I've had real good luck building this Valco 510-11 circuit. For those who would enjoy retrofitting old and good looking vintage cabinets, this design fits the bill. The sound is fat and stuffed to the brim with harmonics. What one could call a "bedroom" amp.
I would be willing to assist in sourcing the 3 common tubes, transformers, and related components. Total cost will be somewhere around $200+ however this circuit is fairly forgiving and used power transformers, sockets, knobs, & chassis not only make the amp look better, it's cheaper as well.
Uses a 5Y3GT, a 6SL7, & a single 6V6. The last one I built went into a suitcase. The preamp section was biased well below maximum, but acted so hot that with the modd'ed preamp volume when turned up added a vibrato. This design is extremely sensitive, simply hammering the neck plays loud.
In this small venue (Cigar Box Nation) I will be glad to share my schematics & links to the most reputable parts suppliers. This amp will not only fit a small foot print, but will preform well with a standard guitar & will allow you, the tube novice (and experienced builder alike) to enjoy the amp that Jimmy Page used to record Stairway To Heaven with.
Search the web for Valco 510-11 images. The drawing is tilted slightly, that's the one.
If there is some interest, I'll post a couple of pics of what I have, maybe a youtube clip as well.
Rest regards, Doug
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The next video is currently being edited and will be up in an hour or so. In this I need to make a correction regarding the wattage of the power supply resistors. I mentioned that it would be OK to use a one watt resistor for R8, R9 & R10. Make R8 a 10 watter at least, then R9 & 10 a 5 watt. I did work alright for me but on paper this simply won't work seeing that the audio output is already 8 watts and all the "juice" (B+) goes through this component R8, the other two can be 5watt.
Here is the 3rd video which discusses layout & machining-punching out some sheetmetal-
The above link is not public.....This link will work https://www.youtube.com/watch?v=wXv2NuutVJI&list=UU9W4Vl201YkwF...
Enjoy
Here is another 2 videos....https://www.youtube.com/watch?v=hw594YI5RcU
the first powering up and the installation of voltage reduction resistors for the 5.0v & 6.3v filament supply. Also everything is installed, almost. Review of the schematic.
https://www.youtube.com/watch?v=g3xpyLCqF8o
These are 2each 10 vids
Also mods from the original included the 3 power supply resistors in addition to the "master" volume add on 1 meg ohm pot.
Last night I ran some mini coax to the pre-volume pot & the master volume pot with the .05uf/600volt signal coupling caps. These are a sweet way of "setting your tone". Typically the larger the value, the more bass you will have. It's not uncommon to see .01uf in these positions or even .02uf, but Valco saw it good to run the larger .05 uf. As you look at them from the front panel facing you, the pots have 3 leads, the far right lead gets grounded, so as I'll show you in the next video; all 3 pots (including the treble pot) have the right lug grounded, with the same wire. Then extending over to the ground lug on the input jack. For now the input jack is where we will get out ground from due to the fact that the chassis and the shield are connected within the shorting contacts. Minicoax was also run to pin1 of the 6SL7 preamp tube as well. I'm grounding the shield at one end only, which is standard practice. Connected to that ground wire for the pots then run over below the 2each 270K resistors on pins 2 & 5 on the 6SL7 tube.
Some info regarding this Switchcraft input jack- The input jack has 3 connections. the largest one IS the signal and located on the very end of the 1/4" male plug. As you will notice,it has a position contact laying against it when a plug is NOT inserted. This electrically is the center lug & needs to be soldered (the lug) to the next lug to the left. Which is the ground (chassis) connection. Now that you have preformed this center & left lug connection, the input is temporarily grounded when NO plug in inserted.
Also completed are the bias resistor install, the filter caps, and the connection of B+1, B+2 & B+3 to the output Xmf, to the 6V6, pin 4, & to the outside of the 270K resistors. Which when you look at the schematic, you will see.
Hope you are all following along. I see over a dozen views of the videos up on YouTube. I believe in another 12 hours or so of bench time, the 3 Tube, 8 Watter will be finished. It should start to sing fairly soon. -Doug
It's alive!!
With my odd power transformer (WWII vintage) I found that my build is very clean, drat! So I am planning to go back to the original 6.8K & 47K power supply resistors. But I will need to do some final work in checking some levels here & there. I will most likely post a new schematic and BOM when I'm done.
-Doug
Having a day at work where I sign a lot of paper so I had a chance to catch up on the videos. I keep getting more and more excited. The idea to do this build along was brilliant! Now I have actuality seen what and why things are.
Anyway, I found a broken small watt combo amp that I am going to buy for parts and when I do get around to building this beauty I will post some shots on this thread.
Keep it up and thanks!
Small watt combo, nice. You might be able to gut the chassis & use it for your build, this way possibly you could still use the front panel. You'll need the 2 watt pots however in this B.O.M.
Give thanks to beatlejuice for compelling me to add the videos.
I've been all over the 6SL7 cathodes trying different caps (2, 5, 10, 22, 47 microfarad) & resistors which are coming in lower than normal. The volume is only half of what I'm used to. I did go back to the 6.8k & 47k in the power supply & no difference. May try lowering the 270K plate resistors. Having a hard time getting the plate load to rise, so these are next. This is measures with the 1 ohm resistor to ground from the cathode, those measured millivolts across the 1 ohm resistor directly convert to milliamps, then which was only .006Ma, this times the plate voltage 373vdc will = the plate load in watts. Lesson for the day!
Doug
It's completed!
May do another video tomorrow. This amp is very, very quite when plugged in with no strumming. Super gluing the twisted 6.3Vac filament wires into the corners really did the trick in that regard. Initially off the amp was low in it's output. I went into the cathode resistors, R3&4 (pre-amp tube), tried a couple different cap-resistor combos, with about a 50% improvement, them today went over R1&2 and clipped one end of R1 & mini-clipped my way into the circuit with my trusty resistor decade box, it only took going to 220k from 270k, with a BIG improvement, then onto R2 which went way down. These are NOS tubes, ended up at 47K which actually set the overall tone & not much volume improvement, but thats OK because it's loud, really loud. My bias is still to high on the 6V6 at 20 watts (max is 12 watts for this class "A"). Guitar amps can enjoy a limited tube life mainly because the owners are used to replacing their tube every hundred hours or so, unlike the HIFi builders who like you may imagine love to keep their stuff running & running all the time. In that case I would bias the 6V6 tube more around 8 watts.
There 2 reasons why I have been tweeking this, actually 3. The last one bascilly is it just was low on volume, the 1st is always that I always seem to have slightly different outcomes, and it's oK because I experiment with different types of components. Example (updated schematic & BOM coming) I used the ever popular .001uf/1500 volt ceramic disk cap across the 1st set of 10uf/450 volt filter caps, ($0.60ea)(connected in series for a 900Vdc rating). This is more like a Silicone diode setup, with no tube rectifier. It's a very small cap designed to catch very fast pulsations (AC) & still turn them into D.C. More of a protection item, but you can't hurt this (any) straight tube amp with almost any power blip. The 2nd & 3rd set of (series-ed) filter caps, C-6&7 were again connected in series & were the larger 47uf/450V ($1.60ea), That is 2ea for C6 & 2ea for C7. The 3 position "MODE" switch, or Mojo switch, is always populated with the pre-amp's cathode to ground resistor & capacitor combos. Trying these lets you find all sorts of tones tested normally with only one of these "MASTER" or "PRE" volume maxed and the other set safely halfway down. For instance, I was looking for the cleanest setting for the full CCW rotary switch position "1" and found another more dirty combo on the 2nd cathode (6SL7 tube). The other 2 positions are for the most part fairly clean except when you have the "PRE" volume turned up, then you can tell the difference. So in your process of tweeking realize that establishing your tone from this amp (or any other) or whats more commonly called "voicing", it seems like a never ending process. Once you learn the different sounds and attempt to find them in your circuit with component swapping, you will realize that at different times, different guitars, venues that your tastes will drift away from what you originally liked. That's OK, and back to voicing you will go. I sometimes simply start another build, but this time perhaps with different manufactures of coupling caps, other values, even using some WWII era caps that seen to test OK, and there always that different Power Transformer.....which changes up more than I want to realize with the high voltage winding being 50 AC volts or so off in one direction or another.
For the most part, using the original Valco 510-11 schematic for your first build can't be bad. My modded "hot rod" more like "Rat Rod" is a fun way to exceed the norms and have your way with the thing. The Master Volume control is simply a way to enjoy splitting up the overdriven sounds of each of the two tubes. You can actually hear the FAT 6SL7 coming in with the "PRE" maxed out and the master volume turned down to halfway, and vise versa. With the Master Volume maxed, and the PRE turned halfway down, there is that smooth 6V6 overdriven sound that many, many guitar amp aficionado will tell you their like nothing else, no 6L6, or anything else can touch. Placing a microphone in front of one of these little gems is a very popular way of studio recording and even live performances. Don't let size fool you. A 1.5 amp fuse is perfect. And by the way, when I called this a "bedroom" amp, well, you could gig with this amp in a small bar, it's loud. Which brings me to another subject, the Speaker~
Speakers for guitars are a different breed. Some say that it's efficiency that makes a good guitar speaker. Well for this amp that's a good point. Warehouse Speakers link http://wgs4.com/ is the most respected outfit with all guitars players & amp techs alike. This model link http://wgs4.com/12-g12q-20-watts ...the infamous 12G is a good deal at fifty bucks, Amazon has this Eminence Cannabis Rex 12 inch link http://www.amazon.com/EMINENCE-CANNABISREX16-12-Inch-Rhythm-Speaker... which last November I found for only $65, not that I'm promoting a weed based amp speaker, but darn, the thing sounds really mellow. Actually any "Eminence" speaker is top shelf stuff. The only thing better is any "ALNICO" type that uses a super magnet- Aluminum & Nickel, that really kicks out the notes, kicks out the notes right out of your wallet too! I have been blessed however with old speakers recovered from junk HiFi sets, old defunct music equipment. Like the old saying goes, someone's junk is someone's treasure, and so it goes. Remember that '46 NOS Fender 10" Alnico in that old radio cab? It sounds like no other I might add. So to close know this, this amp relies on a large emitter, speaker. Even dual 12s or even 10s, or 8s. Single or dual, this is going to have perhaps the largest impact on your tone. Take your chassis (when it's all buttoned up) down to your local Guitar Center & try one of their speaker cabs out. Hey that's what their there for.
Seth; tell us more about that little combo cab you found. What size speaker does it have? I refurbed many of those things. Great for projects like this. Check out your local fabric shop & look for some vinyl table covering material, table cloth. It's a rel nice Tolex (amp covering) type material. plenty cheap & available. Tons of choices. Also the fun thing is to buy your own wood, Lowes & Home Depot will cut your project out for free, and build the period correct looking box that at that time were made (get this) to look exactly like a TV! Has this little rounded corner square hole dead center. Others had a delicate scroll sawed logo across the speaker hole. Speaker covering is also a have to have. I found some real nice stuff at these fabric shops, also the best at Hobby Lobby craft store in the window treatment aisle. link http://shop.hobbylobby.com/products/brown-woven-decorative-panel-wi... this is see through salt & pepper looking with browns, tans & reflective to boot. Would make real nice retro speaker grille covering. Actually the current trend is retro, so ride that tide! Always search on your smart phone for their instore coupon. I found one for 70% off. Presented it on my smart phone to the cashier & whola!
Can't wait for 'yall to start in on yer own 3 Tube 8 Watter. -Doug
Very nice Seth. Hey, you know with a bass, most amps hate those, except a bassman! You think it could be the speaker? Simple test is use a AA battery and see if the diaphragm moves, even an ohm meter (on the ohms scale) will make a small scratching sound, or at least a reading on the meter. Also the Output XMF could of died. If the B+ supply is solid state, could be the rectifier, but normally it will not entirely fail, just sound weird.
Seth, have you seen this? link http://forum.gibson.com/index.php?/topic/48731-new-epiphone-valve-j... Good luck man, let us know how you are coming along -Doug
With the link I read- a puddy knife is needed to open it up. Maybe not so hard if it's already been opened. A resistor? Maybe in the bias supply, or the cathode resistor, both on the larger side. Looks real sweet from the outside.
A friend who does mainly Fender repair says that almost every amp built from the 80s on has failed in one way or the other within 5 years, especially the newest ones from China. Says that they last a year or 2 at best.
The back is barely on right now, so getting it back off will be reasonably simple. I may actually trim it down as I like the option, when recording, of placing a microphone on the back of the cone.
I will attach a schematic I found as well. Things may become obvious when I can finally open it up, or they may not. It it is obvious and simple, I may repair. If I will be chasing gremlins for days, I would rather spend the time building something new. I will post up some updates when I get em.
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