Valve Junior mods

[miroslav]

Originally posted by Kin Corn Karn:

I just want to attenuate the Epi to see what it sounds like.

Turn it all the way up...to "11"...if you want to really see what it sounds like!

 

I have a THD HotPlate that I use with my 40W and 100W tube amps...but I can work with the Epi as-is...right up to "11", without any problems (I don't have to play real soft in my studio )...so IMOthere's no need to attenuate a 5W amp.

 

The whole point of the attenuator is to be able to push the amp into tube distortion...without the LOUD sound levels you can get from higher wattage amps.

But with the 5W Epi...as soon as you get the volume up near 2 o'clock and beyond...the tubes in that puppy are already crunching away...and IMO...it's really not that loud at those settings, and even full-tilt at 11...

...unless of course you got people in the next room trying to sleep or something.

 

I'll try my HotPlate on the Epi this weekend...but from the experience of using it on my louder amps...I have a feeling that as soon as I nock off a few dB with the HotPlate...it will suck the life out of the small, 5W Epi...whereas with the 40W and 100W amps...I got some room to work with.

 

But hey...try the light bulb thing...it may be OK...or it may be a waste of time???

[ChewingAluminumFoil]

The light bulb thing is more than an attenuator, it's probably Nature's Simplest Compressor.

 

By adding this one part you can get a gentle almost organic compression effect. Play softly, the lightbulb doesn't light, it's resistance stays very low, and there is no attenuation.

 

Play harder, the lightbulb lights, it's resistance increases dramatically and therefore so does attenuation. Voila, compression. The attack time of the compressor depends on how long it takes for the bulb's filament to "turn on."

 

A 4w bulb with a Valve Junior yields pretty heavy compression, a 7w sounds nominal, and higher wattages don't do much. With higher wattage amps, the bulb values need to scale accordingly, and with real amps in the 50w and up range you'll start needing to wire bulbs in parallel. Plus it looks kinda cool cuz it flashes while you play.

 

CAF

[Kin Corn Karn]

Would the light bulb mod work as an external box, inline between the amp and speaker?

[ChewingAluminumFoil]

Would the light bulb mod work as an external box, inline between the amp and speaker?

Yes. Not a problem. I built a light bulb box for my Fender Blues Juniors.

[Kin Corn Karn]

I didn't think it would be a problem. It's electrically the same, but I'm also new to amp mods/hacking and you never know. Thanks.

[Broddi]

Just wanted to add an FYI.

A reader at my Forum/Valve Junior mod page has discovered a new flaw. Once he did the mods and his headroom/volume increased he noticed a rattle. He tracked it down to an un-used mounting stud under the board between the tubes. (that spot where Epiphone has a piece of electrical tape). We agreed that over time that could cause a problem with the board. I'm going to dremel off the un-used mount.

CAF ignore that last personal message I didn't realize you already addressed Kin's light bulb concerns.

Cheers!

[miroslav]

Originally posted by ChewingAluminumFoil:

A 4w bulb with a Valve Junior yields pretty heavy compression, a 7w sounds nominal, and higher wattages don't do much. With higher wattage amps, the bulb values need to scale accordingly, and with real amps in the 50w and up range you'll start needing to wire bulbs in parallel. Plus it looks kinda cool cuz it flashes while you play.

While it may look quite cool (my THD HotPlate has a built-in blue bulb that glows and acts as a noise reduction circuit if I want to turn it on) it just seems like a lot of monkey-ing around with a bulb, just to get some very basic compression.

I mean...I got a rack full of compressors that I can dial in any way I like...and an outboard compressor box sure is a lot easier than having to wire in a bulb socket to the amp circuit, and where you have to play around with various bulbs to get the desired amount of compression!

 

But OK...It probably looks cool...

[Broddi]

Actualy I like the idea of a $1.00 light bulb for simple compression over a rack full of compressors.

But I am just a simple man.

The real up-side for me would be for recording I can get sweet tones at lower volumes, more tube saturation without my wife wanting to kill me. I used to record with a 100 watt Carvin 1/2 stack, then I switched over to a Peavey classic 50 watt 2x12 for my main amp, that was replaced with a 15 watt Traynor YC20WR, and now I find the (modded) Epi Valve Junior 5 watt does just fine for recording anything from sweet and clean to nitty gritty ZZ top ACDC and beyond, even holds up with live drums,bass, and vocals. My next tube amp will be less than 5 watts. Either Bum Box,or Fargen.

 

The older and wiser I get the lower my tube wattage needs.

[Ricochet]

A light bulb's a great attenuator and compressor. It's cheap, elegant, and an old idea. Some Hammond organs have a light bulb limiting the output of the reverb amp.

 

Where you can run into trouble is if the bulb burns out and there's no load on the amp's output. That can fry the output transformer.

 

Some amps are already protected by a resistor across the output. The Valve Junior's not. I'd recommend soldering a 5W power resistor of about 80-100 ohms across the terminals of the output jack. (Assuming you're using the original 4 ohm output.) That'll keep the tranny from turning into a spark coil if you play it without a load plugged in.

[miroslav]

Originally posted by Broddi:

Actualy I like the idea of a $1.00 light bulb for simple compression over a rack full of compressors.

Yes...it's a nice idea.

 

Thing is...you really don't have much control over the compression from a light bulb, other than by changing bulb wattage values...which is a bit crude, IMO

...and I just don't find that very precise...though I'm sure you can settle in on a particular sound that a particular bulb is giving you.

 

And...my rack of compressors is already there... so my point was that I just didn't see the need to mod the amp with a light bulb, instead of just using what I already had in the rack

all kinds of compressors, with all kinds of options...which is a bit more precise and flexible than the $1.00 light bulb.

 

Originally posted by Ricochet:

Some amps are already protected by a resistor across the output. The Valve Junior's not. I'd recommend soldering a 5W power resistor of about 80-100 ohms across the terminals of the output jack. (Assuming you're using the original 4 ohm output.) That'll keep the tranny from turning into a spark coil if you play it without a load plugged in.

Just for my own confirmation...if the volume on the amp is turned all the way down...no signal in the circuit...but the amp is still powered and you pull the speaker load...

...there should not be a problem with the tranny...right?

 

Reason I ask...is that the Epi head-only version has three impedance options/jacks on the back (4, 8, & 16 Ohms).

For trying out different cabs...I would hate to have to keep turning the amp on/off...which mimght have it's own bad effect on the components.

 

Anyway...I guess for a $100 amp...doing all kinds of fun mods to it isn't going to be a major risk.

But the Epi 5W head sounds so sweet as-is when played 3/4-to-Full...that apart from a Standby switch...I don't see any reason to mess with it all that much.

 

Oh Broddi...I still didn't get a chance to open the head to confirm if the wiring is the same as the combo version...but I'll do that this weekend, and get back to you...'cuz I will most certainly do your Standby switch mod, as that's about the only thing I see as lacking in the little puppy!

[ChewingAluminumFoil]

Thing is, it's often where you insert an effect that makes all the difference. If racks of stuff were all anyone needed, why mess with tube amps? Lots of racks promise tube sounds.

 

Try the light bulb... it's an interesting type of compression that puts very little between your guitar and the speaker. And the insertion point is really different, between transformer and speaker. The systemic behavior is completely different than a front end compressor-- I've designed those and I know how those work. Ricochet... you seem really knowledgable about all this stuff... you try to explain it.

 

Hifi nuts obsess about how few components or stages there are in the signal chain. I kinda feel the same way about my guitar signal chain.

 

When playing thru effects, always A/B with a guitar plugged straight in. There have been many times where I've messed with an effects patch, then plugged the guitar straight into the amp, and realized how the effected sound was kinda cool but the *punch* of pickup->tubes->speaker was gone.

 

Now it's all very subjective but in the end you can theorize and hypothesize, and still the only real test is listening. My two cents.

 

CAF

[Ricochet]

Originally posted by miroslav:

Just for my own confirmation...if the volume on the amp is turned all the way down...no signal in the circuit...but the amp is still powered and you pull the speaker load...

...there should not be a problem with the tranny...right?

 

Reason I ask...is that the Epi head-only version has three impedance options/jacks on the back (4, 8, & 16 Ohms).

For trying out different cabs...I would hate to have to keep turning the amp on/off...which mimght have it's own bad effect on the components.

If the volume's all the way off, you should be OK, but it's safer to turn it off. If there's any way a pop or crackle could occur in the output of the amp while there's no load on it, that can generate high voltage spikes in the transformer coils.

 

It's nice having a rack of compressors, and you do have lots of control over that, but the light bulb is going to be a bit different. It's a variable resistor with the resistance at full brightness about 10x the resistance of a cold, dark filament. And there's some warmup and cooldown time involved, so it doesn't respond instantly. Just another thing you can experiment with.

 

We've been discussing the effect of a light bulb in series with the output. Another way a bulb can be used is as a current shunt in parallel with the speaker. That lowers the total output impedance. (A series one increases it.) And a shunt bulb acts as a volume expander, because as the signal gets stronger, the higher signal voltage shunts more current through the bulb, the filament gets hotter, its resistance goes up, and that diverts more signal back to the speaker. It shunts more of the current at very low volume levels, so quiet playing gets much quieter and loud playing isn't affected as much.

 

You can work out different combinations of series and parallel bulbs to tailor the amount of attenuation, impedance, and compression/expansion.

[miroslav]

Originally posted by ChewingAluminumFoil:

If racks of stuff were all anyone needed, why mess with tube amps? Lots of racks promise tube sounds.

I'm really not sure what you mean by this...?

 

I don't use my rack gear to try and fake a tube sound.

And I rarely EVER have ANYTHING between my guitar and tube amp.

I don't use stomp boxes and all those floor FX gizmos...though I just picked up a 535Q Crybaby (haven't used a wah in over 20 years!)...and about a year or so ago I bought a MXR DynaComp, which I've only used once on one song I recorded.

I just don't care much for what the MXR DynaComp does to most guitar spounds. But on a very clean amp settingit can be used to a degree to extended the sustain a bit.though it does mess with the tone and it adds a lot of noise to the signalwhich only makes it useable in full mixes.

 

When I say I have racks full of comps and other gear...all of that stuff gets used in the signal chain of the microphone that I stick in front of the guitar amp/cabinet...

...and/or during mixdown.

Not in my guitar/amp signal chain.

So I see no need to stick a light bulb in my amp's circuitas I truly prefer the most simplest signal path...guitar-amp-cabinet.

 

My tube amp sounds come from the tube amps...and not from any of the rack gear.

The rack gear is just used to shape the post-amp/cab sound to make it fit properly into the whole mix.

 

Now...for you live-stage guys...well, you have a whole different agenda/process...so maybe we're talking about two different things here.

[miroslav]

Originally posted by Ricochet:

If the volume's all the way off, you should be OK, but it's safer to turn it off. If there's any way a pop or crackle could occur in the output of the amp while there's no load on it, that can generate high voltage spikes in the transformer coils.

Thanks for the confirmation.

 

I don't really pull the load often when an amp's on...but there are rare occasions when I may want to swap a cabinet "on-the fly" during a recording session...and once the amp's been powered up and running for a couple of hours...I really hate turning it off.

So, I'll just hit the Standby, and also turn down all the volumes to "0"...and then make the cabinet switch.

 

That's why I want to at least do the one mod to the Epi head I just got...and add a Standby switch.

[miroslav]

Broddi, I sent you a PM, but just in case you miss it, here is that info on the Epi head about adding the Standby switch:

 

*********************************************

 

I opened up my EPi head...and looking at your pictures of the Epi Combo PCB and my Epi Head PCB...there are obvious differences...but, it looks to me like the tranny and it's taps/wiring is exactly the same.

I don't have a digital camera handy...

...so here's the layout:

 

The Tranny is a TC00273:

YW PT-779-G-100/115/230/240V

 

BLK - 0 ------> Power Switch

WHT - 100V ---> T12

YEL - 115V ---> Power Switch

BLU - 230V ---> T10

BRN - 240V ---> T11

 

...........

 

12V - BLU ----> N/A

0 - BLK ------> N/A

12V - BLU ----> N/A

6.3V - ORG ---> T5

0 - ORG ------> T6

260V - RED ---> T2

0 - RED ------> T1

 

Looking at that...

Your suggestion to put the Standby switch between the T2(260V) RED wire and the T2 terminal appears it would also work on the Epi head, even though the PCB is a bit different from the Epi combo.

 

Do you concur?

 

Thanks!

[Kin Corn Karn]

Follow-up here...

 

I was experimenting with tubes this morning and tried a JJ ECC81 (12AT7) that I had sitting around... it smoothed the tone out and cut the volume down quite a bit, at the expense of some grit from the power amp stage. I'm undecided about keeping it, as I like the wild distortion I get with the stock tubes and the amp cranked, but it's another option for those of us that don't like playing loud all the time

[Broddi]

Miroslav,

I'll check it tonight (Sat) or tomorrow before band practice. I bet it's the same in regards to the standby switch but better safe than POOF!

 

Kin Corn Karn,

I tried a few low gain tube's as well GT12aT7, GT12AU7 as well as the JJ ECC81. I agree about the lower volume / cleaner tone. I have a large and growing collection of various 12ax7 types both old and new. This amp really reacts differenly depending on what I've got in there. Same goes for the EL84. Everything I have tried so far sounds good but they all have their own flavor. Truthfully even the stock Sovteks sounded pretty good.

The best tube combination I have tried so far is a Mullard el84 (1960's) and a telefunken longplate 1960's. I always go back to new production tubes after taste testing though to save the old stuff for special occaisions or recording. As far as new production tubes for this amp I ended up with a GT12ax7M and a #43 JJEL84. I have some Yugoslavian made GTEL84Y's coming in soon that are graded 1-3 for early break-up. Im going to try the EL84Y graded for early break up and see if I can still get the crunchy tube overdrive with the low gain 12A?7 types.

Here is a 12ax7 roundup I did a while back. I think I should do a new one now because I have more brands / types to compare. Probably even time for an EL84 roundup also.

[jfbaxter]

Hey guys - first time posting here...

 

Just picked up a lightly used valve jr. modded based on the valvejunior.com web page. The hum is non-existent! But I've noticed a "vibration or rattle" when I strike certain bassy notes. Is this the speaker? Has anyone else noticed this?

[Broddi]

Check the first post on this page. It could be the un-used mounting stud under the board between the two tubes. I just removed mine after I noticed the same buzzy rattle after doing all the mods. I did not hear the rattle before doing the mods, I'm betting that after the mods the amp is louder /has more headroom and then the rattle is more likely to occur.

[Broddi]

Miroslav,

Same exact tranny as the regular Valve Junior combo.

Same part # ,same color codes and voltages.

Looks like it's a go.

[miroslav]

 

Thanks

[miroslav]

OK...STANDBY switch is installed!

 

Not difficult at all.

The only "glitch" was in trying to find a toggle switch that was rated for over 250V.

Radio Shack had none...all were 250V...but I managed to find one at the local hardware store that was meant for electric motors...and it was rated at 277V, which is enough to cover the 260V tap out of the tranny.

 

It's a nice sized toggle, not a mini....but being that the amp face is kinda' recessed...the slightly larger toggle worked quite well.

I put it just to the right of the Power Switch...and it came out real nice.

Works like a charm!

 

Thanks Broddi, for the info!

[Broddi]

Sweet!

Yes I was wondering about the amp/voltage rating. I figured if the switch I used was rated 10amp at 125 volts and 6amp at 250 volts. (and here is where assumptions kick in) If the switch only had to handle 3 to 3.5 amps it should be ok up to 500 volts, and 260 volts is only 4% out of the 250 volt spec IF it had to carry a full 6 amps. I did not amp clamp it so I'm gald you mention this. I think I will amp clamp it and make sure I'm not going to burn it up. Any bets on how many amps the switch has to carry?

[Basshappi]

Can I use the Triggerman 4x12 cab with the Valve Junior head?

[miroslav]

Originally posted by Broddi:

Any bets on how many amps the switch has to carry?

.....?

 

The toggle switch I got is rated at 10A/277V and 20A/125V...so I think I'm safe with that.

[LPCustom]

Originally posted by basshappi:

Can I use the Triggerman 4x12 cab with the Valve Junior head?

You can use any cab that is rated for 4, 8 or 16 ohms. Just plug yer cable into the right impedance setting jack and you're set.

[Basshappi]

Cool, Thanks LP

 

I thought so but I had read elsewhere that using a low wattage amp into higher wattage speakers could cause problems. I didn't understand the reasoning so thought I would check.

 

I noticed that the Triggerman 4x12 cab is $229 w/ free shipping, thats cheaper than most 2x12 cabs I'm pricing. I really wish they would offer a 2x12 model. But I like how the styling would match the head (I'm kind silly that way ).

 

Cheers!

[LPCustom]

Originally posted by basshappi:

Cool, Thanks LP

 

I thought so but I had read elsewhere that using a low wattage amp into higher wattage speakers could cause problems. I didn't understand the reasoning so thought I would check.

 

I noticed that the Triggerman 4x12 cab is $229 w/ free shipping, thats cheaper than most 2x12 cabs I'm pricing. I really wish they would offer a 2x12 model. But I like how the styling would match the head (I'm kind silly that way ).

 

Cheers!

I think you'll find that that's backwards. You don't want to run a high powered amp into low wattage rated speakers. You'll melt the voice coils.

 

If you hook low efficiency speakers to a low powered amp it won't get very loud, but it won't hurt it as long as the impedances match.

[Basshappi]

Yep, that's what I figured. In the bass world this is a big issue. But I've never had a low wattage tube amp and wanted to make sure there wasn't some bizarre attribute I didn't know about.(it sounded like BS to me to begin with ).

 

Thanks again LP. If all goes as planned I'll be ordering that VJ head this weekend and the cab soon afterwards. Can't wait to start pissing off my PITA neighbors!

[Ricochet]

Yesterday I finally installed a bridge rectifier and 1000 uF filter capacitor on my Valve Junior combo. The results are interesting. It got rid of the constant 60 Hz hum in my speaker, that didn't respond to the volume control. Now there's a faint 60 Hz hum in the speaker, responsive to the volume knob and noticeable only when the volume's cranked pretty high. But rectifying the current produces short, intense pulses of current through the transformer coils, instead of a smooth sine wave, and that increased the electromechanical hum from magnetoconstriction of the transformer core laminations. So now I've got a 120 Hz buzz instead of a 60 Hz hum. May be a little quieter, but not much. I could probably reduce it further by mounting the transformer with rubber between it and the chassis (which acts like a guitar's top, "amplifying" the transformer hum.) But I've done all I really want to so far as modding this little amp. I'm usually playing through it with P90s, and they pick up plenty of hum anyway! I love the sound of the little amp. Last night I was really wailing on it turned up so it was nice and crunchy, playing through my bridge pickup, till my wife came home and asked me to "turn it down, just a little."

 

I really didn't want to fool with drilling on the chassis, so I just stuck the bridge rectifier to the inside of the chassis with Superglue. I don't plan on removing it. It won't get hot enough to break the glue down, and in the position it's mounted the rectifier's sitting on the metal chassis, anyway. The chassis is the heat sink for it, not that 2A of curent through a 35A bridge rectifier's going to heat it up much.