Dual Tremelo = Auto Pan?

[neddyboy]

I'm moving on to my next project, turning a stereo tube amp into a guitar amp. I'm going to preserve the stereo aspect, and I'd REALLY like to build a tube-driven dual tremelo circuit with each channel set at set at 90° from the other for an adjustable auto-pan effect. With two separate, widely-spaced speakers you'd get sort of Leslie effect. Even cooler would be a switch between straight tremolo and auto-pan. Any thoughts? Am I chasing rainbows? I know I could use a stereo panning pedal, but I much prefer the sound of tube tremelo.

[shooter]

set at 90° 

scope might be handy for that tweak 


I can "see" it digitally, tube phase shifting is past my pay-grade

[Williamblake]

Maybe he wants 180°? Sync wouldnt be a problem if you had one oscilator driving a phase inverter but maybe a wet and dry setup would sound the same and be a whole lot simpler. Dont get me wrong, i dont advocate simplicity. Knock yourself out.

[neddyboy]

I hope you meant "knock yourself out"?  I haven't built an amp with tremolo yet, and I don't know enough to understand your references. Can you point me at a circuit that I could look at to illustrate your examples, ie "one oscillator driving a phase inverter" and "wet and dry setup"? I tend to do things the hardest possible way, preferably with multiple attempts, but yeah, simple is good!

[shooter]

a quick duck hunt found this


https://duckduckgo.com/?q=tube+phase+shift+circuits&t=h_&ia=web

[Williamblake]

Yeah, out, sorry. You could look at the 6G7 to see the lfo being inverted. I think wet dry is more suitable. Meaning one amp has tremolo and the other doesnt. Giving the same effect and taking significantly less time to build.

[HotBluePlates]

... stereo tube amp ... I'd REALLY like to build a tube-driven dual tremelo circuit with ... auto-pan effect. ...

Go simpler than what you're envisioning:  Copy V11 from this AC30 schematic.

The 1st half of V11 is a tremolo oscillator.  Cool, that's basically like every other amp out there, functionally the same as the blackface Princeton's oscillator.  The Speed switch is replaced with a pot to allow smooth variation.

The 2nd half of V11 is a split-load inverter: R63 is a 22kΩ plate load and R64 is a 22kΩ cathode load.  There are 2 outputs that are 180º out of phase.

Where the Princeton achieves bias-vary trem applied to the grid reference resistors (220kΩ) of one push-pull output stage, you will double-up since you will have 2 separate output stages.  One output stage's grid reference resistors are fed from the plate output of the 2nd half of V11, the other from the cathode output.

The end result is one side gets loudest at the same moment the other side is quietest.  So it's a 180º difference you want.

Killing the auto-pan is easiest by simply turning off the trem signal to one side, though I'll leave it to others to figure out if that can be done without popping.  Or simply turn down the volume to one side of your stereo amp, and now you have mono trem (even if the trem signal is not disconnected from the side that's not being used).

[Toxophilite]

Humourously I was asking if this exact sort of thing was possible with the Tremor-lator a few days back and I was told not likely.
S Luckey suggested the Vox circuit mentioned above (I believe) for that very reason though I didn't know if I wanted to reconfigure my stereo amp that much. It is after all working as is but the bias vary can go into blocking distortion and sometimes isn't as deep at slow speeds (I think)
I guess mine is currently a wet/dry setup (as also mentioned above) though in my case one side has full tremelo and the other has just a little bit.
If you like reverb and want a simple one triode stereo reverb look at the ampeg super echo twin, It's a cool circuit that uses one power amp to drive the reverb tank and send the reverb to the other amp, voila 'stereo' reverb.
Sounds very fender like and uses the same pan
My stereo amp might be too hard on 6BQ5/EL84s though I know the Tremelux  ran them really hot. Just so you know the tremelux despite being the only Fender amp with EL84s is said to sound like any other Fender amp of the same era simple because it uses the same circuit. I use Russion 6p14p-ev tubes as they are like 7189s and can handle higher voltages. My amp sounds like a stereo deluxe and looks like this.(note the angled front to the cab to give the wet dry tape delay effect more spread.)
h

[Toxophilite]

oops I lied S. Luckey was suggesting the AC-15 circuit though it looks similar
https://el34world.com/charts/Schematics/files/Vox/Vox_ac15.pdf


it might be fun to build it on a separate board and trying to plug it in to see how and if it works.

[Williamblake]

Nice amp. Whats the handle for?

[neddyboy]

Here's what I'm starting with, a Nutone intercom/stereo. The PT drives a ton of small tubes, so I should (!) have enough juice for reverb, tremolo, or whatever. I think the AC15/AC30 is a great place to start -- mine also uses an EZ81 rectifier, but 6AQ5s instead of 6BQ5s. Two mini AC15s in one cab sounds great! I have a little single-ended 6AQ5 amp that I love.

Any broad suggestions/comments based on the schematic? FYI I don't have the whole Nutone, just the transformers, tubes, and the coupling caps.

[ac427v]

Nice amp. Whats the handle for?

(gasping) best laugh I've had all week.
Your amp is a beaut but must be on the "I'm too old to..." side!

[neddyboy]

I have an Ampeg V4B and an 8x10 from the old days in my spare bedroom. It will never move, at least not until they find me slumped over my soldering iron. Then my kids can bury me in it.

[HotBluePlates]

oops I lied S. Luckey was suggesting the AC-15 circuit though it looks similar
https://el34world.com/charts/Schematics/files/Vox/Vox_ac15.pdf

I should have just used that schematic.  It's the same circuit, just easier to see.  V6 is the only part needed, up to & including C29 and C30.

[neddyboy]

Not sure if this question is answerable, but I'm looking at Toxophilite's stereo schematic, specifically the reverb circuit. I haven't bought a reverb transformer, but I do have a leftover transformer and Hammond tank from a scrapped Organ Mate reverb unit. I've attached the schematic. Could I use this transformer in my new build? I guess most reverb transformers connect to B+, but this one connects to the heater circuit! Possible? Practical? I do like a reverb circuit with a transformer better than the simpler Ampeg-style.

[sluckey]

but this one connects to the heater circuit!

Not so. Look closely. It connects to ground.

This transformer is not suited to the Fender style plate driven transformer circuit.

[neddyboy]

Both?  Thanks Sluckey. I tend to learn stuff as I build, and I've never (successfully) built a reverb circuit. What does the transformer do in a Fender reverb? Impedance matching?

[sluckey]

Both?  Thanks Sluckey. I tend to learn stuff as I build, and I've never (successfully) built a reverb circuit. What does the transformer do in a Fender reverb? Impedance matching?

What do you mean by "Both?"?

Yes, the Fender RT is used for impedance matching.

[neddyboy]

Just acting dumb, I see the difference!

[HotBluePlates]

... have a leftover transformer and Hammond tank from a scrapped Organ Mate reverb unit. ...

... This transformer is not suited to the Fender style plate driven transformer circuit.

There is a lesson here:  If you salvage parts from a tube circuit (especially transformers), you generally have to use them as the original circuit did.  In which case, other elements of the original circuit are needed.  Pretty soon, you've re-built 60-70% of the original circuit.

It's often better to keep the original item intact, and repair/modify it to suit guitar use.

[PRR]

...Organ Mate reverb unit. I've attached the schematic. ....

Deja vu all over again. I know I have dissected that bad Organ Mate drawing here recently.

[neddyboy]

Ha! Yep, same one PRR. I ended up making a preamp with the PT and kept the transformer. That thing gave me so much grief.

HotBluePlates, yes, very true. I finally gave up on the original circuit because A. I didn't know enough to figure it out on my own, and B. the Organ Mate gets terrible reviews as a reverb and it seemed like wasted effort. Anyway, that's why I'm not using the original circuit! I'm going to have to bite the bullet and buy an RT.

[Toxophilite]

Nice amp. Whats the handle for?

(gasping) best laugh I've had all week.
Your amp is a beaut but must be on the "I'm too old to..." side!

I pride myself on having a quick and good sense of humour but I have to admit I don't actually get the joke nor your response. Is it about perceived weight? The amp, for a stereo deluxe is quite liftable. When you're used to carrying a late 70s Super something that weighs in a 53 lbs is not hard to carry and it's smaller than a Twin being made out of braced 5/16" birch ply 25.5 x17.5" x10.5" (at it
's deepest point). It was not at all expensive to build either and it sounds beautiful. Okay enough hijacking

[Toxophilite]

Not sure if this question is answerable, but I'm looking at Toxophilite's stereo schematic, specifically the reverb circuit. I haven't bought a reverb transformer, but I do have a leftover transformer and Hammond tank from a scrapped Organ Mate reverb unit. I've attached the schematic. Could I use this transformer in my new build? I guess most reverb transformers connect to B+, but this one connects to the heater circuit! Possible? Practical? I do like a reverb circuit with a transformer better than the simpler Ampeg-style.

The Ampeg reverb is a transformer driven spring reverb. The fender reverb circuit is like a little amplifier and the tank is the speaker. The Fender RT is basically a Champ OT.  The Ampeg just uses the power amp and the OT from one channel to drive the tank. It's really more about a cool economy of parts and circuitry that produces a very fender-like reverb except kind of stereo, maybe a little more ambient too. I think it's a very cool design.

[neddyboy]

Well, this nukes the title of this thread, but I've decided to go for a quad mono design instead of stereo. I have a Heyboer 18 watt OT, and they say it'll work with a quad of 6AQ5s as it's a total of 18 watts.

I've been doing research, and I'd like to build a Bassman front end feeding the 4 6AQ5s. I'm reeaaally hesitant to post this, but I drew a schematic and I'd like to see what I got wrong! Please bear in mind that I took info from three different schematics (in three different styles), so there may be lots of conceptual errors.

The high voltage numbers I used come from the specs for the Nutone PT. I'm most concerned with the power section of the circuit, plus the simplified input scheme. I only need one input but I don't know if I got it right. I'm also curious if the high voltage is high enough for the preamp tubes in a relatively high gain design. Thank you!

[sluckey]

Input jack needs a 1M resistor. First triode in V2 needs a plate resistor. You are feeding 230V to the presence pot and the PI tail. Gonna burn up some stuff. That 18W OT would be happier with a pair of 6AQ5s rather than a quad.

[PRR]

The 27k surely goes to OT, not B+.

(Assuming you give V2a a load) two sequential 12AX7 stages without a volume control WILL distort bad on any hard strum. (The volume control on one side of V1 won't stop the other side from smacking V2.) (In fact this will play about 80% of FULL gain even with the one VOL pot at zero.)

IIRC (??) the maximum grid R for 6AQ5 is 500k. Which means 250k per parallel pair.

[neddyboy]

First triode in V2 needs a plate resistor.
That 18W OT would be happier with a pair of 6AQ5s rather than a quad.

Hi Sluckey & PRR, and thanks for commenting! I've attached the Bassman schematic I used to draw the front end. I missed the input resistor, but it's in now. And yes, the 27K goes the the OT, duh.

Sluckey, I don't understand your plate resistor comment. I followed the Bassman schem and I don't see one there, or I'm REALLY misunderstanding. And I did speak to a tech at Heyboer about using a quad with the 18 watt OT, and he said okay. No after all?

PRR, what would you suggest for the volume problem? I followed the Bassman plan, but reduced the inputs to one and I intended to send the input from the one jack to both sides of V1. Since I have one input, I removed the second volume pot. The remaining volume pot is at the same stage as the Bassman. What's causing the problem? Where should I put the volume?

And last, are you saying I should increase value of the 2w resistor from 150Ω to 250Ω? Thanks for your input gentlemen, and thank you for your patience.

[sluckey]

Sluckey, I don't understand your plate resistor comment. I followed the Bassman schem and I don't see one there, or I'm REALLY misunderstanding.

The schematic you followed is also missing the plate resistor. That's an error. Look at a real Fender 5F6 or 5F6A schematic to see...

     https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_5f6_schem.pdf

     https://el34world.com/charts/Schematics/files/Fender/Fender_bassman_5f6a_schem.pdf

The amp absolutely will not work without that resistor.

[neddyboy]

Oh thank you, I'm not insane! Will do.

[neddyboy]

Here's a revised drawing with most of the suggested changes made. I haven't changed the position of the volume control as I haven't heard back from PRR.

I have a related question for you all: is there any app or site that helps translate a schematic into a turret board? I haven't had much luck in the past!

[PRR]

> Fender_Bassman_5F6-A_Circuit_Kuehnel.png

That has Kuenel's name on it, but does not look like his style, is not from his site, and has multiple typos. Where did you find it?

[DummyLoad]

is there any app or site that helps translate a schematic into a turret board?

yes, the site is that grey fatty matter in your skull, you're the app. 

--pete

[neddyboy]

Dammit, that app crashes all the time.

[neddyboy]

Hey PRR, I'm not sure where it came from. I grabbed the Fender schematic and will refer to that. So you're saying that some of the schematics posted online are WRONG?    Can you elaborate on the issue with the volume control? I'm going to put the second (bright) input back in, so there'll be 2 volume pots -- still in the wrong place?

[neddyboy]

Here's my latest iteration. I redid the input jacks so there's one bright and one normal, and added the second volume pot back in. I also caught some omissions.

[Toxophilite]

Regarding your OT  and it was mentioned already by S.Luckey, you can usually coax 18 watts out of a pair of 6BQ5/El84. A Marshall 18 watt runs a pair of El84 as does a Vox ac15 I believe. Traynor has it's version. I think the Blues Junior is 2 El84/6Bq5 for 15 or so watts too.
If you have a quad you're usually more in the 30-36 watts range .
You might want a bigger OT

[neddyboy]

The 6AQ5s I'm using put out 4.5 watts apiece, so the total should be 18 watts. Unless I'm missing something! 

[shooter]

nope, you get an A, everyone else gets a B 

[neddyboy]

Well that's a first! Any other issues you guys can see? What about filter cap values? The Nutone used 40uf-40uf-40uf-10uf. I'm hoping to use some 50uf caps I already have, but is that too much?

[shooter]

tube rectified or SS?


if tube, look up the data sheet, there is a max cap value, you can usually fudge up 10-20uF

[echuta13]

I think that the output cathode resistors are a bit under-rated.  I would suggest going with a 250R/5W resistor in those spots for a little extra insurance.

[neddyboy]

Thanks echuta, I made that change. Shooter, tube rectified with a 6CA4. I'll look up the specs.

[Toxophilite]

The 6AQ5s I'm using put out 4.5 watts apiece, so the total should be 18 watts. Unless I'm missing something! 

Oops you're right, for some reason I saw 6BQ5s. You are indeed right.

[neddyboy]

You were sort of right too. I saw today that a different spec sheet says the total will be 20 watts. So, the Heyboer would be overpowered.

[shooter]

I find Bigger OT's is better.......for most guitarist's, the saggy mushy players might not be in that group 

[echuta13]

Fat bottomed output transformers for the win!  Beefy wins every time IMO. 

[neddyboy]

I agree! I'm looking at OTs designed for a pair of 6L6s. Any suggestions?

[shooter]

I don't look at "for....tube....", I look at impedance and watts;
say a pair of 6V6's wants ~8k and ~14w, i'll hunt up something a can get the 8k from (4k:4ohm get's 8k:8ohm with an 8 ohm speaker on the 4ohm tap)
then I go UP in power, so maybe 20-25W
don't over look the OT's freq curve, If I want "full" bass, i'm gonna look at something that can get closer to 20hz than 100hz

[neddyboy]

Hey Shooter, yeah the "what a tube wants" impedance part is what I don't understand yet! I looked up how to choose an OT, but I still don't get it.