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Okay tube gurus [message #27214]

Sun, 05 February 2006 18:32

Leland Crooks
Messages: 212
Registered: May 2009

Master

I have a fender blues jr. 2002 model. I love the sound, but keep seeing folks on the web talking about mods. Have any of you guys looked at the schematic or played with one of these. I'm nervous about screwing with it, cause I really like the sound.

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No Gurus allowed! :-) [message #27216 is a reply to message #27214]

Mon, 06 February 2006 06:51

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

Well, I have no experience with this model (SS/tube hibrid preamp, tube PP EL84 output), nor I`m the professional - but this is my "general" opinion/experience abot the mods. In almost every old amp I checked/repaired (for myself or the friends), somebody soldered some clever tricks. For example - tube rectifier to SS, additional gain stage, master volume, changed various parts to the non-original specifications (from resistors and capacitors to transformers and tubes), decreased/disconnected NFB loop, bias balance pot to bias "range" pot, switches, line-out...
IMO- most of this just ruined the originality/sound, and in some cases ruined amp functionality/stability (oscillations). There ARE some good thought out mods from the people who really know what they are doing, but my opinion is - if it works good, then don`t fix it

"You electricians think you`re so cool. Then you die."

Blues jr. schematic

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Re: No Gurus allowed! :-) [message #27217 is a reply to message #27216]

Mon, 06 February 2006 09:26

Leland Crooks
Messages: 212
Registered: May 2009

Master

Thanks Damir. That was my opinion, but with tube stuff I am a complete novice. If there was something egregious that could be changed I would do it. A little more growl would be nice occasionally, but that's what pedals are for.

It sure is sweet for blues and jazz though.

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no gooorooo here [message #27218 is a reply to message #27214]

Mon, 06 February 2006 19:11

PakProtector
Messages: 935
Registered: May 2009

Illuminati (2nd Degree)

Hey-Hey!!!,
I would have to ask what it is you want to change the amp into. Clearly you like it as it is, yet it would seem you think it can be better.

What does 'Better' consist of?

It looks like a make a change and see what direction it move the amp in is what you're signing up for. Done with enough variables included will mean a lot of trials.

One could beef up the PS, but if it is the PS behaviour dictating some aspect you wish to preserve, it would be counter productive to beef it up as would be traditional with a Hi-Fi set up.
cheers,
Douglas

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Take a look at this page and tell me what you think. [message #27220 is a reply to message #27216]

Mon, 06 February 2006 20:08

Leland Crooks
Messages: 212
Registered: May 2009

Master

I'm thinking this is probably the only one of the mods I've seen I'd seriously consider.

http://home.comcast.net./~machrone/bjr/bjbiasreva.htm

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Re: Take a look at this page and tell me what you think. [message #27225 is a reply to message #27220]

Tue, 07 February 2006 06:32

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

In principle, little lower "standing current" and anode/screen grid dissipation then maximum means longer life of the tube, especially in guitar amps and fixed bias.
But, many classic amps used EL84 that way (Pa max), VOX for example.
Personally, if output tubes life isn`t too short I wouldn`t mess with PCB modifications. Russian EL84 is solid sounding and relatively cheap.

Another modification can be enlarging of screen-grids resistors R24,25 to the 1kOhms value, especially if the amp is frequently overdriven.