Fender Blues Junior

[Nuff Said]

I'd just like to say, although this particular amp might not have a standby switch, if your amp does has a standby switch, I would use it as recommended.
Nuff

https://www.jazzguitar.be/forum/guita...by-switch.html

I looked at LPD's Fender Blues Junior schematic. There is no timing circuit to prevent high voltage being applied before the tube is "warmed up". I DID find something to support my theory that the problem with applying high voltage before proper temperature is achieved lies with the screen grid and not with other theories commonly discussed.

Before getting to that point, however, I made some notes on various amplifiers, regarding amplifier, output tubes used, output power, plate voltages, screen voltages and how voltages were measured.


Low power amplifiers
Fender Champ, 6V6GT (1), 6W, 400V, 350V, measured under signal drive

Medium power amplifiers
Fender Princeton, 6V6GT (2), 12W, 420V, 415V, schematic data
Fender Blues Jr, EL34 (2), 15W, 328V, 307V, schematic data
Ampeg Reverberocket, 7868 (2), 18W, 360V, 350V, measured no signal
Epiphone 25*, EL34 (2), 22W, 400V, 396V, measured no signal
Fender Deluxe Rev*, 6V6GT (2), 22W, 415V, 415V, schematic data

High power amplifiers
Fender Bassman*, 6L6GC (2), 50W, 425V, 425V, schematic data
Fender Showman*, 6L6GC (4), 85W, 450V, 443V, schematic data
Fender Twin Rev*, 6L6GC (4), 85W, 460V, 458V, schematic data


* standby switch included


Of the two newest amplifiers, the Epiphone Galaxie 25 and the Fender Blues Junior, the Epiphone has a standby switch, to allow leaving high voltage disconnected until tube has reached operating temperature. The Fender Blues Junior has NO standby switch but the circuit DOES include reverse polarity diodes on each output plate so that the screen grid can NEVER be at a higher potential than the plate.


Out of the eight push-pull, higher power amplifiers, only two do not have provisions to prevent screen grid failure by the application of high voltage before the tube reaches operational temperature, the Fender Princeton and the Ampeg Reverberocket. There's no particular consistency that I can see; these amplifiers are operating at roughly similar plate/screen voltages as the remainder of the amplifiers.


I think that the relationship of screen grid to the remainder of the tube operating conditions is still not completely understood. My earlier suspicion, seemingly - at least partly - confirmed by the notes posted above from web research on the screen grid, are that the standby switch is a required feature of enhanced tube reliability, although not necessarily for the reasons that many people believe.

P.S. In the previous post, several mentions were made regarding tubes oscillating when screen grid voltages were too high, compared to plate voltage. It may be worth mentioning that my Ampeg Reverberocket - the only medium power amplifier without a standby switch - oscillates when first turned on if there is no input signal. This is a fairly recent phenomenom, occurring in the last couple of years. I imagine that it has something to do with the aging of the tubes. Anyway, I always have to turn volume control all the way "down" before switching amplifier "on".

[Gabe]

I had a Blues Jr and found it to a terrible amp--broke up too easily, terrible for a clean sound.

I always found them too quiet, and break up too early for my liking, but if you can make it work then go for it.

I've heard some people get some great tones with them - its just a shame I can't :/

[jorgemg1984]

At not so loud volumes they tend to have a very compressed tone that rockers and blues players love but that is not exactly desirable for us jazzers. Fine at the house, not so fine on gigs - even drumless gigs.

[peterpanico]

Yeah,had some little Fenders in the past,and the BJ did not nail the sound for jazzin',( to me of course) great for Blues and Rock I'd say.....breaks up early,EL 84s sound too much compressed to me,I have a small Egnater Rebel 20,and when I want to get jazz tones,always turn the pot toward the 6V6s.....with the EL84s,I feel it too "high" and "ringing",also 6V6s don't break up until the end....

[Retroman1969]

Since the views on this amp are so polarizing, I thought I'd A/B my amps, inspect my B-Jr, and do a little research... Out of curiosity, and to see if I'm better off than I was, amp-wise.
(Note: keep in mind that these are the views of a novice who has never played guitar in a band, only horns and piano, but I try to back up what I'm saying as best I can)

On A/B-ing with my SS amp (admittedly a cheap-ish one, but both have 12" speakers, similar output, and no effects other than reverb) I found the SS to be darker, but flat and muddy. Bass is a bit weak in comparison, but highs are well controlled. The harder you push it, the muddier it gets. (settings: bass-9, mid-5, treb-5, vol-10)
The B-Jr is a bit brighter, but much more dynamic. It's more sensitive to my input. Good clarity and separation, and much stronger bass (settings: bass-10, mid-0, treb-3, vol-4, master vol-8). Honestly, I've found the tone warm and clean until I cranked the guitar volume to the point that it was feeding back like crazy (all laminate guitar), then it became a harsh distorted mess.
Overall, there is just more depth to the sound from the B-Jr, and more usable volume at that wattage.

Apparently, tube selection plays a big role in the characteristics and overall tone of the amp. Mine is tubed with JJ EL84 power, and JJ ECC83s pre-amp. Most of the reviews I've read proclaim the stock tubes in the B-Jr (sovtek?) to be brittle, harsh, and break up too early. The JJs have been described as darker, cleaner, fatter, and with late break-up. Two reviews likened them to 6V6s in tone characteristics.

I'm tempted to change out the speaker to a Jensen or Cannabis-Rex to see if I can improve things even more.

Conclusion: I'm sure there are better tube amps out there for jazz (for a price), but for a couple-hundred-bucks I made a big jump up from my previous amp, and it has given me a chance to play around with tubes to see if I like them.

[SamBooka]

Apparently, tube selection plays a big role in the characteristics and overall tone of the amp. Mine is tubed with JJ EL84 power, and JJ ECC83s pre-amp. Most of the reviews I've read proclaim the stock tubes in the B-Jr (sovtek?) to be brittle, harsh, and break up too early. The JJs have been described as darker, cleaner, fatter, and with late break-up. Two reviews likened them to 6V6s in tone characteristics.

I'm tempted to change out the speaker to a Jensen or Cannabis-Rex to see if I can improve things even more.

Glad you like it! If you are planning on investing in the amp (ie. buying a new speaker) check out the BillM mods first. You dont actually have to buy the kits (i did a tone stack mod and cooled the bias for about 2$ in parts (that i probably had in my stores). Wasnt a night and day change but was a nice touch. The biggest things that helped me with that amp were the reverb tank and learning how to set the master vol.

One thing I forgot about that amp that I have NEVER liked... noisy all fn getup. BillM also has a trick for putting a shield between the PT and OT but havent tried it yet.

[AlohaJoe]

+1 on the speaker change. I didn't do any mods but I upgraded the tubes and while that improved things the biggest improvement was a decent speaker. I chose a Weber AlNiCo, but any quality speaker will be better than the cheap one it came with and it's super easy to do.

I was never wild about the reverb so I think Sam's suggestion for swapping the tank out is a good one.

[Retroman1969]

Looked into the back, and yes, looks pretty straightforward. Wow, some of those speakers are pretty pricy!
I'm looking at the BillM site too, interesting stuff. Basically tone-shaping mods with caps and pots looks like? Certainly affordable.

[peterpanico]

Hi Retroman,a speaker change it's the first step in my opnion,go for Webers,or Jensens ;-) but then you should not compare the BJ to a
20 watts Crate SS......they play in two different leagues!!
If you will have the cahnce to hear a "good" SS amp,then you'll probably swap your BJ in a minute.... anyway,stay whith what you like,in the end it's up to you,it's your sound!

[Retroman1969]

Yes, I wasn't comparing them seriously, like a review, it was just for fun to see the change that was made in tone and quality for a relatively small investment (but you probably guessed that).

In my mind, "good" SS amps for jazz in a similar price range (or a little less) would be Princeton Chorus, or the Roland Cube 80x. Or at least among the ones I have tried extensively. Otherwise it starts getting into crazy money.
The problem I have these days with SS amps is that it seems the vast majority anymore are loaded with modeling software which drives me up the wall. I feel like I'm paying extra for junk I'll never use and sounds fakey to me anyway, and it's cluttering up the amp controls. That's the OC part of me I guess. LOL!

[peterpanico]

Yep Retro,i agree about modeling SS amps,never liked 'em,I only meant
"plain" SS amps,with modeling stuff unless it's top of the line junk wich will cost as much as an Evans,you lose all the dynamics of your playing.... the Cube can do,but.....there's something lacking,while on the cheap side, H&K does a couple of combos that sounds pretty nice,and are on the low budget side.Another solution,wich works very well,is to go for an AER Compact or an SR Technology JAM rig,they are small,light, and make "that" Jazzy sound quite right....any box,full hollow or semi,sings marvellous into them
If you can,check them out!

[Retroman1969]

I have nearby dealers for those amps and you're right, they're really nice, but most run in the $800-plus range so I can't consider them seriously. The H&K Blue 30 or smaller is in a competitive price range but no one carries those models in stock locally to try out. (really, I see an Evans in my future if and when I can afford it )

As for changing the speaker on my current amp, I didn't know it could make that big of a difference, but I will take a look at all those mentioned. Thanks for the suggestions!

[peterpanico]

The H&K Blue 30 or smaller is in a competitive price range but no one carries those models in stock locally to try out

I had in mind the "Attax 100"model for instance,in the Edition Blue range,the only one could be the 60 DFX,really; never tried those ones,but the Attax yes,and it has a really rich clean channel.About speakers change,yes it can do a lot of difference...
You should go for a kind of speaker not full of mids and nothing else,like the "rock" ones,instead go for something more scooped,like actual Jensens, ceramic or AlNiCo,or Neodymium I know them well,'cause are made in Italy by SICA,and I have been using them a lot lately, for substitutions;

JENSEN LoudSpeakers

[Retroman1969]

I missed that Attax 100, but they seem to be hard to get ahold of here. Thanks for the link on the speakers. Reading reviews of them now.