SE 5w amp design

Aethelbert · 10-05-2007, 10:08 AM

I am building my first amp and I'd really appreciate some input if anyone would like to help.
It's going to be a small low wattage combo (5w approx) loosely based on a champ/princeton . I have, perhaps rashly, got my parts together and the cabinet is built. I'm at the stage of getting the circuit down on paper and figuring out the layout.
Criteria are for low volume ie suitable for playing around the house with the capacity to dial in some bluesey-rock overdrive, again at relatively low volume. I have been poring over various schematics and reviews to narrow down my options so I'm drawing on Fender champ (5F1/2), Vox AC 4 (without tremelo), kalamazoo model 1 and epiphone VJ and galaxie 10.
So what I have is --deep breath-- a JJ ECC83/12AX7 preamp with an EL84 output (also JJ), Hammond 125ESE op transformer, Jenson C8R 8" Ceramic 4 Ohm and a Hammond 260c power trans with EZ81 rectifier.
I figure this will give me around 320v DC, which I understand is about right for a champ. Does anyone have any comments on voltages/resistor selection for the tubes I've got? Or know of any software or tutorials that would help me?
Also I have not yet settled on whether to go for
1/a simple tweed treble bleed and volume
in--G1--tone--vol--G2------------
2/or go for a blackface bass and treble style setup
in--G1--tone--vol--G2------------
or full tone stack with gain and master pot (more like an epiphone galaxie 10).
3/in--G1--Gain--G2--tone--vol----
Any input on this would be greatly appreciated!

MWJB · 10-05-2007, 11:34 AM

You may not get as much as 320vdc under load, which is fine for a EL84 (Champs run much more than this with a 6V6). Use a grid stopper if going with EL84, use the smallest value that keeps the amp stable, start at 10K and work down if you can.

I'd go for option 1 re tone controls - 5F2A Vol & tone, a full tone stack will increase headroom. In fact, 5F2A plus a switch to drop out the tone pot would be my suggestion (a 5F1 to 5F2A switch if you like).

Aim for 150vdc on 12AX7 plates, tweak value of power supply resistor that feeds 100K plate resistors.

Aethelbert · 10-06-2007, 01:05 AM

Cheers for that, really very much appreciated. It is a job to know quite what to do, as I'm obviously not going for a faithful reproduction. I guess that might have been easier but hey-ho, I think I'm learning more this way!

Aethelbert · 01-11-2008, 11:29 PM

Finally finished my 1st amp before Christmas. It's taken nearly 9 months (granted it gathered dust for 6 of those!).
Anyhoo I'd just like to say here that I can highly recommend bluebell audio- sourced many of the parts from them, delivery was prompt and customer service was absolutely first rate.

Manic · 01-14-2008, 04:45 PM

Congrats on Your build!

If I were to build that amp I might have stepped up to a 12 inch speaker....
since it wasnt going to be a faithful champ/princeton.

FWIW C Smith

myboysherman · 01-15-2008, 01:12 AM

Since you mentioned the AC 4, here are some thoughts for your next amp:

I was disappointed with my AC4. On the other hand, I had great success with the EF86 in another design. Vox uses a 5.5M g2 for the AC4 while my other amp used 1M (like my data sheet suggests) in an otherwise similar stage. Not sure if that explains it since the two amps were otherwise very different after that first gain stage.

I have other plans for the chassis, so I will never know. But you might want to reconsider the AC4 and try it with a few different g2 resistor values.

10-05-2007, 10:08 AM	#1
Aethelbert Junior Member Join Date: Oct 2007 Location: UK Posts: 3	SE 5w amp design I am building my first amp and I'd really appreciate some input if anyone would like to help. It's going to be a small low wattage combo (5w approx) loosely based on a champ/princeton . I have, perhaps rashly, got my parts together and the cabinet is built. I'm at the stage of getting the circuit down on paper and figuring out the layout. Criteria are for low volume ie suitable for playing around the house with the capacity to dial in some bluesey-rock overdrive, again at relatively low volume. I have been poring over various schematics and reviews to narrow down my options so I'm drawing on Fender champ (5F1/2), Vox AC 4 (without tremelo), kalamazoo model 1 and epiphone VJ and galaxie 10. So what I have is --deep breath-- a JJ ECC83/12AX7 preamp with an EL84 output (also JJ), Hammond 125ESE op transformer, Jenson C8R 8" Ceramic 4 Ohm and a Hammond 260c power trans with EZ81 rectifier. I figure this will give me around 320v DC, which I understand is about right for a champ. Does anyone have any comments on voltages/resistor selection for the tubes I've got? Or know of any software or tutorials that would help me? Also I have not yet settled on whether to go for 1/a simple tweed treble bleed and volume in--G1--tone--vol--G2------------ 2/or go for a blackface bass and treble style setup in--G1--tone--vol--G2------------ or full tone stack with gain and master pot (more like an epiphone galaxie 10). 3/in--G1--Gain--G2--tone--vol---- Any input on this would be greatly appreciated!

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10-05-2007, 11:34 AM	#2
MWJB Old Timer Join Date: Jun 2006 Posts: 1,926	You may not get as much as 320vdc under load, which is fine for a EL84 (Champs run much more than this with a 6V6). Use a grid stopper if going with EL84, use the smallest value that keeps the amp stable, start at 10K and work down if you can. I'd go for option 1 re tone controls - 5F2A Vol & tone, a full tone stack will increase headroom. In fact, 5F2A plus a switch to drop out the tone pot would be my suggestion (a 5F1 to 5F2A switch if you like). Aim for 150vdc on 12AX7 plates, tweak value of power supply resistor that feeds 100K plate resistors.

10-06-2007, 01:05 AM	#3
Aethelbert Junior Member Join Date: Oct 2007 Location: UK Posts: 3	Cheers for that, really very much appreciated. It is a job to know quite what to do, as I'm obviously not going for a faithful reproduction. I guess that might have been easier but hey-ho, I think I'm learning more this way!

01-11-2008, 11:29 PM	#4
Aethelbert Junior Member Join Date: Oct 2007 Location: UK Posts: 3	Finally finished my 1st amp before Christmas. It's taken nearly 9 months (granted it gathered dust for 6 of those!). Anyhoo I'd just like to say here that I can highly recommend bluebell audio- sourced many of the parts from them, delivery was prompt and customer service was absolutely first rate.

01-14-2008, 04:45 PM	#5
Manic Member Join Date: Jan 2007 Location: KC MO Posts: 93	Congrats on Your build! If I were to build that amp I might have stepped up to a 12 inch speaker.... since it wasnt going to be a faithful champ/princeton. FWIW C Smith

01-15-2008, 01:12 AM	#6
myboysherman Junior Member Join Date: Jan 2008 Posts: 5	Since you mentioned the AC 4, here are some thoughts for your next amp: I was disappointed with my AC4. On the other hand, I had great success with the EF86 in another design. Vox uses a 5.5M g2 for the AC4 while my other amp used 1M (like my data sheet suggests) in an otherwise similar stage. Not sure if that explains it since the two amps were otherwise very different after that first gain stage. I have other plans for the chassis, so I will never know. But you might want to reconsider the AC4 and try it with a few different g2 resistor values.

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