The Amp Garage

By sheer coincidence I just did this to my 5e3 clone using the Rob Robinette SPDT On/Off/On 3 way switch method. I am impressed by the change the NFB makes, its like a whole new amp, with a very different breakup/OD tone.

And of course I can switch it back and forth anytime.

It seems that a lot of 5e3 clone owners end up with an amp that is stiffer, louder, and won't distort at low enough levels compared to a vintage 5e3. As modern power transformers have lower internal resistance, and utility AC is higher than in the past, its common to find that the B+ voltage in the ...

I use my 5e3 at home (ok ok it's a house, nowhere near any neighbors) and its 'acceptable' without any master because I did the following: 1) Used a low efficiency Jensen alnico speaker (5e3 Speed Shop A12Q - excellent). If you went with a Blue instead, it would be way louder. 2) Coupling caps from ...

Very pleased with the elevated heater center tap on my 5e3 build. It's a quiet amp. An easy way to implement is to put both 100 ohm resistors on one of the power tubes, with one end of each on their respective heater connection, and have both connected to pin 8.

One year after building my 5e3 I finally bit the bullet and have replaced the 2 x 0.1uF coupling caps between PI and power tubes with 0.022uF ones just like in the Edge 5e3. I like it a lot. It's subtle, but overall the amp sounds sweeter and can be pushed harder without that deep bass wearing you d...

Those blue and brown OT leads better be connected to pin 3 of the output tubes! Do you have any experience working on tube amps? They were on pins 3. I built a 5e3 last winter with a selection of the Robinette mods. It works perfectly. This is the first broken amp I've tried to debug. The main stru...

Found and fixed the missing ground. Reran the voltage tests and everything now looks a heck of a lot better except the power tube bias - and the power tube screens which were 170V vs a plate of 450V. Didn't take long to see that the reason for that is that the screen resistors are 470k , not 470 ohm...

Oh wow you are correct. I'll fix that and retest.

I checked all the preamp tubes in another amp and they all still work so we are on a roll here.

Yes, my bad, I now see that I noted 90V on one of the V2 plates. With the missing connections made I did a current limited startup (bulb) and that went well. With the limiter removed I checked volts and found 450V DC on caps A, B, C and D, so the voltages aren't dropping downstream. I assume the pre...

I used an 8 ohm speaker as suggested. Tested with tubes in, found there are no plate volts on tubes 1-3, it's a missing wire on the turret board between the 4k7 and 1k resistors. Should be an easy fix. Also the heater ground resistors weren't hooked up to the heater wires so that might explain the a...

Yes, apologies, I'm doing that and see what you mean. I'll pull the reverb driver only. Is it safe to power up with no power tubes in and no speaker connected?

I plan to use my current limiting bulb for first switch on.

I'm taking a look at a single channel AB763 a friend built years ago. It never worked well - noisy - and a tech recommended he replace some resistors and wiring. He did, and it stopped working. He put it in store for 9 years, and just gave it over to me to see if I can figure it out. He appears to b...

Even though the amp is not spitting out any blocking distortion, I temporarily added a switch with a 470k grid stopper for the PI just to hear what the amp will do with it. And honestly, at first I felt that there wasn't any difference by adding the resistor. But the following day with fresh ears, ...

Just built this amp as my first project ever. I decided to go full throttle on the diy and sorted 100% of the parts myself, without starting with any kit. I also used a blank chassis as I really don't like the facing-up style chassis and wanted all toggles on the faceplate. I finished it literally ...

Ok, next topic - sag. These amps are renowned for sag when pushed hard at high settings. Does this mean the B+ drops due to excessive current draw? Has anyone every measured that? If the B+ drops significantly it might be cool to have some sort of mod which lit an LED when the B+ drops below a certa...