Replies to This Discussion

Permalink Reply by GARAGE HERMIT on February 19, 2013 at 1:30am

it still looked like a rat's nest, so i unsoldered it all again and re-positioned everything, look's a lot better now,

 

Permalink Reply by GARAGE HERMIT on February 26, 2013 at 2:55am

well finished it, powered it up, not a peep out of it,bummer, tube's are glowing, but no sound, suppose it was asking too much for it to work first time,

Permalink Reply by eric gittins on February 27, 2013 at 1:30pm

now the fun begins!

grab your scematic and voltmeter and start logging all your voltages. clip your earth to the chassis, and probe around with the positive lead.  (old habits, but i do this with one hand only - left hand in back pocket. no sense inviting the electricity to run up your arm, across your chest and earth out your other hand).

you should be able to get an idea where the problem is if you have mis wired something this way.  if the power all checks out you could look at injecting a signal at the grid of the power tube, and work back from there.

i suggest checking voltages first, because if you have wired something up wrong, you might be overloading some components, so best to find out before they're toast.

of course, first-first check is visually tracing from your B+ line right through to the first preamp plate, and the earth line to everywhere it sould go, then the signal path.

leastways thats what i do.

Permalink Reply by GARAGE HERMIT on February 28, 2013 at 7:02am

thanks eric, i'll have a go, i only tried the amp with my piezo cbg, thinking not enough oompf in it, i'll try a humbucker git i have, (clutching at straw's)

started collecting part's for a 5C1 champ, my brother bent me a chassis up out of alloy,  i have the valve's and most of the cap's, resistor's etc,  need a quick fix of a working amp, just to bolster me up a bit,

Permalink Reply by eric gittins on February 28, 2013 at 11:46am

with no input at all, you should be able to hear a little hiss or hum at the speaker when you turn the volume to max.  also, if you plug in a lead, just touching the tip with your finger should give you an audible pop and buzz, (not the electric shock kind of buzz though!).

e

Permalink Reply by GARAGE HERMIT on March 27, 2013 at 9:19am

well put a 5C1 together, used the bottom part of a 3-tier steamer for the cab/head, some 3/16" tufnol for the tagboard and some 4mm brass nut's and bolt's for the tag's, finished it today ( -2 degree's in the garage though) worked fine no buzz or hum, only downside it's not very loud, as in talking level loud,  anyone think of anything i can check or change to get the volume up a bit,

 

 

Permalink Reply by eric gittins on March 27, 2013 at 1:57pm

post that little fender schematic with the voltages you are getting on your build.  measure at each valve connection including the rectifier,  at the pos. terminals of the filter caps, and the AC voltages off the tranny, both heater and HT.

check all points that should be at earth potential, to make sure they are, including the HT centre tap.

do these measurements with no input.

you should be able to get the volume on any champ to an offensive level.

(of course - always be careful measuring voltages in a live amp - use a clip to the chassis on your earth lead to your multimeter, so you only need one hand in the amp.  etc etc.)

e

Permalink Reply by GARAGE HERMIT on April 2, 2013 at 11:26am

here's the reading i obtained in red, the heater voltage's for the rectifier & valve's was 5v and 6.3v,

they're lower than standard, but would it lower the volume to talking level,? or is my vol/pot a dud i wonder,

[IMG]http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/cham...[/IMG]

Permalink Reply by GARAGE HERMIT on April 2, 2013 at 11:28am

Permalink Reply by eric gittins on April 2, 2013 at 9:00pm

hey fella,

at a quick glance, most of your voltages look OK, and the little lower than fender shouldn't be a problem. 

the 30v on the speaker isn't right though.  i'm assuming all voltages are DC?

and it looks like you only have one input on the build, can you draw a schematic of how you wired that jack into the preamp?

Permalink Reply by GARAGE HERMIT on April 3, 2013 at 8:22am

hi eric,

all the voltage's are DC,

what should i be looking for voltage wise on the speaker side of the OT,

there's 2 input's on it,

i was wondering could i just have 1 input jack ,

here's the schematic i'm working from, the only change from standard is the wire from pin 4 on the 6V6 now goes to the last 8uf cap and OT connection is moved to  the middle 8uf cap, i was told this mod made it quieter,

the only other strange thing is with no guitar or speaker jacked into the amp if i turn the volume pot to about 3/4 there's a high pitched squeel from one of the valve's, dont know what to make of that,

 

. 

Permalink Reply by eric gittins on April 3, 2013 at 4:18pm

there should be no DC voltage on the speaker side of the OT at all.

the power supply wiring you've used is just like the original.  i think whoever drew the second layout you have must have read the schematic wrong to start with. the only change i can see is the first filter cap going to 16uf, which is fine.

yes you could remove 1 of the jacks,  1 is hot, 2 drops 6dB.  if you remove jack 1, leave both the 75K resistors, and run the one that used to go to jack 1, to ground. you can just remove jack 2 and it's 75K resistor.

looking at you photo you seem to have extra resistors wired to the jacks, as well as the grid input resistors on the board, what are they and what are they doing?

on the 6v6 i can't tell you exactly how much plate current you are running because with that design i can't work out screen current,  but you are biased at 24mA (a bit less that the 32 of the schematic) and dissipating somewhere around 6W, which is pretty cold for a 6v6 single ended.

the squeal sounds like bad lead dress.  the original fender layout looks hoakey, but that kind of point to point is better than the board layout you have used - just not as easy to do, coz it has to be wired in the amp.  looking at your photo, there seems to be a bit too much wire flapping around the input,(though i know a lot of those go to your earth bus).  i would say tighten up the wiring.  but first, turn the amp on, get it to oscillate, and push the wires around with a chopstick (not a pencil) starting with the input section, and see if anything helps.  then address that area.

the dc on the speaker concerns me though, where's it coming from?  is it there with the 6v6 removed? 

also, just noticed, that one of the points that you say is 30V, is drawn as earthed.  check your earths against each other - the mains earth, the HT centre tap, the earth bus bar, the ref for the filament, anywhere on the chassis and the speaker earth.  there should be bugger all resistance between any of these.

e

• ‹ Previous
• 1
• 2
• 3
• 4
• 5
• 6
• …
• 9
• Next ›
• Page