Hoffman AB763 Single Chan having trouble with Trem-o-Nator install

[mresistor]

Hi guys - I'm having trouble with an install of the Trem-o-Nator on my single chan Super Reverb.  Can someone point me to the latest layout for the Hoffman Single Chan AB763 showing a Trem-o-Nator?

I've got no wiggle at all.  Using an Xvive bug.

Thanks.

[mresistor]

I do have some photos..

[mresistor]

The Xvive was sold to me represented as a replacement for a VTL5C1.  I'm hoping someone can help.

[sluckey]

Can someone point me to the latest layout for the Hoffman Single Chan AB763 showing a Trem-o-Nator?

I don't think there has ever been a published layout. Let's see your layout.

[mresistor]

this is what I used

[Lectroid]

The Xvive was sold to me represented as a replacement for a VTL5C1.  I'm hoping someone can help.

I used the Xvive on my Princeton clone and got it working fine. (After some help from sluckey and tubeswell.). Keep at it, you'll get there.

[mresistor]

and this

[mresistor]

The Plate V on V4 (trem tube)  is only 217V .   

[EL34]

Can someone point me to the latest layout for the Hoffman Single Chan AB763 showing a Trem-o-Nator?

I have never heard of such a thing


I only have the info for that board on the library page here.
https://el34world.com/schematics.htm#Hoffman_AB763_One_Channel_

[sluckey]

I have never heard of such a thing

I modified your AB763-2 and AB763-1 with the trem-o-nator. That's my drawing. I don't recall putting the layout on the net but that just shows the state of my memory recall function.   

[sluckey]

The footswitch jack must be grounded to operate.

[mresistor]

thanks Slukey ..  i did use a shorting plug and it still doesn't wiggle.  I now notice that the trem layout shows a 50KRA Int pot and I have the 250K pot in there  - looking now to see if I have a 50KRA.


Sure enough I have two of them on hand.. must of planned on doing this before..   I'll install one.

[mresistor]

50KRA pot made no difference 


I've got   cathode  1.24v
                grid      1.25v
                plate 226-229 fluctuating

[mresistor]

Now it IS wiggling..   don't know what I did   switched it in and out a couple of times is all ..    it is wiggling but it is very weak.. 


Sluckey I think I read in the Tremonator thread that the effect could be made stronger by increasing the voltage on the 12Ax7 plate.  Right now there is 270V dc on the plate. 
Right now there is a 470K resistor between the B node and the plate..  maybe try a smaller resistance here and see.

[sluckey]

Divide and conquer time. Remove the shorting plug from the FS jack. I want the VTL5C1 LED cathode to be open circuit.  Now temporarily solder a 5mm red (or yellow) LED across that 10K just to the left of the VTL5C1 (as viewed on the layout). The LED cathode must be connected to ground. Power up. If the LED blinks and the speed can be controlled by the speed pot, the oscillator circuit is working. In this case, look at the VTL5C1, INT pot and connection to the signal path.

If the LED is dark or glowing dimly, the oscillator circuit is faulty and needs troubleshooting. Look for wrong component values, bad caps, wiring error, etc.

I have two questions... There is a black wire connected from the 10K on board to V5 pin 3. Is this wire really connected to V5-3? Can't tell in your pic.

Why do you have V6-2 and V6-7 swapped?

[sluckey]

Plate voltage on my AB763 varies between 148-345V. I'm supplied from node B at 434VDC. If you have a meter with a MIN/MAX function, use it to see what your DCV swing is. Or if your meter can read AC volts at a frequency of 5Hz, then measure AC Volts RMS on the plate. Should have about 100VAC When the speed is set to 5Hz. Or just look at the signal with a scope.

[mresistor]

The black wire is connected to pin 3  the other black wire to the ground bus. I am using pin 2 grid because I am using the #2 or B triode.  Pins 1, 2, &3.


Ill report back on the led insertion

[mresistor]

Ok..  I used a red led and a white led..  both were not super bright but the oscillator is working and speed is variable with the speed pot.  The min/max plate v swing is 82/306.
The INT pot is a brand new 50KRA.

[sluckey]

Nothing wrong with the oscillator circuit. Turn your attention to the vactrol, wiring, etc.

[mresistor]

The xvive ldr resistance reads 25K ohm on and 20M ohm off and that is spec.  The led has 1.6V on the pos side.  I assume this optocoupler is ok. All the components check out  and the wiring is correct.


I will be reflowing and checking solder joints tomorrow..   the wire is stranded Teflex.   


The tremolo works    I thought it was supposed to be stronger though. I have to turn it up to 8 or 9 to get really decent trem. Is this normal?

[sluckey]

Should be very strong. Right now you have the int pot connected to the bottom side of a 220K mixing resistor. Move that blue wire to the top side of the 220K. Any better? This also puts the trem on both channels.

I did not see the voltage measurements I asked for. The amplitude of the LFO signal determines the strength of the tremolo.

[mresistor]

Note to all read this thread: I had a senior moment yesterday.  This SR amp is a dual channel, aka a normal Super Rev.  I am also working on a Single Channel Deluxe Reverb and although I know what I am looking at when working on it, I got my wires crossed titling this thread.  Apologize for that.  Moving on.......................

Thanks Sluckey  - moving the blue wire to the top of the 220 does markedly improve the trem strength. However it really loads the normal channel down which I really don't want for this amp.


As for LFO output..  not sure what you mean ..  Measured where? I did give the voltage swing at the plate.

[sluckey]

As for LFO output..  not sure what you mean ..  Measured where? I did give the voltage swing at the plate.

LFO = low frequency oscillator. I wanted to know the amplitude of the LFO sine wave output as measured at the plate of the oscillator tube. Use a meter if it can measure at AC volts at 5Hz. Otherwise, use a scope.

Still wondering, why did you swap the connections to V6 pins 2 and 7?

[mresistor]

As for LFO output..  not sure what you mean ..  Measured where? I did give the voltage swing at the plate.

LFO = low frequency oscillator. I wanted to know the amplitude of the LFO sine wave output as measured at the plate of the oscillator tube. Use a meter if it can measure at AC volts at 5Hz. Otherwise, use a scope.

Still wondering, why did you swap the connections to V6 pins 2 and 7? 

I don't have a scope and no way to tell if the LFO is running at 5HZ  The AC ammplitude at the plate with the speed a minumum and the intensity at maximum is max - .536V / minimum .368V  so the amplitude if its a sine wave is .168? I am using a Fluke 87.


Here is a pic of Phase Inverter V6 and it looks to me like it is wired according to the layout.   

[sluckey]

I don't have a scope and no way to tell if the LFO is running at 5HZ  The AC ammplitude at the plate with the speed a minumum and the intensity at maximum is max - .536V / minimum .368V  so the amplitude if its a sine wave is .168?

Many DMMs can read frequency as well as AC voltage. I was hoping yours would.

The min/max plate v swing is 82/306.

That swing is the LFO signal and it's amplitude is 224V_pp or 79.2V_rms. That's plenty enough signal to give a very strong tremolo effect. If you still have the temporary red LED connected, then remove it. If tremolo is still weak replace the VTL5C1.

Here is a pic of Phase Inverter V6 and it looks to me like it is wired according to the layout.

Yes, it is. That pic clears it up for me.

[sluckey]

The xvive ldr resistance reads 25K ohm on and 20M ohm off and that is spec.

How did you check this? Details please.

[mresistor]

I don't really know what the off resistance is. The on resistance with a meter across the LDR in operation and with amp turned off is 24.95K ohms.   Here are specs.

[sluckey]

I don't really know what the off resistance is. The on resistance with a meter across the LDR in operation and with amp turned off is 24.95K ohms.   Here are specs.

The LDR cannot be "ON" if the amp is turned off. You need to light up the LED to shine on the LDR to get an "ON" reading. With the amp turned off the LDR reading will be like 50Megohm. Your meter is showing the resistance of the parallel INT pot.

I suggest a new VTL5C1.