confused newbie

[ALBATROS1234]

hello guys my name is scott, im from new orleans. just a bit of background so you know who i am. i have been working as a union electrician for 3 years but used to be an electronics tech, did copiers and eventually medical electronics repair. i am 49 and have been playing guitar since i was 15 and actually in my younger years did some extensive gigging and opened up for national acts quite a bit. when katrina took everything i owned i was depressed at losing a lifetime of collected gear but since i wasnt gigging anymore had no need to rebuild my equipment arsenal. i did get a couple guitars and a small practice amp. lately i have been severely missing tone but im not in the position to buy anything of substantial cost atm i decided to look into getting some tubes back in my life the old fashioned way. building it. my long term goal is to build a full amp but i started with a preamp. from what i have read i thought i would prefer if the tubes were getting proper voltages rather than the starved plate stuff i have seen. i came across a broken 1950s powered speaker and thought i might used that and whatever else i could cobble together. the "real mctube ii" interested me as i had on hand many wall warts to make the power supply so figured i could start here.

so what i have is a 6sl7 preamp tube from the broken powered speaker (so i figured since it was a high mu dual triode similar to the 12ax7(cept octal) in the real mctube i could start there. so i basically followed the schematic as closely as i could using components i gathered from various sources such as an small unused tv. when i hooked it up the output was really low and noisy. it looked as though there was a dark spot on the side of the tube so i surmised maybe one side of the tube was fried so i hooked up the circuit going from input to triode grid2. after it was rectified i have 165 volts dc applied to the plate thru a 650k ohm resistor. jumped to a 500k pot and to the output. bam rock and roll. it was actually quite overdriven if i turn the knob up. sounding like a 60s cranked supro with channels jumped together perhaps even marshallish . the thing was fed into a cheap ss 10 watt squier amp on clean. i was surprised at how much gain and volume boost there was tbh. but it was lacking overall, the bottom end is loose and slop.

so today i get home and rewire to triode 1 and it sounded the same so i figured i must have boned it somehow.i rewire it back like the schematics and im back to very little gain and bit noisy. i get out my meter to take measurements and oddly im getting 52 volts dc to the plate on the 1st triode and 2 volts on the second. so i fiddle and swap around and i get it to 118vdc on one triode and cant get more than 1 or 2 volts on the other which i find weird because i have been taught in parallel current divides and voltage should stay the same. i decided to put it back to only using one half of the tube and vraaanngg cranking drive tone albeit a sloppy bottom end. it just seems so damn weird to get that gain from one triode of a 6sl7 so start testing volts and amps evrywhere i can think. it turns out im getting 118vdc @6.15 amps to the plate. this amperage seems really high to me.  im guessing this is why this 1/2 of a 6sl7 sounds like a marshall stack (with obvious limits and shortcomings.) i just dont really know what i am supposed to be getting exactly because i usually read guys talking about voltage and very rarely about amperage. and i just dont understand why if i wire the b+ in parallel to feed both plates like the schematic shows do i get the voltage drop on one side of the tube no matter how i re wire it. i guess i need to put it back like the schematics and check amps at various places because it didnt occur to me to check that until i put the circuit back to one triode an hour ago. thanks in advance for any replies, im new here and to tubes although i was visiting as a non member for the last couple months.yo see whenever i google a question it kept bringng me to links from this site so i figured this is the one to join.....scott

[sluckey]

You sound very familiar. Have you been here before, maybe using another name?

[ALBATROS1234]

no  this is the first time i signed up at any amp forum. and first post. just thought the problem was weird and figured maybe i could get some input. my goal is to start doing messing with tubes for a hobby. just cant really afford to get really deep in i eventually want to design my own personalized amp that i can tweek to be exactly what i want. been studying about tubes for no more than a couple months.

[sluckey]

Post your schematic and some hi rez pics of your amp. Maybe we can spot something.

[PRR]

6 Amps in a tube is absurd.

Please draw-up a schematic for what you have built.... you talk about an unknown powered speaker and a Real McCoy and then a 650K resistor... I'm not seeing it,.

And welcome.

[ALBATROS1234]

thats what i thought 6 amps wtf. when i get home from work i will draw a schematic, its the same layout as the real mctube ii at the dogstar site. the 650 k resistor is the one on the plate when running half the tube. on rmt schem its a 680k i used a 300k intsead of a 330k on the plate of the 1st triode. the powered speaker was a western electric 100f ,didnt mention that as i only was using the 6sl7 from that. thanks for your reply this has me scratching my head because when i built the back to back wall wart power supply it was only outputing  1.5 amp iirc.

[ALBATROS1234]

below is my inital circuit, basically a real mctube II without a bypass switch, it sounds weak and noisy, i rewired it twice and in between switched to the second circuit using 1/2 the dual triode it sounds decent but is perplexing as it seems it should not sound like this.

[PRR]

> components i gathered from various sources such as an small unused tv.

Use good parts. Especially when you do not yet know what you are doing.

> fed into a cheap ss 10 watt squier amp on clean.

These are HIGH gain stages. Two of those stages may be far too much to go to the "Guitar" input. I think the Real McCoy runs to its own power-amp? So McCoy was aiming for maybe 1V, your Squier expects more like 0.02V.

[ALBATROS1234]

the real mctube was intended to be a tube overdrive pedal with 2 stage gain . it is intended to go to the input of an amp.i used a small clean amp as thats what i have after having lost 10s of thousands of dollars in equipment. my old guitar rig was a 1971 ampeg v4b thru a marshall 4x12 bottom. but i have ownwed a fender twin and quad reverb, a 1970s 50 watt marshall, a 100 watt traynor etc.  i thought i would begin here and after i got something working add a tone stack and play with the values to tailor the tone. i surmised if i could get a decent preamp sound then i could later build a power amp section and upgrade the transformer etc. parts came mostly from a small tv that wasnt used much, i got input and out jacks from a broken pedal and the 500k pots are extra guitar parts. it was an inexpensive way to get started, i'm sure not the way a true long term hobbyist would approach it but i am limited severely by funds at the moment. i found the way it behaved to be odd and thought i might ask a few questions. i have been a long term member of a ww1 aircraft modelers forum and we are always happy to help a newbie get on the right track. i have seen u tube videos of guys who built that preamp circuit that sounded decent enough to be a starting point. i know i must seem like a pest but it was mot my intention thank you for your time and reply.

[PRR]

Well then, read your DC voltages and we will see if anything looks off, especially in the 2-stage plan.

I know about being broke. But a shorted cap or open resistor will cause far more frustration than it is worth.

[ALBATROS1234]

thanks, i did however double test all components including capacitance value with my industrial grade pro multimeter. im going to continue to pursue my goal of building myself a tube amp thats what i want regardless.

[92Volts]

Multimeters only measure current going through the meter. You'd need a clamp-type meter to measure current in a circuit, otherwise you must modify the circuit to include the meter in place of a low-resistance wire. If you connect probes to points in an otherwise-complete circuit, it effectively shorts them out (then measures the current through the short circuit it has created).

Considering the limitations of most power supplies (not to mention tubes and the resistors connected to the tubes) the only way I can imagine 6 amps is a measuring error similar to that.

[ALBATROS1234]

i think you are right 92 volts, after much experimentation and rewiring i get a lower amps measurement , closer to 3 amps just under to be exact. i think i have narrowed the problem down to one of 2 things. either the bridge rectifier i bought is somehow farting out when i split the voltage to the 2 different plates or their is a fault of some kind in my tube. i dont know enough about tubes but is it perhaps possible to have a short of some kind within a tube so that it works when you hook up one side of the dual triode but shorts to ground when both sides are hooked up? i even tryed another transformer because i though maybe the 2 120v step down to 12v into the secondary 12v to 120v rig could not somehow handle the voltage split. however when i hooked up a more powerful xfrmr that puts out 205v the circuit behave the same albeit when i hook it up to 1/2 of the tube like before it actually sounds better, pretty darn good to be honest. i still didnt expect to get such fuzz/gain for a mere triode/half of a dually but i am thinking this experiment as performed is a dead end. i need to either beef up the bridge and/or get another 6sl7 tube or just abandon the project and try to save nickels and dimes until i can but piece by piece and build a simple full amp, everyone does the champ which is ok but i have been poking around and think i may try to base it on a supro spectator with 6sl7 preamp tube 6v6 output tube and a 5y3 rectifier. just wanted to get my tone better as in my experience great tone makes you want to play that much more. thanks for the replies.