Replies to This Discussion

Permalink Reply by GARAGE HERMIT on April 16, 2013 at 1:45pm

yippiee, got it working ok, swapped the OT wire's to the speaker around, as i'd beed advised, although i cant see how it would make any change,  and tidied up the wiring a bit, it sound's ok but it's clean even at full volume, i was expecting it to distort a bit, is there anything i can change value wise to get it to break up a bit,?

 the resistor's on the input jack's are to keep it grounded when the jack is removed, to keep the amp quiet, my jack's are switching jack's, i removed them anyway it did'nt make any difference, noise wise,

the 30v on the OT, if i have a primary supply i will have a secondary output voltage, all the earth reading's are ok,  

what's wrong with the board layout i've used,?

Permalink Reply by eric gittins on April 16, 2013 at 4:20pm

hey, that's great news fella.

the resistor from input to earth, shared between jacks (1M) that usually go on a fender dual input is not required in this design.  the grid leak bias design (for the pentode input) needs that 5M resistor and does all the earth referencing you need. 

volume wise, if you have wired the jacks as the schematic, the number 1 input will be louder than the number 2 input.  only  the number 1 jack should be wired to switch to earth when not plugged, input 2 is unswitched.

you said that 30v on the secondary of the OT was 30VDC to earth.  a healthy output transformer (or any trans really) will not couple DC current from primary to secondary, only AC.  the only current on the OT secondary should be the coupled AC (the amplified guitar signal) that on the primary side of the trans, rides on top of the B+. 

http://van.physics.illinois.edu/qa/listing.php?id=2354

again, there should be no dc potential between either tab of the speaker side of the trans to ground.  if there is you are loading the voice coil of the speaker, which the AC signal then has to fight. look at the speaker cone closely when you first turn the amp on.  if there is a turn-on thump the speaker will move, but should return to its original neutral position.  if it moves fwd or backward and stays there, you are running dc through the speaker.

i didn't mean any offence about the layout, so sorry if any was taken.  tagboard layouts are fine, as has been evidenced by the many thousands (millions?) of fender, marshall etc amps built using that system.  for production, it is much quicker, and therefore cheaper.  the extra lengths of wires needed though, can cause issues with stability, and make lead dress important - this was one of the problems with fender silverface amps.  the comment was directed towards the general concept of point-to-point over tagboard - not to disparage your layout.

cheers

e

Permalink Reply by GARAGE HERMIT on April 17, 2013 at 12:40am

e,

i was'nt offended by your statement, just thought i'd done something wrong on the board, yes it does end up with a lot of flying lead's, i'll have to try a point to point ,

did'nt know about the AC riding on top of the B+, jeeeze there's a lot more to these tube amp's than i thought, but it's interesting and i'm enjoying it though, i was really pleased with myself when it actually worked, if not quite properly,

if there is some DC somehow getting to the speaker that's probably why it is'nt really loud and wont distort/breakup at full volume, i've taken it apart to put in this small solid state champ lookalike cab i bought cheap, i'll check everything, value's etc of the component's and the wiring, and see if there's anything amiss thank's again eric for your invaluable help,

 

  

Permalink Reply by GARAGE HERMIT on April 18, 2013 at 12:02pm

just been thinking, i did'nt run a ground wire from the speaker secondary like it's shown in the drawing, would this have an effect on the volume of the amp, plus it seem's wrong to be running one leg of the OT's output to earth, or am i missing something,? 

Permalink Reply by eric gittins on April 18, 2013 at 2:28pm

one leg to earth is how its generally done. might not matter in your amp as it doesn't have a feedback loop, but shouldn't be causing a problem.

did you double check that all earths are earthed? clip the neg lead of your voltmeter to one of the mains transformer mount bolts, then check all earth points for zero voltage DC, including chassis, both terminals at the speaker and the speaker frame?

if you have a DC voltage on the speaker, that might explain why it worked a bit better when you swapped leads, with the speaker playing backward, it could pull against it already full travel, when before it couldn't push past that? (fwd or backwards playing speakers don't generally matter unless you are running more that one speaker and they aren't all playing the same direction).

e

Permalink Reply by GARAGE HERMIT on April 18, 2013 at 2:57pm

i've nearly finished wiring it all up in the belcat cab, i'll check to see if the DC voltage is still there, i did check all the earth's for continuity before i stripped it down, all ok,

the backward's speaker thing sound's like it might be that with  DC on the speaker,

i did have the speaker leg earthed, sorry about that, , oop's, 

Permalink Reply by GARAGE HERMIT on April 21, 2013 at 10:19am

finished putting the bit's in the s/s cab, it sound's fine, just that at about 3/4 volume i'm getting some hum, think i'll have to look at my lead dress, or could it be something else, ? camera batteries went flat so only one pic for now, ,

Permalink Reply by David L. on April 21, 2013 at 11:17am

That is a sweet looking amp Garage Hermit!

For my own education could I please ask -  The blue wires look thicker than the ones I use to hook up circuits - are they screened cables or just chunkier wires?

Are you going to call it the Garage valvemaster. the Valve hermit, GH valvetronic MK1 or something else?

David L

Permalink Reply by GARAGE HERMIT on April 21, 2013 at 8:25pm

thank's,

the wire is just what i had in the garage, left over from a job i was on year's ago, it's just 1.5mm, not screened, a bit too big really, i'm not sure what most people use, 1mm or 0.75mm probably, i'm waiting for my brother to gut some old computer's and use the wire from them,
had'nt really thought about a name for it, but "valve hermit" sound's good,

Permalink Reply by GARAGE HERMIT on April 22, 2013 at 11:35am

eric, no DC voltage on the speaker wire's now,
i did'nt think it was loud enough but my wife said she could hear me on the guitar in the garage, so i think it is loud enough,
here it is finished (apart from the hum) tried it with an old celestion 15" speaker, sounded pretty good, it's a well made bit of kit, has some band name scratched on it and the year 1956,

 

 

Permalink Reply by GARAGE HERMIT on April 22, 2013 at 11:37am

 put a pair of sink drainers on the back to let the heat out,

 

Permalink Reply by GARAGE HERMIT on April 29, 2013 at 11:32am

the hum i'm getting on the 5C1 i built, do you think i's the way i've grounded it, ?

 

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