Tube Amp Archive

Just wanted to follow up here, my RF issues seem to have resolved after swapping out the 3 foot long RCA cable (black plastic, like you'd use for a stereo receiver) for separate "vintage" style 15" cables (the braided metal ones: https://www.amplifiedparts.com/products/reverb-cable-set-vintage-style...

Turns out the RF interference (?) is still there, it's just harder to notice if the tone knob is turned below about halfway. The wet signal has a constant crackling sound and some hum/buzz. Additionally, I get radio interference and sometimes full-on oscillation at the output jack of the reverb unit...

Caps across rectifier diodes help, usually, but an even better solution would be to replace the diode bridge with a tag strip to hold a couple of UF4007 diodes. Page 20 of Guitar Amp Wiring Notes also lists a trick I found during writing it up. Making the cap you have across the transformer seconda...

Good news! With the following alterations the reverb performs in a satisfactory manor, with very much tolerable hum even when the mix is set entirely wet and the amp gain is cranked up (which sounds like hell anyway, so not typical usage). 1. 1k grid stopper with 470pF cap shunting it to ground on t...

Well, the snubbers (0.01uF over the PT secondaries and across each rectifier diode) helped, the hum is almost tolerable with the reverb going into the front of the amp. The tank/RF noise/distortion is still problematic, so I will work on RF-proofing it over the next couple of days as free time allows.

...as well as a second resistor to isolate the pots (R22) all visible over in the power supply. Thanks for the link, that is useful! R22 is interesting. For non-pcb mount pots, would you just solder a "ground" wire along the pot backs and connect that to signal ground through the 15R resistor? Also...

Stevem wrote: ↑Sat Jul 05, 2025 5:38 pm This layout works everytime just like it did for Fender.

Point taken, I may have been led astray by reports on the internet that the original had noise issues.

If it were me, I would try doing things to mess with hum introduction. For instance, short that 22 ohm resistor. Did the hum change any at all? Shorting the 22 ohm resistor resulted in significantly louder buzz. Does moving the balance control from full reverb to full dry change the quality of the ...

You know, if I put the reverb in the effects loop of my amp rather than into the front of it, the hum is basically unnoticeable even when set to Dick Dale levels. So I may just be hearing normal hum from one tube device being amplified by another tube device. In which case I can live with it, and un...

OK, I squinted through the layout and pictures. You are a brave human being. Take that wire that runs from the PT center tap over to the ground group on the turrets and move it to the negative terminal of C1 as close to the negative terminal of C as you can solder it. Running it to the board star p...

All jacks are isolated ... used a ground lift circuit ... You might try unbolting both jacks from the chassis, place something insulating (like cloth) between them & chassis, and re-conenct your input/output cabling for a test. It might be whatever insulation/isolation you tried using didn't actual...

Did not realize that about the heater CT. I didn't have a simple way to move the CT to ground, so I tried 1) removing the resistors and just wiring pin 7 to pin 8, and 2) just grounding the heater from pin 7 to signal ground (where the cathode grounds). Neither changed the buzz. I pulled out the sco...

The 1/4" and RCA jacks have insulating washers to isolate them from the chassis. For the heater artificial center tap, two 100 ohm resistors are mounted on the 6K6 socket going from each heater pin (2 and 7) to the cathode, (pin 8 ), which sits at about 23V. I will break out the scope today and conf...

Hello again. I just finished a 6G15-like reverb build, and it works, but it's giving an unpleasant amount of 120Hz hum. It's playable but annoying. Noise seems to be a common problem with this unit, but I am suspicious that there is a problem in my build/design specifically. Attached are my schemati...

Can you use that arrangement to get any arbitrary lower voltage? Are there practical limitations? Are there existing examples in the tube amp context that I should be looking at? Sorry, this has been asked on forums in the past. This would be the specific technique to use, yes? http://el34world.com...