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Suggestion for upgrade of a Fender Blues Junior amp

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6/12/2000 9:10 AM

Suggestion for upgrade of a Fender Blues Junior amp

Hi !
I am upgrading my friends Blues Junior.
He wants more clean and a little
bit more power .
Please let me know if I am doing
something wrong.
I am planning to :

1. Replace input grid resistor from
10k to 68k

2. Replace Blues Junior OT with
Deluxe Reverb OT.

3. Replace otput tubes to 6L6GC.

4. Replace grid stoppers from 100 to
470 / 2W resistors.

5. Add Choke to power supply.

6. Add variable bias for output tubes.

7. Replace PT with new one with
following spesifications :

230VAC / 300VAC - 250mA + 45VAC - 100mA +
20 VAC - 100mA + 6.3VAC - 4A .

Speaker is Eminence 50W / 8 ohm and should
handle increased power . Power supply caps
are rated at 500V ( surprise ! ).
I hope I will get more bass and wider
range of clean sound.

Is there anything I should take care of ?
I am not shure about PT specs . Is 300VAC
enough for 20 to 25 W and will Deluxe Reverb
OT handle this ?

6/12/2000 1:21 PM

This is a just a suggestion but why not just build a new amp from scratch? You're essentially changing all of the expensive parts (both transformers) and you're going to have to completely hack the chassis to get the new tube sockets in as well as mount all the new transformers. It seems more cost effective to just build a new amp and either save or sell the Blues Jr. After all your finished product isn't going to sound anything like the original amp.

MJ

6/12/2000 2:44 PM
Nick	Well, my friend actually likes the tone of the Blues Junior, but wants to increase clean range and to boost power. I wont hack much of the chassis. I have moved speaker and footswitch jack to the right and have mounted one socket into the original hole for EL84 and the other in former speaker jack hole ( after some drilling ). I am still not sure if my PT is appropriate.

6/12/2000 3:05 PM

quote:
"Well, my friend actually likes the tone
of the Blues Junior"

If you change the power supply, the power tubes, and the output transformer, the tone is certainly going to change. Maybe your friend won't like it as much as when the amp was stock. He might be better off slaving the Blues Junior into a larger amp (line out off of Blues Jr. into effects return of larger amp).

Isn't the Fender Blues Deluxe amp (2x6L6, rated for 40 watts) pretty close to what you're going after? Why not just have him buy one of those?

Sorry to say this, but I can't help thinking... I have to wonder if you're enthusiasm for working on a challenging modification project has overshadowed the search for a simpler and possibly better solution to yours friend problem.

6/14/2000 12:17 AM
MJ Harnish	I agree. Going from a pair of EL84's to a pair of 6L6's alone is going to have change the tone. Throw in the rest of the mods and forget it. I had forgotten about the Blues Deluxe; that's a good suggestion. They sell fairly cheap too. MJ

6/14/2000 8:20 AM

God knows why one would even want to try to do any kind of extensive mods to a Blues Jr. I'm just learning about tube amps and stuff, so i'm anything but an authority on the subject, but just looking inside a Blues Jr. and seeing that cramped PCB and all those spade connectors (is that the right term?), makes me really appreciate the simplicity of my '67 Champ. BUT... if one REALLY wanted to do a big project involving the Blues jr. why not look into David Allen's PTP retrofit kit of his Accomplice PTP amp designed to fit into the Blues Jr. case? His site is listed in the amp makers above, and his kits are reputed to be excellent. Obviously if a person already likes the tone of the Blues Jr. (and i do like mine) and just wants a bit more of it, then the Allen kit is way overkill, but it's something to think about...

6/14/2000 8:24 AM
rob	Sorry, i got my message boards mixed up... David Allen's page is located at: www.allenamps.com/accomplice.html

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