valve junior BUMMER!

[toadman]

well....judging from the TDPRI concensus it was a bit of a crapshoot anyway! i ordered a Valve jr on line. hoped to have it in time for my gigs this weekend on Marthas Vinyard. we have to take a ferry over to the island and then play in this TEENY TINY little club. our van is too big to take on the ferry so we really shrink our setup down to next-to-nuthin'. so this little amp shows up at my door today and i'm thinking "cool, just in time". BUT....
i plugged it in and get this hissssing sound. it comes and goes with the volume knob but it's pretty bad at any worthwile volume. i tried wiggling the tubes(thats about the extent of my electronic prowess) no good. looks like i'll have to send it back. UNLESS...
anybody know any tricks an electronic imbecile like myself could try?

if not, there is a pro junior down at the local music shopthat sounded great when i tried it. but they want $319 for it. maybe i should make an offer?

[scooteraz]

At this point, the only thing to do (without voiding the warrenty) is to get a new el84 and a new 12ax7 and replace the tubes. Replace one at a time, and see if any single tube takes care of the problem. Then, you can do both. It is not real uncommon to have tubes go off during shipping.

$319 at the local shop...YIKES. MSRP is only like $250 (for the combo). As you already know, online for the combo is $150-175 for the combo. Maybe that one is modded. If so, depending on the mods, it could be too much, about right or a deal.

Yours is still under warranty, if you purchased new. If new tubes don't fix it, send it back. If new tubes do fix it, call the seller and tell him you want another set sent to you. He probably won't pay for the tubes you bought, but you will have spares.

[SEK_Hakuna]

He said "Pro Junior". That retails for $399 which is the same as the "Blues Junior". $319 is too much for a used one.

[PraiseCaster]

Hmmm? Could be a scratchy/dirty volume knob. Did you try some potentiometer cleaner?

And I think that valve jr. combos are going for about $139.00 street............

[toadman]

Originally Posted by SEK_Hakuna

He said "Pro Junior". That retails for $399 which is the same as the "Blues Junior". $319 is too much for a used one.

thats what i thought! i'd never pay 300 for a pj!. in fact, as a rule, i rarely pay more than 300 for ANYTHING!! i'm gonna try some new tubes and see what happens. i was going to do that anyway! i'll just take my tubeworks combo to the island. it's really not much bigger than the VJ. a lot heavier though.

[bowlfreshener]

Originally Posted by toadman

well....judging from the TDPRI concensus it was a bit of a crapshoot anyway! i ordered a Valve jr on line. hoped to have it in time for my gigs this weekend on Marthas Vinyard. we have to take a ferry over to the island and then play in this TEENY TINY little club. our van is too big to take on the ferry so we really shrink our setup down to next-to-nuthin'. so this little amp shows up at my door today and i'm thinking "cool, just in time". BUT....
i plugged it in and get this hissssing sound. it comes and goes with the volume knob but it's pretty bad at any worthwile volume. i tried wiggling the tubes(thats about the extent of my electronic prowess) no good. looks like i'll have to send it back. UNLESS...
anybody know any tricks an electronic imbecile like myself could try?

Did you get the head or the combo? The very first versions of the combo have a bad hissing issue that can be solved, but not quickly. If you have a combo just do a google search to see what is necessary. But if you have the option to send it back, I'd do that.

[toadman]

UPDATE...........i just replaced the tubes with some crap Groove tubes (the only brand anybody sells nearby) problem solved! i appears the EL84 was the bum. but i replaced both anyway just to make sure it wasn't something else. i definately going to put sme JJ's in there eventually. the 12AX7 will be switched to a 12AU7. but for now it's up and cranking and i'm off to the island with it. i tried all my guitars with it just now and the one that works and sounds best with the VJ is my newest addition...a butterscotch Squire Affinity! go figure!

[Cobra8272]

Single coils always work best with the EVJr unless its heavily modded.

Crank it thru a 2 x 12 Ext Speaker and tell us what u think

Cobra

[tele-martini]

toadman,
I just replaced 12AX7 with a ECC83 and the difference is night and day. i'm going to replace the stock EL84 when I get a chance. The new pre-amp tube really brought this amp to life.
martini

[mistermullens]

I loved mine stock, but I got some used tubes for a steal and installed a JJ12AX7 and it sounded even better! I'll eventually get around to replacing the EL84.

All of my guitars sound great through it. I've got a '52 Partscaster (Nocaster pups), Esquire Partscaster, Squier Tele Custom II, and Casino. I also recently owned a Squier '51 with humbuckers in the neck & bridge, and it sounded great as well.

[toadman]

Originally Posted by tele-martini

toadman,
I just replaced 12AX7 with a ECC83 and the difference is night and day. i'm going to replace the stock EL84 when I get a chance. The new pre-amp tube really brought this amp to life.
martini

my goal for the VJ is to make it distort at a much higher volume. i heard a
12AU7 was good for this. just curious what difference the ECC83 would make?
with the 80 watt combos that i normally use i set the clean channel gain so it's just starting to get gritty. then push it with either a clean boost or a od-2 pedal.
i'd also like to try and squeeze a bigger speaker in the cab. looks like a 10"would fit. and maybe even a 12 with some alteration. an extension speaker would be allright but i really like the idea of only picking up one box! call me lazy!
well the band is here to pick me up. thanks for all the responses!

[toadman]

SO.....the epi VJ worked pretty good for the gig in the teeny little bar on Marthas Vinyard. but it was a bit grittier than i would ultimately like. so i just replaced the 12ax7 with a jjtesla 12AU7. now it breaks up just where i want it BUT...i lost a lot of volume. before it sounded best with the volume at about 1 or 2 o'clock. now i have to max it and it's still not as loud as it is with the 12AX7, so i have a few more questions for the TDPRI international panel of experts:
1)would a higher power output tube solve this problem? (i'm guessing yes)

2)if so what tube should i use? i have an el84 there now.

3) could it just be a bad 12AU7?

remember ...i'm looking to make the amp a little less distorted. not perfectly clean but just less crunchy.

[lemmy99]

Ok, a 12AU7/ECC82 only has and amplification factor of 40, where as a 12AX7/ECC83 is 100, therefore your loss of volume is caused by not driving the power tube enough.

more clean head room is available by removing C3, and changing R6 & R7 to 100K, also adding NFB resistor from the top of R9 to the output jack (optional).

a champ sound can be obtained by changing R8 & R9 to 1.5K and removing some of the flabby overdrive is achieved by changing C4 to 1.1uf or for humbuckers 0.68uf

a better Marshall sound is obtained by changing R8 to 1.5K, R9 to 820 Ohms, C3 to 1.1uf and C4 to 1.1 / 0.68uf (and insane drive by jumping R6 with wire)

and lastly changing the OP tranny for a hammond DSE125 or ESE125, for a killer tone.

[JohnnyCrash]

Originally Posted by lemmy99

Ok, a 12AU7/ECC82 only has and amplification factor of 40, where as a 12AX7/ECC83 is 100, therefore your loss of volume is caused by not driving the power tube enough.

Yes. The 12AU7 swap is not only going to affect dirty headroom, it will also affect overall volume. Especially in a circuit this small with a lone preamp tube.

Originally Posted by lemmy99

more clean head room is available by removing C3, and changing R6 & R7 to 100K, also adding NFB resistor from the top of R9 to the output jack (optional).

C3 is the cathode bypass cap for one half of that 12AX7.

R6 and R7 go to the volume pot.

Negative Feedback is essentially defeated when an amp is clipping/distorting, but it will affect when the amp breaks up on the volume dial, as well as how drastic it goes from clean to dirty.

This may be a very good place to mess with a bit of headroom stuff.

Originally Posted by lemmy99

a champ sound can be obtained by changing R8 & R9 to 1.5K and removing some of the flabby overdrive is achieved by changing C4 to 1.1uf or for humbuckers 0.68uf

R8 and R9 are the cathode resistors for each of the two halves of the 12AX7. The R9 is attached to the C3 that was recommended to be removed above.

Cathode resistors (and bypass capacitors) can affect how much bass is in the preamp/input section. Shaping these can create a type of a "low freq" shelf.

Shaving bass at certain frequencies this early in an amp circuit can help reduce flab, especially when cranked for OD.

Originally Posted by lemmy99

a better Marshall sound is obtained by changing R8 to 1.5K, R9 to 820 Ohms, C3 to 1.1uf and C4 to 1.1 / 0.68uf (and insane drive by jumping R6 with wire)

and lastly changing the OP tranny for a hammond DSE125 or ESE125, for a killer tone.

A bigger/better OT will definitely help the tone and also perhaps volume.

I would personally never mess with a VJr myself, but thats just me. Also, to get great sounds it requires a great deal of tweaking and a new OT.

For more info on mods you can visit the 18watt.com Single Ended forum here:
http://www.sewatt.com/

They're a forum dedicated to single ended amps like VJr's and Champs.

[lemmy99]

I'll recap.
The amp is a poor copy of a GA5.

The input jack is wired with R1 & R2 68K essentially a 'LO' input, to make a 'HI' input for single coils change R2 to 10K and remove R1 and solder a 1M across the tip and earth connections on the input jack.

Fender sound, change C4 to 2.2uf and R8 to 1.5k, remove C3 and change R9 to 1.5K, change R6 & R7 to 100k.

Marshall sound, change C4 to 1.1uf and R8 to 1.5K, change C3 to 0.68uf and R9 to 820 Ohms, add a single pole switch to bypass R6 for a gain boost.

These parts cost pennies but make a big difference, lastly change the OP tranny for a hammond will work wonders with the above but not absolutely necessary if you on a budget.

lastly check you line voltage, from the SEwatt forum USA 115V can be as high as 124V, this will kill the EL84 and it will push its heat dissipation past the 12W limit.. Calculation and changing of R14 is necessary in some cases.

oops, try using a 12AT7 as is has a amplification factor of 60 and might give you back the volume with out the insane gain of a 12AX7

[krashjones]

This amp probably has little if any preamp distortion. It has no phase inverter. The output of the preamp stage, particularly with a 12AU7, is likely very clean (notice I didn't say transparent).

So given that, the point of an amp like this is to produce a lot of power tube distortion. Now, it is a basic fact that if the output of the preamp is clean, and the power tube creates X number of watts of power at the onset of clipping (assume for a minute that's the power rating), then without redesigning the amplifier or changing to a larger (octal) power tube, you will not get more power out of it at the onset of clipping.

You may be able to bias it a big hotter (cathode bias resistor) or find some way of cranking up the plate voltage (power transformer) and squeeze a couple of tenths of a watt more clean power out of it.

If you want more clean VOLUME then the easiest, cheapest, and most effective way to do that is with a speaker. An Eminence Wizard is probably 10dB louder at a given power level vs. the speaker that came in it. Put that in an extension cab and it will have the same sound effect as tripling the power.

I can't figure why someone would want a valve junior and then talk about wanting more clean headroom. For more clean headroom, take the VJ back and swap it for a Crate Power Block IMHO.

[toadman]

wow! thannks for the responses guys! i'm not very electrically inclined and i'm pretty sure if i started messing around with a soldering iron i'd blow something up! so i'll try a 12AT7 and see what happens. my buddy (who makes TubeGuru amps) might be able to help with more involved stuff. this is all sort of an experiment for me, and what better to experiment on than a cheap P.O.S. ! thanks again for your help.

[toadman]

""I can't figure why someone would want a valve junior and then talk about wanting more clean headroom. For more clean headroom, take the VJ back and swap it for a Crate Power Block IMHO.""

two reasons:
1) to satisfy my curiosity.
2) because it's cheap
3) because its fun (oops thats three)

basically i play regularly in a couple clubs that are really small, in fact one club is on an island and we have to pack everything in a volkswagen jetta to get it on the ferry. in these cases small is good! i'm just trying to make things better by minimalizing. last time we played on the island i hung that little JR on the pool que rack at ear level and everyone could hear it over the drums! can't really do that with a P~block and extension cab! but i'm sure it would be fun trying....in the name of science of course!

[krashjones]

hey man I just reread my post and your quote and I realize it came off as kind of inflammatory. That's not what I was getting at. Seems VJ's are about getting crunch tone at a lower volume (compared to a bigger amp), but not really so much about clean headroom.

Anyway, hard to beat the price of a Valve Junior. The cab & chassis alone would cost a home builder that much.

[JohnnyCrash]

Originally Posted by lemmy99

The amp is a poor copy of a GA5.

True, but like you're saying, its inexpensive and a few cheap upgrades will make it a little better.

Not my cup of tea, but I see the appeal.

Originally Posted by lemmy99

These parts cost pennies but make a big difference, lastly change the OP tranny for a hammond will work wonders with the above but not absolutely necessary if you on a budget.

lastly check you line voltage, from the SEwatt forum USA 115V can be as high as 124V, this will kill the EL84 and it will push its heat dissipation past the 12W limit.. Calculation and changing of R14 is necessary in some cases.

I doubt the flucuation of line AC will kill most EL84's... except perhaps the stock garbage Epiphone is throwing in them.

+1 on an OT upgrade.

The output transformer is cheap chinese garbage... even a tonally "hi-fi" transformer like a Hammond will be an improvement in sound and volume.

Originally Posted by krashjones

This amp probably has little if any preamp distortion. It has no phase inverter. The output of the preamp stage, particularly with a 12AU7, is likely very clean (notice I didn't say transparent)...

Exactly. It will be very clean since the circuit is so sparse and both the 12AX7 and the EL84 are integral to getting power AND/OR overdrive.

Originally Posted by krashjones

...You may be able to bias it a big hotter (cathode bias resistor) or find some way of cranking up the plate voltage (power transformer) and squeeze a couple of tenths of a watt more clean power out of it.

True. You could change the cathode biasing... but IDK how it would sound biasing it colder for more headroom and you'd loose some grit as well.

Since it uses solid state diodes for rectification, swapping a tube rectifier for SS to get higher voltages is not on the table.

Changing the R10 and/or R12 dropping resistors in the first two filtering stages would be the only way to get higher voltages to that EL84.

All of these changes I wouldn't bother with because...

Originally Posted by krashjones

If you want more clean VOLUME then the easiest, cheapest, and most effective way to do that is with a speaker. An Eminence Wizard is probably 10dB louder at a given power level vs. the speaker that came in it. Put that in an extension cab and it will have the same sound effect as tripling the power.

This is the best advice I would say. Using a more efficient speaker and/or lemmy99's second line containing these three pieces of advice:
"more clean head room is available by removing C3, and changing R6 & R7 to 100K, also adding NFB resistor from the top of R9 to the output jack (optional)."

Originally Posted by toadman

wow! thannks for the responses guys! i'm not very electrically inclined and i'm pretty sure if i started messing around with a soldering iron i'd blow something up! so i'll try a 12AT7 and see what happens. my buddy (who makes TubeGuru amps) might be able to help with more involved stuff. this is all sort of an experiment for me, and what better to experiment on than a cheap P.O.S. ! thanks again for your help.

Actually, the circuit is so small and sparse it would be the best way to learn about amps. Given lemmy99's post and my details on it, you already know half of what this amp's few components do!

There aint much to it... as usual use common sense and read up on amp safety first... but its extremely easy stuff.

Have fun modding or having your friend mod this cheap amp!

Here's a layout for the non-schematically inclined:

http://www.turretboards.com/valvejr_layout_stock_v2.pdf

[toadman]

Originally Posted by krashjones

hey man I just reread my post and your quote and I realize it came off as kind of inflammatory. That's not what I was getting at. Seems VJ's are about getting crunch tone at a lower volume (compared to a bigger amp), but not really so much about clean headroom.

Anyway, hard to beat the price of a Valve Junior. The cab & chassis alone would cost a home builder that much.

no inflamation on my end at all! thanks for all the advice! i knew you guys would be a fountain of info. and i certainly appreciate you guys helping me squeeze every drop out of this el~ cheapo amp!