Stand-alone true pitch shifting vibrato for guitar

[Willabe]

 

[tubeswell]

Is there a modification to drastically slow the oscillator down. I find I can never quite get it slow enough.

Doubling the capacitance of one or more of the (3) caps in the RC plate-to-grid network in the LFO stage will slow it down. (e.g.; tack another .01uF in parallel with one of the .01uFs) Experiment a bit

[Jhtjon]

cool thanks

[Willabe]

I went online and downloaded the service manual for the Hammond L-100. In it it has the AO-41 and AO-47 schemos + the layout drawings for them and at the very end of the manual a parts list divided into the individual circuits.

Looking at the AO-47 schemo they have a foot note on the LFO drivers tail cathode R133. It say's
"R133 or omitted depending on reactor". The parts list say's;

"Resistor   560 ohm    R133....Use with Red Dot Reactors."    (What's a red dot reactor?   )

It would seem they had at least 2 different SRs. I'm looking at my SRs and 1 is a little different.

I have 8 of them that are the same. The laminations look like E/E and are silver in color. The 1 that is different looks like the lams are really 2 U's side by side making an E/E form and are copper/pinkish in color. They are both the same height but the different 1 is 1/16" less in wide and 1/64" less (1 lam?) in depth.

I have bought 3 units off e-bay, 2 AO-47's and 1 AO-41. I don't remember which unit the copper colored 1 came from. The others I bought as NOS replacements.

The copper colored lam SR coils have all their fly leads insulation in red and black. The silver colored SR coils fly leads that go to the tube phase shifter circuit side are red and black. But they have the fly leads that go to the LFO with yellow and green insulation. And the silver colored 1's have a little bit heaver gauge wire.

I'll take some pics and post them in a little bit.

What do you guys have as far as lam color and wire insulation color. And do you know which unit they came from?

Here's the link;

archive.org/details/HammondOrganCo.-L-100ServiceManual


          
            Brad    

[Willabe]

Here's pic of the copper colored lam SR coil. You can see the split in the coil lams running top to bottom.


             Brad    

[Willabe]

Here's more. You can see the slightly heaver gauge wire and insulation color for the fly leads on these. Note the coil lam color.


         Brad    

[Willabe]

I'm getting ready to finally build the Warbler.  

I brought this idea up early on in the thread about putting in a passive loop for a delay pedal.

I'm thinking that you could send the output back to the input delayed a few milli seconds and it would get phase shifted again. Kinda like the regeneration controll on a flanger?

I think I'm gonna need a couple of R's for a mixer at the grid for V1b? I'm not sure that I need the 2'nd 1M volume pot on the loop return?

Will the 1M send pot be a problem with it being tapped off the 500K output pot?

Do you think it will work as drawn?


                  Brad    

Edit: Fixed send return pots wiring, added mixer R's.

[tubeswell]

I'm getting ready to finally build the Warbler.  

I brought this idea up early on in the thread about putting in a passive loop for a delay pedal.

I'm thinking that you could send the output back to the input delayed a few milli seconds and it would get phase shifted again. Kinda like the regeneration controll on a flanger?

I think I'm gonna need a couple of R's for a mixer at the grid for V1b? I'm not sure that I need the 2'nd 1M volume pot on the loop return?

Will the 1M send pot be a problem with it being tapped off the 500K output pot?

Do you think it will work as drawn?


                  Brad    

This may be one of those suck it and see moments

[Willabe]

This may be one of those suck it and see moments

    

I still think I need at least a pair of 220K R's for a mixer like with a 2 channel input.


           Brad   

[tubeswell]

Not sure whether 220k is necessary, but you may want to consider putting a level control (or some sort of level attenuation and/or frequency filter) on the feedback loop. At this stage its a bit of a guess as to whether the feedback is going to be too much for the circuit. Whatever you do about that, I guess the FX loop idea would be better as a parallel loop - in relation to the NFB loop (rather than a serial loop).

[Willabe]

but you may want to consider putting a level control (or some sort of level attenuation and/or frequency filter) on the feedback loop. At this stage its a bit of a guess as to whether the feedback is going to be too much for the circuit. Whatever you do about that, I guess the FX loop idea would be better as a parallel loop - in relation to the NFB loop (rather than a serial loop).

I have a 1M pot on both the send and return jacks for now in the drawing.

What NFB loop?    

The loop on the bottom of the drawing is dry signal to mix at the output with the phase shifted signal.

The reverse Fx loop, delay loop is in phase output to input.


                Brad  

Edit:  Fixed send return pots wiring, added mixer R's.

[tubeswell]

What NFB loop?    

The loop on the bottom of the drawing is dry signal to mix at the output with the phase shifted signal.

I meant feedback loop

[Willabe]

PRR brought up that the last gain stage could probable be lost. I think it was Dave who tried it and posted it worked for him.

Will this work to get rid of the 1 spare triode? To keep the dry signal in phase with the phase shifted output signal at the mix pot I took the dry signal from V1a K bypass caps ground end.


            Brad    

[Willabe]

Ok, I'm pulling the trigger on this build.    

I feel this is my best layout to date as far as short ground loops and short grid wires. The drawing looks messy because of my trying to show the termination of the twisted pairs being split evenly between their +< > - eyelets/turrets. There's only so much you can do with the Sch program. Drawing is to scale.

I'm really pleased with how the LFO and driver came out, becaues of the LED, at least on paper.

I've got my layout drawing ~95% finished and have almost all the parts I need to build it. I need to double check. I am going to use a pair of Hammond simi-toride PT. 1 for HT B+ the other for 12acv heaters.

Also I'm going to use PCB 5mm x 20mm fuse holders, at least on the secondaries.

With 2 PTs do I need to use 2 fuses for the primaries, 1 for each PT? It would probable be the safest way?

See any mistakes? Please let me know.


            Brad      

[sluckey]

I've been tinkering with my Warbler this week and have made several changes that I think have really improved the sound and added a little eye candy...

1. Added LED to oscillator circuit for visual only.

2. Moved foot switch to provide instant on/off operation. LFO runs continuously.

3. Replaced all three .47µF caps with .1µF caps.

4. Added tone control.

5. Lowered gain of V1A and also provided an output from V1A cathode to send to MIX control. This corrects a phasing problem between the dry and wet signals. MIX works properly now.

Here's an updated pdf covering the changes. I'll update the website early next week.

      http://home.comcast.net/~seluckey/amps/warbler/warbler_rev2.pdf

[sluckey]

Brad, if you are gonna heat the tubes with 12VAC, you need to remove the jumper between pins 4 and 5. Then connect the 12VAC string to 4 and 5. Pin 9 is not used.

[tubeswell]

I've been tinkering with my Warbler this week and have made several changes that I think have really improved the sound and added a little eye candy...

1. Added LED to oscillator circuit for visual only.

2. Moved foot switch to provide instant on/off operation. LFO runs continuously.

3. Replaced all three .47µF caps with .1µF caps.

4. Added tone control.

5. Lowered gain of V1A and also provided an output from V1A cathode to send to MIX control. This corrects a phasing problem between the dry and wet signals. MIX works properly now.

Here's an updated pdf covering the changes. I'll update the website early next week.

      http://home.comcast.net/~seluckey/amps/warbler/warbler_rev2.pdf

Soundbytes with the changes?

[DummyLoad]

you're using a FWB for a unipolar power supply; nothing on the B+ secondary of the PT gets grounded unless you're building a bipolar power supply.
the secondaries are strapped proper for series operation, however, if you ground pin 6 as indicated, it'll leak magic smoke.

if you're building to meet UL/CSA/VDE; then you'd fuse each winding or winding group. but you're not, so use one fuse...   

--pete

[Willabe]

Brad, if you are gonna heat the tubes with 12VAC, you need to remove the jumper between pins 4 and 5. Then connect the 12VAC string to 4 and 5. Pin 9 is not used.

Yes.

Pulled the layout parts from my library which at this point has only been 6.3vac heaters. Thanks for catching that. I would not have wired them up that way. I'll fix that on the drawing and repost.


         Brad      

[Willabe]

Ok, fixed the drawings. I forgot I was using a FWB.

Thanks for picking up my mistakes guys.


              Brad      


Edit; Found a mistake in the LFO/driver layout fixed it, added Sluckeys updates and added fast/slow switch. Will post new updated drawing Sat.

[sluckey]

I highly, highly recommend you make the changes to V1A circuit. It will make the mixer work like it should. It's very simple to do on your layout. Change the plate resistor to 15K. Change the cathode resistor to 10K. Remove the cathode bypass cap. Connect the wire from the .047µF cap on the left side of your MIX pot to V1A cathode rather than the V1A plate. Once you do this, the phase of the dry signal will match the phase of the wet signal and the MIX pot will smoothly blend between all wet and all dry as you would expect. Leaving it wired as I originally did results in mixing out of phase signals and the effect is a thin sound that changes almost like a phaser (but not as pleasant) as you turn the knob from dry to wet. The thin sound is very much like jumping two preamps together when they don't have the same number of gain stages, ie, out of phase. It took a scope and a sig gen to figure out exactly was happening in the warbler.

The added tone stack (stock 5F10, but also very common in other tweed Fenders) is nice but not a must do IMO. The warbler will tend to mellow out your treble tones and the tone stack just helps put some of that back. I like it, but I also have a lot of high freq hearing loss. It's also an easy mod that requires no change in the layout. The added tone pot connects directly to the volume pot.

Moving the footswitch is really a must, especially if you will run the LFO below 4Hz. The oscillator is slow to build up at slower speeds if starting from a dead standstill. It's fine up around 6-7Hz. The new FS interface allows the LFO to run continuously, and simply kills the input to the driver CF. I highly recommend this. Requires no change in layout.

Adding the LED was purely for the geek in me. No performance change. Looks good on the control panel a'winkin' in it's little chrome bezel!

I changed the three .47µF coupling caps in the modulator hoping to brighten the tone a bit. I heard no change with .047µFs or .1µFs. Might make a difference to a keyboard or someone with good ears.

[Willabe]

I highly, highly recommend you make the changes to V1A circuit. It will make the mixer work like it should. It's very simple to do on your layout.

I already changed the dry signal take off point on my layout/schemo drawings last night.

I have been thinking about the phase of the 2 signals at the mix pot. I am toying with the idea of either dropping the last triode stage (to go to only 3 tubes) or adding a 4th phase shift stage to use that spare triode and see if it sounds any better. I'm going to build it as is for the 1'st one then I'll have something to A/B it against.

Any way I was thinking each triode stage flips the phase 180 degrees from grid to plate. So an even number of gain stages stays in phase from input to output and an odd number will be out of phase from in to out. If I drop the output stage or add another phase shift stage then I would have to move the dry signal take off point. Which I posted a drawing taking the dry from the K.

But I think what is going on is that each of the phase shift stages is not being fliped 180 degrees G~A because their split load and are not fliping the phase? Or it get's nullifed? So really there's only 2 gain/triode stages, the input and output in this circuit that flips the phase from G~P?

I think this is right?


              Brad        

  

[sluckey]

I traced it with a scope. Each stage flips the phase 180 degrees (grid to plate) exactly like it's supposed to. That's how I discovered that the dry was out of phase with the wet. Looking back though, all you gotta do is just count the stages.

[Willabe]

I don't understand.

There's 5 stages in to out. Grid and cathode are in phase with each other and are 180 degrees out of phase with the plate. So dry signal is taken from the 1st stage cathode and returned to the 5th stage. Should be out of phase.

I must be missing something.


              Brad     

[Willabe]

I traced it with a scope. Each stage flips the phase 180 degrees (grid to plate) exactly like it's supposed to. That's how I discovered that the dry was out of phase with the wet. Looking back though, all you gotta do is just count the stages.

So you ran a signal into the input and traced it with the scope? Was the LFO and driver going at the time you traced the signal? I'm wondering if the scope would show a different phase at the plate when the LFO/driver where going than when their turned off? When their turned off isn't the cathode signal blocked by the SR?


              Brad     

[Willabe]

Once you do this, the phase of the dry signal will match the phase of the wet signal and the MIX pot will smoothly blend between all wet and all dry as you would expect.

What do the 2 extreme settings, full up on 10 and all the way down on 0 and half way on 5 sound like now? No phase shift effect at 0? Most phase shift at 5 since the wet signal has the dry signal to work against?


                Brad    
  

[sluckey]

What do the 2 extreme settings, full up on 10 and all the way down on 0 and half way on 5 sound like now? No phase shift effect at 0? Most phase shift at 5 since the wet signal has the dry signal to work against?

0 = total dry, no vibrato effect. 10 = full vibrato effect. Since the vibrato signal is larger than the dry signal, the MIX pot does not blend 50/50 when on 5. The 50/50 point occurs much sooner. But what's a number? My knobs don't have numbers. And you're gonna adjust the MIX by ear anyhow.

Your other questions raise some interesting points. I'll put it back on the bench and take another look and get back to you on those.

[sluckey]

Some new test data to contemplate. Refer to http://home.comcast.net/~seluckey/amps/warbler/warbler_rev2.pdf

The overall phase shift (input to output) is about 70-80º. I'm not even gonna talk about phase shifts of individual stages. This phase shift is constant regardless of whether the LFO/driver is on or off. Now with the LFO/driver enabled, increasing the DEPTH begins to slightly modulate the frequency (vibrato or pitch shifting effect) of the 1KHz test signal. Increasing the DEPTH more causes the frequency deviation to increase. The frequency deviation is ever so slight but you can easily see it on the scope. The sound is a varying pitch similar to shaking your finger on a fretted note, or lightly wiggling a whammy lever. Increasing the DEPTH even more begins to introduce amplitude modulation (tremolo effect). The combined vibrato/tremolo gives a sound similar to a Leslie or chorus pedal. Increasing the DEPTH to MAX will continue to increase the AM until the sound becomes choppy (not very pleasing to my ears). And of course, changing the RATE changes the speed of the modulation effects. With rates below 4Hz you get a nice subtle slow pitch changing sound. 6-7Hz is a nice vibrato (chorus-like) sound. Above 8Hz is too fast for me, reminds me of Crimson and Clover on steriods!

[Willabe]

Thanks for going back in Sluckey for more testing and posting more info.  

I remember PRR, HBP and KOC talking about phase shift in an amp/circuit before and the math  was very complicated to me. IIRC all amps/circuit have some phase shift from input to output that is not perfect. Some to the point that their unstable.

Even without the math, scope/signal generator or just counting the stages the circuit is saying and so are your ears, that it likes the dry taken from the cathode and not the plate to be mixed with the output and that's what counts. I don't need to understand all of what's going on in there to build one. I'm just glad you found it.        

Later today I'll go back through the thread and PM the guys who built 1 and point them to your updates .

Maybe PRR or HBP will add some more to the phase topic?

Above 8Hz is too fast for me, reminds me of Crimson and Clover on steroids!

Tommy James and the Shondells? Love it! ("My Baby does the Hanky Panky") I'll have to build a 2nd one to run through the PA if I ever get back in a copy band! Hey, even the Kenny Rodgers song from when he was in the First Edition? "I Just Droped in to See What Condition my Condition was in." I love that song!

" Yeah, yeah, oohh yeah, what condition my condition was in."  Wonder what he was messing with when he wrote/sang that?      


          
                 Thanks,   Brad        

[Willabe]

Oh almost forgot, I thought you put a 500KL for the mix pot? Latest drawing shows 250KL.

And how much loss do you think the mix pot and 1M to ground voltage divider adds? It does act like a voltage divider to ground? Looks like from input to the last gain stage it's double, 200mV PP to 400mV PP. Which is still very small. But maybe the 1M needs to be reduced in value, so in equals out?


              
                  Brad        

[sluckey]

Oh almost forgot, I thought you put a 500KL for the mix pot? Latest drawing shows 250KL.

It is 500K. Don't know how 250K snuck in there!

And how much loss do you think the mix pot and 1M to ground voltage divider adds? It does act like a voltage divider to ground? Looks like from input to the last gain stage it's double, 200mV PP to 400mV PP. Which is still very small. But maybe the 1M needs to be reduced in value, so in equals out?

Yes, the mix pot and the 1M do form a voltage divider that depends on the position of the pot and whether you're looking at the wet or dry signal. When the pot is max CCW, the dry sees no voltage divider but the wet sees a 500K/1M voltage divider (wet output knocked down to 67%). Take the mix pot to max cw and now the wet sees no voltage divider but the dry sees a 500K/1M voltage divider (dry output knocked down to 67%. But when you connect to the input of an amp, these voltage divider numbers change. You then must consider the amp's input resistance. It's true that the MIX is not perfect, ie, goes from all wet to all dry. There's always gonna be a portion of both signals at the output. It works exactly like the mixer on the 6G15. And it's good enough to fool your ears.

There are several things you could do to make the overal gain of the warbler equal to unity, but I purposely wanted to have a little boost on tap for the vibrato signal.

[Willabe]

There are several things you could do to make the overall gain of the warbler equal to unity

Like what?

Here's the layout with Sluckeys changes/updates. I left the .22 coupling caps that I had already gone to from the .47 as the Malory 150's .22 and .1 are the same length and won't change my layout.

1. Moved the dry signal take off point to the cathode and changed it's bias, A/K R's.

2. I added the tone control. I made the tone pot 1M like a 5F10/5E3/5G9, for (maybe) a little more treble?

3. Added the fast/slow switch and fixed a ground mistake I had on the LFO/driver. I needed an extra solder lug which is indicated. Was then able to move a couple more components off the board.

4. Got ride of a few redundant eyelets, which along with above let me add 1 more filter cap. So now the input CLC filter is 66uF/choke/66uF. Should be very quite?

If you see any mistakes or problems please let me know.


                Thanks,   Brad    


Edit; The 20uF 160v filter cap on the dc standoff is backwards, I'll fix it and repost.

[sluckey]

Don't drill your board just yet. You're gonna like what I did today. V3 is totally gone. I boosted the gain of V1A a little to provide an overall gain of two (input to output). Dry signal is once again taken from V1A plate and it's amplitude is slightly greater than the wet signal at the MIX pot. 50/50 blend is back at about half rotation of the MIX pot. The unit still has the same sound but is a little quieter without the output amp. I'll post the new schematic tomorrow when I get it cleaned up.

[Willabe]

Don't drill your board just yet. You're gonna like what I did today. V3 is totally gone.

I boosted the gain of V1A a little to provide an overall gain of two (input to output). Dry signal is once again taken from V1A plate and it's amplitude is slightly greater than the wet signal at the MIX pot. 50/50 blend is back at about half rotation of the MIX pot. The unit still has the same sound but is a little quieter without the output amp.

That's great Sluckey.        

I haven't made my template yet for the board. I'll wait, no hurry at all.

Took me what? Over a year and a half to get going on this.    


  
                     Brad      


Hey do you think 1 of these will sound good through the Warbler?      

[sluckey]

Latest changes. I may be done...

    http://home.comcast.net/~seluckey/amps/warbler/warbler_021113.pdf

[Tom_Hull]

hi guys

thanks ,,,,,,,,for the  topic and this layout .

i must be lucking out here .
i buy a christmas gift for myself every year .got it  in november 
this year it was a hammond organ 112 vibrato.
with 2 12au7 s and a 7247..
the 12au7 s have a tube sheild and 7247 has no sheild .

looks like another project for me ..

Thank you

tom

[Willabe]

Ok, I think I've got it with your latest updates.

The only real constraints I had were lining up the mix pot so the .047 caps would go to pin 1 on V1a and to the output of the phase shifters 3rd stage. The other was the head cabs face plate opening. If it was a another ~1" longer or so on both ends it would've be easer. Fitting in the tone pot was a real pain.    

Sluckey I'm soooo glad you did these up dates to the circuit before I built it. Thank you for posting them!


                  Brad      

[Willabe]

I moved the .047 cap of the mix pot x end and onto the eyelet/turret board. Gives me a +/- twisted pair of wires to go from the pot and output jack to the feed from the dry signal .047 cap and filter cap ground.

I think I like it better.


                   Brad    

[Willabe]

Here's the schematic for V.3 and V.3.1.


                Brad      

[Willabe]

Sluckey, I'm going to start my face/back plate layout/template on Inkscape today, so I can get it made at the laser engraver.

If you think of anything else or see anything wrong in my layout please let me know.

I'm not very good with Inkscape yet so it'll take me a day or 2 maybe.


              Brad     

[Willabe]

HELP!!!!

I just had a power outage for a second, went off and right back on. I had the Sch. program for the Warbler open and now I can't get it back open.

When I try to open it I get a message that says;

InvalidcaseinReadLayoutEntryFromFile0

When I click OK box it then gives;

Run-time error '7' Out of memory

All my other Sch. files can be opened. Warbler file when I hover over the title says 536K. So does that mean it's still in there?


               Brad    

[sluckey]

Power off the computer. Wait a few seconds and boot up. Cross your fingers and try again.

Get a UPS and/or a memory stick and use them.

[Willabe]

Already did that, no go.

Went in to my documents list and it's there too. Click once on it and it asks if I want to open or save. Click on save it says it already exists do you want to replace it?

If I would have posted the Sch. here would I have been able to get it back from here? Or would it still be gone because it was stored on my computer?



              Brad      

[sluckey]

Went in to my documents list and it's there too. Click once on it and it asks if I want to open or save. Click on save it says it already exists do you want to replace it?

Copy it to another folder and try opening from the new location.

If I would have posted the Sch. here would I have been able to get it back from here?

yes

[Willabe]

Copy it to another folder and try opening from the new location.

Hey, that worked! Thank You!    

Now when I open the Sch. program there's 2 Warbler, 1 says copy. Now both will open but the 1st one, when I click on the save button, after 30 seconds or so, message says; Failed to rename."

I have a memory stick I will start to use it from now on.

I have Norton 360 it has back up could I have gone in there and retrived it?

I tried to use a restore point from Windows but that didn't work. Windows has another option in with the restore point, but I tried the copy file 1st, so I don't know if that would have worked too.


              Brad      
 

[Willabe]

Here's the Sch. layout and schemo.


             Brad    


Edit;    Sorry guys, I don't know why it downloaded all the pages from my Warbler?

[Willabe]

Ok, Eyelet/turret boards templets printed out.

Time to work on face/back plates with Inkscape after what turned out to only be a distraction this morning, thankfully.


                Brad     

[sluckey]

Latest changes. I may be done... (I mean it this time   )

    http://home.comcast.net/~seluckey/amps/warbler/warbler_021313.pdf

1. All tubes are now 5751s.
2. Added 180K across Depth pot to compensate for too much LFO signal due to adding LED. Accomplish the same using a 100K pot.
3. Added new voltage readings.

BTW, my LED died on me yesterday. Hope it's just a fluke but I got my eye on the new one.

[Willabe]

Latest changes. I may be done... (I mean it this time   )

I'm going to wait to make the eyelet/turret board until I get my face plate made.

I have to remember how I made the face plate for my 5G9 with Inkscape. I have a friend at church that's a graphic artist that I'm talking with about this. I think he can help me. I sent him a copy of the Inkscape 5G9 FP that the engraver used and a copy of the Sch Warbler FP. I'll see what he has to say.

BTW, my LED died on me yesterday. Hope it's just a fluke but I got my eye on the new one.

Too much current?

I've been wondering how much voltage/current the SR can take. The foot note you have in your drawing on the driver tail R being omitted is referenced in the Hammond manual I posted the link too. It says there was a red dot SR and that's why they have 2 different driver tail R set ups.
You said early on;

I think it's just a normal progression of the circuit. Maybe it was a cost cutting idea (one less tube) or maybe the 12DW7 was not even around at the time the AO-41 circuit was designed. I've played it with both drivers and didn't notice any difference in sound. The driver is not in the signal path.

PRR said they might have had 2 different SR's and made the change when they dropped the 6C4 in the AO-41. But on that model the SR string was biased up to the 6C4 plate voltage.

The '41 circuit is sloppy. The large oscillator swing is cut way down, buffered for no reason, then amplified-up again. The plate swing is probably very much like the oscillator swing. Seeing that, the '47 redesign just put the signal to a cathode-follower, saved a bunch of parts.

The back-story may be more complicated. There may be a saturable reactor re-design before the '41 or between '41 and '47, the older SI needed the bigger drive. An improved SI allowed less drive but the tube-works didn't change right away.

Why all 5751's?



            Brad      

[sluckey]

Too much current?

No way. B+ is 330V, plate resistor is 470K. Even if the tube was a dead short, you could only pull .7mA thru the plate resistor (or LED). Don't know if reverse voltage was exceeded. I'll check that tomorrow. I'd like to believe that either the RadioShack LED just died of natural causes or I inadvertantly shorted something to the LED during my mad gator clip venture. I can't really say but I'm keeping a close watch on the new LED. And I don't have any problems going back to the original cathode RC if the new LED poops.

Why all 5751's?

Short answer... I got a butt load of 'em!

Yesterday I wasted 4 hours chasing a microphonic chassis and also what sounded like a bad ground hum. Naturally I suspected all the tinkering work I've been doing the past few days. Well, the problem was really a GE 6189 (12AU7). The Sylvanias I had worked better. But by the time I realized that, I had rotated several of those tubes in and out of V1 and V2 positions. The symptoms kept changing slightly.

This morning (fresh start) I decided to try the 5751s in V1 and V2 positions. Immediate cure! Old 6189s back in and symptoms returned. I vaguely remember years ago having to go thru several of those GE 6189s in the radar system to get one that worked well.  Anyhow, that problem is cured. Later I decided to try a 5751 in the LFO circuit. Works very well there too. So, for simplicity, I decided to use all 5751s. All 12AX7s would probably work too but I have more 5751s than 12AX7s.