Wanted: Epiphone Valve Jr Hot Rod reverb head schematics/tweaks

[lowatter]

Hi guys...long time no post.
I picked up a Epiphone Valve Jr Hot Rod reverb head and after a couple days of searching I can't seem to find a schematic for it. I haven't even opened it up yet and only tried it out as a stand alone reverb unit for my Musicmaster Bass amp which is my intentional use for it. Actually, it's hard to find much of anything on the net about this thing. The reverb is really pathetic and I'm pretty sure that a new tank is in order though it can only be less than 12" long. It uses (2)12AX7's(Ruby) and a EL84(Sovtek) that I just replaced with a JJ. It has a gain stage that could be better used for my needs. I'm just trying to have some lush reverb for my Musicmaster amp without too much ado. I picked it up cheap and thot it might be worth messing with.
Anyone have any info/ideas? Thanks for all that you folks do here.

BTW...what happened to Schematic Heaven??!!

[topbrent]

Schematic Heaven is kaput.

Doug picked up the ball and ran it in for the win.

http://www.el34world.com/charts/Schematics1.php

[tubeswell]

FYI pile of VJR mod info over at SEWatt

http://www.sewatt.com/faq/38

[lowatter]

Thanks guys but this is the VJ Hot Rod reverb amp or stand-alone reverb unit. I've scoured all the threads at SEWatt. There's TONS of stuff on the Valve Jr but nothing on the Hot Rod reverb head. I'm trying to mod it to hopefully sound somewhat like a 6G15 if possible to add some decent reverb to my Musicmaster Bass amp.

[tubeswell]

Well if you want a 6G15 (and they are the bees knees of stand alone reverbs), then make one of those.

I don't know what's in the Epi Hot Rod Reverb unit, but it doesn't sound like the 'verb is driven by anything much - there is just 2 x 12AX7 and 1 EL84 in the whole unit.

If you only want it for a reverb unit, then you may be able to just gut it, make your own board and use the trannies from that.  The OT would become the reverb tranny and it would be driven by the EL84 with a cascaded 12AT7 driving that. the other dual triode is used for the CF bypass stage and the 'verb recovery stage. I don't know what sort of tank the epi Hot rod has in it. But for making a stand alone reverb (using the OT as a RT) you'll probably need to find a tank with an 8R input transducer. And get a small 40-50mA 3-5H choke for the power supply.

[PRR]

> Anyone have any info/ideas?

No. Nothing you have not found. It's low-cost. It works for some players, not for others. Nobody stays very excited about it.

> I'm pretty sure that a new tank is in order

Why?

There's a lot can be done in drive/recovery to suit the tank.

> I haven't even opened it up yet

Why not?

Take pix.

[lowatter]

Thanks for the interest. Here's a pic of the PCB in place. I was trying to get through this with little ado, but you know how this stuff goes. I'd like to just improve on the reverb in this circuit which sounds really, really bad. From what I've gathered these use a Ruby 2 spring tank. I'd be happy to loose the extra gain stage and utilize it towards the reverb if possible. I do really need a schematic before I go any further with it.

[John]

You probably already found it, but apparently over at 18watt there's a thread about VJ mods; maybe someone's posted a schem there?

[PRR]

> It uses (2)12AX7's(Ruby) and a EL84(Sovtek)

I only see two sockets?

The PCB comes out on <20 plugs and screws. A pain to document and pull, but then the schematic is right there: hold it up to the light. You know the base VJ is a Champ with extra junk; this has to be the same with more extra junk. So mostly you have grid, cathode, and plate resistors, with maybe an extra resistor or cap where a Champ runs straight.

Man, that sure is a computer-aided design mess.

[lowatter]

> It uses (2)12AX7's(Ruby) and a EL84(Sovtek)

I only see two sockets?

The PCB comes out on <20 plugs and screws. A pain to document and pull, but then the schematic is right there: hold it up to the light. You know the base VJ is a Champ with extra junk; this has to be the same with more extra junk. So mostly you have grid, cathode, and plate resistors, with maybe an extra resistor or cap where a Champ runs straight.

Man, that sure is a computer-aided design mess.

The EL84 is located just right of center and is a ceramic socket located beneath the board. I emailed Gibson and a service rep said he'll get back.
Yes, I know that I'm just being lazy(sorry). I'll submit the schematic if they forward me one otherwise I'll will pull the board and document. I'll try to submit a couple of clips on really how bad this reverb circuit is as soon as I can.
I got this little guy for $150 shipped and I thot it would save me alot of time not having to build a 6G15 or revibe etc. but I may just resell it and buy the parts. I guess you can't expect $600 worth of reverb for a yard and a half. I'm(and especially my wife) are pretty tired of me taking on projects. I'm just trying to add some verb to my Musicmaster without too much ado.
And...YES it is a CAD nightmare. Again, thanks.

tubeswell-thanks for the response and recommendations. This amp should have most of the peripheral off-board componants except for sockets to morph it including the cabinet of course. This would make it a pretty good candidate for a drop-in tagboard. I just didn't want to go there just yet.

I know alot of folks here would say to just plop a pedal in front of it but I'm a glutton I guess.
Here's a track with a Zoom GFX-4 multi-effects. I'm playing the intitial lead then accompaning lead further into the track. The verb sounds pretty good but it could be better.
http://www.soundclick.com/bands/page_songInfo.cfm?bandID=854782&songID=8102630

[lowatter]

I just recieved the schematic directly from Gibson. I hope you guys can take a look and see what's up with the reverb. The R&D dept. said just to add a 3 spring short tank instead of the 2 that's in it. What do you think?

[tubeswell]

As I guessed - you're not going to get much 'verb out of that. And going to a 3-spring tank is probably not going to help all that much.  For a truly wet sounding reverb, you need more current driving the pan's input transducer. That means a bigger drive signal from the reverb driver stage - which means probably at least another stage in front and/or a paralleled 12AT7 stage driving the RT.

But you do have an adequate PT supply there for a stand-alone reverb unit - for which you can also use the existing OT as an RT to drive the existing http://www.accutronicsreverb.com/main/?skin=sub01_03.html pan, and (remove the existing RT and) put a choke in-place of the 220R resistor in the power supply filter.

[sluckey]

The reverb circuit looks almost identical to tubenit's one tube reverb circuit. Tubenit's circuit has more than enough reverb for most applications, but won't give that heavy/wet surf sound or Ventures in outer space. One thing tubenit does is to increase the input cap size from 500pF. If you have a standard Fender tank, plug it in to see if that helps.

The typical Fender reverb circuit gets it's input after two gain stages but yours gets it's input after only one gain stage. Yours will naturally be anemic by comparision. One thing to try would be to move the reverb input from the wiper of the gain pot to the high side of the gain pot (I'm sure this is easier said than done!). Or, totally move the reverb in/out points over to the volume pot (This would likely be very challenging).

You keep calling this a stand alone reverb unit. I don't see how. Looks like just a simple low end amp to me.

[VMS]

You keep calling this a stand alone reverb unit. I don't see how. Looks like just a simple low end amp to me.

It can also be used as a stand alone reverb unit:

http://www.youtube.com/watch?v=DifluevOtpY

[lowatter]

The reverb circuit looks almost identical to tubenit's one tube reverb circuit. Tubenit's circuit has more than enough reverb for most applications, but won't give that heavy/wet surf sound or Ventures in outer space. One thing tubenit does is to increase the input cap size from 500pF. If you have a standard Fender tank, plug it in to see if that helps.

The typical Fender reverb circuit gets it's input after two gain stages but yours gets it's input after only one gain stage. Yours will naturally be anemic by comparision. One thing to try would be to move the reverb input from the wiper of the gain pot to the high side of the gain pot (I'm sure this is easier said than done!). Or, totally move the reverb in/out points over to the volume pot (This would likely be very challenging).

You keep calling this a stand alone reverb unit. I don't see how. Looks like just a simple low end amp to me.

Thanks Sluckey. This amp can be used as a stand alone reverb(and what I wanted it for) by jack-switching in the back on the unit. It's a conventional amp head as well.
As far as insertion points, your comments were exactly what I was looking for. I now need to pull the board after documenting and then take a pic of it over a light to get the pcb/component layout. Then I can start to re-route the insertion point of the reverb driver. I have no issues with utilizing/losing the gain stage if necessary.

As this is a new VJ release, I hope this doesn't turn into another monster thread  but it is a quick and relatively cheap and quick way to acquire the components to make a reverb unit. 

I hope you guys will bare with me on this one and any help is very well appreciated. If after this thing is tweaked successfully, others may benefit and have add-on reverb without too much ado or $600 out-of-pocket expense.

[sluckey]

This amp can be used as a stand alone reverb

Ah. Now I see the stereo jack sitting under the OT. Just hiding in plain view! 

[PRR]

The circuit has no obvious flaws. (I assume the 4-way cross to the right of the Gain pot is dotted.)

It's not a lush design; but minimal barely-counts function with LOW price is EPI's trademark.

The 1Meg at V1B pin 7 could maybe be 22K, tame some reverb shrillness, but that won't be a big difference.

Get a standard long Fender reverb tank and try it. Yes, it won't fit in the cabinet; worry about that _after_ you see if the tank is the main problem or just a detail.

Try a 12AT7 in "V1" hole (the hole which, if empty, the amp still plays reverbless). 12AX7 is not a strong reverb driver; maybe the beefier AT makes a difference.

If you don't want speaker output, there is more than enuff stuff to build a good reverb. But it's major rewiring and PCB doesn't make that easy. Alternatively you could rip the PCB and turret-board it properly, but that's real work.

How is the hum level?

[lowatter]

No noticable hum and I do plan to order up another tank. I was thinking the same about the 12AT7(which seems to be the norm in most reverb circuits). I probably should try these 1st before I jump the gun and tweak the PCB too much. I took a risk that the VJ Hot Rod wasn't as bad on the reverb side as the reviews stated but alas, it's worse. The tank needs to be appropriately rated for the output tranny, no? What would you recommend?

Actually, I could/should just sell this thing stock and build a one tube reverb circuit into my Muscimaster Bass, but I promised the misses to put the kabosh on taking on involved projects. I'd like it if it was a grab-and-go amp. If I do decide to go this route, how much work do you guys think that would be? I must resist...I must resist.

Regardless, I need to follow through and try a new tank, 12AT7, and a couple of value tweaks your recommending. Thanks for your patience guys.

[tubeswell]

Try a 12AT7 in "V1" hole (the hole which, if empty, the amp still plays reverbless). 12AX7 is not a strong reverb driver; maybe the beefier AT makes a difference.

It also occurred to me (just now) that the JJ ECC823 or their ECC832 (don't know which cos I don't know which triode of the 'verb tube is which) could be good, if you get the one where the 12AU7 triode is the driver and the 12AX7 side is the recovery side.

http://www.jj-electronic.com/pdf/ECC%20832.pdf

[PRR]

> I promised the misses

Then tube and tank are about your only hacks. Anything else means solder all over the kitchen table or you in your man-cave every evening.

Standard Fender tank. You might check that the stock tank's input resistance is just a few ohms. However it does have a transformer which could be any impedance and the 4 or 10 ohm impedance is by far most common for transformer-coupled.

I didn't mean BUY one. Borrow it out of another amp. Only take a few strums to know "eh", "maybe", or "YES!!"

[HotBluePlates]

The reverb circuit looks almost identical to tubenit's one tube reverb circuit.

That's what I thought as soon as I opened the schematic... And except for some possible precedents out there in budget amps, I felt like the designer might have gotten the idea from Tubenit on this site! Oh well, there are plenty of lurkers picking up the cool ideas...

I just recieved the schematic directly from Gibson. I hope you guys can take a look and see what's up with the reverb. The R&D dept. said just to add a 3 spring short tank instead of the 2 that's in it. What do you think?

Tubeswell said it. The amount of reverb is more about how hard the tank is driven (but this design is driven as hard as it can be without a tube change) or how the mix knob is set (Reverb pot on this amp). The quality of the reverb is what a tank-change will often get you.

I personally like a tank called "6-spring" with medium delay, which is really a tank with 3 springs inside. It sounds more lush to me than a common "4-spring" tank (really 2 springs inside, but each spring has an eyelet in it about halfway, and is 2 delay lines made of 4 total springs). The typical long delay 4-spring Fender tank will do surf better than my choice, but to my ear the medium delay 6-spring tank is a more natural-sounding reverb (as natural as springs get, anyway).

... only tried it out as a stand alone reverb unit for my Musicmaster Bass amp which is my intentional use for it.

Are you actually playing bass through that Musicmaster amp?

You do know that the common feature of all guitar-amp reverbs is that low end is seriously cut off going into the drive circuit, because lows wind up in a rolling, muddy mess when hit with reverb. So if you're playing bass through this, you may be losing all the incoming signal in the small caps feeding the reverb drive circuit.

I asked because I haven't played one of these, and don't know if they typically sound anemic with a guitar...

[lowatter]

Thanks HPB. The tank is a short 3 spring I believe(8AB2A1B). I will try a 12AT7 in V1 as soon as I can. I'll look at the tank you recommend.
The Musicmaster Bass is a 12W bass amp that's terrible for bass and devine for guitar. It's like a push-pull Champ with a transformer in place of a PI and 6AQ5 power tubes. You'd have to hear it to understand why it's considered a keeper by their owners. Here's a clip I did with it(albeit bad)...
http://www.soundclick.com/bands/page_songInfo.cfm?bandID=854782&songID=9689646

[HotBluePlates]

Got it.

You're right about the type of tank; it's a 3-spring, medium decay tank. The catch compared to my description is that it is truly 3 springs. The one I was describing is the type 9 tank, which is 6 springs, arranged in 3 delay lines. So that looks like 3 springs inside the tank. That there are 6 springs, all of different lengths, is what gives the type 9 tank is fuller sound.

Unfortunately, that tank is simply too long for your application.

Okay, you're playing guitar. That means that my possible fault is not an issue; you're playing plenty high enough in the range to get plenty of reverb.

So we're back to whether this is "normal" for this box. And since I haven't played one, I just don't know.

[pwhite]

OK, I am digging up a really old thread but I have had this head for a couple of years now and have never been happy with the reverb. I have a standard Valve Jr as well and have modded it into what I think is a very nice sounding head. I have done some changes to the Hotrod and changed out the tank to a 3 spring medium decay, I have ordered another Mod tank from amplified parts which is the same just long decay and it should be here in a couple of days. My hopes are that if someone else has this head and is unhappy with the reverb as I was will find some of the changes I made useful. I have also found better schematics for it and a lot more info about the circuit. Hope this helps someone and I will try to post some pictures and changes as they develop and maybe some videos or sound clips. One other thing I have done is I changed out the speaker in my cab to an Eminence ReignMaker FDM which is the adjustable one with a 9db decrease.
http://tonebuster.org/home/index.php/verstaerker/vjhr/70-vjhr-schem