tremolus vibro connecticus

[Andy Le Blanc]

spent the morning playing with old fashiond temolo circuits
the occilator is fun and easy but finding the best way to connect
it to the rest of the circuit is elusive... Ive been using a modulator
hooked to the chathode of a paraphrase invertor....been through many examples
like those of supro... valco.... vibro champ...etc but the one that seems to be
the most effective with the least harmfull affect on tone is the
tremolux 5e9-a.....
... any other favorites of this type of tremolo connection?
...any body know of any signifacant differences between 5e9 and 5e9-a
cant find a scheme for the 5e9

[jjman]

Hey Andy

I am currently dealing with where/how to insert the trem on my new build. I tried output tube bias type but the combination of the cathode biased output and the dual-pot type PPIMV caused a problem. The trem was grounding out as the MV was turned downwards. I like the MV so I’m moving the trem.

So I need to go with a setup where the cathode of the oscillator modulates the cathode of a preamp stage. (Using the plate side of the oscillator created issues.) I have only one triode available for the oscillator and I don’t want the trem settings to affect gain, if possible. I’m trying to find a schematic that will do this, (unlike the Vibrochamp) and the Gibson Skylark seems to be a possibility:

http://www.schematicheaven.com/gibsonam ... rkga5t.pdf

The Kalamazoo 2 uses the same strategy:

http://www.schematicheaven.com/bargainb ... oo_m2s.pdf

I like the indicated target cathode cap value of 4.7k since my 3rd stage calls for a 10k and the sharing of it amongst 2 triodes makes the effective value close to 10k for each triode. I would need to leave off the 10u bypass cap which I think would be ok, ..I hope. Only problem is that I don’t see a trem intensity control on these 2 schemes. Can I vary the intensity without changing the DC bias on the target tube? Can I replace the grid-to-ground resistor on the oscillator with a pot/resistor combo perhaps?

[Andy Le Blanc]

so your limited to one gain stage and thats the oscillator?
this limits your choices......
changeing variables in the grid of the oscillator will change frequency
theres an example

http://www.schematicheaven.com/bargainb ... -9058a.pdf

that puts a intensity control between the osc. and the target tubes chathode
this was in several models

http://www.schematicheaven.com/gibsonamps/ga40.pdf

this gibson has the shared chathode and the intensity is a pot. as the plate resistor.....
I saw a similar take off in an ampeg B-22-x but it was used in conjuction with a LDR...
might be a good way to vary the intensity but Id
prefer a selector switch

http://www.schematicheaven.com/bargainb ... y_h410.pdf

this one places it at the grid of a gain stage but gives you control
no matter you do youll have to find the hook up that best suits your ear
gain of the oscillator and the stage to which its connected will be an issue
youll have to try it with and without the bypass but i suspect that the
oscillator will need as much gain as can be found

[jjman]

Hey Andy

Thanx for the links. I was surprised to see the way the Harmony H410 injects the signal onto a grid of a preamp tube. This seemed scary to me so I tried every other possible injection point. I was able to construct the “missing” Kalamazoo/Skylark intensity control that also blocked DC interaction between the oscillator's cathode and the target cathode. Problem was the effect was still not strong enough.

I have a Harmony H415 (not H410) which is fantastic BTW, http://www.geocities.com/jjsant/harmony.html but it modulates the output tubes and has no PPIMV of course to interfere with the it’s trem.

So I wired the oscillator back to tapping it’s plate and injected it’s output on to the grid of my 3rd stage based on the H410. My 3rd stage has a 150k from it’s grid to ground so I replaced it with 2 resistors in series and injected the trem into the middle of them as done on the H410, albeit with different values. Not only is it now working well but it’s too strong! No problem, I’ll just flip the value of the pot and it’s resistor to reduce the max of the trem’s output.

Lastly I’ll need to clean up the trem’s sine wave. When the oscillator’s cathode is grounded or with a bypassed 1.5k it clips on the top side somewhat. With the current (bypassed) 4.7k on the cathode it’s a triangle on the top of the trem wave instead. I’m not sure if that will fix itself when I fix the intensity control. When I removed the oscillator’s cathode bypass cap it stopped oscillating. I’m done making predictions about this whole trem thing. I may have to find a happy medium value Rk after I get the intensity down to an appropriate range.

I've been stalled on this build for a few days with this and didn't want to start tweaking elsewhere until it was resolved.

Thanx again for those schematics!

[Andy Le Blanc]

great......

this is one of those cases where there really is more than one way to skin the beast...
and you do have to try a variety just to see.....
Ive got this old HP low frequency generator.... and one can inject tremolo
just about everywhere in the signal chain... but its how to do it with in design constraints thats tricky....

keep an eye on the wave shape..... a triangle form might be more adventageous to your ear....
differnt wave forms hold differnt harmonics
if you stumble upon a simple mod that changes the wave form use it
you can have a push/pull that changes the feel of the trem