Tubes

trendyironicname · February 04, 2008, 12:15:46 PM

I've been reading up all I can about tubes. I want to use them in pedals and such down the line. I put that so I won't get in too much trouble for asking here. I'm trying to get together enough info and parts to put together my own low watt amp ala the valve junior or something. BUT I'm totally ignorant of transformers. I say this to my shame. This is like my favorite group of people when it comes to this part of my life so maybe someone will help. Google's no help when you don't really know what to look for. I know how they work but I'm still trying to figure out what to buy/salvage. No schematic really has the pertinent info I need. I don't really want to buy something expensive if I can go out to the shed and rip it out of one of old solid state pa amps i have or a practice amp or even maybe use one of the fifty wall warts sitting in the closet. Trying to do it on the cheap if I can. Sorry this is off topic. I'll make it up to yall.

DWBH · February 04, 2008, 12:26:02 PM

Low wattage amps huh?
www.sewatt.com

petemoore · February 04, 2008, 12:54:56 PM

Junk collector [me] got lucky..chassis, OT/PT, 9 pin sockets all geared around El84's...
Fairly common to find old stereo stuff with 6v6 or EL84 output tubes, many products made/bought/sold/used/worn down...
Get a small AC voltage to check tranny's with.
I found one with stated 6vac output, measures 7.6vac..
Putting that to the primary side of the PT, and reading the AC output [watch out for HVoltages while perfoming these tests, clip off and isolate any extra leads coming from iron with electrical tape, I like to clip so there's no insulation stripped off...
Say you get 11v out...do the math and find the reflected impedance.
for simple example...say 1vac is put to the primary, and 2vac appeaers on secondary, you have a 1:2 step up, with this tranny, 120vac will become 240vac..find a PT which is in the ballpark for ac output, by the time you rectify and filter it becomes about 1.4 x this amount, in DC....ie a 200vac output probably ends up around 260 after becoming DC...but it depends on the rectifier chosen...
The OT matches impedance of the output tubes to the speaker, EL84's are about 5400ohm output, the speaker is 8 ohm...the equation goes...find the impedance ratio.
Say it's 26:1...the math would go 26x26 =676, then 676 x 8ohm[sp] = 5408, right in the pocket.

mojo_hand · February 04, 2008, 02:10:08 PM

Quote from: DWBH on February 04, 2008, 12:26:02 PM
Low wattage amps huh?
www.sewatt.com

And http://www.ax84.com

aron · February 04, 2008, 02:18:39 PM

I would go with a kit if possible. I warn you now that hi-voltage is nothing to be fooling around with if you are a beginner. HEED ALL WARNINGS! You might want to consider modding a simple amp first.

ambulancevoice · February 04, 2008, 05:37:02 PM

id start out with a simple tube pre amp (12ax7 or something), rather than an amp
best to get a feel for them before attempting anything close to an amp

also, +1 on the HEED ALL WARNINGS! note, there is ALOT of high killer voltages involved with tubes, any small mistake can mean SERIOUS INJURY and/or DEATH

serious shit

petemoore · February 04, 2008, 08:17:54 PM

Yupp...I get to typing right along...
A foolproof method of amp safety is let an amp technician do the work on it.

trendyironicname · February 04, 2008, 09:50:43 PM

I'm fairly alright as far as it comes to safety. (famous last words) A kit may be the way to go. I've repaired many an amp but the transformer stays as a black box to me, which I hate. I like knowing the intricacies before too long. I was a quality (HAHA) assurance tech for peavey for a while (the signature was only that it was up to their standards, not necessarially my own..) and I've many a one hand in a cs-800 or something BUT I don't know if that makes it alright for me to build from scratch. I'm not scared of it and I'm versed in the "hidden demons" -undrained caps, forgetting to unplug it-and I've been reading every radio book this library has. I've got every other component thoroughly sorted out as to what they do, how they do it and what it takes to get them to do it. I just know jack about transformers. I will hold off on it, if I'm naively thinking I have the safety aspect of it covered. And I'll take it as an honor to wait if you guys still think it best. I see Aron as one of my top 5 mentors on the subject anyway, since the first papers I ever printed out to learn about tubes were written by him. I'll start looking at the websites you guys found for me. I hate asking for help like this alot because I feel like I'm always taking and not really giving. That'll change one day though. And Pete, wow, that was concise and perfect.

If I'm overreaching, thank you guys for bringing me back.

trendyironicname · February 06, 2008, 10:13:06 PM

I really like ax84. I registered for sewatt like weeks ago and still nothing. Wondering if I should attempt to re-register.

aron · February 07, 2008, 03:05:30 AM

Here's a tip, check out these books. I have nearly all of them. Incredibly good and lots will apply to stompboxes!

http://londonpower.com/books.htm

brett · February 07, 2008, 06:33:54 AM

Check out 18watt.com for schematics, advice on where to buy transformers, kits, etc.

Their amps are a bit more serious than what you are describing, but you might be disappointed with a small (e.g. 1W) amp once it's all together. The Epi junior, at 5W, is cheap and totally ripe for modding. Actually, one of its weaker points is the output transformer, so you could buy one and swap the OT for a Hammond (IIRC MartyM did this and was very happy with the results).
cheers

News:

Tubes