The Amp Garage

My thought was keep the load similar to the Second Gen to preserve its character, and allow some plus/minus on the level coming out of the OD wrt the fixed divider in the Second Gen layout. The main point is, however you do it, the Ratio control provides for adjustment of the OD output without goin...

Thanks, Martin. Bear with me for a minute because I'm just a tax lawyer and the theory and math side of EE is not my strong suit. I think what Martin is suggesting would be to add a typical 4th/5th Gen ratio control. In all of the Dumble designs I am familiar with there is a series resistor there (i...

Here is a video of him playing the amp live back in 1988. I believe that is his dumbleator sitting on top of it. I noticed the amp did sounded a little darker here with the dumbleator. It still sounds amazing!! I wonder if the ageing of the components over time also changed the sound of the amp. ht...

FET is sorted and sounds good. At some point in testing yesterday, I realized my standby switch was wired incorrectly (essentially like there was no switch in circuit). I easily found the mistake, but for the life of me could not see where the OT CT, choke, and standby were supposed to be tied toge...

FET is sorted and sounds good. At some point in testing yesterday, I realized my standby switch was wired incorrectly (essentially like there was no switch in circuit). I easily found the mistake, but for the life of me could not see where the OT CT, choke, and standby were supposed to be tied toge...

Stephen1966 wrote: ↑Sun May 12, 2024 1:06 pm How is that J201 sounding? Does it or the circuit do anything to raise the sound floor?

I had to pull it and replace with an NTE 452. The J201 wouldn't bias, I think the drain resistor probably needed to be adjusted too. At least for that J201.

-Dan

FET is sorted and sounds good. At some point in testing yesterday, I realized my standby switch was wired incorrectly (essentially like there was no switch in circuit). I easily found the mistake, but for the life of me could not see where the OT CT, choke, and standby were supposed to be tied toget...

New FET biased up easy. I set it for just under 3 for the Vdd/Vd ratio. It sounds good, but the volume is lower than the normal channel even with the FET trimmer wide open. I may bring the ratio closer to 2.5 and see if that helps. What are the voltages at the top and bottom of the drain resistor? ...

New FET biased up easy. I set it for just under 3 for the Vdd/Vd ratio. It sounds good, but the volume is lower than the normal channel even with the FET trimmer wide open. I may bring the ratio closer to 2.5 and see if that helps. I played the amp for a bit just to get a feel. It sounds very nice. ...

Hi Martin, I think you are correct and it is just varnish. This PT is old and looks a little funky. After I swapped in the JJs, there was still an odor. It seemed like a lot less strong, but at this point my mind may be playing tricks on me. Also, I could not get this J201 to bias in range. It wante...

Thanks guys. I'll leave the bias resistor alone for now. The other tube biased lower maybe around 55-57%. I pulled the tubes, sprayed compressed air, cleaned the sockets with deoxit and a toothbrush, looked for any leads that may be close and causing arcing, cleaned the female side of the socket, an...

Very cool, thanks for sharing!

Preamp glass for now. V1 and V2 are RCA grey plate 12AX7A. V3 is RCA black plate 12AT7. PXL_20240510_164414227.jpg Power tubes are fender branded Sylvania short bottle 6L6GC with double top getters. PXL_20240510_164448700.jpg When I swapped the tubes I noted 2 things. First, with the bias set most n...

All good with the smoke test and forming the caps. Put my startup tubes in and biased the amp. All functions are working. Tone stack is not super effective, but I think that is just the design. Reserving tone impressions as I only played briefly and at low volume. But does strike me as more raw sou...

Looks great!