Epiphone Valve Junior project

[YD]

Awesome!

This will be next weekend's project.

I couldn't resist ordering another combo and a head today.

right on!  Let us know how it sounds.  I bought one of these with the intention of gutting and haven't figured out what to do with it yet.

[PRR]

I was wondering how many messages it took before this board opened a second page...

> The iron will have to be different from the epiphone correct?

No.....

>> how the stock PT will work...it doesn't have a rectifier tap.
> I would just stick with the Solid State rectifier myself.

Agree. An ideal single-ended audio amp sucks a constant current, so there isn't any rectifier sag. A real amp's current varies some, especially in overdrive, but you'd have to smack the stuffing out of the amp to get enoug sag (or rise) to measure. The old amps used bottle rectifiers because they had no choice. You have a choice. Leave the bottles for collectors.

So no 5V winding needed.

Sticking with 1N4007 sand diodes: all the iron works. You have not changed anything that matters.

You might eventually want to try a bigger OPT than what comes in a $99 box; it's probably "junk". But all the old one-power-tube amps were "cheap junk", and sometimes junk is really treasure. Get one of the monster MagnaQuest OPTs and it might just be boring.

[PRR]

> Gibson GA-5 reissue doesn't show NFB loop, old GA-5 does.

That will make a big difference. You will have to re-voice the amp when you add/remove negative feedbag. There is a "sound" in a naked pentode. There is also a sound in a low-feedback amp like the Bassman, and another sound in a high-feedback amp like Sunn or Ampeg V-40. All have been well-loved, but the tone-stack and speakers have to be selected for the basic amp-color.
 
> Gibson used twice the resistance on the NFB resistor, 47K as opposed to Fender 5f1 using 22K.

To compare dem apple to apples, the output tube and load impedance needs to be the same. If one tapped the 4 ohm output and the other the 16 ohm output, a 22K:44K change of NFB resistor would give the same result.

But in DIY-life, you can fiddle that NFB resistor and see what soundz you get. Values of 10K and 5K will give a tight clean hi-fi sound. 22K, 47K, 100K loosens the NFB, lets the cone shake more, lets more distortion out. Break the NFB resistor for naked-pentode sound.

Decreasing the NFB resistor reduces gain. Don't let that fool your ear: crank the volume when you decrease the NFB resistor.

[PRR]

Oh, the choke is charming, but in this high voltage low current amplifier, I bet a 5K or 10K resistor would work as well, with less weight. The screen and preamp current is quite small. The plate current is small so we don't need a high screen voltage. If the screen voltage is low, we don't need heroic voltage on the driver. 250V-300V at the screen should be plenty. Since we start with 360V, we can afford a lot of resistor drop.

> I didn't notice any noise reduction but I am probably hearing heater hum.

That seems to be the #1 fault of this amp. Really stupid heater routing.

I'm surprised that a one-cap DC supply cleans it up. Instead of 6V 60Hz, we have 1V of 120Hz, 240Hz, etc: less voltage but at higher more-annoying frequencies. I once posted a plan for a recording amp, and builders had bad buzz until I added a second R-C filter to smooth the ripply "DC".

Getting the heater voltage OFF of the PCB, and routing the long way around, ought to get the hum/buzz very low. That's the way most studio and hi-fi gear was run: AC heat, just very carefully routed. If done right, it can be next best thing to perfect. I don't say it WILL work for you: there is an art and a knack to routing heater lines, and it is hard to describe. I think DC heat is an expensive cheat, but today the expense is low and results are usually excellent.

If you want a very hasty check of your hum: disconnect one heater line, and use clip-leads to connect a big 6V lantern battery. It'll run a half-hour or more. Since you have to have the chassis open for this hack (Don't get electrocuted!), you'll catch some room-hum, but you won't have heater hum.

[TubeGeek]

I have put together a website.  This is my first attempt at a website. ;D

www.GlacierAmps.com

[radar01]

TG:  Very Nice!


Alan

[tbeck]

nice visual documentation of the mods!

[66merc]

Hey,

I just bought a head version of this amp for $99.  Haven't had much time to test it but it is darn quiet.  More info when I test it more.

66merc

[Geezer]

I just bought a head version of this amp for $99.  Haven't had much time to test it but it is darn quiet.

I think the head version has DC heaters (?)

EDIT:
Yep, here's a quote from MF>>>

This head version of the Valve Junior Tube amps includes features not found in its combo cousin. These include [highlight]DC filaments[/highlight] for both the preamp and power sections, reducing unwanted filament hum. [highlight]It also has 4, 8, and 16 ohm speaker outputs[/highlight] so you can drive any kind of extension speaker, from a single 8" box to a 4x12" cab.

Like the combo version, the Valve Junior Head delivers great tube tone with 5W of Class A power.



Epiphone Valve Junior Tube Amplifier Head Features:

5W
Single-ended Class A electronics
[highlight]DC filaments[/highlight] for both preamp and power tubes for reduced filament hum
[highlight]4, 8, 16 ohm outputs[/highlight] for speaker flexibility

[Geezer]

Well, I just ordered one (a head unit) from MF & it's on the way! I got a "returned" unit for $85! Added a few other items I needed to bring the total up over $99 & got free shipping!
WooHoo....can't wait!   :D
Cheap thrill....  ;)   Jeff

[radar01]

ANybody know yet what kind of transformers epi used?  When I get mine I am going to make a schedule 40, maybe even an additional socket for 6V6.  Less the tube rectifier of course.  What kind of OT would ya'll suggest using if the one in it isn't sufficient?  Like one from a 5F2 build maybe?

Additionally - I have allot of these little turret boards from other projects.  Think a layout like this will work?  See photo.

Alan

[PRR]

> Anybody know yet what kind of transformers epi used?

Cheap! The iron alone "should" sell for $50-$100; Jeff bought the whole box and bottles for $85. The factory cost of the OPT is probably under $5.

BUT cheap iron is an old tradition, and often has interesting sound. I don't see why you would replace it before you wring it out and see what it does.

> maybe even an additional socket for 6V6.

Interesting. It has lower heater demand than EL84, similar plate ratings. But you will need a different cathode resistor, roughly twice the value. Simple: jumper both sockets pin for pin, except give each socket its own cathode resistor and cap.

Gain will be a bit lower, but nobody says this beast is low gain, and there's a little more gain available by hacking around the volume pot.

> these little turret boards

Then do the whole thing properly. Trash the silly PCB, wire-up a 12AX7 Champ turret board, except use EL84 cathode resistor if you stick with the mini-tube.

Something to check... OK. The left-right order of the Jr is similar to an early Champ. If it were laid out right-left, you'd mirror-image the tagboard layout. But the Epi is laid out in Champ order, just rotated the tubes to the big side of the chassis (and omitted the rectyfier).

Hmmmm... the EL84 will "work" with a 6V6's cathode resistor. Power output will be lower, but you didn't buy a 5-Watt to rock the stadium, and "only" ~3 Watts might still be plenty.

[TubeGeek]

PRR...
 
Is there a way to get the output to 1 or 2 watts? If so how?

[Geezer]

OK....rec'd my "Blem/Return" VJ Head today from MF & opened it up to see what kind of mess I bought....It came in an un-opened, factory sealed box. I looked it over from top to bottom/inside & out....I can't find a "Blem" anywhere on it. It's perfect!
They have "improved" the filaments w/ a DC supply (a large bridge recto unit w/ a 4700uf cap beside) & reports I'm hearing are that it's way quieter than B4, so hopefully that's one less mod I'll need to do.
It also has the 4/8/16 ohm speaker jacks, so I can run it thru any/every cab I have!
The iron is larger than I expected...even "beefy" looking.

BTW, this cab is very nice...very retro looking in burgundy & black. It's even shielded inside over the chassis. Reminds me of what a "mini Matchless" would look like.

What a deal for $85!!! (I even got free shipping by ordering another item I needed to make it over $99)
I can't wait to get it home to try'r out!

Jeff

[tbeck]

Tube Geek, if you raise the value of the EL84's cathode resistor, it will limit the cathode current and plate current more and lower the output power.  Watch the cathode to ground voltage when you do that, the max cathode to heater voltage is 100 volts, so I wouldn't go above about 75 volts on the cathode, just to be safe, you'll probably need to change the voltage rating on the cathode bypass cap to handle the increase.
 It will probably go into distortion sooner with the same drive signal from the preamp.

[PRR]

> raise the value of the EL84's cathode resistor....  It will probably go into distortion sooner with the same drive signal from the preamp.

But as you say, the cathode voltage will be higher, so shouldn't it need more signal to overload?

It is certainly worth a try. Whatever the math says, the sound might be useful.

BTW, you probably won't be able to get the cathode much higher than 20V and have anything like a "power" amplifier. To predict this, divide the working screen voltage by the Mu of the screen. Assuming 350V and Mu(g2) of EL84 is 18, that's 19V. The Mu is not perfectly constant, but by the time current is so low that Mu falls off, it is too low to drive a speaker even at table-radio volume.

Also you are increasing plate resistance. Output impedance of a guitar amp is important. The EL84 is a fairly soft pentode (by 6L6 standards) and damps the speaker a little. Shoving it toward cutoff will give less damping. Damping is darn low to begin with, so less damping may be all the same. Try it and see.

One trick for lower power without great change in operational balance is to just reduce the supply voltage. A 120VAC winding, substituted for the ~250V winding, would give around +160V B+ and around 1 Watt. You could add a 120VAC:120VAC transformer, if you can find one. You could do the old dirty-trick: use a 120VAC:6VAC transformer backward on the Jr's 6V heater winding to give 120V (more like 110V) AC to feed the rectifier.

And there is the brute-force approach: big hot resistor to throw-off half the power before it gets to the tube. This can also give improved B+ filtering, and can be bypassed with a switch for when you play the big room.

[TubeGeek]

Thanks I will give it a try.

[bradleyt]

Let me see if I understand this correctly.  I am refering to the schematic snippet above.

To decrease the output wattage of the amp you can increase R14 to say 440 ohms but in doing so you would want to increase the voltage rating of C5 to say 100VDC?  That's interesting.  

I've been playing around with a master volume mod to try and get some distortion at lower volumes.  It's not overly distorted, kind of crunchy, but still needs work.  Just wondering what the best way to attack this might be.

Thanks for sharing the knowledge!

[PRR]

> increase R14 to say 440 ohms but in doing so you would want to increase the voltage rating of C5 to say 100VDC?

No. When you try to reduce a tube's current by increasing the cathode resistor, it fights you. You have to make a BIG change of resistor to get much change of current.

Here's a dog-ear from the EL84's transfer curve. I plotted cathode resistors of 220, 680, 2K, and 20K.


The corresponding operating points look like(*):
220 = 38mA, 8.5V
680 = 16mA, 12V
2K = 6mA, 13V
20K = 1mA, 17V

Note that a 3:1 change of R, 220 to 680, is just over a 2:1 change of current. A 100:1 change from 220 to 20,000 is just a 40:1 change of current.

Voltage does not rise to infinity. Basically because current is going down. Not as fast as resistance goes up, but the voltage tends toward Vg2/Mu, or for this amp roughly 300V/18= 17V. It will get a little higher if the cathode resistor is even larger than a few K ohms... but at just 20K we are passing less current than many preamp tubes! Shame to waste the big 12-watt EL84 for a teeny job.

680 and 2K (or anywhere between) might be interesting operating points. Power will be much smaller. The 20K plot is just to show where we are going: 15-25V max, not to voltage high enough to threaten the heater insulation.

(*) I don't say these are the exact values you will see. The data is not for the same supply voltage as the Jr. I've neglected the screen dropping resistor. Individual tubes vary +/-10%, even +/-40%, from the nominal parameters in the datasheet. But the trend will be like this.

[PRR]

Second thoughts.

> big hot resistor

Splicing a big resistor between the Jr's rectifier and first cap, both of which are on the PCB, is awkward.

Putting a resistor between the transformer and rectifier is easier. And ya know, I think I like it better.

There isn't a lot of call for large-K 10 Watt resistors (all they are good for is wasting power). But at the bottom of the page you can find 5K 5W, and four of those makes a dandy 3-position power selector. Roughly 5W, 2W, 1W... never mind the numbers, a good selection of lesser "full power" settings.

The switch has to be sturdy. Not a lot of current, but over 300 volts, with some inductance in the break. Big toggles or similar.

Normal toggles are 2-way, but an on-off-on ("center off") switch is a common part. Heck, you may have ripped a death-switch out of an old amp; that will work. It is widely available new too. With the on-off-on switch, one way is 5W, the other way is 2W, and in the center is 1W.

If you prefer a rotary for a more logical progression than "up, down, center", the generic $2 rotary may not stand the strain. Our host has a sturdy 3-way: maybe "too good", but it is a lifetime investment you can use in other amps when you tire of the Junior.

These 5-watt resistors will run HOT. Use good terminal strips, put them somewhere the heat can escape.

These resistors have deadly voltages on them, so must not be mounted outside a finger-proof enclosure. If they make too much heat under the chassis, you may have to fabricate a perf-metal doghouse.

[tbeck]

Very interesting! My assumption about the cathode resistor change doesn't work quite the way I thought, but might be effective for a small change, obviously the bypass cap would not need to be more than 50 volt rated, I tend to like to go oversize voltage a bit for a safety margin, it doesn't cost much more.
  I like the resistors in the power supply idea, that should work for other SE amps also, would the resistors  need to be rated at 10 watts for a SE 6L6 amp?  I've been working on a SE 6l6 amp using iron from an old PA amp ( I still need to order the power supply caps, I could get the switch at the same time)

Has anyone put a tone control in one of these Valve Juniors yet?
Is the chassis deep enough for terminal strips?

[Geezer]

Has anyone put a tone control in one of these Valve Juniors yet?
Not yet, but I soon will be trying some sort of tone stack

Is the chassis deep enough for terminal strips?
The chassis is pretty deep...looks to me like it could handle T-strips just fine (it's @ home now so I can't measure) IOW, it's not a shallow SS type chassis.

After firing the amp up last nite, I'm not too impressed w/ the tone. Pretty dark & lifeless w/ the strat until it's almost maxed, then it gets pretty "farty". Also, it's just not very punchy or loud at all.....just not my cup-o-tea, I guess.
So, looks like this one's going "under the knife".
 
First, I'll try some of the mods mentioned here & at some of the other forums. If that doesn't do the trick, then I think a mini "Train Wreck" w/ EL84's in P/P will fit nicely in this chassis. I've got a tranny set here that will work fine for that.
I guess $85 for a nice head cab & chassis isn't too bad! Plus, I'll have the the Tx set for a future project, or I can sell them on Ebay for a few bucks (or to someone here).

Woo-Hoo! Another amp to build!!

Jeff

[YD]

Second thoughts.

> big hot resistor

Splicing a big resistor between the Jr's rectifier and first cap, both of which are on the PCB, is awkward.

Putting a resistor between the transformer and rectifier is easier. And ya know, I think I like it better.

There isn't a lot of call for large-K 10 Watt resistors (all they are good for is wasting power). But at the bottom of the page you can find 5K 5W, and four of those makes a dandy 3-position power selector. Roughly 5W, 2W, 1W... never mind the numbers, a good selection of lesser "full power" settings.

The switch has to be sturdy. Not a lot of current, but over 300 volts, with some inductance in the break. Big toggles or similar.

Normal toggles are 2-way, but an on-off-on ("center off") switch is a common part. Heck, you may have ripped a death-switch out of an old amp; that will work. It is widely available new too. With the on-off-on switch, one way is 5W, the other way is 2W, and in the center is 1W.

If you prefer a rotary for a more logical progression than "up, down, center", the generic $2 rotary may not stand the strain. Our host has a sturdy 3-way: maybe "too good", but it is a lifetime investment you can use in other amps when you tire of the Junior.

These 5-watt resistors will run HOT. Use good terminal strips, put them somewhere the heat can escape.

These resistors have deadly voltages on them, so must not be mounted outside a finger-proof enclosure. If they make too much heat under the chassis, you may have to fabricate a perf-metal doghouse.

RIGHT ON!  Hopefully I'll have time to try that soon

[Geezer]

tbeck,

The chassis measures 7" front to back, 12.5" wide, & 2.75" deep.....very roomy.

Jeff

[tbeck]

Thanks, Geezer,  that's plenty big enough for a number of project ideas.  If a person was to gut that thing, a new faceplate might be in order, especially with more controls being used.
2 EL84s in push-pull would save some space on top, as compared to 2 octal sockets.

[Geezer]

Alright, I'm done with this one..... :(  It stays thin & lifeless no matter what I do.
I tried every mod possible, every tube in my collection....nothing can make me happy with this amp. SE is just not for me!

I'm still glad I got it, as the cab & chassis alone were worth it. I'm going to take some time to study the best locations for controls on the chassis & make a final decision on which circuit to build (some variety of 2xEL84 P/P).....I'm open to suggestions!  ;)

Jeff

[bradleyt]

Thanks for the explanation PRR, some of what you said made sense.   :o  It looks like I would have had to triple the value of R14 in order to obtain the effect I was looking for.   I need to hit the books a little more to figure out the rest of what you explained.  

My whole reasoning to decreasing the output level was to get a natural overdriven tone without rattling the windows.  It would be a shame to do that to an amp, even a 5 watter.  I am achieving good results with the mv control I put in so I will experiment with that some more.

Say Tubegeek, in reply #38 you installed a 470 ohm 5W resistor between the rectifiers and C6/R12.  What did that drop the voltage down to?  I'm looking to do that too but I don't have any spare power resistors laying around to try.  Looks like another mail order.

If your looking to add some quick distortion, I did this over the weekend.  While experimenting with a pot and different values for R6 and R7 to get more gain I ended up removing them and putting in two reversed 1N4007 diodes with a 330pf cap across them in place or R7; the simple circuit used in distortion pedals.  A SPST switch enables it.  I later switched the diodes to 1N4148 for a brighter distortion.  It does pull the output volume down some but that was expected.  

[TubeGeek]

bradleyt...sounds interesting...do you have a pic of your mods? They are worth a thousand words to me. I'd like to try the diode clipping in my amp. I am also interested in your MV addition.

The 470 ohm 5 watt resistor is something I have plenty of in the shop so I used that value.  I was going to order 1k values but decided to use what I had on hand.  I went off of PRR's suggestions in his post:

 "Let's see. If an EL84 isn't red-plating at 350V, it must be running 35mA max. The entire output stage works like 350V/35mA= a 10K resistor. If we insert a 100 ohm resistor, 10K/100= 100:1, B+ drops about 1%, power drops 2%. A C-R-C filter with 100 ohms in the middle will do a lot for buzz, not much for excess volume. A 1K resistor will drop about 10% in voltage, about 20% in power, still not much less loud. You might be going to 5K or 10K to seriously reduce volume. At that point you may want to separate the power stage B+ and the preamp B+, so you can drop the power stage to maybe 150V yet keep 300V on the preamp. "

Since I used 470 5 Watt I 'd figure I have around 5% less voltage and 10% loss in volume.  I cannot really tell there is a volume loss.  I will measure the actual voltage later today...the amp is being used for a recording session today. I'll have it back late this afternoon.

[kriswel]

This thread has inspired me to buy one of those heads.  It's crazy that you can build the ga-5 into this head because an RI ga-5 sells for $599 ($719 list).  

http://www.musiciansfriend.com/product/Guitar/Amps?sku=481209

The tranys might not be as good but I bet you could get pretty damed close to the same sound out of the Epi. jr. and wire it PTP t'boot.

I am going to gut this thing right away and get to work on it with a few terminal strips.  I think I will stick with the 1 knob ga-5 circuit.  I am going to leave it in my friends recourding studio, who has been passing enough work over to me that I could quit my day job.  Though I might go crazy hovering over an iron all day.  It sure is a fun hobby.

kris

kris

[bigsbybender]

BOTH Guitar Centers in Minneapolis were clean out of them when I went to pick one up this past weekend  :'(  Looks like everyone's out. There is a similar thread on the sterilized 18w site that seems to have upped the demand for this unit too.
TubeGeek you opened a huge can of worms.............


J.

[Bassmanster]

I emailed my buddy this thread and he bought one.

I wouldn't mind hearing some clips of your modded one, TG!

[bradleyt]

Sorry no pictures of the work, I don't own a camera.  The diode mod was simple since I used the pads where R7 goes.  It should be easy enough to piggyback the 2 diodes and cap off of the ground end of the resistor and a switch to the signal end.  I didn't experiment with LEDs but if I get some time I might.  

If it’s a whole distortion circuit you want to add then check out this site under the electronics section.
http://www.guitarheads.net/index.html  It's a tube screamer circuit mounted to a pot.  Pretty cool huh?

I read PRRs post about dropping the voltage and wanted to apply that in my unit.  I tried to do the math but my results varied.  I just need to order some parts and try it.  Makes me wonder if the over voltage problem was fixed in the head version along with the heater noise problem.  


As far as the mv control, I originally posted that at  http://www.klugemusic.com/phpBB2/viewtopic.php?t=78    Broddi has done a lot with this amp and that helped fuel my interest in it.   ;)

I used a 1M linear pot and some two conductor shielded cable. With the pot shaft facing me and the pins at the bottom, I number them (left to right) 1 2 3. The braided shield was connected to pin 1.
Drill a small hole in the pcb by R5/R15 (mounted on the underside)
Disconnect R5 and R15
Feed the cable through the hole and make all connections on the bottom side
Connect pin 1 to the ground end of R5 (the shield)
Connect pin 3 to the other end of R5
Connect pin 2 (the wiper) to R15

The pot isn't mounted but I left enough slack in the cable so it can dangle out the front with the chassis screwed in place.

Give it a shot.  I'd like to know how it works for others.  I borrowed the idea from the P1 and other mv amps.  Hope it is electrically sound.

Brad

Long post... sorry.

[TubeGeek]

I just finished jammin out with the head and it does sound pretty darn good for $99.  I connected up my modified ts9 tube screamer to the valve jr and cranked up some eric clapton blues albums on my studio monitring system and jammed out for a good 45 minutes while experimenting with settings.  I know that the stock circuit sound is lacking in high end and a little around the bottom end but what do you expect for $99.  I sure don't expect too much.  But I like this little amp because of the modding possibilities it presents. Heck I was using my 2-12" weber texas alnico speaker cabinet I had built for my twin reverb clone and it isn't so bad.  I could put it to use in the studio for a gig or two, just for fun!

If I opened up a can of worms on this project here on this forum I am glad.  There were others before me that really started it all.  I used their info and experience to work on my amps.  Now it's up to the rest of us to see what we can come up with. :)

I had an idea that these amps would be difficult to come by soon and that is why I bought mine up asap. In fact in about 3-4 weeks I have to relocate across the country for 4 months and then relocate back across the country again...temporary work assignment with my new employer. Ugh This means that I may not have time to work on projects for that time :'( Who knows maybe I could use a break and come back at it in October with a fresh approach.

[TubeGeek]

Bassmanster...you can hear a recording clip of my modified valve jr combo on my website.  See above posts for address and link.

You have to have quicktime installed on your computer....i use macintosh.

[TubeGeek]

If it’s a whole distortion circuit you want to add then check out this site under the electronics section.
http://www.guitarheads.net/index.html  It's a tube screamer circuit mounted to a pot.  Pretty cool huh?

That does look interesting and that is the type of distortion I am looking for.  I think I may try one out in my valve jr's...maybe the head.  Thanks for the link.

I will study your MV mod and maybe give it a try if I can get motivated.  I have been lazy today and just chilled out. 8-)

[mikep]

Hey TubeGeek,
  Mercury Magnetics has a mod for sale $$$$. Kind of expensive but interesting. It's about 2 bills for a tranny set w/choke. Check it out-- http://www.mercurymagnetics.com/pages/specials/ValveJrPjt/EVJ-01.htm

[kriswel]

Gee I wonder why they wouldn't just make it the same as the ga-5 to start with?  And why make an amp that hums so bad?  

http://www.musiciansfriend.com/product/Guitar/Amps?sku=481209

I've heard of this trick before.

kris

[Zaphod]

Alright, I'm done with this one..... :(  It stays thin & lifeless no matter what I do.
I tried every mod possible, every tube in my collection....nothing can make me happy with this amp.

In all these mods, did you reduce the values of the preamp cathode resistors, and also the cathode bypass caps? Also, did you short out the series 1M resistor between the two preamp stages? What exactly are you looking for in this amp, tonewise? There's no reason at all for you not to get plenty of great tone from it, but the stock preamp design is badly flawed. The only thing a two-tube amp like this can't do that well, is give you is lots of sustain.

[Geezer]

Zaphod,
I tried everything! (I have followed your suggestions from the 18w thread)
Lowered/different cathode resistor & Cap values.....
Shorted/removed the 1meg (R6) & replaced the 1meg grid ref (R7) with a 1meg pot as a drive control....
33k on the grid of the input w/ a 1meg ref to ground.

I'm pretty comfortable gutting it, and I think I'm going with a "5F6-84" circuit.....5F6-A Bassman pre into 2xEL84's cathode biased. It'll be a lower power version of my "AC-Tweedy" (tweed pre into an AC30 power section) which, although my first build, is still one of my favorite amps.
Also, I think I'll try the Baxendal tone stack like Tubenit used on his newest build (with a concentric pot to save space on the front panel).

Jeff

[Zaphod]

So what exactly were you looking for that you didn't get with this amp? Was it really about sustain?

[Bassmanster]

Tube geek, it sounds excellent!  About halfway between Fender and Marshall.  Close-miked w/ a small speaker into GB; very nice!  What's your homemade mic pre, if I may ask?

Yes, you are using Tiger with iLife '06 because that's an iWeb site.  I'm a Mac guy from 1986 on.  I don't know why I missed the player under the image since I did the same thing for a while on my site...also made with iWeb.  www.thesoundwaves.com

Cheers!

[Geezer]

Zaphod said:

So what exactly were you looking for that you didn't get with this amp? Was it really about sustain?

No, it just is thin, dull & lifeless....no "fullness" or "body" to the tone at all! Sounds like I'm playing thru a transistor radio w/ a 3" speaker, even though I've run it thru all my favorite cabs....a 15" closed back, 2x12 closed & open backs, 1x12 closed & open.
I've put JJ's in it, a nice 7189, 12ax7, 12ay7...along with all the mods.
Maybe there's a problem w/ the OT?

BTW, the EL84 plate voltage on mine is around 305v....much lower than other reports I've heard.

Jeff

[Zaphod]

Maybe there's a problem w/ the OT? BTW, the EL84 plate voltage on mine is around 305v....much lower than other reports I've heard.

The OT's just about the only part that hasn't been touched yet.  :) Yes, the OT could make a huge difference to the sound. A Hammond 125DSE would be perfect in this amp - or even an ESE, although that one would be somewhat overkill.  

Also, if you find the amp a little too shrill, you can try a trick from Hot Cat's Mini Cat SE EL84 amp, which is a 100k resistor in series with a 2.2nF cap between the EL84's grid and ground.

Another trick for SE amps running at relatively high voltages, and therefore biased cold, is to use a very large cathode cap - ie 1000uF or bigger. This has the effect of stabilising the cathode bias voltage against transients caused by sudden increases in signal level,which can make the power tube go even colder and sound somewhat ratty. The big cathode cap will really smooth the tone of the amp.

I'm real surprised at your B+ voltage, when others have been reporting 350V to 365V. Or is that after installing the power supply mods with the large filter/dropper resistor?

[Geezer]

I've not done any mods to the power supply....that B+ is stock.

I have a 125ESE here on the bench...maybe I'll tack it in & see if there's any improvement.

Thanks!  Jeff

[Geezer]

BTW Zaphod....You're doing your best to keep me from gutting this little thing, aren't you!  ;)

[Zaphod]

I've not done any mods to the power supply....that B+ is stock.

Interesting.... I'm guessing that maybe in the head version they've fixed the power supply, so that it doesn't hum and the B+ voltage is lower too.

I have a 125ESE here on the bench...maybe I'll tack it in & see if there's any improvement.

It shoudl be pretty easy to try for fun, and you've nothing to lose...

BTW Zaphod....You're doing your best to keep me from gutting this little thing, aren't you!  ;)

;D The urge to experiment is irresistable!  ;) :)

[TubeGeek]

I am planning on installing a GA-5 circuit in an epi valve jr.  I found a 5V4G rectifier tube in my box of tubes so I figure what the hay I'll try out the schdule 40 adaptation...soon. ::)  

Bassmanster...check out my website...I just posted pics of my tube and Jfet microphone preamps.

[Bassmanster]

Thanks, TG, I have been eyeing those Hamptones for a while now.  What do you thinks?  The reason I asked is that your sound, given that it's a close-miked 57, is excellent.  I had read that 57s sound good with a good preamp and bad with a cheap one.

Well I guess this adds to the mounting evidence.  How was the build on those Hamptones?  Pretty straightfoward?  I have built a scratch amp, so I wouldn't expect any problems.

[TubeGeek]

Here is my complete signal path....sm57...mogami quad cabling to the tube hamptone....more mogami quad cabling to my mbox2 input one set to line in...mbox2 connected to my mac via usb 2.0.

I used no EQ and no compression.

An SM57 is pretty standard for many recording applications.  They are cheap and they sound good too.  I do find that they sound better when ran through a quality preamp.

The Hamptone preamps are excellent IMO.  They use solen fast coupling caps and xicon electrolytics. Resistors are metal oxide 1% tolerances.  The input and output xformers are custom made and are the same xformers Walter Sears used in his consoles.  The PS uses a torodial xformer.  When I received the kits I was pleased with the organization and instructions.  I built both of these preamps before building any amplifiers and they couldn't have been any simpler.  I was just fresh out of electronics school and bought myself these to keep me occupied.  The preamps do not come with the rear output jacks, that is an addition.

They beat out many other well known preamps in the studios I have worked in.  Scott Hampton is a very nice person as well, I talked with him several times about his projects.

I definately recommend these preamps.

Now if I could only build my own microphones in kit form! I am still looking for this one!  

[Bassmanster]

Thanks for the info.  Yes, I have had a 57 (and a 58) for about 10 years and I know what it sounds like through a cheap mixer.  Which is to say...not at all like your recording.  Thus the queries.

I'm stoked to get one as soon as I save a few pennies.