I have a SS Fender 25W "red knob" which brings out a nice
sound with my 360 12 MG I think because of its PRESENCE
control option. It also has a pre-amp out and in jack. I
have used this little guy to input my 50W all tube Crate 212
combo in the clean channel. But as the gain from the Fender goes up I hear like a soft whistle or "squee" sound.
Is using 1 amp to drive another bad for 1 or the other? I
believe the Crate runs EL84 and 12ax7. In the old days
didn't some players "slave" one amp to another?
Thanks for any and all tips. I'm guessing here and while it works at a practice level I don't want to be ruining either
amp!
AMPS "DRIVING" AMPS
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paologregorio
- Senior Member
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As long as you're using the preamp out jack, this should be okay, but hopefully the output of your Fender is going to a speaker- otherwise you may have other troubles on your hands. Using a power amp out jack into another amp is almost certainly bad for both amps for a litany of reasons.
My guess is that you are experiencing oscillation in the amp, but it is hard to tell from your description. The other possibility is, as Paul puts it, microphonics in most likely the 12ax7. Microphonics usually is a runaway problem, like feedback, that causes the tube in question to resonate at one frequency.
Oscillations in an amp are a bit more complex and are more likely to happen under conditions that the amp wasn't tested under (like being fed a lower impedance/higher gain load in this case.)
The last possibility of which I can think is that you are experiencing radio frequency issues- that the stopper resistor (in the Crate) is insufficient for this set of circumstances. Sometimes amp designers take out the stopper resistor or make it at a tiny value if they don't hear RF coming out of the amp- this helps reduce potential for (here it is again) oscillations elsewhere in the amp, so if this is the problem, finding the right value would be necessary to hopt to avoid the oscillation problem.
A lot of people do slave amps safely (like how you described what you were doing.) Randy Bachman used to slave his amps together from the power output of his initial amp and his amp tech had to build him a special amp to keep from destroying them. That amp became the Garnet Herzog. I believe that Jon Lord, the keyboard player of Deep Purple, went through some amps while figuring out how to properly handle the overdrive issue, as well.
My guess is that you are experiencing oscillation in the amp, but it is hard to tell from your description. The other possibility is, as Paul puts it, microphonics in most likely the 12ax7. Microphonics usually is a runaway problem, like feedback, that causes the tube in question to resonate at one frequency.
Oscillations in an amp are a bit more complex and are more likely to happen under conditions that the amp wasn't tested under (like being fed a lower impedance/higher gain load in this case.)
The last possibility of which I can think is that you are experiencing radio frequency issues- that the stopper resistor (in the Crate) is insufficient for this set of circumstances. Sometimes amp designers take out the stopper resistor or make it at a tiny value if they don't hear RF coming out of the amp- this helps reduce potential for (here it is again) oscillations elsewhere in the amp, so if this is the problem, finding the right value would be necessary to hopt to avoid the oscillation problem.
A lot of people do slave amps safely (like how you described what you were doing.) Randy Bachman used to slave his amps together from the power output of his initial amp and his amp tech had to build him a special amp to keep from destroying them. That amp became the Garnet Herzog. I believe that Jon Lord, the keyboard player of Deep Purple, went through some amps while figuring out how to properly handle the overdrive issue, as well.
"rubber heads don't dent easily"
You can safely run a SS amp without a speaker, don't ever do that with a tube amp though.
Could be an oscillation, doubt it though. Tap your tubes lightly with a pencil with the volume up (for preamp tubes), if they ring loudly (ding ding ding) they are microphonic, many new tubes are a little microphonic, I'm talking a loud ding sound.
Could be an oscillation, doubt it though. Tap your tubes lightly with a pencil with the volume up (for preamp tubes), if they ring loudly (ding ding ding) they are microphonic, many new tubes are a little microphonic, I'm talking a loud ding sound.
Re:
foolproof test. a small screwdriver also merits results, which is usually my tool of choice, but make sure to be gentle.rictified wrote:You can safely run a SS amp without a speaker, don't ever do that with a tube amp though.
Could be an oscillation, doubt it though. Tap your tubes lightly with a pencil with the volume up (for preamp tubes), if they ring loudly (ding ding ding) they are microphonic, many new tubes are a little microphonic, I'm talking a loud ding sound.
Re: AMPS "DRIVING" AMPS
The problem with a screwdriver is it is metal, and metal conducts electricity, and tube amps have high voltages, and high voltages kill easily, and being dead is not cool when there is still a lot of music to play. Use a pencil.
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soundmasterg
- RRF Consultant
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Re: AMPS "DRIVING" AMPS
The graphite in the pencil can conduct electricity too. A screwdriver is king from an ease of use standpoint, but you need to be sure to find one that is completely insulated. I found one at a local Ace Hardware that has a plastic shaft and tip that I use.
Greg
Greg