1965 Deluxe Reverb-Volume Drops when Tremolo Intensity turned up--SOLVED

[wsscott]

A friend has a 1965 Deluxe Reverb and he said that when he increases the intensity on its tremolo, the volume of the amp goes down.  Any thoughts on what could be the cause?  Maybe the Tremolo pot or the tremolo roach?  Thanks.

[sluckey]

The volume should go down some. That's just how the roach tremolo works. But if it goes down significantly you should replace the roach.

[wsscott]

I haven't heard it yet, but its probably significant or my friend wouldn't have mentioned it.  Thanks for the lead.

[wsscott]

I’m looking at it later today.  Is there anyway to test it before taking it out to confirm it’s the roach at issue?

[sluckey]

I would turn the vibrato off with the footswitch or just unplug the footswitch. Now turn the INT pot up. Does the volume still drop?

[wsscott]

Thanks

[wsscott]

With tremolo turned off, the Intensity pot has no effect and volume is fine.

[sluckey]

Turn the tremolo on and turn the INT pot up. Do you think the volume loss is significant?

[wsscott]

Yes

[wsscott]

I replaced the roach, but no change.  Regardless of whether the tremolo is turned on or off with the footswitch or if it is unplugged, the output volume of the amp dramatically decreases as the Intensity increases. There is no tremolo of any kind, regardless of the speed or intensity setting. I checked the 110K and the 10M resistors, and the 100K reads fine, but when bridging the 10M ohm resistor with the meter probes, the meter reads 00.00 or 0.L depending on whether the GND or Pos. probe is on the roach side of the resistor or on the opposite side of the resistor.  My meter reads up to 40M ohms.  Thoughts?

[sluckey]

The vibrato FS jack must be grounded to enable the trem. You can do this with the footswitch or a gator clip test lead.

[wsscott]

Yes, even if the foot switch was plugged in, the result was the same.  No tremolo.  No response from pressing the foot switch. But still has the issue with the volume. Regardless of whether the foot switch is on or off, plugged in or not, as Intensity pot setting is increased to 10, the output volume of the amp decreases.  Like a Master Volume, I guess.

[sluckey]

With tremolo turned off, the Intensity pot has no effect and volume is fine.

Regardless of whether the foot switch is on or off, plugged in or not, as Intensity pot setting is increased to 10, the output volume of the amp decreases.

Which of these statements should I believe?

[wsscott]

Don’t know why it changed, but my last comment is accurate as of this moment.

[pdf64]

Something is behaving inconsistently, the roach seems the most likely suspect.
To eliminate the oscillator / buffer circuitry as being the cause, when it’s acting as per reply #12, it may be worth verifying that its neon really is turning off with the footswitch.

[wsscott]

As I said, I've installed a new roach with the silver dot pointing towards the tubes, and I don't get any tremolo at all, regardless of whether I'm using the old footswitch, another footswitch which I know works, or jumping the center lug (there's only 1 lug on the RCA jack) on the footswitch jack to chassis ground.  And regardless of whether the footswitch is on or off, I don't get any tremolo effect at all, and increasing the Intensity level on the tremolo pot decreases the volume of the output of the amp.

[wsscott]

I just checked the voltage at Pin 1 on V-5, and it reads only 90 VDC.  The schematic shows it as 210 VDC.  Does this help us?  Maybe a weak tube?

[wsscott]

And Pin 6 reads 178 VDC, vs. 345 VDC as shown on the schematic.  It seems these voltages are about 50% of what the schematic shows them to be.

[sluckey]

V5 voltages will be quite different depending on whether trem is on or off.

With trem turned ON.... Measure voltage for v5 pins 1, 2, 3 and 6, 7,8.

With trem turned OFF.... Measure voltage for v5 pins 1, 2, 3 and 6, 7,8.

Report all voltage readings.

[wsscott]

Tremolo ON--(Center Pin on RCA Footswitch Lug jumped to Chassis GND)
1--284.5 VDC
2--1.2 mvDC
3--2.27 VDC
6--241 VDC
7--178 VDC
8--177.5 VDC

Tremolo OFF--NO JUMPER
1--90.5 VDC
2--4.9 VDC
3--5.06 VDC
6--179.2 VDC
7--179.7 VDC
8--183.4 VDC

[sluckey]

Pins 2 and 7 should be negative voltages when trem is off. Please recheck.

[sluckey]

I need to ask a very basic question...

Is this an original 1965 Deluxe Reverb? Or is this a new production REISSUE '65 DELUXE REVERB?

[wsscott]

This is an original.

[wsscott]

Pins 2 and 7 are both POSITIVE VDC.  I've got the DMM's black probe connected to chassis and the red probe testing on the Pins of the tube socket.

[pdf64]

With the trem off, what’s the voltage at either end of the 2M2?
What’s the resistance of the 2M2?

[sluckey]

Post a hi-rez pic that clearly shows the trem circuit on the board AND V7 socket all in one clear pic. I want to be able to clearly read resistor values of everything in this pic.

[wsscott]

Sluckey, did you mean V-5 socket vs. V-7?

[wsscott]

Here's the photo of the tremolo with V5 socket.

[wsscott]

PDF64-The voltages are as follows:
At the point where the two 1.0 M resistors meet with the 2.2M ohm resistor its 60.6 VDC

At the opposite end of the 2.2 M resistor its -63.7 VDC

The 2.2M ohm resistor flashes between 0.L and 0.000---Weird

[sluckey]

Hmm. That's two high value resistors that your meter did not like. Check a new 2.2M and 10M. If they check OK then disconnect one end of the 2.2M and the 10M and recheck. If they still seem wonky, replace.

All these crazy voltage readings are making me think that circuit board may be conductive.

[shooter]

if your test resistors ohm wonky, manually select the range on your meter and maybe battery time


EDIT:
look at the "right side" of  the 220k, if you needle nose the 220k lead, is it solid in the solder

[pdf64]

Maybe the caps are leaking DC?

[wsscott]

The 220k is solid.

I’ll check out the resistors again tomorrow.  I don’t have a 10M, the closest is a 8M, but I do have a 2.2M metal film, but I don’t know it’s wattage.  It’s not shown on the package.

[sluckey]

I’ll check out the resistors again tomorrow.  I don’t have a 10M, the closest is a 8M, but I do have a 2.2M metal film, but I don’t know it’s wattage.  It’s not shown on the package.

Just want to know if your meter is reading correctly.

[pdf64]

…
The 2.2M ohm resistor flashes between 0.L and 0.000---Weird

Are you sure there wasn’t any voltage on it when you measured that?
I suggest to try again after checking the amp is been totally deenergised.
And of course after sluckey’s suggestion to measuring the resistance of a new unused 2M2, as a sanity check on your meter.

[wsscott]

I measured a new 2.2M resistor this morning and the meter reads it fine.  I checked the voltages on the board, and there was about 20VDC remaining on the rectifier tube socket, so I discharged that. Without taking the Dog House off the filter cap section, is there any other place on the eyelet board to discharge those caps? A better recommendation?

I checked the voltages on the 2.2M in circuit and it reads right at 2.0M.  So that one seems okay.  I then read the 10M in circuit and it reads about 3.0M vs. 10M.  I did have a NEW 8.2M metal film resistor and the meter reads it fine.  So maybe its that 10M resistor?

[pdf64]

… maybe its that 10M resistor?

Probably not, I can’t see how that might put +60V on to the grids?
The issue is the positive voltage. You need to identify where that’s coming from.
Likely suspect is the modulation oscillator via leaky caps.
Or the board may be conductive.

[wsscott]

So how do I check for that?  I don't know at this time if it was something that gradually got to this point, or all of a sudden.  I'll try to remember to ask my buddy.

[sluckey]

So how do I check for that?

Connect black probe to chassis. Meter set to measure dc volts. Now probe the board in the area of the tremolo circuit. I suggest to start at the junction of the 2.2M and two 1M resistors. Close to, but not touching eyelets. Use a sharp probe and act like you are trying to punch a hole in the fiber board. Do this in multiple places. A non conductive board will show zero or maybe a few millivolts on the meter. Anything more than a volt is unacceptable.

[wsscott]

I assume the amp is turned ON, rather than just plugged in to a power source?

[sluckey]

Me too!

[pdf64]

Yes.
I suggest never to leave an open chassis plugged into a power outlet.
Amp either on for live testing, or isolated and deenergised.
I’m more prone to inadvertently doing letting my guard down and putting myself in danger in intermediate conditions, when some parts are live (eg amp off but plugged into mains outlet).

[wsscott]

pdf64, yes that's what I always do too.

Any comment on "Without taking the Dog House off the filter cap section, is there any other place on the eyelet board of this Deluxe Reverb to discharge those caps?" ?

[sluckey]

Any comment on "Without taking the Dog House off the filter cap section, is there any other place on the eyelet board of this Deluxe Reverb to discharge those caps?" ?

Pin 8 of the rectifier tube.

[wsscott]

So I probed the eyelet board, and didn't see any reaction at the 2.2M resistor, but up at the junction area of the 10M ohm resistor I got a reading of 0.03 VDC, not mvDC.  And when I pressed on the board I could also hear a change in the background noise coming through the speaker.  That area of the board where the tremolo circuit is located is wavy looking, ie. sort of warped in shape.

[sluckey]

Crazy question... Have you replaced V5?

[wsscott]

No.  I'll see if he has an extra one, or if another buddy has one.

[PRR]

"...any other place on the eyelet board of this Deluxe Reverb to discharge those caps?" ?

Jumper a preamp plate to ground. Wait a minute. The 100K resistor will discharge to about 1V, without spark or drama.

If you are brave/careful, leave the jumper on while measuring because caps will sneak-back a little.

Be sure to remove the jumper before power-up!! Or stock-up on 2Watt 100k parts.

[wsscott]

Thanks, the plate is what I was looking for.  I have a snuffer stick, and I also have a 20K, 5W resistor in an adaptor that plugs into my meter that I learned from D-Lab, so it will drain quickly without a spark.

[sluckey]

Crazy question... Have you replaced V5?

No.  I'll see if he has an extra one, or if another buddy has one.

ARGH!!!!! TUBES ARE ALWAYS THE FIRST THING TO TRY IN A TUBE AMP!

There are four 12AX7s or 7025s (just a low noise 12AX7) tubes in the amp. Just pull V5 and replace with V1, or V2, or V4.