Replies to This Discussion

Permalink Reply by GARAGE HERMIT on October 23, 2012 at 9:35am

think it was just the connection's here that were wrong, what do you think,, and thank's very much for taking the time to draw out the layout drawing, much appreciated,

would it be worth putting a fuse in the B+ supply, 0.1A ??

Permalink Reply by GARAGE HERMIT on October 26, 2012 at 11:57pm

eric,   sorry you've lost me again, my 6.3v  has'nt a CT, so how and where do i connect the earth ref and what value should the resistor's be, thank's,

Permalink Reply by eric gittins on October 27, 2012 at 1:59am

no sweat fella.

to reference the heaters to earth, you create an artifcial centretap by running a 100ohm resistor from each of the ac heater wires to ground.  some old fender amps just earthed one side of the fil to the chassis and ran a single heater wire, but this is a top way of getting mains hum into your signal line.

a heater supply referenced with the resistors will be better (less hum) than a floating heater supply. 

there are better designs yet that reference the ac heaters to an elevated dc voltage to lift it away from the voltage range of the cathode and grid of the preamp valves, but the resistors to earth is a good start.

e

Permalink Reply by GARAGE HERMIT on October 28, 2012 at 2:02am

thank's for that eric, made a bit more progress, just waiting for some more resistor's i've ordered to arrive, it's starting to get a bit cold in the garage now, 4 degree's last night, but i'm still enjoying it, just thinking when i get this working it might be an idea to solder all the component's to the underside of the chassis instead of the seperate tag board, less soldering and a lot more compact design, 

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

Permalink Reply by eric gittins on October 28, 2012 at 12:12pm

ah, heading into the depths of another dark UK winter!  just cominging out of our own now - 29 degrees today and 16 overnight.

when you say 'solder components to underside of chassis'  you mean on shorter tag strips, yes? not direct to the chassis?  like proper point-to-point wiring (which i suspect your donor radio would have been)?

earth connections direct to chassis from multiple points regularly create earth loops, and signal earth running through the chassis picks up noise too.

your schematic is fairly simple, so you could try point-to-point.  to do that, i would draw the layout with the valve bases in their real placement & rotation in pen, and start drawing in the other components in pencil, and just keep working until you're happy.

you could also just split your tag-board.  isolate the separate parts onto their own boards - preamps / power amp / power supply.  that way you can still do the assembly on the board before you go into the chassis, but you can place each board in the best spot for your valves.

the thing about tag-board construction like you have, is that it's fairly easy to identify and access individual components to tweak values when the amp has been up and running.

from what you have, i would seperate the power supply components to make the space a little easier for the rest of the circuit.

don't know where your new resistors have to go, but it looks like its done. have you powered it up?

oh, and i have only ever fused on the mains side of the trans. haven't fused the B+ or HT. can't really say on the advantages or dis of doing so.

e

Permalink Reply by GARAGE HERMIT on October 29, 2012 at 9:21am

no, not soldered directy onto the chassis,

yes, good idea that, still keep the tag board but in seperate section's,

just realised it myself, i'm nearly ready to power it up, finger's crossed, just waiting for the 100 ohm resistor's to arrive,

 think my next project will be a fender " 5C1- CHAMP" look's a lot simpler,

 

Permalink Reply by eric gittins on October 30, 2012 at 11:22am

i reckon it will all look a lot more simple when it goes in the chassis and you lose the miles of pink wire.

already thinking of the next amp before this ones powered up - sounds like you're hooked!

don't know about the UK, but over here through the 50's, we had stacks of mantle radios and radiograms with a 5y3 rect. and a 6v6gt - that's a pretty good start on a champ.  the radiograms often had a 12" speaker with the output trans mounted on the back, they sound really good for guitar.  keep your eyes peeled.

then of course you'll need to find the parts for your vox ac15 clone, and your marshall plexi, and your tweed delux....

Permalink Reply by GARAGE HERMIT on October 30, 2012 at 12:17pm

yes, same over here, valve radio's and radiogram's, i've bought a few, plus the valve reel to reel tape recorder's, record player's, etc in the pic's, yes i've been well and truley hooked, lol,  cant wait to build some more amp's after this one, but i have to learn to crawl before i can walk, what i'd like to build is an amp using the big old coke bottle shape valve's, a bit frankenstein looking, just got the bell sound the other day, not really sure what the amp type thing is in the alloy chassis, i only bought it because i might be able to use the transformer,

Permalink Reply by eric gittins on November 16, 2012 at 12:58pm

that bell sound amp look completely awesome! what a find - is that 2 6v6 push-pull?  it looks like it's practically a 5C3 tweed deluxe in a head unit.

it's been a while and no updates - didn't give yourself a nasty shock? blow anything up?

hows the amp?

e

Permalink Reply by GARAGE HERMIT on November 17, 2012 at 8:54am

hi eric, no nasty shock's, or anything like that, just started a new job on a power station build, 12 hour shift's 6 day's a week, so it does'nt leave much time for amp building, plus the temperature's dropped quite a bit, and no heating in the garage,

the bell sound is all original, i got it quite cheap about £20.00, as it's 117v no one seemed to want it, i've a transformer 240v down to 117v so all good there, the valve's in it are 5Y3GT, 6SL7, 2 x 6V6GT, 2 x 6SC7, think it'll be push pull as it's a hi-fi amp,

bought a few more thing's for part's etc,  about £10.00 to £15.00 each, nobody seem's to want thing's like this, which is good for me, when i get a bit more free time i'll get back into it,

 

 

 

 

 

 

Permalink Reply by GARAGE HERMIT on December 29, 2012 at 4:00am

found this schematic, the thing that interest's me is the power reducing zener diode's coming off the rectifier, could this system of reducing power output be used on my amp,?. or any amp for that matter, and why is the B+ coming off the 5 volt rectifier heater supply, if it's too involved to explain, that's ok, i was just wondering about it,

Permalink Reply by GARAGE HERMIT on February 17, 2013 at 1:38pm

un-soldered everything, it was just too messy, it's still quite busy, but better than it was, hope to get it finished tomorrow, here's hoping,

 

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