I am currently using an EH soul food as my drive pedal from my electric guitar into a clean solid state acoustic guitar amp. It sounds great.
However, I have recently acquired for free an old reel to reel tape deck from the 60s, and inside it are several Mullard valves and power and output transformers with which I could make a Mullard 3-3, as the amp built into the reel to reel seems to have been based on the exact same tubes.
If I buy the required caps and resistors to reconstruct a simple Mullard 3-3 3watt power amp, will this work well as a power amp using the Soul Food as a pre-amp? I would use a single Celestion 10" Blue or Gold as a driver. Would providing a large voltage from the Soul Food send the 3-3 into a nice overdrive, or would it be a really bad idea? It is a hifi amp after all.
Many thanks for your considerations.
However, I have recently acquired for free an old reel to reel tape deck from the 60s, and inside it are several Mullard valves and power and output transformers with which I could make a Mullard 3-3, as the amp built into the reel to reel seems to have been based on the exact same tubes.
If I buy the required caps and resistors to reconstruct a simple Mullard 3-3 3watt power amp, will this work well as a power amp using the Soul Food as a pre-amp? I would use a single Celestion 10" Blue or Gold as a driver. Would providing a large voltage from the Soul Food send the 3-3 into a nice overdrive, or would it be a really bad idea? It is a hifi amp after all.
Many thanks for your considerations.
The 3-3 sounds OK as long as you don't require much power. I can remember constructing one in about 1960, followed by another to get stereo. Well audio reproduction has improved since then, perhaps except for the Williamson amp and Baxandall preamp. Please excuse the reminiscing. Seeing mention of the Mullard 3-3 brought back memories of hifi past.
If you're after a versatile little practice combo amp that does clean tone really well, what you describe will fill the bill. The Celestion Blue is a really chimey speaker, though. If the amp gets very fizzy or swirly at high volume, it will either give you a rush or a headache. Depends on your style.
The configuration you ponder was used in the Hundred Buck Challenge with success by more than a few builders. The pentode front end can deliver more gain than a triode, and it doesn't act the same when overdriven. This makes the little rig more versatile, but harder to tame with knobs at high volume. Matching and voicing the preamp stage to the power valve is super important.
The configuration you ponder was used in the Hundred Buck Challenge with success by more than a few builders. The pentode front end can deliver more gain than a triode, and it doesn't act the same when overdriven. This makes the little rig more versatile, but harder to tame with knobs at high volume. Matching and voicing the preamp stage to the power valve is super important.
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I was unfamiliar with the Mullard 3-3, but having looked at it, I have two concerns. First, there is a tonne of negative feedback applied to bring the THD down to a specified 1%. And second, the design goes to extremes to extract the maximum possible voltage gain from the EF86 (pentode) preamp stage.
A single-ended EL84 is likely to have about 10% THD, so this suggests at least 20 dB of negative feedback. That is a lot for a guitar amp - certainly more than I've ever seen in a valve guitar amp.
Heavy negative feedback is a good thing for Hi-Fi, but likely to sound bland and "too clean" for guitar, up to the point where clipping starts; and when the amp does clip, it is likely to be abrupt and harsh. In other words, the opposite of what guitarists call "progressive" or "touch sensitive".
The circuit is very simple, though, and if the excessive negative feedback turns out to be a problem, you can dial it down, or remove it entirely, without too much trouble.
The second issue - too much gain from the EF86 - tends to lead to several problems, including microphony and "fuzz box" sounding distortion on overload. Merlin Blencowe's website (The Valve Wizard) has a section on pentode preamp design, and will give you the information needed to revise the EF86 input stage to produce a more usable amount of gain, along with a better quality of overdrive.
Here's a link: The Valve Wizard -Small Signal Pentode
-Gnobuddy
A single-ended EL84 is likely to have about 10% THD, so this suggests at least 20 dB of negative feedback. That is a lot for a guitar amp - certainly more than I've ever seen in a valve guitar amp.
Heavy negative feedback is a good thing for Hi-Fi, but likely to sound bland and "too clean" for guitar, up to the point where clipping starts; and when the amp does clip, it is likely to be abrupt and harsh. In other words, the opposite of what guitarists call "progressive" or "touch sensitive".
The circuit is very simple, though, and if the excessive negative feedback turns out to be a problem, you can dial it down, or remove it entirely, without too much trouble.
The second issue - too much gain from the EF86 - tends to lead to several problems, including microphony and "fuzz box" sounding distortion on overload. Merlin Blencowe's website (The Valve Wizard) has a section on pentode preamp design, and will give you the information needed to revise the EF86 input stage to produce a more usable amount of gain, along with a better quality of overdrive.
Here's a link: The Valve Wizard -Small Signal Pentode
-Gnobuddy
For your vintage fix: ELPICO AC25
Same tube line up as the Mullard 3-3. I recall someone posted a schematic on AX84, try searching for it.
Same tube line up as the Mullard 3-3. I recall someone posted a schematic on AX84, try searching for it.
Lovely looking little guitar amp, that Elpico!
I failed to find a schematic on AX84 (though I found references to this amp). But so far, every vintage pentode-input guitar amp I've discovered seems to have lifted their pentode preamp design straight from the manufacturers data sheets - and the datasheet design was usually optimised for somthing very different than a guitar pickup. Usually the goal was squeeze the highest possible voltage gain out of one pentode, probably to help offset the high cost of a new pentode at that time in history.
I've done a little tinkering with pentodes in guitar preamps. I think they can be used both to get very nice "tubey" cleans, and to generate bluesy preamp distortion that sounds a lot like a single-ended output stage. But IMO, 1Meg anode loads and microamp anode currents are not the way to get there.
-Gnobuddy
I failed to find a schematic on AX84 (though I found references to this amp). But so far, every vintage pentode-input guitar amp I've discovered seems to have lifted their pentode preamp design straight from the manufacturers data sheets - and the datasheet design was usually optimised for somthing very different than a guitar pickup. Usually the goal was squeeze the highest possible voltage gain out of one pentode, probably to help offset the high cost of a new pentode at that time in history.
I've done a little tinkering with pentodes in guitar preamps. I think they can be used both to get very nice "tubey" cleans, and to generate bluesy preamp distortion that sounds a lot like a single-ended output stage. But IMO, 1Meg anode loads and microamp anode currents are not the way to get there.
-Gnobuddy
Here is the AC25 schematic from AX84 with some corrections:
To get the maximum voltage gain from the pentode, the plate was starved on purpose in the Mullard design. In the OP's case, since it is driven by a pedal/preamp, the EF86's gain can be dialed down quite a bit, and the NFB network needs to be changed or it can be skipped altogether.
To get the maximum voltage gain from the pentode, the plate was starved on purpose in the Mullard design. In the OP's case, since it is driven by a pedal/preamp, the EF86's gain can be dialed down quite a bit, and the NFB network needs to be changed or it can be skipped altogether.
I have been given an old 3w mono hifi (ish) tube amp from a 60s reel to reel tape recorder.
The tubes are all Mullard. I have the right tubes and transformers to make a Mullard 3w mono power amp, like the 3-3 Mullard 3-3. Three Watt Amplifier
If I want to make a nice cheap combo, could I use the Mullard 3-3 as a power amp, and feed it with a Klon Centaur clone, like the Electro Harmonix Soul Food? I'd probably use a 10" alnico speaker, like maybe the Celestion blue or gold, although that's a pricey option, and build the cabinet from some spare oak floorboards, dovetailed together on my router.
Would the Soul Food provide enough preamp control, do you think, or would a volume control be a good idea on the power section? I like the idea of having an effects loop, and without a volume control, I could simply have my reverb pedal at the end of my pedalboard chain, right?
Many thanks
Lucas
The tubes are all Mullard. I have the right tubes and transformers to make a Mullard 3w mono power amp, like the 3-3 Mullard 3-3. Three Watt Amplifier
If I want to make a nice cheap combo, could I use the Mullard 3-3 as a power amp, and feed it with a Klon Centaur clone, like the Electro Harmonix Soul Food? I'd probably use a 10" alnico speaker, like maybe the Celestion blue or gold, although that's a pricey option, and build the cabinet from some spare oak floorboards, dovetailed together on my router.
Would the Soul Food provide enough preamp control, do you think, or would a volume control be a good idea on the power section? I like the idea of having an effects loop, and without a volume control, I could simply have my reverb pedal at the end of my pedalboard chain, right?
Many thanks
Lucas
@LucasAdamson - Posting the same topic in multiple threads is against the forum rules.
Sorry about that!
Still looking for a go to design using my newly acquired tubes. The best suggestion I've heard so far seems to be the AC25 design, right?
Thanks Lucas
My first recommendation is actually to leave the tape recorder mainly intact, and use it as your guitar amp. In my teens I used an old Grundig tape recorder as a practice amp and it gave some fabulous tones. I just put the guitar into the mic input, and set it to Record with Monitor on. You might just want to disconnect the motors, and maybe build yourself an external speaker cab. BTW Richie Blackmore is famous for using an old tape recorder on stage during his Rainbow years, connected into his Marshall Major amps by means of a dummy speaker load.
Alternatively, consider using the valves to build a Vox AC4 instead of the Mullard 3-3. Just one warning, if you use a high efficiency speaker with either of these options, it will be really loud for home use.
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Alternatively, consider using the valves to build a Vox AC4 instead of the Mullard 3-3. Just one warning, if you use a high efficiency speaker with either of these options, it will be really loud for home use.
Sent from my LG-D801 using Tapatalk
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I meant to say consider using its valves and transformers. You can save yourself quite a bit of cash on the transformers. One word of caution, EF86 preamp stages can be prone to microphonics, which means you may need to use some form of shock mounting if you want to build this into a combo amp. Alternatively, build the P1 project smo from AX84, which has a 12AX7/ECC83 front end, rather than EF86.
Also returning to the original question, I would not expect the signal swing from a guitar FX pedal to be sufficient to directly drive an EL84 power stage. You will need at least one preamp stage in front.
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Also returning to the original question, I would not expect the signal swing from a guitar FX pedal to be sufficient to directly drive an EL84 power stage. You will need at least one preamp stage in front.
Sent from my LG-D801 using Tapatalk
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