Which is the better tremolo circuit in SE amp ?

[kagliostro]

Assuming we have an SE amp (a 5C1 or a 5F2 or other)

there is a tremolo circuit (not only the oscillator) that has better performance compared with the other ?

which is the best oscillator signal insertion point ?

and that you would recommend ?

Thanks

Franco

[sluckey]

Fender Vibro Champ comes to mind...

     http://el34world.com/charts/Schematics/files/fender/Fender_champ_vibro_aa764_schem.pdf

You can also use a single triode oscillator to vary the grid of the output tube.

[kagliostro]

Many Thanks Steve

You can also use a single triode oscillator to vary the grid of the output tube.

something like this ?



There are so many way to do this thing and this confused me (the following are some examples, but I think there are others)

On V1:










Between V1 and V2:




On V2:






Thanks again

Franco

[shooter]

Thank you for doing my *homework*
I want to add trem to my next build, SE also, I think the vox 4 looks the coolest, anyone have player experience?

[kagliostro]

A pair of questions

1 - The vibrato at V2 (like in the AA764) is usable also if V2 is connected to the NFB like in the Gibson GA1 RVT or if there is the NFB

is better to connect the oscillator at the grid of the power tube like in that Gibson ????

2 - Is the 6SL7 vibrato oscillator (like those used in Ampeg m15) usable like the 12ax7 oscillator in the AA764, is presumable they have the same performances ?



Or I must simply use the AA764 oscillator schematic with the 6SN7 tube ?



Thanks

Franco

[sluckey]

1 - The vibrato at V2 (like in the AA764) is usable also if V2 is connected to the NFB like in the Gibson GA1 RVT or if there is the NFB is better to connect the oscillator at the grid of the power tube like in that Gibson ????

Either circuit works just fine.

2 - Is the 6SL7 vibrato oscillator (like those used in Ampeg m15) usable like the 12ax7 oscillator in the AA764, is presumable they have the same performances ?

6SL7 works fine too. Here's another 6SL7 single triode trem circuit that drives 6V6 grids...

     http://sluckeyamps.com/RCA/Ampeg_J12B.pdf

Or I must simply use the AA764 oscillator schematic with the 6SN7 tube ?

6SN7 doesn't have enough gain to be used in a trem phase shift oscillator. Did you mean 6SL7?

[kagliostro]

Thanks Steve

Either circuit works just fine.

Do you mean that V2 + NFB + Vibrato can be used and to the oscillator to the power tube grid with NFB on V2 or you refer to the oscillator to the power tube grid with NFB to V2 and oscillator to V2 without NFB ?

Here's another 6SL7 single triode trem circuit that drives 6V6 grids...

Thanks, I didn't remembered your improved version of the single triode oscillator 

If there is only a single triode disposable is the single triode performance paragonable to the double triode version ?

I've find also this other complicated Ampeg Tremolo circuit that uses 2 x 6SL7 tubes (yes, 4 triodes), but I'm not able to understand exactly the purpose of the secons tube and as this schem has no power section I'm not able to understand how it connects to the power section or preamp section



Point B seems the output and the resistor and capacitors that precede it seems the filter for the oscillator frequencies

but which is the purpose of point A at the grid of the fourth triode ???

Did you mean 6SL7?

My fault, I was meaning 6SL7

so the right question is

Or I must simply use the AA764 oscillator schematic with the 6SL7 tube ?

Franco

[kagliostro]

Well, I think I've understand (I hope)

The second triode is used to modulate the audio signal with the oscillator signal, it acts something like a mixer where the signal from the oscillator feeds the first grid of the second 6SL7 and the audio signal is applied to the second grid of the second triode

the output is from the second plate (or both ??) and reach the next amplification stage through those capacitors and caps that to me forms a filter to stop the oscillator frequency component on the signal 

I'm in doubt about the point at which is taken the signal that feeds the audio signal to the grid of the second triode of the second tube (?)

will this triode be placed in V2 position on in one other place ??

Franco

[jojokeo]

I want to add trem to my next build, SE also, I think the vox 4 looks the coolest, anyone have player experience?

One of my first builds years ago...the trem didn't work, at the time I didn't know what was wrong or how to figure it out? :(

[shooter]

how to figure it out? :(

I'm pretty sure you could now
my only concern is PRR's comment about cathode wiggling sounding like "a dog in a dryer", a cat would be fine, but not a dog, that's just wrong

[kagliostro]

Some time ago, due to my job, I was in a country house, well, it was a raining day, but to open the door of the oven of the wood stove

and put inside the dog to dry him seemed excessive to me (also if the oven was only lukewarm and the fire on the wood stove was off)

and I say this because I love dogs, not the integrity of wood stove

Franco

[HotBluePlates]

... I've find also this other complicated Ampeg Tremolo circuit that uses 2 x 6SL7 tubes (yes, 4 triodes), but I'm not able to understand exactly the purpose of the secons tube and as this schem has no power section I'm not able to understand how it connects to the power section or preamp section ...

Look in the Tone Control portion of the schematic above it, and you'll see boxes "A" and "B". Those are the points to which the Dry signal path connects to the tremolo circuit.

In my opinion it looks like Ampeg went overboard on that amp (feeding the tone control circuit through a triode to add in trem).


I think this topic is actually being made harder than it is.
 -  You want to inject trem somewhere along the signal path of a single-ended amp.
 -  Anywhere from V1 through to output tube screen are fair injection points.
 -  The required size of tremolo signal will be smaller the closer you get to the input jack as the injection point.
    >  You could inject tremolo at the output tube screen, but the signal size would need to be a couple-hundred volts to get adequate volume change, and the screen couldn't be connected to the usual filter cap.
    >  You could inject the trem at the V1 grid and needed signal size would only be a couple-hundred millivolts, but the tremolo circuit would either load down the guitar signal or the guitar volume control/pickup would load down the tremolo circuit.
 -  Injection point is then a balance of required signal size (smaller might be better/easier) and injection point impedance (injecting at a cathode might require a cathode follower as a buffer between the trem oscillator and injection point).
 -  Choice of V2 instead of V1 may be all about the oscillator typically making a large enough signal that V1 is overwhelmed, so trem is injected at V2 where signals are a little larger.

Anything else is probably detail and preference.

[sluckey]

my only concern is PRR's comment about cathode wiggling sounding like "a dog in a dryer",

My Marshall 18W clone is a cathode wiggler. Sounds very good. Nothing like I imagine dog in a dryer.

Vibro Champ (another cathode wiggler) sounds very good too.

[HotBluePlates]

2 - Is the 6SL7 vibrato oscillator (like those used in Ampeg m15) usable like the 12ax7 oscillator in the AA764, is presumable they have the same performances ?

Look at the Ampeg schematic you provided in this reply:
The tremolo oscillator is buffered by another stage, from which the tremolo output is taken from the plate (high impedance). This signal is applied to the output tube grids, which have a relatively high impedance to ground.

The VibroChamp buffers the tremolo oscillator with a cathode follower, with a low output impedance taken from the cathode. This signal is applied to another tube's cathode, which has a low impedance to ground.

This reinforces what I said earlier, which is that the impedance of the injection point will likely decide what, if any, buffer stage is required between oscillator and injection point.

[kagliostro]

Many Thanks HotBluePlates

Those are the points to which the Dry signal path connects to the tremolo circuit.

Now I see, thanks for pointing to that part of the schematic

After your explanations I think I have understand the situation

I have a pair of questions

1° Is possible to use a 6SL7 tube instead of a 12AX7 and follow the schematic of the oscillator of the AA764 with same components  ?

2° I think is possible to use the schematic of the Ampeg m15 oscillator feeding the power tube like in the Gibson GA-1 RVT (schematic above), am I wrong ?

Thanks

Franco



p.s.: My deductions on reply #7 were correct ?

[HotBluePlates]

1. Yes; consider the 6SL7 something like a 5751. It's very much like a 12AX7, but slightly lower gain (Mu of 70 if I recall correctly).

2. Maybe, but with changes. The Ampeg M-15 circuit is already driving the grid of an output tube, but is using much lower resistance-to-ground around the tremolo oscillator than the Gibson circuit. You might want to split the difference and use 1-2MΩ to ground as seen in the typical Fender oscillator. Of course, if you try the Ampeg values with no luck, it's probably not too hard to replace them with higher resistances later.

[shooter]

Thanks Steve, I'm wiggling the cathode, on paper for now, and Franco, I to love dogs, all I have now is cats, to many, so 1 or 2 together in a dryer.....

[kagliostro]

Thanks Again HotBluePlates

The Ampeg circuit that connect the vibrato circuit after the ToneStack remembered to me one other way I've seen in one other Ampeg amp

the Gemini 15



as Fender did a neon lamp + photoresistor is used but in a different way, Fender (if I'm not wrong) shunts the audio signal to ground

using the pothoresistor, Ampeg put the photoresistor in series to the signal and feed the ToneStack through the photoresistor

Is the use of the photoresistor useful to semplify things like impedance mismatch between circuits ?

Also I think that this way there are no problems related to the presence of an NFB on the amp (correct ?)

Franco

[HotBluePlates]

... Fender (if I'm not wrong) shunts the audio signal to ground using the pothoresistor, Ampeg put the photoresistor in series to the signal and feed the ToneStack through the photoresistor

Is the use of the photoresistor useful to semplify things like impedance mismatch between circuits ? ...

Look again at the path into the tone stack, through the 220kΩ resistor, through the Bass pot, and through the 22kΩ resistor to ground.

Ampeg is using the LDR as the upper leg of a voltage divider through this resistive path. There is a 4MΩ Intensity pot, which by itself causes a large loss of volume as the upper part of that voltage divider with the rest of the tone circuit as the lower part of the divider. It's a little backwards: as the LDR shunts the 4MΩ Intensity pot, the volume increases.

[kagliostro]

I've understand near all what you say, only one thing I would like to be explained with other words

It's a little backwards:

I think I'm losing the exact meaning (due to my translation)

I've translated it in something like: it is a bit odd or also contrary to the norm

but I'm not sure about

--

I would like to know your opinion (if you have one about) about the advantages (if there are some) of the use of the photocoupler against the connection at a tube cathode or the connection to the grid of the power tube, obiouvsly I think that to modulate the power tube (as you say previously) require a high oscillator impedance and higher signal respect to the cathode connection on preamp tubes

To me the use of the photocoupler permit to get rid about the strongness of the signal of the oscillator and his intrinsic impedance, am I wrong ?

Thanks

Franco

[HotBluePlates]

It's a little backwards:

I've translated it in something like: ...[/color] contrary to the norm[/b]

Yes, that's correct. "Backwards" or "opposite/contrary to the norm" or "abnormal" because the typical Fender use of the LDR grounds/reduces dry signal when the LDR is in a low-resistance state. However, the Ampeg uses the LDR as part of a voltage divider, which increases volume of the dry signal in the low-resistance state.

... advantages (if there are some) of the use of the photocoupler against the connection at a tube cathode ...

I would not use it at a tube cathode. Normal tremolo circuits use a cathode follower buffer between tremolo oscillator and the tube cathode. For these, do not think of the cathode follower as having a voltage input and output... Think of the follower as having a voltage input, which causes it to pull current through the resistor connected to its cathode (this resistor being the cathode resistor of the signal stage which trem is injected).

This variational (a.c.) current pulled by the cathode follower changes the current through the other stage's cathode bias resistor, which changes the bias of that tube, and superimposes the tremolo signal.

You could compare this to the similar 12AT7 stage in the 25L15 which receives signal from the tone control in the feedback loop and thereby controls current through the other 12AT7 stage in that amp.

The low frequency, along with the low impedance output of the follower is how this buffer can influence the injected stage's bias even though there is often a large bypass cap across the resistor at the point of injection.

The LDR seems like it could be used in parallel to the cathode bias resistor, but the circuit impedance at that point is very low compared to the LDR off-resistance (the LDR might be several-MΩ) and I'm not sure about how low the LDR's on-resistance is (will it be below 1kΩ?).

... the advantages (if there are some) of the use of the photocoupler against the connection at ... the grid of the power tube ...

This would be more like the standard Fender blackface way of adding trem, which I think is fine. As long as fixed bias voltage isn't being applied at the same point (or is blocked by a coupling cap), this seems okay.

The original Fender optoisolator sounds choppy mainly because it used a neon bulb which is more on-off. Some LDR's may use a light source which has a range of light intensity (and so a range of resistance) between on/off. I have not experimented a lot with LDR's so I really don't know which are best, but I do notice there are tremolo pedals (like Fulltone's Supa-Trem) which use LDR's inside and still can give a rounded waveform as well as the choppy sound.

[kagliostro]

Many thanks for the answer, all this is very interesting and I'm glad to you that now I know

only one thing, when I told

... advantages (if there are some) of the use of the photocoupler against the connection at a tube cathode ...

I was not suggesting to use photocoupler connected to cathode, I would say if the use of a photocoupler (connected in some way on the circuit)

gives advantages compared to the case in which the oscillator is connected to a cathode (like in the AA764 or U-45)

I apologize, I expressed me badly

Franco

[HotBluePlates]

You're doing great expressing yourself! It would be easier for both of us if we had schematics, but I'm on a new computer with no ability to draw them.

[shooter]

Think of the follower as having a voltage input, which causes it to pull current through the resistor connected to its cathode (this resistor being the cathode resistor of the signal stage which trem is injected).

Would the Kalamazoo ver2 K shows above be an example of this?
thanks

[kagliostro]

Think of the follower as having a voltage input, which causes it to pull current through the resistor connected to its cathode (this resistor being the cathode resistor of the signal stage which trem is injected).

Would the Kalamazoo ver2 K shows above be an example of this?

 

I think the Vox correspond better to the description ( or it seems so to me )

Franco

[HotBluePlates]

Think of the follower as having a voltage input, which causes it to pull current through the resistor connected to its cathode (this resistor being the cathode resistor of the signal stage which trem is injected).

Would the Kalamazoo ver2 K shows above be an example of this?

Every amp in Reply #2 with the headings "On V1" or "On V2" are examples of this.

Some of those amps dispense with the buffer and connect the oscillator's cathode to the cathode circuit of the stage where trem is injected.

[shooter]

Thanks HBP, I thought they all *met the requirement*, the Kzoo, just seemed *odd* as a CF-CF, shared Ck Rk kinda design.

[HotBluePlates]

Thanks HBP, I thought they all *met the requirement*, the Kzoo, just seemed *odd* as a CF-CF, shared Ck Rk kinda design.

Note that in the Kalamazoo Model Two, neither V1a nor V4a are cathode followers. They are simply "cathode-coupled" and share a common cathode resistor, so when the tremolo tube pulls current at the rate of the trem, it modulates the signal in V1a.

[kagliostro]

I put together the 6SL7 Ampeg J-12B oscillator modded by Sluckey

http://sluckeyamps.com/RCA/Ampeg_J12B.pdf

with the CF of the tremolo oscillator of the AA764

http://el34world.com/charts/Schematics/files/fender/Fender_champ_vibro_aa764_schem.pdf


and obtained this



Is this feasible ?

(Which can be the consumption of this 6SL7, 5mA for oscillator and 10mA for CF, more ??)

Franco

[PRR]

> wood stove ... put inside the dog to dry him seemed excessive to me

I know you are joking.

You know how bad burned dog-hair smells.

But I realized sunny Italy may not have the type of clothes dryer which is common in the US. For one, ours uses 4,500 Watts, and we know your homes are not wired to supply that much for very long. However the dryers can also be made to use gas fuel, and must be common in laundromats (commercial clothes-washing establishments, sometimes coin-operated).
_____________________

> inject the trem at the V1 grid and needed signal size would only be a couple-hundred millivolts

Here we must consider the dog-to-dryer ratio.

A 3-pound Chihuahua in a 30-pound dryer drum will hardly wobble at all. Put in the Corgi, it is rock-and-roll.

Likewise to get any good variation of gain, we must drive the tube HARD. Say the tube runs Normal with 1mA. We want at least a 0.5mA-1.5mA variation of current to get a 5dB variation of gain. To get "deep trem" we may have to push to 0.1mA-2mA. Essentially "zero" to "double".

This means the peak trem grid voltage will be "similar" to the bias voltage.

Many guitar first-preamp stages run 1V bias. A "couple-hundred millivolts" is a start but may not be satisfying.

Note that with 1V trem and 0.1V guitar, the 10Hz wobble at the plate is likely to be ten times bigger than the guitar signal. The stage after may pass guitar fine but be overloaded by 10Hz. Most of the low-level tricks "need" a several-stage C-R low-cut filter after the tremolated stage.

IMHO, Push-Pull is THE answer. You run the signal out-of-phase, the trem in-phase, and wire the output to reject in-phase variations. Conveniently this will usually be your HIGH-level stage (6V6 etc) so the trem/signal ratio is not so big.

If you can still get them, photo-resistors are a natural. They are tricky to set up, and I don't think they have the "soul" of beating big bottles push-pull, but can be used with any type amplifier. Sadly they are going extinct.

VCAs (controlled gain amplifiers) are what we really want (after cheapness, simplicity, sound, and elegance). The old '3080 wasn't too good and is also going extinct (more fakes than reals on the market). THAT Corp has excellent VCAs, but cost more than a buck, and mucho-mucho mas by the time you house, interface, and feed them inside a tube amp.

To state the obvious-- the Usual Culprits sell $49 trem pedals at the nearest banjo shop, $29 on Saturday Sale.

[shooter]

Note that with 1V trem and 0.1V guitar, the 10Hz wobble at the plate is likely to be ten times bigger than the guitar signal.

Ok, my heads still spinin some from your analysis, n dogs, n...
If they were *balanced* better, say downstream, so each signal on it's own swings your 0 to doubleish, will hard Low-cut filtering need to be considered as much?

You run the signal out-of-phase, the trem in-phase, and wire the output to reject in-phase variations

The phase relation is about each signals insertion point at the mixer, not the relationship of the 2 signals to each other?

[kagliostro]

I've not read the reply (I go now to read), but ....

I know you are joking.

Absolutely no

the stove was similar to this



the door of the oven opens towards the bottom and form a platform




on the oven and on the door was placed a white dog

smaller that this but with the same fur



as told the fire was off and the stove only lukewarm

BTW seemed that he was also happy to be there, but to me to see that old dog on the oven was a pain

Franco

 

[kagliostro]

VCAs (controlled gain amplifiers) are what we really want

Is the 6BE6 tube acting as VCA circuit in the Playmaster 103 ? Is this what we want ?



---

BTW You say that neon bulb has the tendency to chop waves, but looking to old Gibson I've seen that their photocuplers used a filament

lamp not neon, was the tremolo on Gibson better than Fender ? (talking of those who used the photocoupler)

Franco

[shooter]

the 6BE6 tube acting as VCA

Wait for the experts, but you have found an *example* that makes sense for me, I see the signal (input at g1) out of phase with the output and trem at G2 in phase with output.  Guessing the cathode does the *rejecting* or controlling gain of both signal and trem?

was the tremolo on Gibson better than Fender

when I try and get this answer from players, they seem *biased*, I gave up on quantifying questions like that

[PRR]

> signal (input at g1) out of phase with the output and trem at G2 in phase with output.

How does that matter?

G3 is really the "signal grid" in the original application. Wobbling this wobbles the plate much more. Looking at datasheet, from 3mA to 0.2mA. (Less here, but similar max/min ratio.) There is a BIG 10Hz wave at the plate.

Which is why it is followed by a 2 or 3 stage C-R bass-cut filter.

A "real VCA" cancels the modulation input so it is suppressed in the output.

http://www.thatcorp.com/2180-series_Pre-Trimmed_Blackmer_IC_Voltage-Controlled_Amplifiers.shtml

Ah, I just recalled that the Blackmer dBx THAT VCAs are log-law. For trem a linear VCA makes more sense. There's lots of those although I do not have one handy.

The front end of a "Vari-Mu Limiter" is a fine tube VCA but needs two triodes and two transformers.

[sluckey]

BTW You say that neon bulb has the tendency to chop waves, but looking to old Gibson I've seen that their photocuplers used a filament lamp not neon, was the tremolo on Gibson better than Fender ? (talking of those who used the photocoupler)

Is it better? That's a matter of opinion. The Gibson will have a smoother sounding tremolo because the brightness of the incandescent lamp can be varied. This causes the resistance of the LDR to vary from high resistance to low resistance slowly and smoothly. You cannot vary the brightness of a neon bulb. It's either dark (off) or bright (on). No in between. This causes the LDR to change resistance very quickly, producing a choppy sounding tremolo. The Fender neon system is still being used 50 years later. Which system is Gibson using? 

BTW, I've never heard a Gibson tremolo, but I've heard plenty of Sunn tremolo. Sunn used an incandescent lamp optocoupler to produce a very smooth sounding tremolo. Unfortunately, that optocoupler is extinct today. Here's a Sunn schematic. Look on page 3 for the original...

     http://sluckeyamps.com/sunn/sunn_sceptre_1971.pdf

[sluckey]

You run the signal out-of-phase, the trem in-phase, and wire the output to reject in-phase variations

The phase relation is about each signals insertion point at the mixer, not the relationship of the 2 signals to each other?

There is no phase relationship between the two signals. The phases are completely random and nonsynchronous to each other.

PRR's statement applies to bias vary trem for a push/pull output stage. The two guitar signals from the PI are 180° apart and will be out of phase with each other at the grids of the output tubes. The single trem signal is applied thru the bias to the output tube grids, Since the same trem signal is applied to both grids, the trem signals on the plates will be in phase with each other and will cancel each other when combined in the OT. That's called common mode rejection.

[shooter]

There is no phase relationship between the two signals

I knew that, that's where I got confused about *what* outta phase PRR was referring to, hence the incorrect logic,

How does that matter?

, applied to Francos 6BE6

Which system is Gibson using? 

That's fair, but what % do you give branding over substance? as electronics, non player, I've listened to 2 Gibs, 4 Fenders, and 1 ampeg, honestly the GA5T wins, (for me), but it doesn't meet the opti coupled criteria.  Thanks for the learning, truly top notch.

[PRR]

> You cannot vary the brightness of a neon bulb

You can. As long as you get over 110V and let it drop to 70V, 1mA is brighter than 0.1mA.

Even G.E. says so. General Electric Glow Lamp Manual

"...in direct proportion to the current..."

I swear that pencil circle is in the PDF, not my marks.

Also a plot showing how a nearby LDR will vary resistance with neon current.

IIRC, most neon-trems have a 1Meg keep-alive resistor or equivalent, so they stay in "dim glow" at minimum current so we don't have to get over the 110V-60V start-up bump each cycle.

[PRR]

The "smoother sound" of incandescent trem is because an incandescent lamp won't change light output quickly. Thermal inertia.

Incandescent = hundreds of millSeconds
LED = faster than 1/1000 mS
Neon = 1-10 mS
Photo resistor = 10 to >100 mS

10Hz trem wave = 16mS (slower is more mS)

Neon or LED with fast photo-R will work fast, but reveal any "glitch" in the LFO wave.

Incandescent with slow photo-R will be very smooth, but weak at fast rates.

[sluckey]

Take a look at the waveform on a Fender neon trem...

     http://el34world.com/charts/Schematics/files/fender/Fender_65_twin_reverb_%20manual.pdf

I've never seen a dim glow inside a Fender roach. It flashes then goes completely dark, then repeats.

[PRR]

> the waveform on a Fender neon trem...

That's a voltage waveform. We want a current waveform.

However I agree that this seems to be "mostly off" (no current). Signal is "full" 3/4 of the time and "lower" 1/4 of the time.

It does look half-sine on the bottom?

Fender's choice. A more smooth wave is possible. Instead Fender chose to bias V5b near-off and bump it on for part of the wave.

Shoveling in the depths of my mind-- I recall why I "know" neons can be linear. I had an AM/FM radio. It had a Magic Eye which guided AM tuning. No guide for FM centering. I had neons and 300V transistors. I wired a long-tail diff-pair. Tail to -50V from bias supply. Collectors through a neon apiece to B+. One base to ground, the other to the ratio detector.

If ratio detector were at zero, both lamps glowed equally. If it was way + or -, one side went dimmer and then out, the other side glowed brighter to double-current. Very smooth. Visually nicer than the diff-pair LEDs used on some limiters to indicate under/over threshold. The bright side did not look "twice bright" for the same reason double-voltage is not quite double-loud: your senses compress. But it definitely got brighter, and faded from there right down to "equal", "dimmer", and then "dark".

[kagliostro]

All is very interesting, I'm happy I've start this thread

The Fender neon system is still being used 50 years later. Which system is Gibson using?

Before you put this question I was wondering for a possible reason, reliability, is possible that the neon is still in use because it has less

problems than filament lamp ? After all a neon seems more durable, a filament bulb has filament aging problems and the filament can also

break due to transport vibrations (I don't think they use automotive filament lamps inside the photocoupler)

---

No one can say something about the oscillator I've draw ? (see post #28)



Thanks

Franco

[sluckey]

When I read your first post I understood that you had "put it together" meaning you had actually built the circuit. You mean you have "put it together" on paper, right?

I think the oscillator will be too strong with the LED and probably cause a "thumping" sound that will be hard to get rid of. Remember that I used that LED circuit to wiggle the grids of the 6V6s and that requires much more trem signal than the Champ circuit. But you don't need that much signal to wiggle V2's cathode. Replace the LED with a 1K||25µF as used in the original J12 schematic. I think this will give you plenty of trem for that Champ circuit.

It's been proven that the 6SL7 has enough gain to work as a tremolo oscillator, but I think a strong 12AX7 makes a better oscillator. The only reason I would chose the 6SL7 would be if I was building an all octal amp, as is the case with the Ampeg J12 that I put in that old RCA radio cabinet.

Is this just a brain exercise or are you possibly considering an all octal build?

[kagliostro]

Sure I expressed me badly, sorry

Thanks for the answer Steve

I'm planning a vintage style SE (OCTAL + UX7), so the interest for the 6SL7 tremolo

Unfortunately I realized that it will be a problem to add the tremolo to the circuit, due to the PT I've under hand (270V AC @ 80mA - 14V AC @ 2A)

may be (but I'm not sure) I can find one other PT on my stock that can fit better (if I don't find one I'll renounce the tremolo)

Here is a possible scheme, but not sure at all about it, I'm still thinking about this version

6SJ7 > 6SL7 CF > Tone Control > 6SL7 > Power Tube

or something like

6SL7 > ToneStack > 6SL7 > Power tube (same of AA764) + 6SJ7 OD to be connected between TS and the second 6SL7



Franco

[shooter]

All is very interesting, I'm happy I've start this thread

yes, thank you for letting me tag along.

[kagliostro]

Franco

[kagliostro]

Today I can't go searching for one other PT on my stock (because there is a lot of confusion on my shop)

however I've seen this one that I can order if I find nothing of usable (it also is not expensive)

Pri: 0-220-230-240 V (blue-black-orange-yellow)

Sec 1: 250 V / 0,1 A (red)
Sec 2: 6,3 V / 1,5 A (blue)
Sec 3: 12,6 V / 1 A (green)
   
http://www.tube-town.net/ttstore/Transformer/Power-Transformer/Toroidal/Toroidal-47VA::5391.html

Voltage for B+ is a bit less than the other transformer I've, 250V AC instead of 270V AC but current is higher (100mA instead of 80mA)

and this has also 6.3V AC & 12.6V AC for filament while the other had only a 14V AC winding

if I rectify SS, DC will be in the order of 350V

Will the 100mA be enough to supply the whole circuit included the tremolo oscillator ?

Franco

[tubeswell]

Will the 100mA be enough to supply the whole circuit included the tremolo oscillator ?

yup - for those 3 pre-amp tubes and and that output tube 100mA is plenty for the HT winding

[kagliostro]

Thanks Tubeswell

Franco