The Amp Garage

I'm feeling a bit more optimistic about my project tonight. I've always been a bit suspicious of the original 1960's wiring in the downstairs of my home, so I decided to move the project upstairs to a clean power source. The mechanical hum is still present, but at a much lower intensity. As I began ...

The sharded cathode and plate in the fender circuit is on the 12AT7 which is V3" not 4. Unless you want to use a real power tube to drive the input of a 8 ohm reverb pan then strapping the triode is the only way to go! The reverb design I uses a single triode to drive the pan via a transformer. The...

You need to narrow down which gain stage the issue is starting with. Starting with the first preamp gain stage lift the plate load resistor to unpower the tube and keep going down stream unpowering gain stages untill the issue stops and then you will know which area of the amp to focus on. Would pu...

We need to nail down what your hearing! Low E on a guitar is 82 HZ, so is the hum your hearing below that which would be 60hz like coming from the heaters , or is it above 82 HZ which would a 120 HZ ( a octave above 60 HZ) and coming from the D.C. Side of the power supply. One thing that gets folks...

Thanks for the comments. I decided to implement a Fender-style Hi / Low input scheme to give it a bit more flexibility.

Here's the most current picture of the chassis: IMG_20190127_210917703.jpg I finally installed the chassis into a cabinet, which has aluminum tape beneath the top panel. Unfortunately, this did nothing to reduce the buzz from the reverb circuit. What's worse, the amp now has an audible hum that was ...

So, I was able to filter out the hum by replacing the .01uf that connects to the reverb pot with 500pf.
However, I still have a residual buzz that is quite annoying.
Could this be resolved by bypassing the filter caps with a film cap? What value should I try? Other ideas?

Try to put the transformer and the tube after it on different power supply nodes [/quote] This does seem like a reasonable idea. I assume you mean that the triodes in V3 should be connected to different supply nodes? Thanks! [/quote] Darn it! I moved the recovery triode to another power supply node...

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Try to put the transformer and the tube after it on different power supply nodes
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This does seem like a reasonable idea. I assume you mean that the triodes in V3 should be connected to different supply nodes?
Thanks!

You didn't mention swapping the tube out. Did you try? Yes. I actually went so far as to remove the reverb tube altogether... the hum is still mostly there. It would appear that hum is being injected directly from the reverb pot into the grid of V2b. The connection between the reverb pot and V2 is ...

Then that means the source of the hum is the circuitry around the 1 tube reverb itself. Is there some stray high voltage or output transformer wiring near the tube? It could be injecting hum in that way, does it seem like 60hz or 120hz hum? ~Phil The only transformer near the reverb tube is the rev...

I just remembered... most of the hum is still present with the reverb tank disconnected. I'm not sure what to make of this observation...

Another common issue is the tank grounding. Sometimes you need to test by jumpering between the tank and the chassis to see if grounding it works (I.e. some tanks aren't grounded from chassis to the rca jack(s). If that resolves it I think it's just a matter of connecting the chassis of the reverb ...

Can you show us how this sits in your whole circuit relative to that Vox schematic. I made one of these a year ago and appreciate the idiosyncrasies of that schematic!! The reverb circuit replaces the original V3 and all the components directly connected to it. C5b is the same C5b you see in the or...

Thanks for the comments!
The chassis is not yet installed in a cabinet, so there is actually quite a bit of distance between the transformer and the tank. I've also tried another tank and cables from another complete amp; same issue.