I've had the ampmaker site bookmarked for a long, long time, but I finally decided to give one a go. The old SE-5a has been improved with a couple of front panel switches so I ordered a kit a few weeks ago:
It's a lot of work, I spent at least two wet and windy weekends on it. The instructions are fantastic, especially bits that help avoid you getting into over-fiddly situations where you can't get a soldering iron near where you need it because there's previous wires in the way.
The instructions come with a list of comprehensive tests split into several stages. I followed them carefully because I've never worked with high voltages before. There was one voltage that was 100V lower than it should be but it didn't take me long to spot the mistake (I used to be an electronic engineer) - a 1M resistor when it should have been 100k. I had damaged a couple of resistors (twisted the legs off) and bought spares from Maplins, so luckily I had a spare 100k to put in the right place.
Thermionic emission!
The finished article. Currently with an EL34, hoping for a proper Marshall sound. I have an EL84 to try as well, courtesy of Karltone.
I have a cab on order and I'm looking for a used Greenback for it, but I couldn't resist using the 2x10"s of my AC15 for a quick run-through. It sounds pretty good, the VVR voltage scaling works well, turn up the gain and the master, bypass the eq for a really smooth power valve distortion.
Comments
Yes, that is bloody good for a first attempt!
Tip on the heater wires. Hook the wire to something fixed, like a bench fixed to a wall! Then, as the wires tighten up "go with them a bit" then stop the drill and let it relax. Takes a bit of practice but you can get a really tight twist that does not unwind.
And, my personal bête noir! Bare mains connections! I am surprised the kit did not contain boots and sleeving for deading conns!
But very well done.
The actual power into a load is not really related to the valve dissipation. You need a big, 100W, load resistor of the correct value and a source of steady 1kHz sine tone (computer) . Connect an AC meter across the load and P=V squared over load R....VERY rough and ready without a scope but it will tell you if the power out is in the ball park. (10W for EL34. 5W for EL84).
Dave
Insulating mains connections only makes sense in equipment where all the 'lethal' voltage terminations can be covered.
The point being that in most modern equipment (from hifi to industrial stuff) once you're past the power supply there are only 'low' voltages present on the system (5V, 12V 15V etc). It's easy and logical therefore to insulate any exposed mains or other 'high' voltage terminals, and render the equipment as close to 100% safe as possible. This enables reasonably safe Live working.
Additionally, most modern equipment can be regarded as essentially 'off' when unplugged.
Neither of these are the case in a valve amp. It can never be regarded as 'off' due to the filter caps, and there are so many dangerous contact points in the amp that the only safe way to proceed is to regard ALL terminals as live ALL the time. NEVER touch anything EVER inside the amp unless you know you have unplugged the amp, drained the caps and checked with a meter that there is no voltage, AC or DC, anywhere.
IMO it is bad practise to insulate some of the lethal voltage terminations in an amp, worse than insulating none of them. It's about the mindset of the technician/operator and the level of care exercised, and might lead to a belief that Live working is in some way safe.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Hope you had as much fun as I did.
More pics when it's in the cab...and some sound samples/video would be nice too
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Supportact said: [my style is] probably more an accumulation of limitations and bad habits than a 'style'.
Nice work, btw!