Tremolo Help

[tubeswell]

Put your VAC meter on the input lug of the trem intensity pot and turn the speed all the way up. You should be able to get a VAC reading this way. The peak voltage will be 1.4 x the VAC (or at least at close-enough-is-good-enough sort of ballpark indication)

[C Moore]

In the trem circuit.....Yeah...I removed that 0.10 cap.
I replaced that 470k with a 130k...after THAT resistor I have two 0.10 caps leading to the dual Intensity pot.
I will check the caps...I assume you are talking about the PI coupling caps.

Just saw Tubes post.
Will check that also.
Thanks

[martin manning]

No not the PI couplers, measure voltage or scope after the two 0.1's going to the dual intensity pot. The scope will give you a much more accurate picture of what you have there than a meter reading will.

[C Moore]

OK...
Into the intensity pot...from that 130k resistor and caps...about 1.00 VAC at each input. That is with the speed pot dimed.
Will check with the scope and get back

[C Moore]

Will explain this the best I can...maybe I should take a picture.
Scope is at 10mV. With a x10 probe it also shows probably close to 1VAC...it is hard to read.
The sine wave has no bottom...it just shows a rather square wave at the positive amplitude. It is the same after both caps...into each input of the dual intensity pot.

[martin manning]

Sounds like the 6SL7 idle point isn't centered very well, but the amplitude isn't much either. What kind of voltage do you have on its pins? Can you disconnect the bottom or wiper of the speed pot (which should stop the oscillator) and measure?

[C Moore]

Yeah...I will.
Talk in an hour or so.
Thank You

[martin manning]

Don't forget you'll have to have the trem switch on for current to flow. Get the supply voltage too (on the other end of the plate resistors) while you're at it. The oscillator apparently works, but I'm wondering if the other section of the 6SL7 is any good.

[C Moore]

Sorry Martin -
You are probably going to have to dumb this down even more for me.
Was I supposed to get/check AC somewhere.?

On the Trem Tube.....
Plate supply is 352 VDC.
Coming across each 220k plate resistor I see.....
Pin 2 is 158 VDC
Pin 5 is 148 VDC
My DMM shows no DC or AC on the grids.....I think.
Pin 3 and 6 are 1.9 VDC

[martin manning]

These voltages are with the speed pot disconnected and the trem switch on?

[C Moore]

Yes the bottom of the speed pot...that goes to ground...is not connected.
The Tremolo is turned on.

[martin manning]

That looks like a good DC operating point, and says that the 6SL7 is OK.

Now how about reconnecting the speed pot and disconnecting the oscillator output from the bias supply. Put your scope on the plate of the output stage. That should show you what the unloaded voltage swing and waveform look like.

Then you can reconnect it and see what happens. The load is mainly the dual intensity pot... maybe it should be increased to 500k.

[C Moore]

Can I disconnect the plate of the oscillator from the input of the dual intensity pot, and leave that connected to the bias supply.?
That is to say...do I have to run the bias supply direct to the 220k resistors, or can I still run it through the dimed dual pot.?
Thanks

[martin manning]

It can go through the dual pot.

[C Moore]

How normal does this look.?
Just showing one power tube plate.
Amplitude is 0.20 Volts per division.
x10 probe
V T B pots are on zero.
No speaker connected.
Trem plates are disconnected from bias.
Trem switch is off.