The Amp Garage

Is anyone sure this is Dumble's work? IMHO this looks like a Rivera modified Fender, especially the 6 position mid switch. I have had a couple of these come across my bench back in the mid 70's when I was living in SoCal. It could have been how they recorded it, but the ones I played sounded much be...

Ok, I see the error of my ways. AC coupled follower input, not output.

AC coupled, huh? I guess I looked at the wrong schem. for a SSS. What is the point of running AC coupled followers to drive the PT's since they can't supply much grid current? Is there some other sonic effect that one gets?

I played a modified silverface DR that sounded very much like that amp on the video. Opened it up to see why it sounded so bad and found the 1st stage from the normal channel was cascaded into the vibrato channel thru a 0.047 cap. Terrible sound for me, but some people that tried it thought it sound...

Here's a thought that's maybe > 10 yrs too late for this thread. For a SSS amp, if you have cathode followers in both sides driving the power tubes, even if they are generating 2nd harmonic, it should be cancelled out (depending on how well the two sides are balanced) since the two sides are opposit...

Interesting. No grid stoppers on the power tubes? I have had a couple of 50 watt Marshalls (1987) on the bench that were like that(using EL34's however). They looked original. Personally, I like them with 5k6 grid stoppers..............but that's me.

If that is Webers take on the old JBL’s with the aluminum dust cap, then I agree. That should work well for a clean twin kind of sound. Never cared for those pushed into distortion, but for clean........

If this is like most of the VVR circuits I've seen, the zener is there to protect the gate (so as not to exceed the breakdown voltage of that oxide) of the MOSFET. If you look at the data sheets the Vgss is usually a fairly low voltage. If you exceed this you'll have to replace the MOSFET as you'll ...

Did you ever get this twin working? Like xtian had stated this doesn't look that bad. The sloppy lead dress is standard CBS Fender assembly as I have seen many times. I had a twin back in the late 70's that I used in cover bands. To be honest, I never really liked it that much. It had the pull-maste...

If you're worried and you don't have a VARIAC, then a small wallwart (that outputs AC) can be used. Most of these are DC(rectifier, filter cap) but there are some that are AC(just a stepdown xfmr). Something 6 - 12VAC would be fine and you could then verify 1:1 turns ratio using the low voltage AC o...

Current thru v2b is actually lower than the others based on the Vk and rK. Is the supply voltage the same on all the sections? You could try disconnecting the coupling cap feeding V2b....but if it was leaking you should have more current. The other thought I have right now is oscillation on that sta...

If you don't care for the std. volt. divider 68k - 68k setup, you might consider designing the input stage around a 12AU7. That way the headroom should be plenty high enough(and gain lower) and you wouldn't have to compromise input impedance. Just a thought.

Agreed regarding the Sound City 120. I had one back in the 70's. It had active tone controls, (6) EL34's, and the tone sucked. I think this might have been the amp that prompted the derogatory moniker "Sound Shitty". I ended up putting a modified Marshall circuit in it. It rocked quite hard after th...

The only thing I remember about late 70's was lost in a alcoholic binge of epic proportions.................seriously, I had a couple of Rivera modified fenders come across my bench back then. Here's what I remember(it's not much) 1. Fat switch was 6 position rotary switch that had caps in series in...

I think Gingertube's advice is good regarding the chance for low freq oscill. I had a deluxe rev that I had modded to an MB mark 1(sort of) by adding a gain stage on the front end. I ran all 4 preamp stages(2 pre tonestack, one post tonestack, one post rev 3.3meg resistor) off one PS node, but I was...