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Blues Junior Amp Upgrades


We at CAST Engineering have worked with Allen Amplification and spent countless hours testing different components and speakers and materials involving our options for upgrades. We have picked everything that sounds most musical to our ears. Please know that doing these upgrades to your Blues Junior Amp will take a good amp and turn it into a great amp. 


Please contact us with any questions or concern



Option 1 - $299 *introductory pricing

Base upgrade to include completely going through the circuit, upgrading the tone stack, 

upgrading all filter capacitors, adding a presence control, correcting bias issue (can either do fixed bias 

or cathode bias, your choice)and performing several other small upgrades. Amongst many tonal 

improvements with this upgrade you will also see an increase in wattage of 3 to 5 watts depending on 

your bias option.


Option 2 - $179 *introductory pricing

All of the base upgrades performed with the addition of a new speaker baffle and 10 inch 

speaker. We have several speakers to choose from that we have done extensive testing with to give you 

the tone you are looking for. This option bolts right into the existing cabinet, the 10 inch speaker gives a 

much more focused tone over the 12 inch in this small cabinet. This price is in addition to the base 

upgrade price. 


Option 3 - $479 *introductory pricing

($399 with option 1 purchase)

Complete re-housing of chassis into a hand built, highly figured flame maple cabinet. This 

cabinet is built with all dovetail joinery, high end hardware and stained to your color choice. The cabinet 

is about 20% larger than the stock Blues Jr. which makes it a perfect size for a 12 inch, 2x10 inch or 15 

inch speaker, your choice. There is a slight upcharge for the 2x10 inch speaker option. This cabinet is a 

huge improvement over the smaller MDF cabinet that comes stock. Also included is an upgraded, 

Accutronics reverb tank. The stock reverb tank is a short 4 spring tank which we upgrade to a long, 2 

spring, medium decay tank. As with the speaker options we have performed extensive testing on several 

different tank options and have found this tank to be an absolutely amazing sounding reverb. The price 

is in addition to the base upgrade price.

Option 4 - $279.95 w/no mod or $99.95 w/mod 

A little history on this project... I wanted to make something very special that would not break the bank. The Blues Jr. circuit is a very nice circuit with some magic hidden inside. The EL84 mod is awesome in its own right but this conversion is special. This conversion utilizes a new power transformer that David Allen (Allen Amplification) designed that has a high voltage center tap which will supply the higher plate voltage needed to properly run 6L6 tubes. It also has a proper output tranny installed for the circuit. With all that said the magic is the countless hours spent re-voicing the circuit to capitalize on the 6L6 tubes. Then we spent hours testing different speakers, I have to say the Tonetubby speakers are the real thing, even the ceramic magnets sound amazing. We tried 4 different ones in this prototype and loved them all for different reasons... Not 1 sounded better or worse than the other one, just different.




CAST Engineering Blues Junior Amp Upgrades, 3 different levels, Allen Amps, taking a good amp and making it great, Guitar Player Magazine, Premier Guitar, Vintage Guitar Magazine
CAST Engineering Blues Junior Amp Upgrade, Level 3, hand built, rehoused cabinet, Guitar Player Magazine, Premier Guitar, Vintage Guitar Magazine
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