5E3 summary of small issues

[fredouille]

Hi all, I built directly a modulus kit with mods..

I have small issues on which your comments are welcome


I moded the diode protection + diode switch.. the pre rectifing diodes make me loose a lot.. 400v with no 6v6 and 300 loaded !!!... 450 with diodes and 380 loaded.. a bit low no ? looks like nothing to do or removing pre diodes

negative feedback goes directly into oscillation (robinette mode 3 positions 56K on 8 ohm output), I suspect of course out of phase signal, so to do : invert output transformer to plates wires, can you confirm ? (I will check with oscilo of course the phase between input and output before doing the change, it is not easy as I have the half power mod, a lot of wiring there)

small disturbing stuff.. between channel isolation.. I have signal from 1 channel to another even not plugged on the right channel.. I will check grounding of each jack, maybe global grouding issue

outside this, guitar playing speaking, very powerfull and overdriving easy, bright channel on humbucker impossible to get a clean sound. interesting amp but no reference to compare. I tried with a dussenberg guitar which as a lot of gain, no telecaster available here
not at the level of bassman 6g6b or blackface still, here I can compare as I have 2.
need to check another cab, I tested on a laney 2x12 a bit dark, will test later on fenders ones

[fredouille]

update for myself in did negative feedback issue solved by crossing wires

debugging noises a bit.

none of the B+ have any V AC, neither anything visible but see attached

blue is output.. no signal injected, all the ground, volume a 0 and tone at the middle

yellow is where I catch first time 50hz in tracing signal which on V2A plate (12AX7).
around the plate I get small 50hz.. on B+3 flat.
on grid flat also..
cathode flat also..
interesting where this 50hz could come from.. filament?

in did the mod for negative feedback arrives on the cathode and some wires are running a bit far but again nothing on the cathode..

[martin manning]

interesting where this 50hz could come from.. filament?

Most likely. Rectified DC voltage would be 100 Hz, and sawtooth in waveform.

[fredouille]

interesting where this 50hz could come from.. filament?

Most likely. Rectified DC voltage would be 100 Hz, and sawtooth in waveform.

yes.. so this 50hz is caught by induction from filament, still the level is low.. 0,0Xmv..

[Stevem]

Can you post up several good pictures of the guts?

[fredouille]

Can you post up several good pictures of the guts?

I will look but it is difficult to see around power tubes.. due to added switches on the rear

no comments on the low B+ voltage ?

[Stevem]

The low V+ is why I asked what is the idle current the output tube is pulling.

[fredouille]

The low V+ is why I asked what is the idle current the output tube is pulling.

not much I have 16v on the cathode resistor.

so 300 - 16 / 250 ohm

I will test something I'm suspecting that maybe I lost 1 of winding in high voltage transformer (dead diode or bad solder or bad tranformer)

[Stephen1966]

A schematic with your mods might be more helpful here. Not assuming you've done anything "wrong" just, it's a whole lot easier to reference from.

What is the voltage at the speaker output jack? With a signal and the amp dialed up to clipping.

[fredouille]

A schematic with your mods might be more helpful here. Not assuming you've done anything "wrong" just, it's a whole lot easier to reference from.

What is the voltage at the speaker output jack? With a signal and the amp dialed up to clipping.

yes thanks for not assuming, but I first do assumed that I was wrong it is normal

update is.. without load. HT disconnected (standy is connected before B+)

transfo output 300 V on each side, so transfo is ok, but should deliver 400 V

after each diode I have 180v around

after tube rectifier I have 300 v. which looks logical voltage drop.
without tube rectifier but with diodes 350 v which is logical.

in terms of schematic the mod is here : https://robrobinette.com/5e3_Modificati ... ier_Switch super simple

what I'm sure is that I was getting 400 V or more before the mode, but without power tubes. power tubes in standy are draining only heaters so.

but I will try to remove them to see

at the end I may remove the first diodes and keep the diode rectifier option .. but I liked the idea to protect the rectifier


update : I added a 500K resistor in // on the 1st cap for voltage draining, might affect voltage divider, but not on the first point B+ I guess

[fredouille]

last update

on the 2 diodes 1N5408 i have DC drop 10v without the rectifier tube.. 20v with the tube.

I guess the diode have an issue.. diode tester give them at 0.5

I will remove and check.

unless I forgot in my electronic lessons.. I should not have more than 0.5 DC drop

[martin manning]

Where exactly is your standby switch? When you are measuring the B+ in standby is there a reservoir capacitor connected at the rectifier output? Post a schematic of what you have built.

[fredouille]

Where exactly is your standby switch? When you are measuring the B+ in standby is there a reservoir capacitor connected at the rectifier output? Post a schematic of what you have built.

no I have standby switch just out of rectifier

I removed diodes now before rectifier, on startup I have 380 then doing down to 300, I guess draining current

16v on cathode on 250 ohm which is not a lot 55% dissipation which is too low.

I thinq is transformer is set for 240v , I'm on 220.. so on secondary I have the same difference + the freaky diodes which i guess were fake

[martin manning]

What voltage do you get with the tubes removed and the standby on "play?" This will give you the correct no-load condition. With no reservoir capacitor connected you are measuring average DC of a FW rectified sine wave.

[fredouille]

What voltage do you get with the tubes removed and the standby on "play?" This will give you the correct no-load condition. With no reservoir capacitor connected you are measuring average DC of a FW rectified sine wave.

i can't disconnect caps

without power tubes 480 v. premap tube plugged. I loose 180 on load.