Trem Oscillator Question

[AZJimC]

Hi Guys,
I am planning a conversion of my oscillator from a 6AV6 to 6AU6. I've already drilled my panel and installed a red led that connects to the AV6 cathode. In the Dano Schematic, and most all others I have seen the cathode of the 6AU6 is grounded. My questions are, one, can I get by using the LED on the cathode as shown? And second, Would switching the cathode ground as shown help the Oscillator start quickly? Any other issues and/or caveats I should think about?

[sluckey]

A couple things...

The LED is drawn backwards.

Your circuit is grid leak biased, ie, cathode grounded, big grid resistor with dc blocking cap. The LED trick is meant to replace the resistor/cap on a cathode biased oscillator. IOW, you can't use the LED in your circuit.

As for switching the cathode, that will totally kill the oscillator. When you close the switch it will always take some time for the oscillator to start up. This slow start up is usually annoying to me. That's why I let the oscillator run all the time and just interrupt the trem signal later in the circuit. Need to see the entire schematic to know if this is an option for you.

[AZJimC]

Okay, I was afraid of that. I hoped the LED on the cathode would just lower the gain a bit, hoping I could overcome that elsewhere. Now, what to do with a shiny LED on panel between the speed and intensity knobs? The only reason for the swap to pentode is the trem is weak, and I don't have another triode. The rest of the drawing is unfinished, but it is grid connected like bias vary, to a pair of 7591's with cathode bias. I'll use the full Dano/Silvertone circuit I guess. I just need a bigger, stronger, swing on trem voltage. Darn, I really wanted that LED for a preview of speed.

Oh, and about starting, I was reading about that and saw a design that used the act of switching to assist in starting a voltage swing that resulted in a near instant startup. That one was using a switch on the grid side, and grid leak was slightly elevated so ungrounding it would allow it to rise, and start the swing. (I see the elevated voltage isn't on grid, but between the two caps.)

See the Foot switching section: http://www.valvewizard.co.uk/trem1.html

[sluckey]

Just build the oscillator from the Princeton Reverb, or Doug's AB763 amp. Or use this circuit...

http://home.comcast.net/~seluckey/amps/RCA/Ampeg_J12B.pdf

[AZJimC]

That ampeg looks like a good candidate. Looks like that should work okay with a 6AV6? I wonder if .047 caps would work for the .05's. It would shift the frequency slightly, however I have no clue which way, haha.

[HotBluePlates]

I wonder if .047 caps would work for the .05's.

0.047uF is the modern 0.05uF cap. If you had an old 0.05uF cap, a measured 0.047uF is only 6% low, which is probably tighter than the tolerance of the original caps.

[AZJimC]

Okay, after spending all night playing with that ampeg circuit, I've got a huge trem. It will go anywhere from mild wobble, and at one of the lowest rates I've ever heard, to total helicopter. It starts instantly, and remains solid throughout the range. I didn't try the big caps, but stayed with the .02's and resistors in the ~1M range. I split the resistor from grid to ground, 2M, into two x 1M, and the speed range switch works nicely by simply grounding that junction, reducing the resistance to ground by half. That could be foot switched as well. Didn't check it, but I'd bet it works down to 3Hz if not slightly lower, and still starts right up, and remains solid.

Seems the thing causing the weak shaker was the 473 cap coming off the plate to depth pot. I swapped it for a .1 cap, and it became so strong that I will have to replace the 1.5M depth pot with a 1M. The thing will even operate against the cathode bias at overdrive input levels.

Oh, and I now have a clue which way the smaller caps would take it. It would result in a slight gain in speed, as does less resistance.

Thank you guys! Sometimes it feels lonely when nearly all my friends have no clue what the heck I'm even talking about, so it's great to have this discussion forum to share, vent, or whatever.

NOW, I can Jam that "Delirium Tremolos" album by Ray Wylie Hubbard :)

[AZJimC]

I had a chance to do some measurements, and the low frequency is at 2.1 hz, and still solid. It takes no more than two cycles to settle in at 2.1. The speed range is 2.1-4 Hz on low setting, meaning the 2x1M resistors from grid to ground. when on hi, with only 1M to ground, I get a range of 3 Hz to 5-6 hz. Hard to tell as meter drops it very slightly. It falls apart and stops shaking at full up on the speed knob, but is otherwise strong. Meter won't measure voltage, at that frequency, and I have yet to look at it on the scope. I may use a 1.5M x500k divider on the grid to offer a bit more distance between the speed settings, but if successful, I could build a speed/trem footswitch. I even thought about converting an old vol pedal to see of I can create an adjustable speed trem on footswitch. Likely a whole new set of problems, but would be nice if implemented successfully.

I'll be documenting the final result, and planning a turret board layout for a head version of this amp. SO far it chimes, tinkles, growls and screams equally well, and does so reliably, and nothing gets too hot even after hours of hard running. Most distortion levels are easily controlled from the guitar, but I still would like a boost button on the pedal. That has me up to a four button pedal and I guess a Din jack and cable for that many conductors.

[eleventeen]

There are fewer connectors I dislike more than DIN connectors. I guess they are or can be cheap, but they are even more cheaply made nowadays than they used to be. I'd be a little resistant to using a DIN on a foot-pedal thingy that can be stepped on though I am sure there are plenty of examples out there.


Consider more-than-3-pin XLR. Or a simple D connector. Yes, out of the catalog they are probably more expensive, but since nobody uses them, sometimes they can be had cheaper then 3-pinners from a surplus guy.  I have a bag of 5 or 6 pin XLR pairs somewhere deep in the archives.

[AZJimC]

There are fewer connectors I dislike more than DIN connectors. I guess they are or can be cheap, but they are even more cheaply made nowadays than they used to be. I'd be a little resistant to using a DIN on a foot-pedal thingy that can be stepped on though I am sure there are plenty of examples out there.


Consider more-than-3-pin XLR. Or a simple D connector. Yes, out of the catalog they are probably more expensive, but since nobody uses them, sometimes they can be had cheaper then 3-pinners from a surplus guy.  I have a bag of 5 or 6 pin XLR pairs somewhere deep in the archives.

Good call on that, beside I wouldn't want some guy to try his Midi pedal in it. I had forgotten the XLR's, and that would be less apt to be plugged in to someone's latest Midi box of sand. My whole objective with this design is to have a recordable, gigable, do it all amp that could be used in most any setting without the monster pedal board filtering out all the mojo before it hits the first tube.

[eleventeen]

I will make you the following offer:


I am not going there for a week, but I know for certain I have some either 5 or 6 pin XLR pairs in my storage space. Clean, used Switchcraft. Both sexes. I will never use them. I know you probably want to button up your amp, that's the only rub. You can, by the way, remove the header, the plastic part that holds the pins together, from a cable-type connector and put it into the metal shell of a chassis-mount connector. So, you can convert one to the other.


If you can wait perhaps 3 weeks for full completion of this, I would happy to give you two pairs of the S'craft 5-6 pin connectors and I would throw in some chassis-mount 3-pinners because I have tons of them and thus you get whatever chassis-mount shell you might need, both sexes. Everything is clean used once-only pulled from clean gear, perfectly reusable. In a flat rate little USPO box, this is a $5 or $6 freight proposition and you send me a $6 check when it's done and you're happy.  Just say the word, I will never use those connectors.

[AZJimC]

A great offer my friend. As far as buttoning the amp up and calling it finished, I'm into the second year of design and tweaking on this beast, so no big deal waiting for the connectors. The amp gets gigged/practiced every Friday, and Sunday at church. Monday's I rip the chassis out and pop it in the cradle, and one or two sections gets reworked to solve an issue or enhance the utility etc. This amp has actually been a bread board of sorts, so it ain't pretty inside, but it is sturdy and reliable.

For now, I'll keep those connectors in mind while installing a regular Marshall two button, and begin planning a 4 button, or so, box. I have a few of the three pin, but could sure use a couple or so panel mount male three pin. I hope to include an XLR output wired from a divider off the OP transformer. Don't know how that will sound yet, but maybe it could save a mic if implemented well. Had in mind to use XLR and possibly split it into two outputs, one for main out, the other for reverb output, so I can use two mixer channels and have huge reverb sound. I already have built a couple of adapters for the snake that split the XLR into two 1/4", for instance on the stereo output from the keyboard.

Thanks very much for your offer, and know things like that make a big difference to a guy spending more than he should from a fixed income on amp parts. Let me know via PM when you get hands on them, and I'll send the address. I'll gladly refund your shipping and beam with gratitude. Also, no real hurry, so do this at your convenience.

Jimmy Three Hats