Peavey Windsor 100 watt head. Hmmm...
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mayfly
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kboman said:Thanks for the tip
But seriously, what exactly is an o/p amp and a phase splitter?
ooohhh - this is gonna take some time. We're getting into the theory behind amp design here. Question before I start: Do you have any sort of electronic or technical training?
mayfly said:kboman said:Thanks for the tip
But seriously, what exactly is an o/p amp and a phase splitter?
ooohhh - this is gonna take some time. We're getting into the theory behind amp design here. Question before I start: Do you have any sort of electronic or technical training?
None, and no experience either. My high school programme was natural sciences but I chose nature courses over technical ones (sort of - school terms always translate terribly between counttries). I do know that a preamp does signal processing and a poweramp does signal amplification, roughly speaking. I think?
mayfly
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kboman said:mayfly said:kboman said:Thanks for the tip
But seriously, what exactly is an o/p amp and a phase splitter?
ooohhh - this is gonna take some time. We're getting into the theory behind amp design here. Question before I start: Do you have any sort of electronic or technical training?
None, and no experience either. My high school programme was natural sciences but I chose nature courses over technical ones (sort of - school terms always translate terribly between counttries). I do know that a preamp does signal processing and a poweramp does signal amplification, roughly speaking. I think?
Not quite true. Generally the voltage gain is all done in the pre-amp stages, and the power amp stage (as a whole - tubes and o/p transformer) provides enough current to drive a set of loud speakers at the given voltage of the pre-amp. There are exceptions to this of course (the AC30 being one), but generally there is little or no voltage gain in the output section.
ok, let's see if I can explain this without getting too technical. First some definitions:
o/p stage. The output stage. In a typical push/pull class A/B tube amp this consists of the output transformer, the output tubes, and a phase splitter. I'll get to the phase splitter in a bit.
pre-amp stage. In a typical tube amp, this consists of an input voltage gain stage of fixed gain, feeding a passive tone network and/or volume control, feeding a make up stage of fixed gain. Other stuff (like tremolo or reverb, or an effects loop) is usually added in after that. These effects are subjects all on their own so I'm not going to talk about them.
triode - (usually) a pre-amp voltage gain block. A typical pre-amp tube has two triodes in it. There are examples of triode power tubes like the 300B, but we won't concern ourselves with these tube types since they were not used in the guitar amps that we know and love. BTW, a typical power tube that we know and love is called a pentode - but I won't get into that either. :evil4:
back to the output stage. The output tubes and transformer work together to generate enough current at the input voltage level to drive the loudspeakers. The power tubes provide the current, and the transformer changes the impedance to match the load. Remember, instantaneous power (not RMS) is voltage times current, so if you can get the current up, you can generate the required power. I'm glossing over a lot of stuff here so all you amp designers out there feel free to fill the appropriate gaps.
Now let's get to the phase splitter. A typical tube amp above 5 watts or so uses a circuit topology called "push/pull". This topology uses tubes in pairs to drive different phases of the output signal. Here, one (or more) tube(s) is used to drive the output at the top half of the signal, and one (or more) tube(s) is used to drive the output at the bottom half of the signal. When the "top half" tube(s) are driving, the "bottom half "tube(s) are essentially cut off and are not generating current. When the bottom half is driving, the top half is cut off. This means that at any given time, either the top half or bottom half tube(s) are not on, are not generating current, and (this is why this topology is used) not dissipating plate power. This design lowers the dissipated plate power of the tube to a level that it can stand without overheating, and still generate good power.
Some examples of this. A Fender deluxe reverb uses two 6V6 output tubes to generate 22 watts of power. One of those 6v6 tubes drives the top half of the signal, and the other drives the bottom half. At any given moment, one of them is off - which allows the amp as a whole to push that power without the tubes overheating. Now, a VOX AC30 uses four EL84 tubes to generate over 30 watts of power. One pair of those EL84s drives the top half of the signal, and the other pair drives the bottom half. Now an Ampeg SVT uses six 6550 power tubes to generate over 300 Watts of power. One trio of those hefty 6550s drives the top half, and the other trio drives the bottom half. The different wattages a tube can generate all comes down to the amount of current it can generate and still stay within it's plate dissipation specification. This varies from tube type to tube type. For example, the plate dissipation spec for a 6v6 type is 12 watts (but this was under-rated by the original manufacturer and Fender ran them way above these design limits in the deluxe). For an EL84 it's again 12 watts, but unlike the 6v6 this was probably over-rated for this tube type. For the big 6550 it's a whopping 44 watts - which is a hell of a lot of plate dissipation which means that these tubes can push a hell of a lot of current without overheating.
A quick aside - you can start to see why most tube amps require matched sets of tubes. If the tubes are not matched, one tube on a side will have to generate more current than the other tubes it's mated with - causing that tube to wear out faster and hasten the failure of all the tubes in general.
ok - since one set of tubes drives the top half, and the other set drive the bottom half, a special circuit is required to transform the pre-amp signal so it can be used by these sets of output tubes. This circuit is the phase splitter. it can be a single triode, or a dual triode, but in any case, it takes the single phase pre-amp signal and generates two output signals - each 180 Deg out of phase with the other. Imagine a teeter totter with one kid on one side, and another kid on the other. When one kid is in the air (the upper part of the signal), the other kid is on the ground (the lower part of the signal). Replace the kids with triodes and imagine the arc of each end of the teeter totter to be the two output signals and you can visualize the operation of the phase splitter.
Ahem - now back to the original question. If you are designing an amp for a lot of clean headroom, you want to design the various gain stages in the amp to overdrive only after the next stage in the chain has reached saturation. If you follow this rule, you'll only get overdrive once the output stage is in overdrive - the idea being that you'll never run it there because it will be impossibly loud. A typical guitar amp does not follow this rule. A blackface fender, for example, will have the phase splitter start to saturate well before the output stage starts. On my black face amps, this happens at volume '4' or so. Not really great for clean headroom (but for most of us, we like it that way). On the later silverface amps, the phase splitter was changed to have a lot lower gain, so it reached overdrive a lot later. Great for clean headroom - but bad for sales because the amps just didn't play the same and people didn't like that.
I imagine that you'll have questions - so let 'er rip. I'll do my best to answer them. Hopefully I don't have any errors in the above - but if I do I imagine folks will chime in and call me an idiot :icon_biggrin: :evil4:
Wana_make_a_guitar
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What kind of 'grit' are you getting out of this machine? I now have some of that rare stuff called money, and I might have more when I sell my current amp. I've seen this head before and thought it looked pretty cool, then I kind of spaced that the idea of buying it from my from your first post in this thread, and now i'm interested again if all you have to do is shell out $25 for new tubes ( even though it will probably work out to be more like $70 bucks here, and I might have a bit of trouble trying to put 'em in ).
I'm interested in an amp that will have awesome cleans, get some nice british rock tones and may even get come chunky metal riffs goin' ( though if all goes the way I plan, which it probably won't, i'll have a pedal to do my metal for me).
I'm interested in an amp that will have awesome cleans, get some nice british rock tones and may even get come chunky metal riffs goin' ( though if all goes the way I plan, which it probably won't, i'll have a pedal to do my metal for me).
Hi Vol.
Glad the tube swap helped.
Just so that I get it straight in my mind, only cos I'm interested.
Did you
a) try a 12AT7 in the first pre socket, and THEN try an 12AU7 in the first pre socket? .......... or
b)put a 12AT7 in the first, AND a 12AU7 in the second?
Gratuitous Thread Hijack.
Wana. Why not try and see if you can pick up a 2nd hand Laney tube head. Something like the GH50L. (or VH50 combo) They are pretty cheap, and sound great. I had one, it was my first ever foray into the wonderful world of tubes. Paul Gilbert uses the GH50's and GH100. and Tony Iommi's signature amp is based on the GH100.
Glad the tube swap helped.
Just so that I get it straight in my mind, only cos I'm interested.
Did you
a) try a 12AT7 in the first pre socket, and THEN try an 12AU7 in the first pre socket? .......... or
b)put a 12AT7 in the first, AND a 12AU7 in the second?
Wana's_makin'_a_guitar said:
Gratuitous Thread Hijack.
Wana. Why not try and see if you can pick up a 2nd hand Laney tube head. Something like the GH50L. (or VH50 combo) They are pretty cheap, and sound great. I had one, it was my first ever foray into the wonderful world of tubes. Paul Gilbert uses the GH50's and GH100. and Tony Iommi's signature amp is based on the GH100.
I'm not really sure which is slot one or slot two.
But, if you are facing the front of the amp, the one on the left got the 12AU7, the one on the right got the 12AT7, and the one in the back to the left of the four EL34s is still a 12AX7.
Mind you, I dial the preamp gain knob to about 11 o-clock, there's a wee bit-o-grit at that point that dissapears when I roll back the guitar's volume knob, I use this to "season" my sound as needed. And I need to get a footswitch and a nice long cable, one cool aspect of this amp is the "Lead" switch, which boost the volume and mids just enough to make it worth using for leads.
The more I play with this critter, the more I'm looking forward to Friday night's gig.
But, if you are facing the front of the amp, the one on the left got the 12AU7, the one on the right got the 12AT7, and the one in the back to the left of the four EL34s is still a 12AX7.
Mind you, I dial the preamp gain knob to about 11 o-clock, there's a wee bit-o-grit at that point that dissapears when I roll back the guitar's volume knob, I use this to "season" my sound as needed. And I need to get a footswitch and a nice long cable, one cool aspect of this amp is the "Lead" switch, which boost the volume and mids just enough to make it worth using for leads.
The more I play with this critter, the more I'm looking forward to Friday night's gig.
Wana_make_a_guitar
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That sounds like a good Idea. The only challenge is finding a dealer here. I know two local dealers that sell peavey, Lanely may be a little tricky.jimh said:
