Two years gone by - New Amp

It's been two years since I last posted here.  I've started a new amp project.  This one will involve combining the Fender Twin Reverb power amp, with the Sunn preamp used in their Sorado, Sonic II, 200s, and Sonic I-40.  An additional twist will be the use of 1614 tubes in place of the 6L6.  I am using a chassis I took from a Conn organ.  In the photos here I've mounted the power and output transformers.  No measuring for everything else.

Vibro Champ now running

Completed amp

Over the past couple of weeks I have tried to eliminate the HF oscillation that I have been getting from this amp. Taking my Dad's advice I removed the feedback loop.  This eliminated the problem completely.  The amp is now quite.  I am still experimenting with the two different power tubes that I have wired this amp to accomodate:  7C5 and 6V6.  Everything seems to work but I will check the voltages to see if anything is out of range.  Top photo is the complete amp minus the cab.  Second photo is the bare chassis after stamping of letters and numbers.  I also buffed with wire brush.  Bottom image is the schematic as things are at this point.  Not shown is the 7C5 socket wired in parallel with the 6V6

Chassis after letter stamping

schematic showing feedback removal

My latest acquisition.

Vibro Champ Update

The chassis prep is nearly complete. I have pots nearly all selected. I am adding push-pull pots to enable switching for tone stack and feedback loop. I've settled on a PS design with the help of the PSU design software from Duncan Amps. This allowed me to make use of a 4-part electrolytic capacitor. I had hope to use a 5.5H choke I pulled from a Knight-Kit, but an over zealous drill operator (guess who) over penetrated while drilling pot holes, and wrecked the choke. Import stuff: pilot light will be green. The 7C5 tube base had to be move from bottom mount to top mount. This 7C5 will be wired in parallel with the 6V6, which will allow "either/or" operation. Hope to have chassis fully loaded by end of August. If you get this update as an email remember to go to the blog to see full size photos.

Vibro Champ Clone

I've decided to postpone the Frankenstein amp (Conn 6020) and pursue a Vibro Champ (AA764) clone. Like the Frankenamp I have all of the parts that I need, but I believe the Vibro champ will be easier. With the other projects I have going I think it is a better fit. I have two solid state amps that will get attention soon. I will say this for the benefit of those who wanted to know how I was going to convert the Conn 6020, I am looking at the Ampeg Portoflex SB12 as a basis. As far as the Vibro Champ, I have one thing to resolve: the power supply. I have been rendering some old Knight Kits and one old Conar kit for parts. I hope to use a pre-Stancor Chicago Standard transformer and a 6X4 rectifier taken from a Knight-Kit O-scope.

Carmen Ghia Goof

It turns out that the problem I've had with this amp hasn't been a bad component but my error.  When I converted the Hammond AO-35 using the Phoenix schematic, I failed to ground a resistor that was tied to the terminal strip on the side of the chassis.  Grounding this resistor solved all of my problems.  My Dad found this problem while we were trouble-shooting this by phone.  Thanks Dad.  Click on the image to see it enlarged.

Frankenstein Amp to be "born"

It has been one year today since I last posted. Since then some caps on the Carmen Ghia have started leaking and producing awful noise. That project will be this summer. Now I am designing a "new" amp to be made from the main amp (model 6026) that came from the Conn Model 542 Minuet organ. What I hope to do with it involves adding a single preamp to drive the two power amps in parallel. The twist is that I hope to tie the two output transformers in series on the secondary side. Schematics will get worked out before November this year. I probably won't finish this until 2014.