I have finally "finished" my first build and I've had a few questions pop up.
it's a bridge-rectified 6l6 version of an 18 watt Marshall. (I did that because the OT was salvaged from a 6l6 amp.)
It sounds pretty nice to me but I wish it broke up sooner. Too much clean headroom for me. What are some good options to get earlier break-up?
http://i167.photobucket.com/albums/u148/gabel1337/BN_18_SCHEMATIC_2B.jpg
If I got one of those Weber copper caps would it reduce the B+ at all? (I'm curious about sag)
Bias currents are different by about 3 mA. Is that a small, medium or large problem?
Could I change the circuit and use 6v6 tubes instead?
Well thanks for reading
it's a bridge-rectified 6l6 version of an 18 watt Marshall. (I did that because the OT was salvaged from a 6l6 amp.)
It sounds pretty nice to me but I wish it broke up sooner. Too much clean headroom for me. What are some good options to get earlier break-up?
http://i167.photobucket.com/albums/u148/gabel1337/BN_18_SCHEMATIC_2B.jpg
If I got one of those Weber copper caps would it reduce the B+ at all? (I'm curious about sag)
Bias currents are different by about 3 mA. Is that a small, medium or large problem?
Could I change the circuit and use 6v6 tubes instead?
Well thanks for reading
Add VVR. Reducing B+ at will lets you dial in clean to mean point +/or adjust for different power tubes.
If you apply the VVR to the whole amp, you probably won't need the PPIMV.
It's the situation where you drop the voltage to the power tubes and let the preamp 'rip' that leads to too much (over) drive to the power tubes.
That's my understanding, anyway. I tried just regulating the power tubes in a non-PPIMV amp and it was way too much overdrive.
The VVR would probably be one of the easier options- aside from just using a good overdrive pedal, but that may be a different sort of sound than you want. You'll need to break into the B+ supply, possibly adding another filter cap (before the take-off to the VVR), and find a spot to mount the VVR pot (assuming you want to play with the VVR - otherwise you could just put in a trimmer under the chassis, or something similar..
What kind of speaker are you using? Speaker can make a huge difference, though experimenting can get expensive.🙂 Something like a P10R will break up quite readily, IME.
If you switch to 6V6 tubes your OT may not be such a good match -not a huge issue IMO since it's a guitar amp - do you have a choice of speaker secondaries on the OT?
How much re-wiring do you want to do?😀
I think you could add a gain stage with half of the V1 tube, but perhaps I'm mis-understanding the parallel preamp setup on the 18W (though I did build one some years ago).
The usual 'whole amp' VVR setup (I've only done two, so I'm no expert) is to 'cut into' the B+ line and route to the VVR and back to feed the PS filter bank, so the VVR is working 'upstream' from the B+1, B+2, B+3 etc. The heater circuit/wiring isn't affected. Perhaps you're thinking about using a Variac on the whole amp and the problems from dropping the heater voltages?
It's a bit more complex in a fixed bias amp - not an issue for your build (or mine🙂).
I'm just learning. I have 4/8/16 on the OT. I'm using a full range 12" speaker atm. I want to purchase a celestion a-type (and an alnico blue someday)
I was thinking that a vvr toggle might be good enough to suit me. I don't need tons of control, just a way to use the amp at tv volumes if I can.
I was thinking that a vvr toggle might be good enough to suit me. I don't need tons of control, just a way to use the amp at tv volumes if I can.
It's surprising how little power you need to be 'too loud' for bedroom use.
Some folks are happy with the VVR result when the amp is cranked 'way down' - I found that there was a big tonal change as well as output drop- not objectionable, but not just the 'same sound, but less of it' I wanted.
Other things you could explore:
-Headphone out
-Pentode/triode switch (though this doesn't drop the volume a whole lot)
-switching the output tube bypass caps as in the 'Da Geezer Attenuator'
-letting some of the drive to the output tubes 'cancel' by switching in a resistor across the two grid leads from the PI to the power tubes. This was done in the Reverend Goblin 5-15 amp by switching in an 82k resistor.
EDIT: Found the thread I was remembering:
http://166.63.127.229/Forum/index.php?topic=4401.0
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That describes most (all?) of us here!🙂
That gives some possibilities for playing around with putting the speaker on the 'wrong' secondary tap to reflect a different impedance back to the primary (so you can use the 6L6 OT for different tubes if you want).
If it's a 'hi-fi' type speaker your amp won't sound like it will with a guitar/instrument speaker connected, in my experience. What speaker is it?
If you can afford it at all, spending a bit of money on a guitar speaker (I've liked the Warehouse Guitar Speakers I've bought, and Eminence makes some good and not very expensive speakers also) will make all your other experiments with the amp more realistic.
But till then there are some cheap mods you can try - most anything can be unsoldered and re-used.
A pot would probably be easier than a lot of experimenting with a lot of different fixed resistors - you could put the pot out of the way and use it with a switch.
You originally were talking about more/earlier breakup. Did you mean that the amp and speaker sound OK wide open, but you just need to attenuate the power level, and try to keep the same sound quality but at a lower volume level?
Or, are you not happy with the sound, even wide-open? (Keeping in mind the speaker issue...)
I have been using a multi-fx pedal (zoom g3) that has cab sims. The amp actually sounds very nice to me at lower volumes. It is clearly more responsive and tone-full than the solid state combos that I also use.
I own a Fender Mustang 2. I use that as a make-shift speaker cab for the tube amp. That is the 12" full-range speaker I've been using.
With the zoom plugged in I have a set-up that resembles a hybrid modeling amp such as Fenders super champ x2 or the Peavey tube vypyr. That's cool but I'd love to be able to bypass the zoom distortion sounds and get some real power tube breakup from the amp itself. At the present time I've got a cleaner amp than what you'd expect from a deluxe reverb. It's not fender twin clean, but it has to be turned way up before you can get some decent breakup.
I own a Fender Mustang 2. I use that as a make-shift speaker cab for the tube amp. That is the 12" full-range speaker I've been using.
With the zoom plugged in I have a set-up that resembles a hybrid modeling amp such as Fenders super champ x2 or the Peavey tube vypyr. That's cool but I'd love to be able to bypass the zoom distortion sounds and get some real power tube breakup from the amp itself. At the present time I've got a cleaner amp than what you'd expect from a deluxe reverb. It's not fender twin clean, but it has to be turned way up before you can get some decent breakup.
I've never heard of the geezer mod. I'll be looking into that first.
I tried to turn my parallel gain stage into 2 successive gain stages and I didn't like the results too much. I converted the tone control into an extra gain control but even so there was too much gain for me. The amp was beyond my capability to tame it in that configuration.
I tried to turn my parallel gain stage into 2 successive gain stages and I didn't like the results too much. I converted the tone control into an extra gain control but even so there was too much gain for me. The amp was beyond my capability to tame it in that configuration.
I think I poorly phrased some of my thoughts. Please excuse me and I'll re-phrase.
The 18 watt amp (I've been told) has a relatively clean pre and pi, and it's designed to get some power tube distortion from the el84s.
I'm not particularly fond of el84s anyways and I also saved a lot of money by making a 6l6 power amp. (I had the parts on hand)
I didn't anticipate that it would clean up as much as it did. I'd say it sounds like a slightly cleaner "Marshally" take on a deluxe reverb. It's got a very nice Marshall sounding clean sound and it sounds kind of like a medium crunch Marshall when you dime it. It doesn't have the el34 sound exactly. I guess it's less mid-focused?
I'm very happy with it as it is, because it does sound really good to me. But I can't use it as much as I'd like. I can only use the zoom pedal and set my amp at a low, clean setting. That gets me any emulated clean that the zoom can provide, plus a cab SIM. I can also hear the zoom's modeled distortion sounds which are nice, but not as nice as my amp sounds when I dime it.
I know I need a real guitar speaker.
I'm about 99% certain that I'm going to add a Weber copper cap and a toggle switch so that I can have some sag when I want it.
I don't have a plan for the loudness problem yet.
I'd be okay with less clean headroom and more overall gain. A range of distortion that's similar to what you can get from a standard EL-84 equipped 18 watt would be great for me. But I want to get there without using EL-84s. I'm trying to avoid using EL-84s.
I hope that was a better explanation of what I'm hoping to do.
The 18 watt amp (I've been told) has a relatively clean pre and pi, and it's designed to get some power tube distortion from the el84s.
I'm not particularly fond of el84s anyways and I also saved a lot of money by making a 6l6 power amp. (I had the parts on hand)
I didn't anticipate that it would clean up as much as it did. I'd say it sounds like a slightly cleaner "Marshally" take on a deluxe reverb. It's got a very nice Marshall sounding clean sound and it sounds kind of like a medium crunch Marshall when you dime it. It doesn't have the el34 sound exactly. I guess it's less mid-focused?
I'm very happy with it as it is, because it does sound really good to me. But I can't use it as much as I'd like. I can only use the zoom pedal and set my amp at a low, clean setting. That gets me any emulated clean that the zoom can provide, plus a cab SIM. I can also hear the zoom's modeled distortion sounds which are nice, but not as nice as my amp sounds when I dime it.
I know I need a real guitar speaker.
I'm about 99% certain that I'm going to add a Weber copper cap and a toggle switch so that I can have some sag when I want it.
I don't have a plan for the loudness problem yet.
I'd be okay with less clean headroom and more overall gain. A range of distortion that's similar to what you can get from a standard EL-84 equipped 18 watt would be great for me. But I want to get there without using EL-84s. I'm trying to avoid using EL-84s.
I hope that was a better explanation of what I'm hoping to do.
We're pretty 'spoiled' with the modern effects and sims, I think. You'll never get the range of sounds from an actual amp that your Zoom will give you, IMO. And, there's no way that a 6L6 PP amp will be overdriven and quiet!
Well, the speaker in your solid-state guitar combo is a real guitar speaker, so a big step up from a hi-fi speaker. I've been re-building a few small SS amps into tube amps this fall, and generally the speakers in those combos (Fender Frontman, Tryanor practice amp, Fender Champion 110) didn't seem very 'tube friendly' - the tube amps sounded a lot better with different speakers. Since there's so much power on tap in a (even a cheap) ss amp, I think they put lower-efficiency speakers in those combos. But you have lots of power on tap in your amp, so not a problem.
You may find that's a subtle difference. I'd get the basic sound worked out first.
I think either the 'Geezer' cathode cap bypass thing (he didn't invent it - it was used in some commercial amps, but he did the drawings and pushed the concept along with variable resistors, etc) or the VVR would be the route to go for you. The cap bypass would be simpler and cheaper, so perhaps try that first if you don't have the parts for the VVR handy.
Update: I'm just finishing up an amp project (PP EL84) and I installed both the bypass cap 'Geezer' switch AND a VVR in the amp today.
I'd say that, of the two, the VVR is better if you really want to crank down the volume to bedroom levels.
I'd say that, of the two, the VVR is better if you really want to crank down the volume to bedroom levels.
Most EL84 amps are biased very hot but yours is not el84. How are the OP tubes biased? What is the cathode voltage, cathode resistor value and plate voltage? They may merely need to be biased hotter to get closer to breakup. But there needs to be slack in the wattage department to move in that direction safely.
I'm out at a Christmas party and I can't double-check but I think I used this drawing to build my power amp. I picked it because the voltages are very close. Whereas this one says 307 at the center tap, I think my voltage was 312 or so.
http://www.lh-electric.net/img/nfa.png
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