Help with getting trem into 5e3

[ratgon]

Hi all. I got my 5e3 up and roaring the other night and was just looking around for some mod ideas. At this point the motivation for anything i do is really just to continue to learn. Rob Robinette, over at his amp site... https://robrobinette.com/Amp_Stuff.htm  has quite a lengthy list of mods he's done to 5e3's and i was immediately drawn to the tremolo mod. I love tremolo. I wish the whole world was experienced through it but that's another topic.

Anyway, it seems simple enough, but they all do until I again, can't get any tremolo happening. Trying to add tremolo to every amp I've built so far as come up null so I'm reaching out now that I actually have schematics and layouts to show.

I built the 5e3 using the excellent documentation and layouts from here..thanks again for all the work the team of you guys who put all this info together...it's invaluable to someone like me just starting out and learning as a mistake and press on. So anyway, the %e3 is working great and sounds great and again, I've tried to add trem but no go. I'm gonna post Robinettes simple approach and schematic and just for ease of use, reposting the layouts and schematic from here. Any help would be extremely appreciated. I'm sure I'm just missing something simple but honestly I'm not even exactly sure of some of the terminology going on here as far as where to insert the bias wiggle and what not.

So here are the schematics and again, thanks in advance

[octal]

The schematic diagram you've provided is for adding trem to a fixed bias amp, not a cathode biased amp.
You'd need to attach the power tube grid resistors to the wiper of the intensity pot and ground the end of the pot which would have gone to the bias supply in a fixed bias amp. (This is not the best way to do it though- if the pot fails, your tubes will have runaway bias. )

The best thing to do is to find an existing amp that's topologically similar (i.e. 2X6V6 outputs, cathode biased, cathodyne phase inverter) with trem and crib ideas from that. 


HTH


Nathan

[Fresh_Start]

There are several ways to introduce tremolo. One is diddling the bias voltage of the power tube(s). This can be done with either fixed bias or cathode bias power amps. Another is diddling a preamp tube's bias. Third, you can directly diddle the audio signal. The second and third approaches allow you to insert the tremolo anywhere in the preamp - very first triode, last one before PI, or someplace in between.


You might be better off copying the tremolo from a Vibro Champ, applying the tremolo to the triode driving the phase inverter. This uses both halves of a 12AX7, but you're adding that tube anyway. Bias vary tremolo is a bit harder with a cathode biased amp like the 5E3 because the cathode bias is "self adjusting" to a point.


Hope that helps,
Chip

[eleventeen]

" I love tremolo. I wish the whole world was experienced through it but that's another topic."


You mean...it's not?

[ratgon]

Thanks. As always, I appreciate the help. What you're saying makes sense, to the extent that I'm just starting to learn what most of it means. the reason I went with this approach was simply because it was one of the many mods the guy says he's personally done to his 5e3s. So i figured I must just be doing something wrong. But are you telling me that his trem circuit wouldn't work in a 5e3 anyway?

Man, all I want is to build an amp and then add reverb and tremolo. Not build one that already has it.  Well I guess it's back to the breadboard and the books. I'll figure it out eventually. 

[tdvt]

I see on that site where the trem is on the list of mods he's done to his 5E3. But it seems like even though he starts with the 5E3 stuff, it kind of morphs into general circuits gathered from many sources without any separation, which makes me think he didn't actually add trem to his 5E3.

The trem circuit shown is from a Princeton, which as Octal pointed out, is not a cathode biased amp.

Check out the two attached schematics.

They are from the DeArmond R5 & R5T amps, one with trem & the same amp without, so you should be able to break out the trem easily.

This is a small SE amp like a Champ but is cathode biased & forum member Leon C has installed it in his larger Martin/DeArmond build which is very similar to a 5E3.

There are also a bunch of Valco/Gretsch/Supro models with/without trem to compare.

[jjasilli]

I think we need to redirect focus on adding trem to a 6V6 PP amp, cathode biased. 


One solution is the trem circuit in the Silvertone 1482.  This is power tube bias vary tremolo and works fine in my experience.  It is what I would use.  Also see the Kalamazoo Reverb 12:  http://schematicheaven.net/bargainbin.html for a 12ax7 driven design.  Note that 6V6's & el84's use about the same signal voltages & bias, so the trem should be interchangeable between these tube types.  Also see:  http://www.lynx.bc.ca/~jc/tremoloCircuits.html


For home brew designs, we need to avoid redplating.  Different B+ supply voltages, and the bias set by your cathode resistor will affect how much trem voltage swing is OK.  So, know your bias setting, and measure the voltage swing of the trem to see what it is really doing to your bias voltage.  The thing to avoid is redplating of the power tubes.  To test, run the amp for awhile with strong string signal & tremolo (preferably into a dummy load) at various speeds.  If there is redplating, mod the trem circuit to reduce its output voltage to a safe level (no redplating).  Info is available on the web.


The other solution is a trem circuit that feeds a small bottle tube, as Fresh_Start mentions above.

[sluckey]

Rob's trem circuit comes from a Princeton Reverb and it will work well in a 5E3. But it needs a couple changes. I'll assume you have built the oscillator circuit correctly. Look at the Hoffman layout. Find two 220K that have their bottom turrets strapped together. There is also an under-board jumper (dashed line) that connects to the negative side of a 16µF cap. That dashed line is also ground. Totally remove that dashed line under-board jumper but leave the bottom ends of the two 220K connected together. Connect the bottom end of those two 220Ks to the wiper of the intensity pot. Connect the end of the INT pot to power transformer ground lug. That's all.

[jjasilli]

Didn't check Rob's site.  But it looks pretty cool and worth a full study.  +1 to Sluckey's recommendation (seems similar to the Kalamazoo Reverb 12)

[ratgon]

Thanks all and especially thank you Sluckey. I implemented yoiur suggestion and at first it resulted in a very LOUD impenetrable almost MOOG sounding fat low distorted noise. SO i looked around and found some screwed up input jack leads from pulling the board up. So I sorted that And now I'm back to a beautiful sounding yet tremo free amp. i can't help but feel like i've screwed up the oscillator yet I've checked it many times over. Is there some way to test the oscillation beyond just having the tremo work. By the way, I'm pulling the oscillators juice from point "A" on the Hoffman schematic. The filaments are fine. I'm not far enough along on this whole endeavor to know what i should be looking for at certain points in the circuit but following Rob's schematic I'm tapping in from point A at 415V but winding up with 86 v at the Osc plate. So I dropped his 220k to 100k to get the plate voltage up to 148...i read somewhere alomg this journey that the !2ax7 needed atbleast 100 v to get moving. So I really have no idea how to even tell if it's oscilating at this popint. I should maybe leave well enough alone as it sounds so good but I've really become obsessed with tremolo'

I spent the lasy year making a full double record and the time spent trying to replicate certain tremolo sounds from the past was unbelievable. I'm sorta nuts about tremolo/ A full day figuring out Gilmour's trem on Money. Well, any day in the studio is a fun day.

[sluckey]

After closely looking at Rob's tremolo oscillator schematic, I see several errors. It cannot possibly work as drawn. So, use the schematic I've attached. And put the 220K plate resistor back in. And pick up B+ from node B, not node A.

If you do the above correctly it will work. That circuit is Hoffman's Princeton Reverb design and it's correct.

[ratgon]

Sluckey....thanks so much. Hopefully I'll have time tonight to give it try.  I really appreciate the time spent sorting this out. I'll keep ya posted..

[sluckey]

I just realized that you are ADDING trem to an amp and that you will have an unused triode in the added tube. Duh! That being the case, I would use the improved 6G16 Vibroverb tremolo circuit. Very easy to convert the Princeton Reverb circuit. Here's the schematic...

[shooter]

I know the *improved* 6G trem works, I'm just curious on the 204v at pin 8.  Is that simply "close enough" for cathode to heater spec?

thanks

[sluckey]

Those voltages were taken from my recent AO-63 conversion. In a real 6G16 that voltage would be more like 255-260 back in the day, even higher today. It's just a cathode follower. Fender, Marshall, etc, etc, have been ignoring the cathode/heater max voltage spec for a long time. I'm OK with that too. 

[shooter]

I'm OK with that too

thanks Steve, that's what I figured the answer would be

[tubeswell]

FWIW the Fender Excelsior is a cathode biased PP 6V6 amp with trem. Copy that circuit and add a depth control by replacing R15 with a 1M pot wired as a voltage divider (where the pot wiper is the voltage divider output).

[Fresh_Start]

FWIW the Fender Excelsior is a cathode biased PP 6V6 amp with trem. Copy that circuit and add a depth control by replacing R15 with a 1M pot wired as a voltage divider (where the pot wiper is the voltage divider output).

Interesting circuit!  Hadn't seen a commercial tremolo that used a MOSFET buffer before.  Interesting way to inject the tremolo voltage onto the control grids too.  I thought "Wow! 470K grid return resistors with 6V6s."  Then I realized there was a second pair of 470K resistors in parallel, and the tremolo signal comes through that pair.  470K||470K is pretty close to the "normal" 220K grid return resistor we see with 6V6s.

Thanks,
Chip

[tubeswell]

[...Hadn't seen a commercial tremolo that used a MOSFET buffer before...

Yes I have my suspicions... The excelsior turned up only 2 or 3 years ago. We here on this forum (and other forums many of us frequent) were using MOSFET buffers and posting our schematics here before then. Maybe one or two of the Fender design crew is a member here too. ;-)

[sluckey]

Any progress?

[ratgon]

Hey all! Sorry for the delay in getting back to here after all the help you guys posted

@Sluckey. Progress for sure. It's still not working perfectly but your final approach opened the door for me and its def at the tweaking some values to clean it up and hearing it aS a full fledged trem. But in so doing I also had to admit that this probably wasn't the test amp to be adding term to. Very little room left in there to add the circuit AND it's such a classic tone to begin with I figured I should probably focus on getting the straight up circuit running as best I can. So now I'm  transferring it over to another amp that I'd made from a kit when I first started ( The Ardmore from guytronix.com). So all the help you guys have given me haSnt been in vaIn, in fact it's going to maKe the other Amp much more like the type of amp I've envisioned to begin with. So thaNks again. You're help and earlier aDvice of focusing has aCtually led to two great little amps instead of one.

[PRR]

> I thought "Wow! 470K grid return resistors with 6V6s."

Totally legal for cathode bias.

We see 220K in fix-bias where the book said 100K Max and Fender cheated it up.

Interesting kick-start on the LFO.