kalamazoo model one tremelo sound when cranked.

[nosaj]

I have a kalamazoo model one clone that makes a tremelo sound when cranked.

Is it possible the 6.3 heater supply is not enough and could cause that?
thanks
jason

[Tom Phillips]

I have a kalamazoo model one clone that makes a tremelo sound when cranked. Is it possible the 6.3 heater supply is not enough and could cause that?...

I say no. What is your thinking in suspecting that? Do you have previous suspicions that the heater supply is inadequate? Are you thinking that the heater supply voltage is low or that it cannot supply the required current?

Anyway...I think any link to a tremolo sound is a WAG.

[nosaj]

I say no. What is your thinking in suspecting that? Do you have previous suspicions that the heater supply is inadequate? Are you thinking that the heater supply voltage is low or that it cannot supply the required current?

Anyway...I think any link to a tremolo sound is a WAG.

I think the original transformer used 6au6, 12ax7, el-84. This application used 6x4, 12ax7, an el-84. I thought it should be enough. Following schematic at Kalamazoo Amp Field Guide: Model 1 Schematic

I did originally use the 1k at r12 and they guy said it kept cutting out when it was dimed and the el84 glow would pulse to the strums. So I sent him a 2.5k 5watt resistor he soldered it in and now says it makes a tremelo sound when dimed. i probably need to look at it though.

Thanks,
Jason

[Chuck H]

If the grounds are daisy chained it should be redone with something more like a star ground scheme. If the grounding is good both in design and implementation you can try reversing the OT leads. I know it's a single ended amp, but flipping the phase may break the oscillation. This problem is usually a grounding issue or sometimes bad filter caps.

[Tom Phillips]

...guy said it kept cutting out when it was dimed and the el84 glow would pulse to the strums...

I suspect that he was talking about a blue gas glow rather than the heater glow.

[nosaj]

So the tremelo sound would that also be called motorboating?

jason

[Chuck H]

I suspect that he was talking about a blue gas glow rather than the heater glow.

I thought the same. It's always dicey trying to interpret just what a guitar player means when they talk about amp problems. Best if you can witness it for yourself. I've fixed many problems where the amp wasn't broken at all just by having a player demonstrate it and seeing/hearing what's actually happening. An incomplete list of problems that I've seen players incorrectly attribute to amps:

Bad cords
Bad batteries
Bad use of unity gain controls for effects processors
Broken guitar bridges
Loose jacks on guitars/effects/etc.
Microphonic pickups
And my favorite of all... No understanding of how things are suppose to work. As in "I turn up the bass but it just gets flabby, not more bass." or "When I turn it past five it doesn't get louder, just more distorted."

[Tom Phillips]

So the tremelo sound would that also be called motorboating? jason

Could be. As Chuck H explained, it's sometimes difficult for someone to describe what they are hearing in words that make sense to others. I could believe that someone who isn't familiar with motor boating would describe it as tremolo.

It appears that you not only have a remote person trying to describe symptoms but also doing parts changes. All hard to control and lots of opportunity for misinterpretation.

[nosaj]

Here is a video he made. I gave him 3 new caps 22uf, 10 uf and 10uf. He said after replacing them noise is still there. It was not when I built it though.
Any ideas or what to check?

Jason


https://drive.google.com/file/d/0B6x...ew?usp=sharing

[Chuck H]

Wow! That's not motor boating.?. That's straight up tremolo!?! Something in wiring and/or ground scheme must have enough positive feedback to be acting as an oscillator. The solution could be as simple as altering the phase or local feedback of any one part of the circuit to break the oscillation. Which is pretty much how intentionally oscillating circuits are switched off. Things to try:

Move a couple of preamp grounds to a different point.
Parallel another 10uf cap with the preamp decouplers/filters one at a time and if one stops the oscillation install it permanent.
Capacitor bypass one of the preamp cathodes. This will have the side effect of raising gain, but may stop the oscillation.
Capacitor bypass the power tube cathode. This shouldn't change the tone notably.

And as a last resort... On the downstream side of either preamp coupling capacitor add another capacitor in series (.022 or larger). From the junction of the two capacitors solder a 1M resistor to ground.

My hope is if there is some small signal sharing one of these measures will stop it without altering the tone too much.

[g1]

I'd get it back, find a way to put speed & intensity on it, & try to make a fortune .
Single 12AX7 and a 6BQ5 with tremolo? That's insane!

[nosaj]

I say no. What is your thinking in suspecting that? Do you have previous suspicions that the heater supply is inadequate? Are you thinking that the heater supply voltage is low or that it cannot supply the required current?

Anyway...I think any link to a tremolo sound is a WAG.

What about the rectifier being on the same circuit as the pre and output tubes could this cause enough sag when crank to modulate ? Because all heaters are on same tap.

It was a random thought in traffic the other day, and somewhere reading that the rectifier and audio circuit should be separate filaments.

Thanks,
nosaj

[g1]

All those amps with 6xxx type rectifiers run them off the same heater winding as the other tubes.

[Chuck H]

All those amps with 6 series rectifiers run them off the same heater winding as the other tubes.

And 99% of them DON'T modulate the signal. See post #10

[g1]

Agree Chuck. Just saying not to chase the issue of the rectifier using the same filament as the other tubes. It's the normal way it's done in these amps.
The items you suggested in post #10 are much better suspects