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3 preamp gain stages with gain and master volume controls
The 'VJ' is a guitar amplifier from Epiphone, aka Gibson USA - China division. It's features are very few and it is a distant cousin of the old Gibson GA-5 or Fender Champ amplifiers of the mid 1950's. The cost of these amps is not too extravagant, and they are nicely packaged units with a sturdy cabinet and a high quality speaker (designed by Ted Weber, now they have an Eminence). My VJ has had some modifications which I did the day after I got it and hence the reason for this page. If this was a Gibson priced amp I would never have touched it but this baby is just begging to be modified.
THE MOD'S Step 1. Eliminate the hum (Series One amps have an AC heater circuit hum problem. Later versions fixed this at the factory). This is only two components, a bridge rectifier, and a capacitor. Very easy to do. Step 2. Improve the input impedance and remove chassis grounding of board and input. Again, very simple to do with only a small piece of wire and a 1meg resistor needed. Step 3. Add an extra preamp valve for more gain at the front end and a master volume to tame the volume for a more comfortable practice volume. With my instructions you should be able to do this comfortably.
The first two mods are not unique as I have referenced material from two web sites which are both very good. I suggest having a look at these sites and you will see how I have taken both sets of mods and used them on my little baby, and then I have performed what I call the 3rd stage of mods which was my real intention with this amp. http://www.euthymia.org/DIY/VJmods.html SO those sites show the noise fixing, and the benefits of input impedance to pickups, and the third stage was to add a MASTER VOLUME and a 2ND 12AX7 to give 3 gain stages and a cathode follower in preparation for driving a tone stack. The result is an amp with plenty of growl at volumes that are a little more bedroom/neighbour friendly. First do the DC heater filament conversion as per website 1. Then do the input impedance changes from website 2, but leave the voltage divider he talks about removing. You may wish to experiment with this point by jumpering or removing the resistors. I left them in after having taken them out prior to the additional tube mod. Do the input earth wire mod also. I also added the 47uF/440V cap to the power supply to reduce the ripple. Then a 2nd preamp valve was installed.
The amp chassis has to come out.
You remove the rear panel screws and remove the panel.
There are four plastic plugs in the top of the cabinet. You need to carefully remove them using a small screwdriver.
Then there are four large headed screws which you remove. The chassis will drop onto the wooden rails and not fall onto the speaker. Unplug the speaker and slide out the chassis. Using a multimeter measure the voltage on the filter caps to establish a sense of safety, are they charged up or not? by measuring now you will know. Typical filter cap voltage will be about 360Volts and that could give a nasty shock. Discharge the filter caps using a wire with a resistor in series.
The circuit board is attached with some screws. Unplug the spade connectors, making a note of yellow, white, red/red, orange/orange positions for reassembly. I suggest getting paper, drawing a rectangle, and putting a dash labelled yellow, etc etc. The simple things work well sometimes and it minimises any mistakes you could make and saves brainpower as you just look at the picture. The two orange wires are the 6.3V ac taps from the power transformer. As described in website 1 add the bridge rectifier. You will need one that will pass about 1.5 amps however a 6 amp one is bigger and easier to work with. As he says it should bolt to the chassis for cooling. To attach drill a small hole, and use a screw and nut with some thread lock. Remove R1 and solder a 1meg resistor across the input jack. Add a wire from the ground pad of the input to the ground plane of the board. The preamp valve plugs into the valve socket which is attached to the chassis. You need to drill a hole to allow the socket to poke through, and two small holes for screws to attach the socket to the chassis. I suggest wiring the socket before screwing it onto the chassis as it's much easier that way. I drew out the preamp circuit after I had done the mods so as to not forget what went into it. I have scanned this picture as shown here. You can take the point where R5 meets C2 on this diagram as being the input point to your additional valve circuit. There is a large pad you can cut in half to separate R5 from C2 (see below) which gives you two places to attach some hook up wires which will run to the valve socket. You then work your way around the pins of the valve socket one at a time attaching components and wires until you are finished. The output of the 2nd tubes 2nd stage goes to the master volume control which then returns to the board on the R5 side. The heater circuit can be driven from two of the jumpers (1 and 3) on the board which go to pins 4-5 and 9 of the original 12ax7. The power comes from the filter cap and the ground can go to the filter cap also. (see below, 2nd pic)
Christopher Lloyd Gordon (C) 2005-08 Written: Friday 30th December 2005 by CLG (B.Tech) email blupup8@optusnet.com.au
SCHEMATIC'S Below are some useful schematics. The top one I drew to outline the insertion of the extra pre-amp tube. The other two are drawn by other people. The one on the middle left is the very first version schematic which is what my amp is. The one on the middle right is the head version which is also known as version 2. The bottom left is a regulated heater supply I have implemented and the bottom right is the output transformer.
MP3's Sample 1 - (Progressive Funky Sound) Using an MI Audio Crunch Box with it's gain at 12 o'clock, amp gain also at 12 o'clock. Gibson Les Paul Junior Special Plus Sample 2 - (12 bar Blues Sound) Just the amp with the Les Paul Junior Special Plus. Backing by Casio Keyboard :) 20th July 2008 - Update Sample 3 - (Bluesy Canoodling - Low Volume Setup) A demo of the amp's low volume performance (with new output transformer). This is with my Les Paul Junior guitar which I was playing quietly late at night. I had the amp set up with the low volume switch on low, the volume control at 9 o'clock, the gain set to 2 o'clock, and the MI Audio Boost 'n' Buff also set to 2 o'clock. The guitar volume and tone controls where wide open. I think the sound is dynamic, responsive and has good harmonic content. Also the recording sounds like the amp sounded so it's a good representation of actual performance. I should mention the details of the high/low volume switch. It's a voltage divider with 1meg and 33k resistors connected to a switch to either bypass or attenuate the signal before it is fed to the volume control. It's basically providing two ranges of volume control operation. It's good to get the volume down into the 'play while watching tv' range.
BLOG 1st January 2006 - Update Today I did two adjustments to the inter-stage attenuation. There is a spare cap space on the board in parallel with R6. I jumpered across to check response and ended up placing an additional 1meg here to increase the signal level. Without any inter-stage attenuation (jumpered) the amp encounters some slight blocking distortion or farting out. The 1meg/1meg stock is fine, but a tiny bit more gain has been squeezed out still in a warm fashion by changing this divider without any unpleasantness. There is also the same 500k/1meg voltage divider between the 1st and 2nd valves (2nd/3rd gain stages) for the same reason. These two changes give about 30% more gain through the preamp. The amp goes from clean jazz through to early Van Halen with ease.
17th January 2006 - Update Today I changed the output tube to a JJ Tesla made in Slovak Republic type. The original Sovtek made in Russia which I was happy with was annoyingly making a noise on certain notes. The tube seemed obviously faulty as when touched (with a wooden paintbrush handle) it made a vibrating noise internally so I changed it over and the fault went away. The new one is probably smoother and more harmonically complex than the older one. It seems more balanced and not as raw sounding. If not faulty a replacement would not be considered by me, however having changed it over the sound is very good. Some people prefer the JJ sound. They call it an improvement whilst describing the original valve as cheap and unusable (the drama queens). I think it is a step away from the rawness of the Sovtek which I like as it reminds me of my Marshall. A change for the better, in terms of a more balanced smooth and complex sound, but certainly not an essential one.
29th May 2006 - Update This evening I installed a switch to allow for a normal/attenuated volume control. At 3 in the morning for example, it is good to have a very low volume and the standard volume is almost on or off at the extreme left of the dial and is difficult to adjust. This way the volume has two ranges of operation, from very soft to normal, and from normal to flat out. I also added a 100pF cap to the original volume control to brighten the amp up a bit. This is a good mod to do tone wise especially if you play a Les Paul guitar as the treble is given a boost. This is like turning on a 'brite' switch. You could use a switch but since I want it to only sound that way I don't use a switch. You could also use a cap across the 1M R6 which will create a 'treble peaking' circuit since higher frequencies are bypassed whereas lower ones are attenuated. This type of thing is what people remove from their Marshall JCM800's to reduce the brightness.
20th Sep 2006 - Update Today I dusted the top of the amp, and took a better photo of it (as seen above). It shows the switch that was installed last time.
Fun with Speakers
November 2007 - Update - Fun with some speakers Recently several speakers have been tried out. A Jensen C8R which was very bright and punchy. I used this one for a few weeks and decided it was not bad. Then I tried a Weber Blue Pup 8 which seemed to have had a weird fuzzy thing going on. It reminded me of some Vintage 30's I had which had this fuzzy noise when played clean. I posted a message on the Weber speakers forum about this sound. I got a reply that maybe it needed breaking in, but that's a fairly general observation I thought. I ended up selling this speaker and I tried a Jensen Mod8-20. It was very smooth and balanced, British sounding and reminded me of the balanced sound of my Celestion G12H's I have in a speaker cab. The Mod8 has remained and I would recommend this speaker if you would like a change which is warm and relaxed and not quite so aggressive as the original speaker. Jensen Mod8-20 has a smaller magnet than the C8R. I think of it as a scaled down Celestion G12L-35. Kind of a soft edged crunch. I cannot comment on the current models' Eminence as I have never tried one. It should be mentioned that I built a few solid pine speaker cabs loaded with Jensen Mod12-70's and they sounded great together. Maybe I am biased towards the mods. Having said that, the fact is the Weber Blue Pup 8 is the best sounding speaker except for that upper midrange buzz.
I also installed a switch on the back which when up is an 8ohm output tap, and when down is the 4 ohm tap. You can pull out a little bit of the speaker cable to allow you to unplug the original freely, then plug in an 8ohm cab and flip the switch. I have a 2X12 cab made of solid pine, open backed, with 2 Celestion G12H speakers. The response of the VJ through this cab is beautiful, and the balance of the sound is similar to the Mod8.
17th December 2007 - Update The act of unplugging the original speaker, then plugging in the bigger cab and flicking the switch got old fast. I decide to use a DPDT on-on switch and an additional speaker jack. Now it has the internal speaker as per original, and above that another jack which the 2X12 Celestion G12H cabinet is plugged into.
As per my standards flipping the switch up (up position means bigger speakers, higher ohmage, more sound - easy to remember) gives the big cab, and down is the internal Mod8. So now with the flip of switch you can go from day time to night time operation.
Changing the Output Transformer 20th December 2007 - Update I am considering a new output transformer. The Hammond 125ESE, which is a 15 watt unit optimised for single ended amps, is a popular choice for both value and performance. Electronics Valve and Tube Company stocks Hammond transformers in Australia. Evatco have them for around AU$120 for the Hammond 125ESE. WeberVST does a clone of this transformer which is model number WSE15 and it is US$28. Getting one in your hand may cost around AU$60 which is half the price for a similarly spec'd product. Seems like a better choice for the money. The main reason is that on my Valve Junior (early model) the primary coil is rated at 7.5K which is not what a single ended EL84 should optimally use. It should be closer to 5.2K, and the WSE15 has a 5k primary impedance which is just about perfect. Another thing whilst in the vicinity of the output transformer is the 220ohm cathode resistor for the EL84 should really be a larger value of 270ohm to bias the EL84 more correctly and improve the tone and the tube life.
4th January 2008 - Update A couple of weeks back after my last entry I went ahead and ordered a WSE15 transformer and a couple of components from WeberVST. They shipped my order within an hour or two of placing it. You can't argue with that for service. The goods arrived here in Melbourne a week or so later and little 'VJ' was once more dragged out from hiding and taken to the downstairs dungeon, um...that would be the garage where I have a small work desk because I'm not allowed to solder in the house. I have taken some pictures below documenting the activities. The first thing I did was to remove the C1 and C2 coupling capacitors and the R14 cathode resistor. I had heard that the original caps were "muffled" and "lacked clarity", and of course the cathode bias resistor was too small. I replaced them with a type of Weber capacitor modelled on the Sprague Orange Drop 716P series. Part number PPC223-630 0.022uF, 630Volts and a 270 ohm 5W resistor part number *RES270-5
The new caps are larger The heat from the EL84 has shown up as a bit of light browning of the area surrounding the tube socket and a slight buckling of the board. In case there was ever any doubt? NO you don't design a valve amp with tube sockets on the PCB. I find the best design is chassis mounted tube sockets and a turret board for the circuit (see below). You can change parts over and over without destroying any PCB tracks because there aren't any. Eyelet boards are ok, and point to point is ok, but I think the turret wins for being able to do mods easily. Of course costs dictate a PCB mounted construction for the VJ and that's fine.
I tested the amp after I changed the coupling capacitors and the cathode resistor. It sounded really good, better than before. Better how? well it seemed more open sounding, not as muffled and less restricted. I think the better biasing is responsible for it sounding more open, and the caps for making it less muffled. With the amp at this stage you could be forgiven for not seeing the need for a new OT, because it was sounding fine. With both controls dimmed it was tonally very similar perhaps to a Marshall JCM800 in response and tone (through the G12H's). The only thing was it wasn't ridiculously loud. Incidentally the sensitivity of the Jensen Mod8-20 is about 6db less than the Celestion's. This means the Celestion's are twice the volume as the Jensen. The Jensen on full volume is still a pleasant volume level, whereas the Celestion's on full tend to make the room start to vibrate etc. because they move more air around and are twice the volume level
The new transformer is a lot larger In changing over the output transformer a plan of attack was needed regarding positioning of the beast so as to fit in the cabinet. On a head it wouldn't matter so much, but my first positioning soon revealed it wouldn't fit in because it hit the speaker. I repositioned it and drilled two more holes and screwed it on. This time it was ok for fit so I proceeded to do the wiring up.
Now with a single ended transformer there is no primary centre tap, just two wires at each end of the primary coil to connect. On the original VJ circuit board these correspond to the Yellow and White leads with spade connectors toward the back of the board. On the WSE15 white is the blue wire, and yellow is the brown. The secondary has Ground and 2,4,8,16 ohm taps. I used the 4,8 taps as per my previous switch on the back wiring arrangement. So I wired it up and took it to my speaker cabinet to test it out...and then...NO SOUND!??? So it's not working? Hmmm, I wonder why? It was just working before, but now it's not. All I did was change the output transformer. I checked the wiring of the output selection switch and yes it was correct; the output jack was connecting to the correct transformer secondary tap. After sitting for a while staring and thinking I decided to unplug the two spade connected primary wires and plug on the original transformer. I soldered a jack onto the 4 ohm tap and plugged in the speaker lead and powered up. Again no sound was coming out. More sitting, staring and thinking..... Then I noticed that the valves didn't appear to be glowing anymore. Hmmm, that's odd am I imagining or what. I will check the voltage I thought. With the tubes unplugged it has voltage on the heaters so that must be ok then. I tried again and looking carefully the valves didn't seem to be glowing. Was it the bright light of the room or something else? no a little tap with a finger tip and no heat. A thumb and a couple of fingers holding on to each valve and none of them had any heat on them. Checking the filament voltage with the valves plugged in it was very low so maybe a valve was faulty. Unplugging one valve at a time should yield a correct voltage however all three had to come out before a correct voltage was measured. I sat and I stared, I stared and I sat, with a blank look of maybe that was just that! Is the power transformer stuffed? It works until you put a load on the 6.3v lines. Something to try? Ok well there is a 12volt tap unused on it so I tried it on a 12ax7, a cheap Chinese test tube that I have as a spare, and it lit up. SO I decided to use the 12V tap rather than the 6.3V tap straight onto the bridge rectifier and then use a 5V regulator (LM2940T-5.0) with a couple of diodes on the earth leg to raise the output up by a volt or so. I wired it all up, super gluing the regulator to the chassis for heat dissipation, and now we had glowing valves and it had sound. IT'S ALIVE!!! The current these regulators can supply is in excess of 1A (from spec sheet). Since each 12ax7 needs 150/300mA @ 12/6V and the EL84 about 760mA @ 6.3V that adds up to 1360mA, well in excess!. If this causes the REG to overheat it has thermal overload protection, so it wont die, but the valves won't be heated! In this case you could use a 2nd regulator and run one for the 12ax7's and one for the EL84, problem solved. The thing is if you super glue it to the chassis it won't get hot and it won't shut down so there is no need to worry. In going through this I noticed the heater voltage across the orange leads was about 7.3V which I thought might be ok when it's under load. On closer inspection of the power supply primary leads I noticed mine was using the 230V tap so I unplugged it and connected the 240V tap. The heater voltage seemed to be just right now. SO now it has a REGULATED heater supply and accordingly some of the residual hum that was considered by me to be acceptable, has now disappeared completely. That's a good thing :)
1st February 2008 - Update Today some mods were done to the circuit. Some components were changed for different values to get it to be a little more like my Ceriatone JCM800HW which in itself has some minor changes to the circuit. There are changes to the first gain stage cathode resistor and bypass capacitor. There are changes to the grid stopper resistor of the second gain stage and to the voltage divider before the third gain stage. The cathode follower stage has been removed as I have never gotten around to doing a tone stack and don't think I ever will. There are changes to the power tube cathode capacitor and grid stopper resistor. Also another Weber Blue Pup 8 Ceramic has been purchased. This time rather than put it in and say I don't like it after 1 minute of usage, I hooked it up to a transformer for 8 hours straight with a 3.5VAC 50Hz signal. It should sound pretty much like it is always going to because it would be reasonably well broken in. Ok so I fired up the amp to test it out at 10:30PM for a few minutes and once again I really don't think I like the speaker. I am thinking about pulling it straight out and putting the Jensen Mod8-20 back in. It is a great little speaker and it has a large dust cap which reminds me of a scaled down G12-65 sort of speaker cone. I am getting a pair of Celestion G12K-100's which also have the bigger dust cap. I don't know if these use the 1777 cones that my G12H-30's had so I will wait and see. A larger dust cap defuses the treble and gives the speaker a warmer top end response. I think that is why I like the Mod8-20 so much because it is so warm and crunchy. I believe that after trying two Weber Blue Pup 8's that they are all going to sound like they sound. There is a high ended fuzzy buzzy sound that I don't like. I suspect that the Blue Dog's may be that way also from their description.
2nd February 2008 - Update Today I tried it out again and found it was not as bad as all that however I did end up changing the speaker back to the Mod8-20. I tried it out and with the circuit changes the difference between the two speakers was not too great. One thing the Weber has over the Jensen is a huge magnet which gives a lot of punch and clarity. There seemed to be a bit of that high end fizz coming through with the Jensen now which was weird. I decided to try changing back to the Weber Blue Pup 8 but this time I also removed the bright cap I had put on some time ago. The amp sounds really good now. That high end thing was probably in part due to the speaker being fairly detailed in the high end and also the 'brite' cap. With the revoicing of the amp it was a little more aggressive in the upper mids and all over a bit bright which when combined with overdrive didn't sound the way I wanted it to. Once again it's 10:30pm and I gave it a quick test out but this time it sounds perfect. It has a very similar sound and response to my JCM800. It cleans up nicely with the guitar volume and is all together working entirely in the way one would expect. I have never been as happy with this amp as I am now. I would completely recommend doing the mods I have done to anyone who has a Valve Junior. I feel I have turned a really good value amp with some design flaws into a fantastic amp that I will continue to use everyday. The main costs of these mods are a transformer and a speaker. Also a valve socket and valve, and a few caps and resistors. This is not that much to spend on an amp to get a practice and recording amp that has the most important features of all, great tone and great feel.
12th February 2008 - Update Today an MI Audio Boost 'n' Buff has arrived. The Crunch Box was boxed yesterday for eBay. First impressions of the Boost 'n' Buff was omg it's very harsh sounding I'm not sure this will do. I was thinking I might go back to the Crunch Box but then I thought this sounds harsh because the Crunch Box is very smooth sounding. After 5 minutes with the Boost 'n' Buff it sounded like my amp but with more front end gain. Also there is a lot more treble coming through from the guitar because of the 5 meg input impedance of the Boost 'n' Buff. This means less top end is lost coming from the guitar to the Boost 'n' Buff. On the neck you get more treble detail which is really good for turning the volume right down to get a clean tone straight into the amp in Boost 'n' Buff bypass. On the bridge pickup with the Boost 'n' Buff you need to start rolling off the tone to tame the treble so there is treble in reserve so cutting through is like a laser beam. With the Boost 'n' Buff engaged and gain at 2 o'clock you can roll the neck volume right off and adjusting the tone you can get a fat punchy clean tone or a thinner tone, then a little more volume and it's high gain city. Also this pedal with drive doesn't compress like the Crunch Box when you dig in. Instead you can almost feel the speaker cone being smashed forward with a huge punch. This is where picking sensitivity and clarity of sound is enhanced. Interesting stuff. Just thinking how this is such a great companion to a single channel amp. If you want clean crunch lead you can use this pedal to give you back the top end you lose with the volume right down for clean, due to the input impedance, and then you have crunch as per normal amp operation, and a boost when you want it for leads. Very simple to do with clicking only needed for boost. Also you can clean up the sound with the volume when the boost is engaged anyway. I don't really know if I need this pedal, but it's a good thing to have for lower volume practice. So in that case why not keep the Crunch Box? It always seemed to chop out some bass and compress the sound which kind of annoyed me because I like to just plug into the amp direct. So this pedal is almost like being more direct. If you turn up your JCM800 master volume full, you hardly need any preamp gain to get a singing lead tone so I am not sure I even need this pedal other than for the bedroom. Of course if you put the Master down to 3 o'clock and the preamp at 12 o'clock then there is scope for a booster to be used for higher gain. Same with the Valve Junior, which is responding similarly to the big amp in terms of gain and volume controls. In any event by having a boost for leads you get to use less gain so you can clean up the amp with the volume control. Having a boost is going to be handy for this.
27th February 2008 - Update Yesterday the amp stopped making any sound. I suspected tubes or the heater circuit. Today I looked at it and sure enough the valves were not glowing. The 12V transformer tap had failed probably due to being overloaded. I used the other 12V tap to correct the problem. It will probably fail again if it is being overloaded.
1st March 2008 - Update I have sourced a replacement transformer again from WeberVST. This model is called the WPTGP. You also need to order end bells to convert it from a standing up model to a lying down type. It is described as a "General purpose multi-tap transformer for bridge rectified high voltage supplies. 120, 220, and 240 primary." This will give a 280VAC output which is close to the original spec transformer which outputs 260VAC. As mentioned further back originally this amp was running at 230VAC wall supply tap so the secondaries where all running hotter. This would put the 260VAC output at 270VAC and that was using the 220ohm cathode resistor for the EL84. The tube still works properly and now that I have a 270ohm cathode resistor which gives less idle current it should handle the 280V supply just fine, however.... One thing that concerns me is the plate voltage on that output valve. The rectified voltage is about 325V or 365V, I can't remember which but it is certainly over 300V which from data sheets is supposed to be a maximum for an EL84. So while there is less bias current the plate voltage will go up possibly too much. You could always lower the B+ voltage using a Zener diode and power transistor circuit.
Changing the Power Transformer 9th July 2008 - Update It's four months later and here we are at the replacement of the power transformer section. I think that the extra preamp valve requires another 300mA of heater current and possibly that overloaded the heater winding on the transformer. The original valves require 760+300mA of heater current. Adding another 300mA is a 28% increase in current requirement (EL84 heater current 760mA, 12ax7 heater current 300mA). Another factor may be that my amp was setup as a 230VAC mains model whereas in Australia we have 240VAC mains. This places the output voltages 4.35% higher than they should be. Those two figures combined would mean a 34% increase in current for that heater winding which may have been too much. After the above entry (Update 1st March 2008) I received an email on 26th March from a visitor to the site named Josh regarding my plate voltage concerns. The short of it is don't worry it's going to be fine. To paraphrase his email Josh has built a Vox AC30 type amp and he says the secondary winding on the power transformer is 280VAC. Also he mentions the Marshall 20W amps had plate voltages of 400Vdc. To change the power transformer you have to do two main steps. 1). The physical attachment of the new transformer, and 2). the connection of the wires. 1). PHYSICAL ATTACHMENT You have to remove the old transformer and position the new one such that you can pass the wires through the chassis, and also such that the transformer clears the cabinet when you put the amp together again.
2). CONNECTING THE WIRES There are three things to connect. The primary side, the secondary side, and the heater winding. The transformer has the wires labelled incompletely. I had to connect my signal generator to the primary and measure the secondary voltages to determine which wires corresponded to which output voltages. In my case I set the primary for 0.240VAC to represent the 240VAC mains voltage and measured the output wires. I found the outputs to differ in two cases from what the data sheet said they should be. I must email Ted Weber so he can investigate and update the data sheet. It's not a huge drama but none-the-less since I bought the transformer based solely on the spec sheet it's a bit of a big deal in that way since the tap of interest to me was one of those that significantly differed. It was obvious that the output taps had been wound to obtain specific voltages in steps of around 70V so it was the data sheet that was clearly wrong, not just a little variation but 50V off.
I used the original spade connectors by opening them up with pointy nosed pliers and connecting new wires to the connectors by soldering them into position. Don't forget to put the clear rubber hooded part on the new wire before soldering on the connector part. Trim the wires so as not to have too much slack. If you look at my picture I have used some cable ties to make it all sit nicely in position.
24th August 2008 - Update I have been shopping and bought some new UF4007 diodes. I also got a 2nd 47uF 450V cap to further boost the first power cap. When I dig into the low E string at full volume the amp sags a fair bit. I made a recording which captures this effect. I thought I would bolster the power supply a bit and see how the amp responds. Also I have purchased some L7800 series 1.5Amp 5V regulators. I am planning on using the 5V/3A winding in series with the 6.3V/5A winding to give 11.3V/3A combined winding and running the regulator off that. Since the maximum dropout voltage is 2.5V using 11.3VAC at the input should work perfectly. These three changes should make the amp quieter for recording or even just playing. I have purchased a better microphone. This month (August) these mics are on special, and for a somewhat tightarse/sceptic the price was right to take a chance. To my delight it's actually a lot better sounding than the old $20 Genexxa mic from Tandy (Radio Shack) - hehe no surprises there I guess. It's got more top end response and less proximity effect. It's a Bock BK-5.7a which is a copy of the Shure Beta57a supercardioid instrument microphone. They are exclusively distributed by Super Hard On Music Pty Ltd. So this is part of the reason for the current quiet kick. The other part is than in using the regulator on the heaters for the time the old transformer 12V windings held up, the amp was a lot quieter. When I went back to a non-regulated supply with the new transformer it has a hum to it again. I probably should cut the heater tracks and connect the heater wires directly to the tube sockets but can I be bothered when the regulated DC is silent. Stay tuned...
1st October 2008 - Update I went back into the amp and added the extra 47uf/450V power supply filter cap. I also swapped the old power diodes for the high speed UF4007's. I had added a regulator which was supposed to supply 1.3A of current but it seemed to fade out over time and the voltage would just drop out. It was better before with the 1A low dropout regulator I had in there. I should have put that back in but instead I just removed the regulator and went with just the rectifier and added another cap onto it's output. That solves the noise problem well enough once more, and the diodes get rid of a clicky switching sound you can hear on these amps.
29th November 2008 - Update I have a guy ask about getting his VJ Head made brighter. I did some mods for him and he was very happy with the results. I took some photo's of the insides of the amp. I noticed a different layout of the tubes and transformers. Getting another valve in there would have to be thought about for a while by a version 3 Head owner. At least speaker clearance isn't an issue.
8th March 2009 - Update Today I was finding it a bit bright with my Hamer 1994 Special. It has nicely aged Mahogany and has a deep sound and a bright spankiness to it all at once. It's brighter than a Les Paul. I also tried different pickups in it. The original Seymour Duncan 59/JB covererd ones, a Seymour DUncan AlNiCo II Pro in the neck with an Alternative 8 SH-15 in the bridge. Neither combo was quite right so I was about to change back to the 59/JB when I thought I'd try a set of Tonerider Rocksong's that I had on the shelf. Well that did the trick it sounded good with those and they have been in it a few weeks. I am thinking about a tone control or high cut switch of some sort. Sure I have a treble booster so I turned it off and upped the amp gain control a bit. It was darker but still quite bright. Then I tried my Gibson ES-335 with '57 Classics and it to had a bit much brightness on the bridge when up full. I now have a suspicion that maybe a tube is needing replacement but I am not sure. I checked back to this page for the last tube change and well, there never really has been one. So maybe I could say 4 years is time for a change.
27th April 2009 - Update I have changed the tone pot in the Hamer to a 300k linear instead of the almost 400k custom tapered Hamer one. I also changed the tone cap to a PIO 0.022uF. Now I have a proper tone control and also a little top end is calmed down. I also changed the bridge pickup magnet from an AlNiCo II to and AlNiCo 8. Then I bought another guitar, it's a Gibson ES-135 and I put some Seymour Duncan pickups in it. The neck is a Vintage P90 and the bridge has a Custom P90. I haven't put it down so Hamer sits on it's stand lately. I bought some 12ax7-EH preamp tubes. I will try them out in the Valve Junior.
29th April 2009 Today a pair of 12AXEH tubes arrived. I put those in along with a new JJ EL84. It sounds a bit quieter than it was with the Sovtek 12AX7WA's. The reason would be the spiral filaments on the Electro Harmonix valves. There's really not much changed to the sound it just sounds punchier, clearer and more detailed in the treble. On the old ones I noticed a brown discoloration around the top parts of the tubes which I've read is a sign of a lot of hours use. I have some Tung Sols in my 2204 amp, I wouldn't mind pulling them out and trying them in the VJ just to try it out. I do think people put far too much stock in what valves they have though. Sure they make a difference but a different cap value here or there or a speaker change can really alter your tone.
9th January 2010 I have been meaning to update the page for a while. A while being since I last fixed my amp after it broke down again. It seems like yesterday but it must be 6 months ago that I replaced the power transformer again as it broke down. After the tube swap in April the amp blew a fuse a month latter. I replaced the fuse and it worked so I didn't think too much of it. Then about 2 months later the fuse blew again. This time a replacement fuse blew immediately so something had died in the amp. I removed the tubes and ordered a new power transformer from Weber. I got the same model as I had previously used. When I finally got the new part I swapped it over and the amp was working fine again. The next day I noticed I didn't have as much volume. I thought that's odd, and noticed I did have as much gain. I thought the output tube must be bad and changed it back to the old one I'd had in for a couple of years. The volume came back. I switched them a few times to verify and then threw out the faulty tube and ordered a few new ones. I decided upon a pair of 6P14P-EV new old stock from the 1980's. I found them on eBay of course at LCI Electonics. I put one in and have one spare. The sound was fantastic! Much better than the Tube Amp Doctor EL84 I had also bought but was also faulty. I got a replacement but in the meantime found these 6P14-EV's. When the new TAD arrived I tried it and it was sterile by comparision. So the amp was running well until... Yesterday the amp stopped working again. It's weird that I never had any problems with my amp until I changed all the valves. So having discarded the faulty output tube I am going to remove the two Electro Harmonix 12AX7's and put in some new Sovteks. Also I have ordered another power transformer but not from Weber. After I ordered a transformer it dawned on me that it may not be able to supply enough current. The HT is 250-0-250 at 50mA. The Weber tranny I had in it was 150mA. I don't care, I will put it in and if it works a day then so be it. If it keeps going then I won't worry. It wasn't a lot of money (AU$50), R-Core Power Transformer Tube preamp amplifier 6DJ8 from Analog Horn Audio. It has 6.3Vac at 3Amps so there will be no problem with the heaters. The transformers for the Fender Tweed Champs were 70mA and the original Valve Junior transformer was tiny so I think it will manage just well enough. If not I think I will get a better branded one and possibly put in a loaded turret board replacement at the same time. IF there is something dodgy about my pcb or some of the components other than tubes, that is causing the transformers to fail, then a new board should sort it out.
19th January 2010 Put the new transformer in today. So far it works well. No word from Weber reguarding the email I sent them about two faulty transformers. Did they have a bad batch? Is there a warranty? No reply at all. Since Ted has died the little kid TA is running the show now. I wish I'd not bought a second power transformer from Weber. The one I put in today was half the price and it works perfectly.
Final Words... Working on a Valve Junior can be fun and enjoyable. I enjoy my little amp and I wanted to bring the joy I feel about it to others. Feel free to email me about things and I will try to find info for you or offer free advice. People have emailed me regarding modifying their amps. One guy put a 6L6 in the output of his Valve Junior after we discussed clean headroom and I sent him a schematic. Other people have added the extra preamp valve. One guy even started making his own turret boards for his Valve Junior. It's always nice to hear about how this page might provide some inspiration or how to information to others. I have tried to document my experiences as a readable and accessible page with some explanations of why with more of a focus on the how. Sometimes when I write things I think I'm "rambling on", but hey we all love Led Zeppelin. Have a good day, from Chris. :) |
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