Epiphone Valve Junior => Supro

briggs · Post by **briggs** » 27 Feb 2008, 12:39

Ok. I've just bought an Epiphone Valve junior with a mind to mod the hell out of it! Here is a scheme of the mods that I'm looking to perform. Can any of you guys that are far more experienced than me with amps see any glaring errors? Any suggestions to furthur improve these cheapy amps?

I'm going for that classic "Supro" sound so that is where I've got most of my mods from - those classic old amps...

greenskull · Post by **greenskull** » 04 Mar 2008, 00:52

Hey Briggs - I've got a Valve Junior head sitting right here ready to be modded also. I can't comment on making it sound like a Supro, but I do know there are some other things that need to be addressed to make this thing sound decent to begin with. If you have an earlier model you've got to do quite a bit including changing the OT for one with a 5.2k impedance and switching the heater voltage to DC. ALso dropping down the voltage going to the EL84 is recommended. I'm new at the amp stuff so I'm just going by what I've come across on the net. Waiting on some parts this week and will get my hands dirty with it for the first time.
For other mods besides the Supro, look here:
http://www.sewatt.com/vj-faq

Other VJ mod sites:
http://www.valvejunior.com/
http://www.premierguitar.com/issue/webe ... riches.asp
http://www.euthymia.org/DIY/VJmods.html
http://users.telenet.be/svokke/valve%20 ... 20mods.htm

There's loads more, but that's a start.

There's a list of the "gold" and "silver" mods mentioned on the old 18watt.com forum that has been reposted on another message board, but I can't find it..... try google. I'll keep digging for it and will post if you are interested.

briggs · Post by **briggs** » 04 Mar 2008, 10:27

Thanks greenskull. I think I saw those mods drifting around somewhere. I think my head is a later edition, I'll be able to confirm this when it arrives. Hopefully all the boring stuff like changing the heaters to DC is done. I'm swapping the OT for a hammond one - not too expensive and said to give good results. The thing I'm most concerned about is the biasing of the two preamp stages, if this arrangemet is going to be OK for the tubes... Also about the tone control and the output imedance of that final preamp stage, will that be OK I'm wondering!?

Really looking forward to getting stuck into this thing - it'll be my first foray in tube amps!

Expect a full photoessay

Regarding parts - I think I'm going to be using a few high wattage resistors and mallory caps mainly - just a few general upgrades, then I need to come up with a new paint job

greenskull · Post by **greenskull** » 05 Mar 2008, 00:20

Good luck with it and keep us posted on the Supro conversion..... that's gotta be a first! I read somewhere that changing the OT to a Hammond will change up the voltages a bit so you might want to measure for biasing again after replacing. A photo essay would be great!!
I'll make notes on my modding attempts and will try put something together about the results on a separate thread.... if I don't just blow it up in the process.

briggs · Post by **briggs** » 10 Mar 2008, 21:39

Job done! It's sounding pretty cool - still needs a new Output Tranny but so far I've got all the other mods in (Apart from a few of the mods that don't really affect the tone too much). I'm impressed with this little amp! I'm just waiting on some quality parts now to really make this thing sing, the parts used so far are just bog standard resistors and caps - No mojo value at all! I'll put up a few crappy pics of the modified amp so far

briggs · Post by **briggs** » 11 Mar 2008, 01:17

http://bp3.blogger.com/_y4AYtND8Hz8/R9X ... roto_2.jpg

sorry for the crap photo, my digi-cam is down! See more info on my blog

noelgrassy · Post by **noelgrassy** » 12 Mar 2008, 10:55

Are these single ended with one EL84, one 12AX7? I have an old Harmony with that topology. I might wanna try these mods on this sleeper. Was DC filaments really a necessity? Most folks [not the audio types] don't notice any benefit from the change compared to the standard AC heaters. Do the xfmr's have the fils voltage center-tapped? How many volts do you see at V1 plate? How many on the power tube ~~plate? Thanks for the cool links greenskull!~~

briggs · Post by **briggs** » 12 Mar 2008, 12:32

Hi there noel, yes they are 1 x 12ax7 and 1 x EL84. I'll post full voltages when I have my quality parts and I've installed them - I still need to drop the overall voltage and bias the power tube a little cooler. The parts were shipped today so I expect them end of week

My head is a version 2 so the heaters are already DC - I didn't have to make that change, I've only ever heard these things with DC heaters so I can't comment on the differences in sound regarding AC/DC heaters.

This thing sounds great already - an it's only using cheapy parts, I'm expecting a furthur increasing in quality level when I get the JJ/Tesla tubes (Stock are sovtek) in there and also the high quality audio caps and resistors, I'll be ordering a new OT when I have some extra cash....

OrionManMatt · Post by **OrionManMatt** » 12 Mar 2008, 15:15

I'll be looking forward to updates, pics and (dare I say?) sound clips. It's pretty interesting to see how well these have done despite their obvious initial shortcomings. Have you looked into the Blackheart amps? Seems like they're a Crate version of the amp with some modifications to the circuit, such as equalization.

Matt

noelgrassy · Post by **noelgrassy** » 12 Mar 2008, 19:17

What speaker do they play well with? Actually, I'll wait untill your "kine" stuff shows up and you've massaged the little puppy.

Spelling Bee south of the Mason-Dixon line. By God, they're alot tougher!

briggs · Post by **briggs** » 18 Mar 2008, 15:49

Here are some pictures of the finished article. Voltages - on the EL84 plate = 300V, EL84 cathode = 9V, that is after rebiasing the power supply. I dropped the overall voltage to the whole amp - it was up at 320V!

I'll draw up a final schematic when I have got everything else done. The only part I am still waiting for is a new output transformer - I imagine I will have to tweak the power tube bias once again when I get that and install it (A nice new Hammond 125CSE, bloody hard to ind in the UK!)...

At the moment it is sounding exactly like I wanted it too - nice chime at low volume on the "treble" input building up to a sweet treble-laden overdrive. The "regular" input is a little darker and more bass rich, much better for a "jazzy" sound. I don't have any recording gear (I used to!) so can't make sound clips

Notice the small "mod boards" I made on perf board and then plugged into sockets on the original PCB - a great way to alter the PCB layout without having to cut through traces and damage the board! Also cleared up all that messy wiring that was in the stock model

Strangly enough the Supreaux sound samples on OLC circuits give a good idea of what this thing sounds like - but without the VOLUME! heh....

marshmellow · Post by **marshmellow** » 18 Mar 2008, 20:33

Look here.

culturejam · Post by **culturejam** » 19 Mar 2008, 14:36

Very nice work, Briggs.

I, too, have a Valve Jr (combo) that I intend to modify. I can tell you that this little amp benefits greatly from a tube swap and a new speaker. I tried a lot of tubes in there, and my favorite combo is this really old RCA EL84 I found at a flea market and a new production Ei 12ax7. The next best tube lineup was a nice pair from JJ/Tesla. For the money and availability, you just can't beat JJ tubes.

I also put in a Weber Signature Alnico speaker. The bass is tighter now, and it stays tight even with the volume all the way up. Also, the amp breaks up a little earlier with the Weber in there. For $35, it was a very good investment in tone.

I plan to add a master volume and simple tone control, and possibly a negative feedback switch.

briggs · Post by **briggs** » 20 Mar 2008, 00:05

Cheers culture - you really can turn these into cracking little amps for the time and money spent on them! I'm running a pair of JJ tubes in mine, sound nice and bold! Thanks for the link marsh - that is where I'm getting the OT from

I can't wait to put it in, I'm also thinking of getting some different tube sockets, need to get those tubes off the PCB!

Post by **modman** » 22 Mar 2008, 14:33

http://www.guitariste.com/forums/le-coi ... ml#5371488

This French guy is having some fun with a DIY attenuator box between his Valve Junior and speaker. S'il y a un problème linguistique, je traduirai.

M

JiM · Post by **JiM** » 23 Mar 2008, 21:47

Hi,
I just finish prototyping this bridged-T attenuator on my GA-5 (Valve Jr. clone, with these mods : input impedance, removed "tonestack", master volume). I've done a quick n' dirty circuit with some screw-type contacts (called a "domino" in french) and the biggest-wattage low-value resistors i had around.

With R1 = 1ohm/1W, R2= 15ohm/1W, R3 = 4.7ohm/3W and R4 = 4.7ohm/0.25W, it gives about 14dB of attenuation, the loss of volume is sensible, and the tone seems unchanged. Now you can crunch at home, but it's still way too loud to play at night in appartment.

With R1 = 0.47ohm/0.5W, R2= 39ohm/0.5W, R3 = 4.7ohm/3W and R4 = 4.7ohm/0.25W, it gives about 20dB of attenuation, and it's really quiet now with clean or crunchy sounds. I still need to lower the master volume to crank the gain all the way up without being too loud, but now it's no more stuck to the minimum. With these values, R3 should be at least 4W, but it's all i have right now, and it did not get hot at all so i think it will be fine.

So it's definitely a useful addition for use as a practice amp at home, but i'm still looking at a triode switch for the EL84 or a preamp-output tube (12AU7 or 6N1P).

PS : Here is another page about bridged-T attenuators for english-speaking people : http://www.fmsystems-inc.com/eng_tee.htm

Post by **modman** » 06 Apr 2008, 12:36

I found another extensive page about modding the Valve Junior, as it starts out with one of the first versions, but goes on to mod it to 3 gain stages from two 12ax7 valves into a single EL84 with a gain and master volume Epiphone Valve Junior Eyesonly Mods

TWANG · Post by **TWANG** » 01 May 2010, 05:58

I've done a few vjs.

I'm new here, by the way. second post. came in to learn a bit about pedals. Hello.

I've got two EL34s I'm working on.
I blew a Supro build completely, and never did figure out what went wrong.
Terrible buzz.
gutted it and made it marshallized.

I've done the 6V6 replacing the EL84.
I'm going to do a dual preamp tube next, try to get a tone stack in.

I'm not all that fancy with the cabinets but here's some of mine.

I make control panels out of pickguard material, *I make and sell pickguards*.

messing with the cabinets is fun. Lots of people like the screen upfront.

Here are my first two.

ssmc · Post by **ssmc** » 20 May 2010, 20:00

culturejam wrote:.....a new production Ei 12ax7....

I am sorry for offtopic but where did you found these EI?I live in a country where Ei is and I think that place is dead from 2002.I even called them but didn't get the answer.

BIGSMITTY · Post by **BIGSMITTY** » 04 Jun 2010, 23:03

turretboards.com has a "suprolicious" mod for valve jr.