Firefly - First build problems

[flood]

hi to all from bombay, india.

this is my first tube guitar amplifier build - the only thing i built before this was the 12W hi-fi EL84-Ultralinear oddwatt which worked like a dream.

perhaps it was the simplicity of the oddwatt that facilitated its function. the firefly, however, just reported a loud distorted humming.

i must admit that i am not especially proud of the construction. i think i thoroughly underestimated the project and fooled myself into thinking that it was simple. i managed to screw up on a number of counts - i designed the layout on paper, forgot t reverse it while building so now all the components are facing inwards, making it impossible to tell which component is wired to what... strike one.

lacking access to glass epoxy board (you won't believe how difficult it is to DIY in india, even in a metropolis like bombay! my years in germany have spoiled me.), i foolishly thought that perf board (with the wider hole spacings though) would be a good compromise. strike two!

and to top it all, i forgot to horizontally flip the component layout for the first tube, so that a bunch of wires are crossing each other all over the place. stirke out.

i still think i can make it work somehow without dismantling the whole thing. i havetried to mantain 90° cross points, and maintain the fundamental principles of shielding.

for all signal paths, i used 1.2mm tinned copper wire with a loose but thick shield. shielding was done only at one end.

heaters were hooked up with tightly twisted wires (i could have used thinner ones, i think). used two 100ohm 2W metal oxide resistors to create a virtual CT for 6.3v.

grounding - is complicated, to say the least. it's not exactly star grounding - 1. i put an eyelet close to the ground of the IEC socket. let's call it the "faux star ground" 2. ran a length of unisolated 1mm copper wire on the "PCB" so that all components to be grounded would be grounded there. this connected via wire to "faux star ground" 3. speaker outs are grounded at one point, which is connected via wire to the "star ground". 4. OT 0 ohms grounded directly at faux star gnd. pictures will make this messy description a little more understandable, i think.

all resistors metal film/metal oxide, almost all capacitors ERO (now roederstein) or philips orange/trop fish.

transformers were wound locally according to the specs on the firefly schematic - 215VAC and 6.3V secondary, OT - 22.5k Pri, 0-4-8-16 sec.

i think i should mention here that the voltages i am getting are surprisingly low. unloaded, i got 300VDC - 280V and 270V. for some reason this has now dropped VERY low - to 190v and 186V on V1 and V2. will measure V3 tonight, but i would doubt it exceeds 210V. i attribute this to high-impedance transformer secondaries. am i right?

also, i dont know if this is a cause for worry. i have the two transformers in an L shaped configuration because fitting them at opposite ends or next to each other at a relative 90° angle was causing problems elsewhere. could this be the root of the problem? will try shielding the mains tranny off and see if it has any effect.

the symptoms:

a HUGE hum and very little of anything else. i can faintly hear the guitar coming through the speaker, but it's so soft, it could just as well be the unamplified thing! the hum is quite loud, perhaps i perceived it as being louder than 2W because it was 2 a.m. the funny thing is, this isn't quite what i would call motorboating, which i've had in a couple of modded overdrives. the volume pot has little effect - the only thing that changes with the volume pot is that beyond a certain point, the hum becomes more treble-laden.

i will try poking around (albeit a little more carefully than last night - i popped my cherry in the stupidest of ways, not from the caps but because i forgot to pull out the IEC cable!). i will also take some pictures, which i will be very ashamed to upload - very shoddy work, i promise that my next amp is NOT going to look like that.

i would appreciate any suggestions that are thrown my way (as well as the brickbats when you see the pics! :S)

[flood]

i examined the firefly today by first checking all ground connections. i hit the jackpot in the first round itself - i had, like a total idiot, forgotten to ground the filter electrolytic caps! using a thick piece of copper wire i rectified this error, and flipped it on again. it was dead silent this time - i my first thought was that i had forgotten to connect something, but when i pluged in my bass and turned up the volume it roared into life. it was very quiet even with the boost on.

i can't make any definite comment on the guitar tone as such - i just moved back to bombay and need to do a full cleaning, stringing and setup job on my fernandes. i also need to hook up a guitar speaker - i have a WGS reaper and a veteran 30 waiting to be installed in cabs.

i expect a good tone, however, given the quality of the components used and the faux point-to-point construction (perforated board).

putting finishng touches on it - the bleeder resistor i have used is 220k + 100k, 2W each - reason being that they are in the circuit all the time, and the voltage drop on V1 would be considerable with smaller resistance values (the CRCRC values are 47/22k/47/22k/47). the junction is convenient to raise the reference voltage, in case i need to squeeze out the last few dB of heater hum (inaudible as yet).

so thanks for whateverhelp was coming [] - i've finally built my first tube amp! yippeeyahoo.