Reverb tank without reverb transformer

[Leevi]

I don't know the origin of the schematics below but I think it's related to Swart AST amp.


I'm wondering the wiring of the reverb there since there is no transformer
before the tank.

According to my understanding it works if the input impedance
of the tank is several thousend ohms? Are there that kind of tanks on the market?

http://s301.photobucket.com/user/Nathan_C/media/Atonic2.jpg.html


Leevi

[TIMBO]

Hey Leevi, Some info here.http://el34world.com/Forum/index.php?topic=7957.0

[kagliostro]

Seems that the tank used in that project is an 8FB3C1C

http://forum.ampage.org/forum.php?cmd=vt&tid=22699

The old italian brand FBT used ofthen on theyr amps a cap coupled reverb circuit

but on the schematic there was not a number, only "Rev. unit Hammond"




K

[sluckey]

Check out the reverb driver in this Hammond AO-43 amp...

[jjasilli]

Leevi:  there are old posts on this issue;  maybe so old they are gone.  Your schematic shows what's often called "capacitor driven" reverb, which uses no reverb tranny.  The cap blocks HT B+ from escaping to the reverb tank.  This is used by Traynor, e.g., Guitarmate YGM-3, and some Ampegs like the V4 (which uses an off-beat tube).  It's not as lush as "Fender reverb".


Re impedance matching:  in my experience the mini reverb tanks that come with some solid state amps work fine with the Traynor circuit.  If you're trying to save space, that's an option to consider.

[terminalgs]

almost all 1960's Ampegs and Magnatones used a Hammond/Gibbs/Accutronics/Belton 4FB/9FB tank directly coupled to tubes via a capacitor.  look at the Ampeg Gemini's, or the Magnatone M10A, M13, or M8.


 output impedance for tube recovery can be 2K or 10K, but the 9FB/4FB 2K Zout tank is the most commonly used tank.


valve wizard also has a good chapter on the subject (free, online).

[Jack_Hester]

The Oliver G-300 used a 6DR7 to drive the Reverb tank. 

Jack

[Jack_Hester]

Or, you could drive it from the OT, like some 60's Ampegs. 

Jack

[Leevi]

Thanks for the responses and links guys.


Yes, the tank seems to be cap connected. I suppose the term comes from the cap that removes
the DC voltage level from the plate voltage?


However I think the input impedance of the tank must be high in order the get the reverb working and
the driving circuit with 12DW7 must be set for that purpose?


http://www.parts-express.com/accutronics-8fb3c1c-rg25r-3-spring-reverb-tank--269-844


/Leevi

[sluckey]

However I think the input impedance of the tank must be high in order the get the reverb working and
the driving circuit with 12DW7 must be set for that purpose?

That's right.

[PRR]

A happy load for a tube is (depending on the tube) 2K to 200K.

A happy winding for reverb tank is 1 Ohm to a few K Ohms.

Fender found a glut of 15K:4 OTs made for old tube radios about the time that transistors started eating that business, so he used a modest tube plus a cheap transformer into a 4-10 Ohm tank.

When that glut ran low, others used beefier tubes with higher impedance tanks. Also transistor/chip amps tend to use the few-K tanks.

The cap is not magic. But you need SOME way to keep the tube plate's DC out of the tank's coil. You also need a beefier tube and a pretty beefy plate resistor.

The transformer is more efficient (less DC power for the same tank drive). But everything else is against it (cost size weight). Being in the same chassis as a 10Watt-50Watt amp, the raw efficiency hardly matters, 0.1W or 1W of DC to the tank driver.