ROBERTLATHAM1

30watts is plenty for most small bars. 100watts will put you in any venue you want to play most peeps really only need a 50watt tube head most of them hit thier sweet spots at a tolerable level. i use several heads one as a pre amp mainly for tone and two others for power one is about (harmony) 45 watts the other is a (bogen) 100watt monster. yhe pre amp head is a marshall vs100. i use a 4x12 with g12m70's and the 100db mark aint sh--!

hey guys just got one of these bogen 100w pa's off of ebay. whats the posabilty of one of you guys having a scheamatic? its pretty straight forward though prob not need other than prescribed voltages ad so forth. havent received it yet so dont know if i will do the 6l6 coversion or not. any suggestions as i like the marshall brown sound but cant get enough of the fender pristeen cleans. p.s. mine was $130 and that was after going through several actions! thanx robert latham

from the b+ supply. i failed to draw it in. but i am very aware of where it is fed from. as for the fuzz stomp box this is a pre amp section from a marshall vs100, which does not sound like a fuzz tone, fuzz face, ect... in fact it is very versatile amp. it can go from a clean unsaturated sound to a blues top of the wave clipped signal or switch to the od 2 channel and get the "brown sound" run a ts-9 in front and go further or switch back to the original harmony stock undisturbed pre-amp for a really close fender twin tone. as for the errors on the drawing i admit it was thrown togather, but i know clearly what should be where lol. this is my absent mind at work again!

lmao! i liked those little amps back in the day LOL! well i do like tube tone, but i guess i am not what you would consider a purist. i like the tone that i am getting by using both a ss/hybred amp and a pure tube amp togather and would like to have the common features between the 2. so i guess the mod is possible, but not a recomendation for the tube purist ? has anyone here had the chance to use a marshall vs100(8100)? if you have ? you have to admit the amp does have good tonal quality and does have more warmth than a ss amp. grant it, it is no jcm! but does have a certain degree of warmth, not found in ss amplification.

well i agree that it is getting more along the lines of the jcm 900 with the jfets, but this circuit is what is used in my marshall 8100 hybred for the boost channel. i do like the way it can go from clean to blues crunch and then with the click of a switch you can go from classic rock to insane distortion. the tone stack has far more control than just the bass and treble(bass being master control) cuts of the harmony. however i do like the pristeen clean and warmth of the 5881's in the harmony so when i went to ad this circuit i wanted to be able to switch between an undisturbed harmony pre-amp and the hybred pre-amp for flexability as the harmony made a very good blues tone but volume had to be around 5 and as it is rated at 30watts this is way too loud for some places that i play. hence the need for the o.d. section as run my rig in stereo. i can also a/b switch between the two amps. this gives me the ability to get that clean jazz tube tone and still be able to come back to a big high gain sound. on the marshall i have added foot control to select between od 1 and od 2 as this was not a stock option. hence the same set up on the harmony. why settle for a vw when you can have a bugati! harmony-------\ guitar----ibenez ts 9-----alesis quadraverb+--< --- 4x12 cab with center bridge for stereo. marshall vs100/ p.s. i thought almost all the new tube amp lines use op amps now. is this not true? thanx

ok guys tell me if im right or wrong here, but i think this will work. here are the mods(od and tone stack) http://i49.photobucket.com/albums/f279/rob...harmonymods.jpg here is the original amp http://i49.photobucket.com/albums/f279/rob...am1/harmony.jpg i would really like the real amp techs here to tell me what they think. is this a posable mod or will this never fly? thanx robert latham

ok i have a harmony 535 tube amp with the same situation. no preamp gain control. i have been studing a circuit (a marshall design) and believe it will work if put in the right place. which i would break in the signal chain just behind the first gain stage on either chanlle of your amp. this is an untested design and really needs one of the guru's here to look over it and give me thier thoughts. if you pm me i will send a copy of the circuit to you.

really good artical makes you really think about more power. but! i have a 2x 6L6GC amp that i assume was rated at 35 watts but i think its closer 45 to 50 watts that is just a touch lower in perceivable volume than my 100watt marshall valvestate (solid amp with one tube in preamp) and niether seperate or togather can keep up with a heavy hitting drummer. i use a 4x12 cab with celesion G12m70's. so i.m.o.p. i think that 1 i need more efficiant speakers or 2 the need of 100watts tube power is needed to keep up with a double bass drummer bang the crap out of a set of drums. sorry! citadelmusic i just realized that was off topic

so the signal is merley pased and conditioned not boosted and the impedence is low so the tone stack is better able to filter the signal. this is the way the tube in the marshall valvestate 8100 is configured so im assuming here that it was used just for the tube conditioning and not for high gain(saturation)? and this is the cathode follower in a pure tube amp.

hey guys here goes another stupid question. i was looking at the marshall dsl 401 scheamatic and the signal on valve 3(last tube of pre amp before inverter) appears to be comming from the cathode of valve 3 to feed the phase inverter tube 4. the plates are still feed from b+ voltage(450vdc or there about) the first plate (pin 1) looks to directly feed the second grid of valve 3. the second plate of valve 3 goes straight toB+ with no junctions. the first plate of valve 3 has 1 junction to b+ and to the second grid of valve 3. the first grid pin2 is fed from earlier gain stages. woo! ok now my question is how does the signal feed through the cathode and not the plates for the signal gain? (signal is only tapped off the second cathode of valve 3). i have seen this on other marshall amps. the 8100 valvestate uses the same tube configuration on the boost channel. my question still stands "how and why does this benefit the signal. thanx robert latham

thanks pual very good reading there much better understanding of the design now.

hey guys can anyone shed some light on how LEDs are used for distortion in a cicuit. i understand the clipping part but where in the circuit and how to contol them with a pot. or even how to get a gain control circuit on 12ax7 for tube overdrive.

this looks like a very good read i will down load it and do some reading thanx lovekraft i think i have been bitten with tube amp addiction lol!

lmao! well you know i have read for months now on these things and i just about get the guts up to do a mod and then i talk to the guys on here and they prove that most of the stuff im reading is misconstrued in form or fashion to make it seem an easy thing but everything you do in one of these monsters is going to cause a chain reaction so everthing else has to be ajusted to compensate. so the mods are a reality but you have to ask yourself if you are willing to do all that has to be done. peace bro best of luck robert latham p.s. my best guess on the 5150 is a higher voltage on the plates and posablely smaller resistance on the grid resistors ala more gain and headroom at less distortion

thanx for your help paul as always you guys have managed to keep me from mutilating my gear lol

not certain but the 5150 prob has more of a early marshall design than the fender. it might even have more preamp tube stages i dont have scheamatic for 5150. but there are many places to get more gain out of most amp designs. the trick is not to try to get to much out of a single stage spread it out gradually through out the entire preamp and allow the power section to do most of the work you will get more of a managable overdrive/distortion. just my theory dont take it to hart im still learning these valve driven beast myself lmao!

well i have 5881 mesa tubes whoever it is that mesa buys thier tubes from. but i dont want to do it if its going to fry them. i have one old sylvainia 6L6GC that could prob take such a voltage but i think im going to use it along with some rca 12ax7 tubes that i have to build a single ended amp. (first ever build) so i think i might purchase some nos sylvianias they were the original tubes in this monster and it had a little more volume level than the marshall with them before i busted on out of its base duh! stupid move but hey live and learn!

it was in webers book guitar tube amplifier essentials it was on nos and new tubes i dont know how well the new tubes would hold up in real life. things are much different in some gurus shop than out in some dirty powered bar lmao! but i guess instead of wasteing my time and money on this harmony i should just go and buy a jcm800 and be done with it but being a poor electrician somewhat limits my gear budget. thanx for the info though you guys are always a great help.

i have read of tube testing done on the 6L6's with a bias at 35mA and a plate voltage being around 470VDC. this test included the EL37 and came out in favor of the valve art 6L6GC! but i have also read of some amps useing the 7581A or a few other tubes for sheer power rateings. hence the old marshall "50 watt" head walking all over the fender tweed as far as output db is concerned. i dont know but i think some of the 6L6 line can be pushed up to 80watts rms total amplifier output. i think the did it by pushing the plate and grid voltage as high as safely possable.

well this beast resembles a fender, but it truely is a design of its own. the tone stack is really wierd! there is a scheamatic in the gallery(harmony model h-535) i have gone through it. it is built well. point to point hand wired mallory caps RCA 12AX7 and two mesa/china 6L6GC's some of the resistors have drifted and need replaceing. while i am rambling. cuold i increase the plate voltages(present voltage 409V) on the plate and respectivly the grid to get more power out of the 6L6's. i have a marshall 8100 valstate that is 100w SS hybred and the harmony is just a hair under the volume output of it. so i would like to get the harmony up to the same volume level. i would like to run them in stereo. kinda get that early marshall tone out of the harmony and the later marshall tone out of the 8100. wierd but just me lol!

"tube guitar amplifier essentials" by gerald weber really good espeacialy for you vintage fender fans but does cover the british stuff too!

well yeah that does make sence! but however that is the process i used and those are the figures i came up with so i dont really know iam new to this tube stuff but trying to get a grip on it. i bought gerald webers "tube guitar amplifier essentials" and it has been a really big help i would like another book that has more step by step proceedures do you know of any? after looking again it would seem iam i little cool on my bias at 29.12mA this is useing the voltage drop across the tube. thanx for the clarification.

as you all well know i have been playing with this 6L6 monster lol! i took the voltage reading on pin 3 of the 6l6 (409v) i then measured the voltage across the cathode resistor(30.8v) which has no bypass cap (would adding say a 25uf cap here improve the bottom end?) anyways the cathode resistor=195ohms. now that the stage is set. i then began my calculations. i took the 30.8v cathode voltage and divided it by the 195ohms cathode resistance and came up with .154amps or 154ma. i then multiplyed this by the 409v plate voltage and came up with 62.986w disapation. now this is a combined load of both output tubes as they are both useing the same cathode resistor. so i then divided the wattage by 2 and came up with 31.493w per tube. does this sound like the bias is a little hot for 6l6 and would acount for quicker break-up and lower headroom? or even still have i completely fouled the whole bias calc process up?

wow ok lost but i think i will try this thing out wow!!!!!!!!!! electronics to an electrician is like brain surgery to a mechanic

well i checked all voltages and resistances and everything looks fine but the voltages are a little high (15 volts average over scheamatic voltage) i really dont know how to check the caps though my meter only has a palce to plug the cap into it so other than pulling them of the board i dont know . they are in a metal can with 3 seprate in each can. so........... but i think you r right with the cheap chine/mesa tube thing!