Gies Audio 18 Watt 2 Channel Tweedish AB763ish

[purpletele]

One of my first Amp Projects was a Marshall 1974x Clone from GDS Amps.  It has been a great platform to experiment.

The amp had been remodeled twice, and I wasn't satisfied and thought I could do better.

I discussed my concerns on the amp with Joe Gies.  He is familiar with my projects and inventory and suggested that we get away from the Marshall thing slightly by adding the 'Tweed Tone and Volume Control'

He designed an AB763ish circuit for the second channel.  We added a Pull Out Presence Control which really engages a change of tone!

We used top shelf components and I have some nice tubes throughout, the amp sounds fantastic.

Recently I contacted Joe to discuss the second channel and it's intensely strong signal.  We discussed options, the first was a PPIMV.

I went through the surgery to install the PPIMV which works wonderfully, however it didn't affect how the second channel reacts,  The volume on the second channel would get REAL loud at 7:30, where 6:00=zero.

Joe recommended a Plate Load Resistor Voltage Divider which was very easy to implement and it worked wonderfully.  The difference in volume between the channels is still large, but the tone of each channel individually is really unique and definitely a keeper.

The cabinet was made by Stagecraft and the speakers are a C Cream and a C Gold.  They sound fantastic, but very efficiently loud in the closed back cabinet.  Great Jazz/Blues Amp with Deep Rich Bass

The work that Joe did was really special and the drawings were top notch and accurate.  Very much appreciated.

Purple Tweed all Through My Head

Very Cool Amp for the lab/studio.

BV

[purpletele]

Update:

Blending the channels can be a sonic delight!  That is new for me

Killer tones! :

[sluckey]

Blending the channels can be a sonic delight!  That is new for me

That surprises me. Your schematic shows the two preamps will be out of phase at the point they mix together. Jumping the inputs together should result in a lot of signal cancellation the usually sounds thin or even a bit nasal.

[purpletele]

Blending the channels can be a sonic delight!  That is new for me

That surprises me. Your schematic shows the two preamps will be out of phase at the point they mix together. Jumping the inputs together should result in a lot of signal cancellation the usually sounds thin or even a bit nasal.

SL,

I will wait for Joe to describe what we have going on as far as phasing.

From a sonic standpoint it sounded cool, I will try that again to make sure it was a muddy mess I was hearing.

I did have a large variance of signal coming through the second channel.  We installed a voltage divider on the Plate Load resisters that that helped quite a bit.

BV

[jojokeo]

Blending the channels can be a sonic delight!  That is new for me

That surprises me. Your schematic shows the two preamps will be out of phase at the point they mix together. Jumping the inputs together should result in a lot of signal cancellation the usually sounds thin or even a bit nasal.

It's what I also thought sluckey. I worked with what was there to work with. This was using the existing tube sockets, control panel holes, component board, etc. Since PT already had a few other amps I mixed some Fendery preamp ideas with mostly an 18 Watt power section. Ch 1 to be tweedy and defeat the Presence for the old school tone and feel then the AB763 basic idea with some NFB. I figured it would need another stage for proper phasing as PT mentioned on trying but that wasn't the end goal here and I didn't want to cascade Ch 1 defeating that tweediness. The paralleled tweed stage is fantastic as is and I'm sure you've done this many times already.


I've not built this amp myself only parts of things here and there as it's all sort of basic. The one thing I considered doing was utilizing the other side of the phase inverter for the second channel but phase issues would still remain but I'd not have had the Presence option.


Another neat option idea would be to make a switched jack on the back from Ch 1 with a voltage divider to then run into Ch 2 for some cascading high gain onslaught grind!? But it's PT's amp and playtime.

[jojokeo]

I did have a large variance of signal coming through the second channel.  We installed a voltage divider on the Plate Load resisters that that helped quite a bit.

Remember, that these can easily be changed to adjust the output to the desired amount to better match Ch 1's and just chose 50% as a starting point.

[purpletele]

Another neat option idea would be to make a switched jack on the back from Ch 1 with a voltage divider to then run into Ch 2 for some cascading high gain onslaught grind!? But it's PT's amp and playtime.

I like that idea, but I think I want to get to know and understand the amp for a while.  It's slated for a show soon with the nice speaker cab. So far I haven't had any amp failures during shows so I am really pleased with that.

I have a feeling I am going to be learning a lot about the Wrecked Bassman circuit real soon as that on comes together. 


BV

[jojokeo]

I like that idea, but I think I want to get to know and understand the amp for a while.  It's slated for a show soon with the nice speaker cab. So far I haven't had any amp failures during shows so I am really pleased with that.

I have a feeling I am going to be learning a lot about the Wrecked Bassman circuit real soon as that on comes together. 


BV

As long as the tubes & trannies hold up the amp will be solid and very dependable.

Please re-read my comment on the other thread.

[chocopower]

There are a mistake in the schematic.
Are you grounding the cathodes of the parallel triodes?

[sluckey]

There are a mistake in the schematic.
Are you grounding the cathodes of the parallel triodes?

You are correct. Surely that's just a drawing error?

[purpletele]

Chocopower & Sluckey,

Thanks for the catch. 

I am getting much better on working with a schematic, however, I need to consult with Jojokeo to review, inspect and correct if required.

I looked on the schematic and I cannot determine where the parallel triodes that are shown as grounded.

Thank you, I am interested in solving all of the above.

BV

UPDATE: I am not sure of what the error as mentioned would do to the tone, but this amp has a wonderful tone in each channel, but nothing exotic, just cool tone.

[sluckey]

.

[purpletele]

.

Thanks Sluckey!

I can say for certain, I wouldn't have referenced that detail unless I had an issue and we had to trouble shoot deep.  I am sure Joe will see this soon and correct the error.

So I have to deduce that the layout is correct and my wiring is correct.

BTW: I blended the channels again to see if I heard what I heard before.  I did get a fantastic tone again, but it is really just feels and sounds like the second channel just swamping the first channel and taking over.  It sounds killer, but it sounds killer when you unplug the blend, so big deal, right.

It is being discussed to be used at a show this Sunday for the band Auburn Road.  My colleague has been helping as rhythm guitarist.  Supposedly a cool trio of young gal singers.

BV

[jojokeo]

There are a mistake in the schematic.
Are you grounding the cathodes of the parallel triodes?

You are correct. Surely that's just a drawing error?

Yes, simple mistake with jsch program, thanks for helping point it out.