Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hesamadman on June 09, 2017, 01:53:23 pm
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I built a reverb circuit based upon a Hot Rod deluxe. It uses TL072 ic. Non tube. The reverb tank that it calls for is a 4EB3C1B. I know the 4 stands for reverb pan type. So its a type 4 pan. The E is suppose to stand for its measurement of input impedance and the B is the output. This has an input of 600 ohms and an output of 2250 ohms. I built this into an amp head. I mounted the pan on the top side of the inside of enclosure. Face up. This is 17 inches long and the edge of it is just over my output transformer. This is introducing a little bit of hum into my circuit. It isnt to terrible. Realistically I could live with it, but this amp is soooo quiet otherwise. I would rather find a solution. I think I would like to try a shorter tank. I have a tank from a Blues Jr that utilizes a TL072 also. It works just fine in installed but I really dont like the tone. I would like to try a couple other options. I know I need to stick with something along the lines of an xEBxxxx model. My question is this. If the E stand for 600 ohms input impedance, why do any other models I see with an E there have impedance of 800?
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the are basically three tank families: 4,8,9 - a google search will provide the answers:
go here: (https://www.amplifiedparts.com/tech-corner/accutronics-products-and-specifications)
the there are differences in mounting position, delay, and input output connector grounding. the latter is the most important and depends on your circuit. what are the complete part numbers of the two tanks you're using?
input/output jack grounding may be the source of your hum. on the blues jr. tank if you can't find the part number, with a DMM measure from the RCA jack outer shell to the tank body - do this for both input and output jacks. compare that to the long tank. see below.
the blues jr. tank wants input insulated, output grounded - IOW the output jack is the only jack connected to the tank body. compare that to the long tank. if your long tank has a grounded input jack you can modify it to be insulated by clipping the jacks outer shell connection to the tank body.
--pete
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My question is this. If the E stand for 600 ohms input impedance, why do any other models I see with an E there have impedance of 800?
The 4E input coil and the 8E input coil are probably the same with the same number of turns and the same DC resistance. The 8E has a longer core length and core length is proportional to inductance. The inductance is proportional to the impedance, so the longer core length of an 8E will result in a higher impedance at any given AC frequency.
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> If the E stand for 600 ohms input impedance, why do any other models I see with an E there have impedance of 800?
Read the very fine print. They are measured a little different. They are probably the same coil.
Anyway, 600 == 800 for all practical purpose. And it will really be 120r in bass and 6K at the top of the audio band.
> like to try a shorter tank.
> I have a tank ... but I really dont like the tone.
There you go. Real reverb wants to be several feet long. The 17" is a cut-down for a rig you can move. The 12" are severely cut. The 6" sound like the top strings on a cheap piano... dink dink. Use the biggest tank you can.
> the edge of it is just over my output transformer.
Shouldn't be a lot of hum off the OT. (PT is different.)
WHICH END is over the OT?? If it is the output end, turn the tank around. The input end is much less sensitive.
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WHICH END is over the OT?? If it is the output end, turn the tank around. The input end is much less sensitive.
Such an amazing yet simple solution! It is the output end. I didnt even think of that great idea.
These problems to me are great forms of discussion and I usually take a lot of great info from them all. Thanks everyone.