of these use a long tailed pair in the phase splitter and there are not enough tubes for that.  The phase splitter is the only thing that could come from the G100TR schematics out there that I see.

So we have a conundrum. 

 

[thebutcher85]

Mayfly, you are legendary. This thread is awesome!

 

[fdesalvo]

where's that mad scientist emoticon?

 

[mayfly]

Gentlemen,

I think I have run into something that will save my ass:

http://www.garnetamps.com/book.htm

I've ordered up a copy!  We shall see.

 

[bagman67]

Are you sure it was stock when you initially got it?

 

[mayfly]

Yep.

 

[bagman67]

Hm.  Maybe you got some Garnet employee's experiment. Very interesting.


Just let me say, also, Trevor, that this thread is a sterling example of why it's cool to hang around on this forum:  tremendously knowledgeable folks, sharing their interests and experience, and gleefully charging into opportunities to learn and do and make stuff.  Thanks.