Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jeff on February 19, 2013, 11:04:43 am
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Does anyone know the input and out impedance of a hammond "F" tank? I know it's not the same as an accurtonics "F" but I'm not sure what it is. Hammond tanks used a different code than accutronics so hammonds "F" is not accutronics "F"
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1475 ohms is the number I see on the internet.
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Measure the DC resistance of the hammond coils with your ohm meter and compare them with the Accutronics chart.
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Whoops. I think I got some wires crossed upstairs for a second, my bad. That is in fact the accutronics number I referred to.
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Measure the DC resistance of the hammond coils with your ohm meter and compare them with the Accutronics chart.
Thanks, that's a good idea. Problem is I don't have the tank, I'm building off a schematic that uses a hammond "f" tank and need to know what the equivitent Accutronic tank is.
Thanks
Jeff
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Show us the schematic and we can probably suggest an appropriate tank.
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http://www.fliptops.net/catalog/cat-100031/reverb-tanks-pans (http://www.fliptops.net/catalog/cat-100031/reverb-tanks-pans)
a bag.. cables ,,
did not check the link for the f tank,,,,,,, first sorry
the f tanks donot link for me maybe there are no more f tanks .
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Thanks Tom that was very useful.
"Type "f" 2 spring reverb tank for vintage Ampeg amps with speaker driven reverb: Echo Jet, Echo Twin, B12X, B12XY. For most Fender amps with transfomer driven reverb: Twin rever, Pro Reverb, Deluxe Reverb etc... 4ab3c1b"
So it sounds like the Ampeg uses an 8 ohm tank. Ampegs F = accutronics xABxxxx.
Basically what I built is a speaker driven reverb. I stole the idea.
Schematics kinda a mess but it's basically two amps. The schematic is one amp on the left and the mirror image second amp on the right. Look at the OT/speaker on the left. You take the signal from the main speaker run it through a 330 ohm bypassed with two 25uF caps back to back to make a nonpolar and then to a 27 ohm resistor then to the input of the tank. That feeds the input of the other amp(right side). The output goes to the other amp for 100% wet. The main amp is still 100% dry.
I tried the 8 ohm tank and it sounded good but I also tried a Accutronics xFBxxxx tank which is 1450 ohms input and suprizingly that also sounded good. Better to me actually but that may just be the difference between 2 and 3/ long and short tanks.
Is there anything wrong with using the 1450 ohm tank instead of the called for 8 ohm tank?
I'm not really sure what tank impedance really means.
Will I hurt anything? tank? main amp?
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> Schematics kinda a mess
Indeed.
I've extracted the Reverb bits so as we can see what it is.
> I tried the 8 ohm tank and it sounded good but I also tried a ...1450 ohms input and suprizingly that also sounded good.
With 8 ohms the speaker level is cut-down by a factor of 46 for bass, about 4 for mids-highs. For practical purpose, it cuts bass below 400Hz.
With >1K tank it gets full bass.
With coils wound for 8 versus 1450 ohms, we expect the hi-Z coil to "want" 13 times higher voltage. We are only giving it 4 times higher voltage for mids-highs. So in that way it is "safe", but may be "tame" (won't make you sea-sick).
The bass "wants" to be cut so the spring doesn't bang. Very few well-designed reverbs drive the spring hard below 400Hz. The few that do usually have complicated limiters to reduce banging.
If it sounds good, do it.
However I suspect it might like a 0.5uFd-1uFd cap in series to cut the bass.
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You're right about that. The higher Z tank does sound darker. And maybe that's why I like it better. The 8 ohm tank sounds high and "pingy". It's great if I wanna crank the reverb amp and hang ten with Dick Dale but for anything else the 1450 sounds richer. I'll try the cap if I have one though because there may be a little too much rumble down below.
What would you suggest for adding a dwell pot?
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I'd replace R54 with a 25K pot, top to reverb tank, bottom to ground, wiper to V6-4. But I bet you don't really need a dwell for that circuit.
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That, I think, would act more like a reverb level(volume) than a dwell.
I want to reduce the signal to the tank. As it is, with the 8 ohm tank, it's great for surf stuff. The 1450 gives a more mellow sound which also sounds good but different charater. If I turn the level down with the 8 ohm tank it sounds quieter but the springs still sound driven hard, pingy. Still surf but quieter surf. If I could reduce the level to the tank and then turn the recovery amp up I think it would sound more subtle and mellow same volume less surf, more cave. In other words same loudness of reverb but not so driven. Kinda like using a gain and master volume knob to get the same loudness but different driven sound.
Right now the 8 ohm tank sounds pingy and the 1450 sounds mellow, I'm wondering if that's because the 8 ohm tank is actually driven harder and with the 1450 tank the springs don't shake as much because it's 8 ohms. I figure with a dwell I could get both sounds or anywhere inbetween. The dwell would controll how hard the springs shake.
I get the concept of a pot as a voltage divider but what I don't get is how to determine the value. If you make a VD with two 1K ohm resistors or two 1M resistors I can understand that the output voltage in both cases is half the input voltage, but what determines the value of each resistor(or in this case the value of the pot)?
Also this is hanging off my OT so I don't want to load down the main amp. So I assume I can't use a pot too small.
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That, I think, would act more like a reverb level(volume) than a dwell.
You're right. I just posted that too quickly!
To control the input to the tank, just put a 500Ω or 1000Ω pot across the OT output. Wiper goes toward the tank. This size pot will not load the OT.