Legacy Valve Edition 15

[niftynev]

Gidday guys! My first post!. Yeah that's my first amp & guitar there in my avatar. Legacy Diamond Classic collection guitar - it looks beautiful!. Both chinese copies i know. I could only afford the $1k for both of em. Supernoob but starting to learn to play. I've been a tech for years. Fixed a few amps, built quite a few transistor & mosfet amps, but never played guitar through em! I've been on the other side of things, so to speak.

Anyway, before i dive into the amp, i was wondering if someone may know about these amps cutting out sometimes?. It was brand new when I got it & it's only been used for just a handful of hours.

I suspect it's a heating problem, as the back of it is pretty much closed in, compared to other guitar amps I've seen. I can see 5 valves protruding downwards, through a long oval screened cutout in the back. 3 of them have a metal shield around them - probly the phase splitter & preamp valves i'd guess, with the output pentodes unshielded.

If it is a heating problem, would a small computer fan in the top of the chassis induce much hum or noise into the circuit? I'd guess a fan at the pentode end, where the output stage is, would cause less interference.

The chassis section is just over 60 mm high, so probly a 50 mm fan would be the go, if I was gonna use one.

I'd appreciate any help; a circuit would be awesome!

I'll try to help youse guys where i can, in other areas.

[gary]

the equivalent epiphone range is/was known for problems with cheap fuse holders.

[niftynev]

the equivalent epiphone range is/was known for problems with cheap fuse holders.

Wow thanks Gary! - You found it in one! I found a cheap white plastic in-line fuseholder hanging off the power transformer. It had partially melted, so there must have been a voltage drop where there shouldn't have been. The offending fuseholder was on the dark blue 6 Volt winding for the valve heaters. And you scored another goal Gary too - my investigations have lead me to believe that my amp is basically identical to an 'Epiphone Valve Standard Amp', down to the same boards! I saw a video of epis being built in a factory - in China! This then leads me to believe that my amp was probably built in an Epi factory! As someone mentioned, the pcb for the speaker outputs has had some (epiphone ?) numbers ground off - perhaps so it's not too obvious that this is an epi pcb - just built into a 'Legacy' chassis instead.

So I've been trauling the net for info & problems with the 'valve standard', & tried to work on the main ones.

ricach, from the Vintage Amps Forum, said - "The PT is underpowered in the 6.3V tap. The heaters draw more current (2.42A) than that tap is rated (1.6A)." So there's 2 problems in the heater area now! I'll fix them both. I'm waiting for a 6V 3A toroidal mains transformer from a friend, to take the load off the underpowered winding in the original p.t. I've had to move the main transfomer about an inch closer to the rear of the chassis to make room for the 77mm diameter toroid. I'll just use piggyback spade connectors on it's mains leads, as they will connect across the existing transformer's mains input terminals. I'll use the 100 ohm resistor to earth off each 6V lead of the new toroid, but I'm not sure what I should do with the (now unused) 6V winding, perhaps another pair of 100 ohm resistors?

I'm gonna remove the 3 mid-air cheap fuseholders & use heavier duty panel types inside the chassis, on maybe a perspex panel.

ricach also mentioned - "the tabs where the PT connect to the pc board will eventually break the connection on the board." So I desoldered & removed all the existing spade terminals from the board, & drilled 1/8" holes in the board at each point for brass bolts. I then modified some piggyback spade terminals to use & bolted them up tight before soldering everything together. Should be no more problems there now.

bigjoe, from the Music-Electronics Forum, was getting popping, clicking, crackling, squealing & humming noises from his EVS, & found C7 & C27 to be the culprits. These are both .022uF 400V 'brown turd' caps. So that's tore it for me! I've now 'flushed' all the brown turds from my amp now, & am eagerly awaiting delivery of some nice 'orange drop' 600V caps to replace the 400 volters, plus a few other bits, from WES components.

I've got pics of my progress so you can see what I've been doing.

[niftynev]

Some more pics of my progress.

[niftynev]

more pics of my mods & preparation for mods.

[niftynev]

more shots of the progress so far.

Someone was really peeved about breaking their rear cabinet panel into 3 pieces trying to get it off! I can see how this could happen with the weak points at the ends of the oval cutouts. It took me a fair bit of effort to get the thing off safely in one piece, But I managed it. I got some baby powder & a hobby scalpel!

The rear panel is a very snug fit inside the main cabinet, & the vinyl covering sticks the panel & cabinet together. First, I gently tipped the amp over & Layed it on its front. Then I sprinkled baby powder into all the cracks around the outside edge of the rear panel, where its vinyl-covered edge was in contact with the vinyl-covered inner edge of the cabinet. I sort of worked the powder into the crack, trying not to get powder all over the place! I loosened the blade of the scalpel & turned it around so that the blade end was held in the handle, & the 'blunt' end of the blade was sticking out. I then used the blunt ent of the hobby knife to sort of 'work' the powder into the gap, by carefully pushing & wiggling the blade along, & trying to push more powder in as I went along. I had to be careful to cut or tear the vinyl, but it worked pretty well. Just about the whole blunt end of the hobby knife slid down into the gap. The whole point of the powder was to put a film of powder between the 2 surfaces, so they would release without sticking.

After I'd been around the rear panel with the knife & powder I was ready to try & prise it out. In the end I used a pretty solid teaspoon, with the back of it against the rear of the amp chassis, & the front tip just under the edge of the panel. The gently curved rear shape of the teaspoon meant it wouldn't leave any scratches. Slowly, slowly bit by bit the panel started to move. Then it just separated after that.

[Structo]

Welcome to the forum Nifty.

Looks like you are well on your way to fixing your amp up.

Many of the Chinese amps have inferior components and soldering.
That's why they are so cheap!

Your amp may be soldered with non lead solder as per ROHS regulations.

Not sure if Australia is ROHS yet or not.

But, it looks like you are using some good quality leaded solder that is superior in it's wetting and bonding properties.

For the life of me I don't know why they instituted that standard before they had the formulas and techniques down.

I have fixed several amps with non lead solder that all were a result of faulty solder joints.

[niftynev]

Thanks Structo! As a matter of fact I'm just about to jump on the 'treddlie' & ride round to the post office & collect my 6V 3A toroid transformer, some tagsstrips, & a 4700uf 35V electro I bought from a friend (thanks Andrew!).

I'm still waiting on WES Components (hurry up guys!) to deliver me a set of orange drops to replace all the brown turds (lol!), a couple of other electros, a dirty big rectifier bridge & some decent fuseholders.

I'm gonna rectify the output of the toroid to DC with the big bridge, & connect the 4700uF across it. Hopefully then, there'll be less hum-radiating conductors running along the circuit board for the heaters. I'll keep the 100 ohm resistors in place.

I'm replacing C28, the first filter cap across the HT rail after the fuse, with a 100uF 450V, which is double the original value. I can't remember where I heard this, but it sounds like a good idea anyway.

There's enough room just to the left of the input socket on the front panel of the chassis for another switch. I was thinking about an appropriate looking black DPDT rocker switch, to bypass all the dsp if required. I could switch from normal to 'full valve' mode. Do you think that would be worthwhile? Now's the time to do it, if I'm gonna, while the things in bits. What do youse reckon?

[niftynev]

I picked up my new heater transformer & got it mounted on the chassis today, with a tagstrip for the parallelled 6V windings. I glued a 10,000 uF 16V electro (thanks again Andrew!) to the chassis with silicone next to the tagstrip, & connected its wires to the other 2 tagstrip terminals. When I get the bridge rectifier there'll be good connection points for it. There's also a convenient spare 4mm mounting hole for it in the chassis. A couple more progress pics here too.