Problem with amp tremolo

[bob p]

It's a bit convoluted:

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[Chuck H]

All I can say is, Awwwww

[mdancakster]

Sorry but I still canīt get to the thumbnail. Up to that, there isnīt any shown in the post now. Could you upload it again please.. Many thanks..

[Chuck H]

You're messing with me, right? Are you seeing the picture of the pretty girl with the kitten? You uploaded images yourself. Are you working on a Tandy 64K?

[Chuck H]

Ok... Look, it's simple. Put a 10k pot wired as a variable resistor across (parallel to) the 3.3k resistor. It's on the bottom of the 68k cathode resistor at the end of the tremolo circuit. You uploaded the schematic and there's no other 3.3k resistor in the amp.

[mdancakster]

Iīm really sorry for messing.. There must have been some misunderstanding.. Iīve made some scheme according your advise.. You can look at it.. Just values are different (instead of the 22k resistor thereīs should be the 3.3k resistor and instead of the 3.3k thereīs should be the 2,7k or a 10k pot wired as a variable resistor).

I should notice that my amp is basically the 5e9A circuit using just EC tremolux cathodyne PI applied, so the tremolo is still that of 5e9A original fender schematics (it means that the tremolo is connected to the circuit straight to the 250k depth pot from the 1.5k resistor by which the driving triode of the PI is biased - pin 3!!!)

The depth pot in the EC tremolux is not included, just trio of the 2,7k, 3,3 and 68k resistors, so thatīs why Iīm a bit confused.. I would like to managed it leaving the depth pot (with the 100k resistor on it) in and at the same time solve the problem with the ticking tremolo..



many thanks
regards
Martin

[Chuck H]

So the schematic you posted isn't even the circuit you've had me working on and considering. Did you think that a depth pot made no difference? I still not at all sure what the hell the actual circuit is. I'm outy.

[mdancakster]

once more.. the amp was built according Fender tweed tremolux 5e9A schematics precisely.. because of the amp was a bit muddy I changed the PI section from paraphase to cathodyne using EC tremolux schem as a model (BTW it's the same like 5e3).. unfortunately the change of the PI badly influenced the working of the tremolo (which remained that of 5e9A, haven't been changed).. so the question is still the same what can I do to solve the tremolo workings.. hope understood now.. regards. M.

[Chuck H]

Ok... Sorry to get impatient. I'm going to try something to get things on track. In an effort to get us on the same page I put together a schematic (at some effort) that I think should represent your amp as you have described it. I hope you will be able to see the image. Please let me (us) know if this accurately represents your circuit.

[Tom Phillips]

I don't see the image in the post.

[Chuck H]

Huh? I see it enormous just viewing the thread. Maybe a restriction in place on your viewing preferences here or even your browser? I've added a click file in case that helps. Thank you.

[mdancakster]

Iīve made two changes in your schematic (however they probably wouldnīt have any influence on the tremolo working).. But, yeah.. thatīs it. Thatīs my amp.

[Enzo]

the amp was built according Fender tweed tremolux 5e9A schematics precisely.. because of the amp was a bit muddy I changed the PI section from paraphase to cathodyne using EC tremolux schem

Do you see the contradiction saying I built it exactly thus but changed something? Exactly the same but different.


So the result I see, and tell me if I am screwing up, you changed the trem feed from the cathode of the phase inverter to the cathode of the stage before the phase inverter. SO you now have extra gain on the tremulant?

I am not fully awake yet today, but were it mine, I might restore the lower phase inverter connection to the 56k resistor rather than the cathode of the PI. Then divorce the trem intensity from the triode stage where it now sits. And couple the trem LFO signal to the cathode of the phase inverter via a cap instead.

[Chuck H]

Ah. That was my mistake in the re draw. And there's no issue with the addition of grid stops on the power tubes. I'll amend the larger image and the link in the post above. Ok... So now we have a working schematic

My earlier consideration that the LFO was swamping the affected cathode no longer applies because you have an intensity control to mitigate that. So lets forget about that for now. I always wondered about the reason for that 10M resistor (maybe someone else could explain it's function?). It's not a part of other oscillator circuits and may not be playing well with the new PI design. I might try lifting one end and see what happens. But that's just a shot in the dark.

Something you haven't reported on yet is whether the trem is functioning correctly other than the noise. Does it sound right? Is there anything odd or wrong with how it functions?

I haven't read the tick fix link above yet. But I'm going there now. I'm thinking it's either an AC artifact in the LFO or something abrupt (a distortion) about the LFO waveform that's impressing itself on the affected cathodes bias and acting like AC.

Please report on the trem function. I'll amend the schematic and consider the matter.

[pdf64]

...I always wondered about the reason for that 10M resistor (maybe someone else could explain it's function?)...

I think it may be there to give the oscillator a dc 'kick' when it's switched on at the footswitch, to best ensure it starts oscillating immediately.
Without that, it may take a while for oscillation to build up, especially if the tube's gain has got a bit weak, or the cathode bypass cap is tired.