Fender Blues Junior Amp Resurrection

chromium · August 07, 2016, 05:39:56 PM

I had been wanting to pick up a small tube amp for guitar for some time now, and I came across a non-functional Blues Junior on Craigslist back in June. It was in minty condition cosmetically, but it had "blew a fuse" according to the owner. I took my chances, made him an offer and brought it home.

Upon tearing into it, it looked like one of the power tubes may have failed and smoked the corresponding screen resistor.

I cleaned up and fixed that mess, installed a new set of JJ tubes, and it fired right up!

Since these are pretty popular units to modify, I did some research and decided to make some of the common improvements while I still had it partially disassembled:

- Replaced the cheap PCB-mounted input jack with a Switchcraft
- Replaced the cheap PCB-mounted "fat" switch pushbutton with a toggle
- These are fixed-biased kinda hot from the factory, and so I added a trimmer to provide adjustable bias... and set it up to be a little gentler on the power tubes
- Upgraded the caps in the tone stack, and implemented the "Twin mod" on the midrange pot for a greater range of adjustment
- Replaced/upgraded the power supply filter caps
- Added a 3-position progressive Carling power switch that provides for a "standby" setting in the middle position (nice to mute the amp)
- Grabbed an amber jewel lamp for it just for grins

(haven't installed that yet)

I ran that way for a couple of weeks, and during that time got a promotional email from Antique Electronic Supply advertising a 10% off sale in July. Figured that offered a good excuse to grab an upgraded driver and reverb tank for it!

That MOD tank made a vast improvement in the sound and sensitivity of the reverb, and the C-Rex driver really tightened up the low end. It sounds great for a cheapie amp! I'm happy with the results, especially considering I'm in it <$300 after all is said and done

Dave W · August 07, 2016, 09:54:38 PM

Is that a Hamer on the right?

Good deal on the amp, especially since you know how to do the mods. I paid just under $300 for mine 15 years ago. Never modded it since it only gets light use and it sounds good to me.

amptech · August 07, 2016, 11:59:50 PM

Fender amps with smoked screen grid resistors must be the most common sight in my amp shop.
It's a good thing you installed a bias pot, all in all it's worth it to do some safety mods to these amps.
I install 5W screen grid resistors on all these fender amps. In theory you do not need 5W, but 1W or 2W units do
blow up all the time on these amps. The IC caps is also not he best, they fail fairly common too.

But they are good amps when they work!

Pilgrim · August 08, 2016, 09:00:51 AM

Nice work, and you built some really cool ideas in there. Love the MOD tank addition!

chromium · August 08, 2016, 10:41:12 AM

Quote from: Dave W on August 07, 2016, 09:54:38 PM
Is that a Hamer on the right?

Good deal on the amp, especially since you know how to do the mods. I paid just under $300 for mine 15 years ago. Never modded it since it only gets light use and it sounds good to me.

Yes - that goldtop is a '94 Archtop GT model. 1pc maho body w/maple cap, and 1pc maho medium-chunky neck with large tenon. Previous owner had replaced the stock SD P90s w/Lollar mini-humbuckers. Always wanted a goldtop, and couldn't resist this one with the pickup and bridge upgrades. That's my favorite guitar to date.

The Jr. is a '00 Hamer that one of the dealers had built more to "50s spec" - all maho, thin headstock (compared to the later production Korina models), Tone Pros plate tuners, and this one has a Lollar P90 and Gibson Historic wrapper bridge.

Quote from: amptech on August 07, 2016, 11:59:50 PM
Fender amps with smoked screen grid resistors must be the most common sight in my amp shop.
It's a good thing you installed a bias pot, all in all it's worth it to do some safety mods to these amps.
I install 5W screen grid resistors on all these fender amps. In theory you do not need 5W, but 1W or 2W units do
blow up all the time on these amps. The IC caps is also not he best, they fail fairly common too.

But they are good amps when they work!

Thanks- great to know! I had gone with 2W carbon films that I had in the parts bin just to get it running, but I'd like to (at minimum) switch those to metal film for something "flameproof"... but may opt for 5W ceramics based on your advice. Planning to swap those when I tear it down for the gratuitous jewel lamp install

Also picked up some spring retainers for the EL84s that I still need to install.

Quote from: Pilgrim on August 08, 2016, 09:00:51 AM
Nice work, and you built some really cool ideas in there. Love the MOD tank addition!

Thanks! I based most of them on info that Bill Machrone had published on his wonderful site. He used to sell kits and services for a lot of this stuff, but apparently he's been battling cancer and not doing so well

http://billmaudio.com/wp/

The MOD tank really did wonders. Without changing any of the reverb circuit, what required a setting of "10" previously I can now get on "4" - and the overall reverb sound is more dynamic, with maybe just a slightly longer decay compared to the stock tank. $16 (on sale) well spent!

Dave W · August 08, 2016, 08:45:17 PM

I figured you were talking about Bill M.'s mods. Sorry to hear he's ailing.

Also, I was referring to the Junior-style guitar on the right. Never saw one like that before.

chromium · August 19, 2016, 11:15:28 AM

Got the final mods wrapped up last weekend. Went back in and replaced those temporary screen grid resistors (per above), added some retainers for the power tubes, and executed the completely frivolous jewel lamp installation

Done! Couldn't be happier with it... great bang for the buck.

Pilgrim · August 19, 2016, 11:27:00 AM

It ain't a classic amp without a jewel light!!

And those tube retainers are pretty slick, too.

Dave W · August 19, 2016, 04:38:24 PM

Nice work!

amptech · August 20, 2016, 02:44:35 AM

Looking good!

Highlander · August 20, 2016, 03:06:08 PM

+1 a couple of times...

Dave W · November 04, 2016, 11:37:01 PM

Joe, in case you didn't already know, Bill Machrone passed away the other day.

http://billmaudio.com/wp/?p=1815

http://www.pcmag.com/article/349186/remembering-pcmags-bill-machrone

BTL · November 05, 2016, 09:55:22 AM

Nice work!

Sorry to hear about Bill M...his Blues Jr. mods are ubiquitous.

chromium · November 07, 2016, 08:01:03 PM

Quote from: BeeTL on November 05, 2016, 09:55:22 AM
Nice work!

Sorry to hear about Bill M...his Blues Jr. mods are ubiquitous.

Thanks- that was a fun little project, and I've been enjoying it.

Quote from: Dave W on November 04, 2016, 11:37:01 PM
Joe, in case you didn't already know, Bill Machrone passed away the other day.

http://billmaudio.com/wp/?p=1815

http://www.pcmag.com/article/349186/remembering-pcmags-bill-machrone

Sad news. Another one of the good guys gone too soon