Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Toxophilite on April 28, 2015, 12:48:57 pm

Title: Reverb Tanks
Post by: Toxophilite on April 28, 2015, 12:48:57 pm

Hi
I was talking about this in another thread but thought it maybe deserved it's own examination as it could useful to others in the same situation


I have 4-5 old identical Gibbs reverb tanks, only one of which has measured resistance to match a fender reverb circuit
(I say resistance because I can't measure impedance with my meter and there's a website telling approximate readings for various tanks in ohms, also my meter seems to read .7 ohms by itself)
i'll give them a rating out of 10 as to amount of reverb produced


A- 1-1.7 ohm in - 176 ohm out  (it works really well  a 10 )


The others are:(all in ohms, give or take an ohm)


B - 176 in  176 out  (very quiet but works  , about a 2)
C - 176 in  176 out
D  - 1 in   44 out  (very usable but not quite as 'surfs up' as 'A' about a 7)
E  - 1 in  44 out


As you can see 2 have  the proper input resistance while the other two have the proper output resistance


the parts are all identical looking and the inductors(yes?)spring suspending units at either end mount with a little brass rivet


I think with careful drilling out and remounting with a little bolt and nut, one could possible swap the output section of one of the 176 ohm output units into the 1 ohm input put units, thereby creating a unit that is more usable in a fender style circuit , be it AB763 or 6G15


Mechanically I think it's entirely possible with a little care
But is it an electrically sound idea?


What say those in the know??

Title: Re: Reverb Tanks
Post by: terminalgs on April 28, 2015, 03:02:22 pm

you tested them with a fender circuit?  the ones that sound good, sound good because they are low input impedance, like 10ohm or so.  that matches your fender's transformer.  The 176/176 DC ohm units are probably 1K-2Kohm input and output and would be more suited to driven directly by a tube with a coupling cap (like an Ampeg or a Magnatone).


your "D" and "E" are probably 400-600ohm output and better suited for solid state recovery, like a peavey or an Acoustic.  I'd skip them.  you can make the same fender reverb circuit,  just use a driver from an Ampeg circuit instead of a 6k6 and a transformer.

Title: Re: Reverb Tanks
Post by: Toxophilite on April 29, 2015, 12:21:55 am

I realized that maybe this should've been in effects, my apologies
Anywho I tried swapping a 176 ish ohm output from a 176 in 176 out tank  into a  1 in  44 out  tank and it worked a treat
Drilled out the brass rivet/grommet and installed the new output section with a tiny bolt (which you can see)
The input has small plastic coated wires while the output has fatter cloth covered wires
Neat
Now I have two tanks that work well with the fender circuit one for my amp and one for the 6G15
The 1st picture is the two tanks mostly disassembled
the 2nd is the finished unit
the 3rd is the input section
the 4th is the output section


this page was reasonably useful
https://www.amplifiedparts.com/tech_corner/spring_reverb_tanks_explained_and_compared (https://www.amplifiedparts.com/tech_corner/spring_reverb_tanks_explained_and_compared)

Title: Re: Reverb Tanks
Post by: terminalgs on April 29, 2015, 09:29:45 am

very cool!

Title: Re: Reverb Tanks
Post by: bakerlite on April 30, 2015, 09:25:21 am

'In a pinch'


is there any danger or ill effect of using a reverb tank with a 150ohm input where the original item calls for  a 600ohm input?

Title: Re: Reverb Tanks
Post by: eleventeen on April 30, 2015, 03:54:33 pm

Probably not. If you are driving a rev tank from a Fender type circuit, we are actually talking about a 2-3 watt audio amp (in the form of the the 2 halves of the 12AT7 reverb driver tube strapped together) through a little output transformer not much different than what one would find on a little record player. The output impedance of the transformer wants to see an impedance much like a speaker---8 ohms.


So there is real power being delivered to the input coil/transducer.


But if a tank w/a 150 ohm input impedance is installed, that transducer would see massively less power. It may well not be enough to drive it. I am not confident enough in my impedance math to say that the tank would see 1/20th as much power (8/150) but the resistance of the input coil would in and of itself reduce input power by quite a bit.


Likewise, if the driver circuit is 150 ohm and the tank input transducer is 600 ohm, we would expect ~~~1/4 the power to hit the reverb can. Might be enough to drive it, but you'd have to crank your reverb drive. As the "reverb" control is on the receive end of the tank, you might have to turn that all the way up (instead of "3-1/2" which is about where you use a Fender reverb unless you are doing Dick Dale.)  That would probably be noisy.


So it would work strangely, if at all. I doubt anything would be damaged.


In Accutronics;

Reverb Type	1	Short (9¼") 2 spring unit
4	Long (16¾") 2 spring unit
8	Short (9¼") 3 spring unit
9	Long (16¾") 3 spring unit
Input Impedance	A	8 Ohms
B	150 Ohms
C	200 Ohms
D	250 Ohms
E	600 Ohms
F	1,475 Ohms
Output Impedance	A	500 Ohms
B	2,250 Ohms
C	10,000 Ohms
Decay Time	1	Short (1.2 to 2.0 sec.)
2	Medium (1.75 to 3.0 sec.)
3	Long (2.75 to 4.0 sec.)
Connectors	A	Input and Output Grounded
B	Input Grounded, Output Insulated
C	Input Insulated, Output Grounded
D	Input and Output Insulated
E	No Outer Channel
Locking Devices	1	No Lock
Mounting Plane	A	Horizontal, Open Side Up
B	Horizontal, Open Side Down
C	Vertical, Connectors Up
D	Vertical, Connectors Down
E	On End, Input Up
F	On End, Output Up

Title: Re: Reverb Tanks
Post by: 2deaf on April 30, 2015, 04:53:04 pm

Quote

Is there any danger or ill effect of using a reverb tank with a 150ohm input where the original item calls for  a 600ohm input?

What are you driving it with?