Accutronics 8DB2C1D Tank - How to drive it with a tube ?

[kagliostro]

Is possible to to drive an Accutronics 8DB2C1D Tank with a tube ?

INPUT IMPEDANCE = D = 310 Ohm
 
OUTPUT IMPEDANCE = B = 2575 Ohm

Usually the use of a reverb transformer is devoted to 8ohm input Tanks

so what to do ? try to use it with a standard reverb transformer or try a capacitor coupled circuit that didn't use a transformer ?

Thanks

K

[terminalgs]

see this http://www.valvewizard.co.uk/reverbdriver.html


At the bottom he specifically mentions a 300ohm tank using the SRPP.


If you want to just try to drive it with a parallel 12AU7 or 12AT7... Merlin has an example.. There is also this Magnatone M10A example:







This M10A tank is a 1.2K input tank.    You might need a series resistor with the tank to make the load closer to 1K-2K (like Merlin has in his example).   If you do this with a circuit designed for a 1.2K tank,  the reverb might be quiet (voltage divider), needing more gain out front (of course, reverb circuits are usually loud enough at 3-4 on the volume knob, so you might find that 6-7 is the "new 3-4".


Keep in mind that the tank is an inductor, so the impedance rises as the frequency rises.  So it is 1.2K at some higher frequency. 


If you have a tube driven reverb circuit working in another amp,  plug it in and see how performs.  I'd do it with a 25K or 50k pot in series to trim the load and play with it.

[PRR]

> Usually the use of a reverb transformer is devoted to 8ohm input Tanks

No.... use a transformer when ever the load is much less than the several K Ohms of a tube plate resistance.

The plan above has two pretty-hot half-12AU7, so 3K plate, and 5K DC feed, so just under 2K. A 1.2K tank is not a bad mis-match. A 300 Ohm tank would be significantly worse.

300 ohms is much-much less than tube impedance.

Also 1uFd is already a large cap, but you need 4X bigger. 4uFd. As an electrolytic, not too bad, but e-caps leak DC which might be bad for the tank coil.

You could go with four 12AU7 parallel, but the total current and power would be similar to a 2*6V6 amplifier.

Better to find 5K-10K to 600 ohms transformer.

Or rig up a 24V DC power rail and use a chip amp.

[kagliostro]

Thanks Terminalgs & PRR

I'll try to find a 10k/600ohm transformer, and I've thinking also to a 220v/25v small PT to be tried

Some investigation will also be devoted to the use of an SRPP

I've also one other idea, what about to try to drive the Tank taking the signal from the cathode using a capacitor  ?

I'm not sure to remember it well but I'm afraid about the fact that a Tank require voltage and not current to be driven, is it so ?

K

[rzenc]

Ciao K


How about an ECC88 CF?  You could use one section as CF and the other as recovery. Arranged as a CF it may give around 77 ohms Zout. Low losses to 300 ohms input. Also, the huge e-cap here can be changed to poly - Solen fabricates it. The other section can be arranged to mix dry and wet signal.


With respect,


R.

[kagliostro]

Ciao Rzenc

That is interesting, very interesting

I'm still confused about the fact if a CF with his lower voltage is correct to drive a reverb tank

Franco

[terminalgs]

FWIW This is an example of a CF driven reverb tank uses a 6U8A triode as the CF.

the DCR readings for the tank are 186 input, 181 output,, which I believe makes this a 1.2K in / 2.2K out tank.  the schematic doesn't show it properly, but the shield on the rca connections are circuit grounded.

[rzenc]

I'm still confused about the fact if a CF with his lower voltage is correct to drive a reverb tank

Ciao Franco,


Do you have a signal generator and a scope? if so, use channel 1 as your reference signal and channel 2 as your output.
Drive verb tank with some sort of signal and measure it's output. Change signal input amplitude and measure output again. With a couple of measurements, you will be able to find how big your input signal should be.


While at it, change frequencies and note if there is differences in the outcome.


Do you know how much HT will be available to verb driver?


Ciao,


R.

[kagliostro]

The project at the moment has a deviation towards SS

mainly because to use more than a tube isn't much pleasant

Franco