Hoffman Princeton Reverb Trem-O-Nator 2nd Attempt

[purpletele]

I am making another run at the Modifying the PR with the Trem-O-Nator Circuit.  I was unsuccessful a few years back, but I was ecouraged to try again.

First photo is the amp in good operating condition prior to the demo
The last photo shows the amp ready to drop in the Vactrol component.

Should I drop the component in place and test it, or should I do the LED test?
If I do the LED test, where do I place the LED.

Thanks in advance


Brian v

[sluckey]

I suggest doing the red LED test. If the LED blinks and you can change the speed, then the oscillator is working. Then remove the LED and put in the VTL5C1.

But first... REMOVE THAT JUMPER!

[purpletele]

I removed the jumper and then installed a LED with the configuration as indicated in the nice detail that you had provided.

I am not getting any illumination of the LED when I power up the amp and the intensity Pot does not change anything.
The amp is operational and plays fine.

Seems like that was where I left off last time. 

Let me know your thoughts.

[sluckey]

No wonder it doesn't work. The LED is connected to nothing! You disconnected the wrong jumper. Look closely. The arrow is pointing to the very short jumper that is ***BETWEEN*** those 2 turrets. So remove that jumper and reconnect the orange wire.

The LED must be red or yellow. White or clear will not work. I have some red LEDs that are in a clear plastic housing. If that's what you have then that's OK. But if it ain't red then get a red one. Different color LEDs have different voltage drops. Red gives the proper voltage to bias the oscillator triode.

[purpletele]

The connection didn't make sense to me after I put it together, so your response makes sense.

I had ordered a couple of red LED's and they are showing up soon.  I'll clean up the jumper and be back in action in a few days.

Thank you

[purpletele]

A source of power is always good!

I removed the Turret jumper and replaced the orange wire tying the circuit back together.

The little white LED lights up and I can control the pulsation with the speed knob, so it appears that I am good to go with the VTL5C1.  I'll tie the Turrets back together and drop in the new component.

I filmed a short video of the LED test for future viewing.  I will post that a little later, and if everything turns out good then I'll get a video of the new Trem circuit in use.

BV

[sluckey]

I'll tie the Turrets back together

NO NO NO NO NOOOO! Those two turrets should not be connected. Look at your layout drawing.

So the oscillator is working. That's good. Hopefully you will have tremolo when you install the VTL5C1. But remember, there may be a bit of experimenting to get it to sound as good as your AB763 amp. There are several different ways to connect the INTENSITY pot shown on my Trem-O-Nator web page.

[purpletele]

Well that was silly on my part, it's very clear that the jumpers do not belong there with this circuit.

Thanks,

I'll move forward

[purpletele]

I dropped in the VTL5C1 into place and had the Hot side of the intensity pot connected as shown on the attached layout.  I had no pulsation and no control with the intensity knob.

I removed the shielded wires that I was using for the Intensity Pot leads, and I am now using a test lead for the injection testing.

I connected to the point where V3-7 ties into the bottom of a 470K and that didn't produce any control or change, no pulsation.

I have a 50K RA Pot installed with one leg grounded. I'm prepared to change that Pot value if that is the next recommendation.

I reflowed the connections on the Vactrol component, I've read a lot of past threads.  It appears that this particular circuit/layout has not adopted the TON integration yet, but the beefed-up PR with 5881's was close.

I will gladly take more recommendations or tests.

[sluckey]

I just finished reviewing your original thread. No need to repeat all the tests we did previously. I recommend you re-read that entire thread too.

     https://el34world.com/Forum/index.php?topic=25758.msg279715#msg279715

OK, here's a new test... Disconnect the wire from the wiper of the INT pot. Set your meter to read resistance. Connect one probe to chassis. Connect the other probe to the dangling wire you just removed from the INT pot wiper. Use gator clip lead because we want to leave the meter connected like this for a while.

With amp power OFF, the meter should read some very high resistance. Does it? What is the reading? Now turn the amp power ON and allow to warm up. The bar graph at the bottom of your meter display should be bouncing back and forth, left to right, at the speed of the tremolo. (Probably help to set the speed slow.) Is the bar graph bouncing? If so, press the MAX/MIN button only once to enter MAX/MIN mode. Wait about a minute. Now press the MAX/MIN button again to display MAX Ω reading. Press the MAX/MIN button again to display MIN Ω reading. What are the MAX and MIN ohm readings? Press and hold the MAX/MIN button for 2 seconds to return to normal mode.

This concludes this test. Report the three ohm readings.

[purpletele]

Thank you for the reply, I had a full day of work going on today.

I recently bought a Fluke 87 IV from a colleague that upgraded.
   
I re-read the thread on the previous attempt; we went pretty deep into the weeds. 

Current Testing

I disconnected the yellow wire at the Intensity Pot wiper and clipped on a lead, the other end of the wire was soldered on to the right bottom leg of the Vactrol component.  I have the other test lead clipped to the chassis.  I am getting an OL.   

[sluckey]

     ARGH!!! You failed that test big time.

Now finish the test!

[purpletele]

    ARGH!!! You failed that test big time.

Now finish the test!

Getting OL when the power is on as well.

[sluckey]

Wait a minute. Disregard my previous post. I just noticed you don't have a footswitch plugged in. So, connect a ground to the tip of the footswitch jack to enable the trem. Now see if the trem works. Disregard the resistance test for now.

[purpletele]

Wait a minute. Disregard my previous post. I just noticed you don't have a footswitch plugged in. So, connect a ground to the tip of the footswitch jack to enable the trem. Now see if the trem works. Disregard the resistance test for now.

I tried a Fender pedal that I bought for this amp for the first test.  When I engage the pedal I am getting a real weak but noticeable oscillation, I can manipulate speed and intensity but it's mild.  When I hard wired the jack it seems much weaker?



   

[sluckey]

Repeat the test in reply 9.

[purpletele]

Repeat the test in reply 9.

When I have the Ground clipped to the tip
Max Reading 42.8 K
Min  Reading 25K


EDIT
When I have the pedal plugged in

Max Reading 156K
Min Reading  149K

[sluckey]

I expected a bigger spread than that. Surely you disconnected the wire from the INT pot wiper to do this test? At this point I suggest a new VTL5C1.

[purpletele]

I expected a bigger spread than that. Surely you disconnected the wire from the INT pot wiper to do this test? At this point I suggest a new VTL5C1.


I had the wire disconnected from the INT wiper. I bought an extra VTL5C1.  I'll try a new one later and report back.

Thanks,

BV

[PRR]

purpletele, why are you deleting the {/quote} after Sluckey's words?

I can't tell who says what. (I am easily baffled.)

Leave the {/quote} and put your reply after it.

[purpletele]

purpletele, why are you deleting the {/quote} after Sluckey's words?

I can't tell who says what. (I am easily baffled.)

Leave the {/quote} and put your reply after it.

Thank you, I was going to look into that. 

[shooter]

why are you deleting

fwiw I have to select quote icon, paste txt, click the cursor to AFTER the pasted txt, select quote icon again, THEN manually add  \  so it looks like this AFTER the text>>> [\quote]


even after all that the fond size sometimes changes to 8pt, then I have to select any text I type after "my fix" and change font to 10pt

[sluckey]

You been smokin' in the bait shop again?   

[purpletele]

I repeated the test from reply #9 with a new Xvive VTL5C1 and the spread between High and Low is even tighter

Max 25K
Min 21 K

I used the foot switch and I tried by grounding the input jack, both had similar results. Very faint oscillation when I plug in the guitar.

Willing to try something else if you have ideas.

[shooter]

 
I couldn't figure out why it kept screwing up, til I realized i was using the "commands" in my example, bet I tried 5 times before I figured it out!!
but ya, it was after 420 

[purpletele]

I was restoring my amp after the Trem-O-Nator part II story.  I had see a video from P2P Amps where he was talking about his lush Tremolo.  I happen to jot those little nugget notes down.

I implemented the changes that I picked up from Mike Skaggs and it worked well!  Very satisfied.

I have attached the Color Layout with a red cloud around the changes.

Here is a video of the new and improved Tremolo on a Hoffman Princeton.  I seem to have a very sensitive microphone.  I'll try to re-record a better video tomorrow.

[sluckey]

Glad you have some tremolo. The stock circuit should serve you just fine unless you try to run 6L6s. With 6L6s the trem may become bias dependant and a bit finicky. I still don't understand why the Trem-O-Nator did not work out for you, but I have no other suggestions. Would have loved to put it on my bench.