The Amp Garage

Well it may be preferable to ground the power amp components at the other end near the PT but if it`s working ok thats good. The main thing though is just make sure the earth ground from the ac inlet is on its own on a short wire from the inlet socket and very securely fixed to the chassis as the l...

Here is the current state of the chassis. All grounds connect to the Ground Lug near the inputs, except the Dwell Pot, RCA Jacks, and Tremolo Foot Switch Jack that are grounded to the chassis. Once parts arrive, I plan to isolate everything, so there is only a single ground connection point on the c...

Ok then, what hum frequency are you reading at idle at the speaker jack(s)? Is it only there when you have a speaker plugged in as compared to a load resistor? I revised the grounding scheme so the center taps, earth ground, filter caps, and speaker jacks Re all grounded at the lug near the inputs....

Yes, that's what I want to know at this point! Bypass that whole dam circuit and pump it into the PI section and report back please?! There is hum even without any if the preamp tubes, so there must be a grounding problem. With each added tube, the hum increases a bit. I think I will start by isola...

earl2 wrote: ↑Fri Feb 01, 2019 7:53 pm I ground them where the center taps go next to the power transformer and everything preamp at the other end near the input jack. Never had any problems doing it like that.

Dang... New filter caps, changed grounding... Same issues! I'm out of ideas...

I recommend multistar grounding with one star grouding for each power supply node. Keep the distance between the different grounding points at least 2" Would it be best to ground the power tube filter caps near the speaker jacks? Alternatively, I could simply ground it to the same location where th...

As I pulled the filter caps in anticipation of installing new ones tomorrow, I realized that my grounding scheme may be to blame for some of the hum. My original layout connected all the filter cap grounds to a lug near the inputs. When I install new caps, I believe I should connect the ground of th...

I measured ac ripple in my power supply. The first node has 5.5v. The rest are more like 0.1 - 0.3. Is that typical? It's very normal for the first node to have 5v or more ac ripple with a typical cap input filter. Could a leaky filter cap cause hum that isn't reflected in the RMS ripple measuremen...

There is a corrected version of the schematic labeled OS/026 which is included in the limited edition of the book Vox Amplifiers: The JMI Years I don't own the book, but I've seen the schematic. It is much easier to interpret. I didn`t know about that revised schematic. Had to make my own. In any c...

have you tried a 100k reverb pot ala fender? I tried this tonight... Unfortunately, no difference. Possibly even worse buzzing than before. I also shielded the grid wire to V4 gain stage, but that didn't seem to make a difference either. I measured ac ripple in my power supply. The first node has 5...

Vox tended to bias them pretty hot, but remember cathode biased can be biased much higher, say near 90% vs grid biased. at around 360VDC, that's 30mA per tube. you said your measurements were 'about 12V' that's not super exact. To be sure you need to know two things: 1. the exact measurement of the...

Hello - As you probably know, I'm trying to sort out multiple issues with my AC10 SRT clone. I recently decided to check the power tube bias, and I believe they are running very hot. This amp has a cathode biased pair of EL-84 tubes with a shared 130-ohm cathode resistor. I'm currently seeing 360V o...

When I built this amp (no reverb) I definitely had to add a grid leak resistor on the triode before the phase inverter. Without it the amp made all kinds of howling noises. The original schematic doesn`t show one which always seemed strange to me. Don`t know if you added one. Mine also benefited a ...

Roe wrote: ↑Wed Jan 30, 2019 8:18 am have you tried a 100k reverb pot ala fender?

I have not, but I definitely will try this! I believe I have a 100K linear pot in my parts bin. Did Fender use a linear or audio taper?

Here's a sample of what I'm hearing. My cellphone mic seemed to pick up some high frequency harmonics that aren't really noticeable in person. But the fundamentals are accurate. There seems to be a rushing water sound now that I never noticed with the other speaker!?
https://youtu.be/F--kBveuOpU