tremolux 5 e9 cuttig when switching tremolo off

[leon]

hi all
i ve just finished to built a 5e9 tremolux. sound great .only a problem. if i switch the tremolo off using the foot switch with the depth from 4 o clock (9) to max the sound cuts off. the tremolo works all the way. any idea ?
thank you!

ps: the circuit is standard appart from adding a negative feedback loop

[HotBluePlates]

Is your amp build from a kit or layout from a company?

How did you decide to add the feedback loop? Where in the circuit does it connect? If this is a change you decided to make, what was your intended goal with adding the loop?

Also, does your build have the 10M resistor from B+ to the trem oscillator/footswitch jack?

[leon]

hello hot blue plates
I ve built this amp from scratch following fender original layout and shematic.
i ve fitted the 10 meg resistor between B+ and trem jack as shown on 5e9 layout.
 for the negative feedback I added a 56 kohms resistor from output secondary on speaker jack to cathode of second preamp valve(pin 3,which is bridged with pin 8 . pin 8 linked to cathode bypass cap and to depth control.. I could  easily try without the feed back loop. what do you think?  thanks for your help

[leon]

ps: the reason i ve added a feed back loop was to increase the clean headroom and i ve  built a 5e3 type previously and it worked pretty well with the feedback loop added so I tought it will be a good idea on that one

[HotBluePlates]

Disconnect that feedback loop for the moment.

I'm wondering if that loop is causing the problem.

[leon]

I ll do that tomorrow and i keep you inform
thank you

[leon]

hi I' ve disconnected the feedback loop and the problem is still there.. I ve measured the value of the 10meg resitor and the result shows randoms variation that i can t figure out. i mesure across the resistor and i get all sort of values ranging from 2 meg to 200kohms and also changing value when i swap polarity on multimeter . fautly resistor or result of electricity phenomenon in the circuit?? . I ve checked with amp turned off and switched open and closed. since the problem occurs only with depth turned close to or to maximum . I found difficult to understand.easier when stop working completely..Thank you very much for your help...

[sluckey]

The 10MΩ resistor should not be the cause of this problem. All it does is quickly 'shocks' the trem oscillator back into operation when you open the footswitch. The oscillator would restart without the 10MΩ but would turn on slowly.

I think the problem is associated with the voltage on the cathodes of the second tube. I bet that voltage becomes a fairly large value when the amp quits passing sound. Measure that voltage on V2 pins 3/8 while the amp is working and then again when the amp is not working. What are the numbers?

And of course, you should triple check your wiring in the area of V2 pins 3/8, the depth control, and V3 pin 3. And be sure the depth pot is 250K and the resistor on the depth pot is 100K.

[leon]

hello all I've measured voltage on V2 pin 3 : 2.6 volts but when I turn depth up to 3o'clock i get 3.1 volts and the volume start to go down a bit
turning to 4 o'clock i get 3.9volts and the volume dropped  a bit more
turning to 5 o'clock I get 4.7 volts and no sound...so I think that you are all right the voltage seems too high there...
the pot is a250k and the the resistor a 100k .I ve 71.9 kohms  when depth turn all the way up, across 100 k resistor which seems normal and i double check is where it should be. it really intrigues me now ...

[HotBluePlates]

Since you built this amp, we should suspect a wiring or part error. Nothing personal, everyone makes build errors.

There should be a 100k resistor connecting the middle and left lug of the Depth pot, when you look at the back, with the lugs pointed up. Make sure that is actually 100k, and not a 10k resistor or 100 ohm resistor. Depending on the brand of your resistors, it could be very easy to confuse the yellow, orange and brown color bands which make the resistor 100k, 10k or 100 ohm, respectively.

I know I've made that mistake before, especially with yellowish incandescent lighting.

Once you're certain the resistor is right (measure if you need, with the Depth pot set to minimum), make certain The wires from the Depth pot run to the cathodes of the tubes they connect to. If the Depth pot connects to the plate of the intended cathode follower stage, the high voltage being applied through the parallel 250k pot and 100k resistor would force much more current through the phase inverter bias resistor, causing the effect you describe.

[leon]

i double checked  resistor and it s a100k resistor connected to left lug and middle .left lug goes to cathode of v3 pin 3 ant right lug to 1.5k / cap 25/25 to pin 8 v2 linked to pin 3 i ve done every thing as on original layout . I used 25/50v cap instead of 25/25.but that shouldn t change anything .value  depth pot across 100k ; 0.2 ohms when turn at minimum an 71.9 ohms when turn to max. i carry on looking and double checking but can t found what the problem is so far . please help!!

[sluckey]

Turn the amp off. Measure the resistance between V2 pin 3 and V3 pin 3. With the depth pot set to minimum, the resistance should be about 71K ohms. With the depth pot set to maximum, the resistance should be about 250K. What do you actually read?

[leon]

that s strange  i get the opposite 215 k ohms with depth at minimum
                                                72 K ohms with depth at maximum

 

[sluckey]

that s strange  i get the opposite

You're correct. I wrote too hastily.

Do you have enough depth before the amp cuts out?

[leon]

i really like the sound with the depth close to the max and i would say it won t be enought when set to 3 oclock when volume start to c ut down when trem switched off

[leon]

there something i noticed  the 5e9 shows  two .02 caps to v2 pin 6 and V2 pin 1 when the schematic shows two .01 instead..I used two .02 as shown on the layout and I wonder if that could cause the problem

[leon]

hi all I m still struggling with this amp cutting off when switching tremolo off with the depth near the max and I ve tried with a 68k resistor on the depth pot instead of the 100k as i thought  it will keep the trem in more reasonable value and it did a little bit, so now it will cut only by the max ,but the voltage at V2 pin 3  goes higher around 6 volts with depth at the max and the trem sound really harsh near the max..

[tubeswell]

I suspect you have a wiring error. Take a break from it for a week and then go back and triple-check your wiring and your component values. The oscillator's cathode follower should not cause the bias at the PI to go into permanently into cutoff when the intensity increases.

[HotBluePlates]

there something i noticed  the 5e9 shows  two .02 caps to v2 pin 6 and V2 pin 1 when the schematic shows two .01 instead..I used two .02 as shown on the layout and I wonder if that could cause the problem

No. The schematic matches the layout.

[HotBluePlates]

hi all I m still struggling with this amp cutting off when switching tremolo off with the depth near the max and I ve tried with a 68k resistor on the depth pot instead of the 100k as i thought  it will keep the trem in more reasonable value and it did a little bit, so now it will cut only by the max ,but the voltage at V2 pin 3  goes higher around 6 volts with depth at the max and the trem sound really harsh near the max..

There's got to be a wiring or part-value error somewhere.

When you say "V2" do you mean as the tubes are laid out on the chassis? So the cathode voltage of the phase inverter rises when the trem depth is turned up?

If so, you have a wiring error likely relating to the Depth pot, the phase inverter and/or the tremolo cathode follower. Don't change parts values. Verify the wiring (perhaps with continuity tests for underboard wiring), verify the installed resistors are indeed the correct value.

[tubeswell]

Hi Leon

Have you tried disconnecting the NFB loop?

[leon]

Hi all  I ve made progress on this issue ,I have disconnected the NFL since it doesn t seem to do anything on this circuit any way. I obviously double check the wiring once again and couldn't see anything wrong. I ve replace the 100 k resistor across the depth pot for a 220 k and I've got a tremolo that sounds still good and the amp doesn't cut anymore when i switch the trem off with the depth pot from 4 o clock to max ,using foot switch. So i think i ll keep it like that. so thank you all for your advises that made me understand this circuit better.