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How Many Watts Can You Squeeze Into A Blues Junior?
I'm goin' with 40.
Here's a few pics of a conversion project I mentioned. The transformers and choke are from the Hot Rod Deluxe (the Nibbler tool makes the larger power transformer fit a cinch), therefore a bridge rectifier is being employed in the same manner as in the HRD. I'm using a single 4-section filter cap can (40/40/20/20) to save on circuit board real estate (also soldered in as well as clamped; grounding is EVERYTHING!). The power transformer bolts are mounted with neoprene washers on both sides to eliminate hard metal-to-metal contact, which will help reduce eddy current hum induction at the output transformer. However, there is a ground wire on one of the PT bolts for shielding ground purposes. The grounding scheme uses brass buss plates soldered into the chassis at strategic points. Easy to solder to, and excellent conductivity. The preamp ground is kept as far away from the heater center tap resistor ground as possible, to minimize preamp noise, which is a real issue here because of the EF86 pentode preamp. All carbon comps in the signal path, with Panasonic poly coupling caps, which have a very clean tone vs. the ubiquitous Sprague 715 or 150. No tone stack, only a Brilliance control across the grid inputs of the power tubes, similar to Vox. Controls are therefore Vol, Tone, Master. The power section is cathode-biased 6L6, no NFB, so the bias winding on the transformer is unused. This will generate close to 40W, but probably will spec out at around 36W or so. You can see the heatsink-enclosed 250 ohm 25W resistor mounted on the glass-epoxy board closest to the PT. The cathode bypass cap next to it is rated at 105 degrees C for maximum lifespan.
I've built this design many times before as a head. First time I'm squeezing it into an existing chassis, and one this small (I used plastic hole plugs as necessary to clean up the look). It's sort of a Tweed tone, but on steroids, with some Vox chime in the mix. The speaker is a Jensen C12K, which is part and parcel of this amp's tonal signature.
Here's a few pics of a conversion project I mentioned. The transformers and choke are from the Hot Rod Deluxe (the Nibbler tool makes the larger power transformer fit a cinch), therefore a bridge rectifier is being employed in the same manner as in the HRD. I'm using a single 4-section filter cap can (40/40/20/20) to save on circuit board real estate (also soldered in as well as clamped; grounding is EVERYTHING!). The power transformer bolts are mounted with neoprene washers on both sides to eliminate hard metal-to-metal contact, which will help reduce eddy current hum induction at the output transformer. However, there is a ground wire on one of the PT bolts for shielding ground purposes. The grounding scheme uses brass buss plates soldered into the chassis at strategic points. Easy to solder to, and excellent conductivity. The preamp ground is kept as far away from the heater center tap resistor ground as possible, to minimize preamp noise, which is a real issue here because of the EF86 pentode preamp. All carbon comps in the signal path, with Panasonic poly coupling caps, which have a very clean tone vs. the ubiquitous Sprague 715 or 150. No tone stack, only a Brilliance control across the grid inputs of the power tubes, similar to Vox. Controls are therefore Vol, Tone, Master. The power section is cathode-biased 6L6, no NFB, so the bias winding on the transformer is unused. This will generate close to 40W, but probably will spec out at around 36W or so. You can see the heatsink-enclosed 250 ohm 25W resistor mounted on the glass-epoxy board closest to the PT. The cathode bypass cap next to it is rated at 105 degrees C for maximum lifespan.
I've built this design many times before as a head. First time I'm squeezing it into an existing chassis, and one this small (I used plastic hole plugs as necessary to clean up the look). It's sort of a Tweed tone, but on steroids, with some Vox chime in the mix. The speaker is a Jensen C12K, which is part and parcel of this amp's tonal signature.
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