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Old 28th February 2003, 04:35 AM   #1
sangram is offline sangram  India
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Default Tube guitar amp

www.ax84.com

I've been thinking of building a tube amp for my guitar for a while, and I finally landed this site.

The P1 is a 5-6 watt EL84 SE-based design specifically for rock guitar. The attarction of the low power is to be able to crank 'er up to get nice tube OD sound without being evicted from the neighborhood.

The catch is, I've never built a tube amp before. Experienced SS constructor, but no experience with tubes except for the fact that I pulled apart a very very nice radio-gramaphone made by Garrard at the start of my electronic career. I did such a great job, nobody could quite put it back together.

I've been looking for the transformers and I finally found one shop in the market that carries a full line of products for tube amps, including the transformers - which is what I couldn't get at first try. I will be stocking up for a bigger 30 or 50 watt design, too but I need to build the smallie first.

I will be looking at a single 10" or even 8" speaker without a horn as this is only for guitar. Maybe an open-backed combo or a head/cab arrangement depending on how I can get someone to metal/woodwork the whole thing out, that's where I have a few problems and I don't want to buy/don't have space for lots of machining equipment.

Any specific tips and hints? I think I'll survive a few minor electrocutions but is there anything I need to really know well before starting out with tubes?
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Old 28th February 2003, 05:19 AM   #2
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Howdy,

The AX84 looks like a straightforward enough project to attempt. As you're already an experienced SS amp builder, simply use all the same techniques as you do for that, ie star earthing, always remembering that you have about 250V for a power supply, not 60 or so. 250V can give you a much bigger kick.

I would build it point to point, unless there's a PCB available for it at a good price. Order your parts, and lots of terminal strips, then spend some time mocking-up the layout so all the parts fit meatly, get it so all your earths come to one point, keep your filament wires away from the signal path as much as possible (around the inner edge of the chassis) and so few parts overlap. When you're confident the layout is OK, solder it up, and check the parts and any wire links off the schematic as you go. Otherwise, start to build it, carefully, and ask more specific questions as they arise. Best place to post them would be in Tubes.

There have been a couple of threads recently in Tubes about wiring amps, with some pix IIRC that might help.

www.tubesandmore.com are an excellent source of parts, as are www.angela.com

HTH some
Cheers
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Old 28th February 2003, 05:23 AM   #3
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Oops, I just looked again, and saw you're from India, so the two parts sources I listed in the US may be expensive with shipping and duties. Is Europe a better option for parts? Because if we know what is practical, someone may have some links to help.
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Old 28th February 2003, 08:52 AM   #4
sangram is offline sangram  India
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Thanks.

Yeah, I don't think I need any parts at all, I've managed to find someone who can supply me everything I need, locally and at half-decent prices, like RCA 6L6 for about 7 USD equivalent... I'm going to mainly have problems with the chassis and the cab. That is where I will have to depend on someone else to do it for me.

That apart, yeah I will be taking lessons from SS but since I'm dealing with higher voltages and some high currents, I'm a little wary. I would go for 8 way ribbon wire that's readily available, and basically mock up the circuit on vero with outlinks to the tube sockets. I'm going to have major issues with the tube sockets - I'm shaky about mounting them on the chassis. I need a good aluminium guy.

I will wait for a mod to move my post. Else it will be like a double post.
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Old 28th February 2003, 08:55 AM   #5
sangram is offline sangram  India
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Biggest Q, though is: What are the chances of getting electrocuted off one of these things in a band practice situation? I wouldn't want my mates to think that I played especially well the night I popped off, or something like that. Will I have to use mains earth or skip it like some of the newer cabs do? Since I'm coupling directly into a valve, will I live if the valve dies or passes some current into the grid?
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Old 28th February 2003, 11:26 AM   #6
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Default Small Guitar Amp

So long as you take care with the construction, and have the amp in a suitable cab/box, then it should be no more dangerous to use than any ss amp. I would ensure it has a mains earth, but if a valve fails it will not feedback to or damage your guitar in any way - if you are still worried you could always isolate the input of the amp from the guitar leads by using caps - 1000vdc rated would be more than enough.

If you are building a EL84 SE job and its for practice, not a Hifi job, can you cannibalise some of the bits from the Garrard system you dismantled? I'd have thought that the mains transformer, and possibly the output transformer, could be put to use once if they check OK.
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Old 2nd March 2003, 03:54 PM   #7
sangram is offline sangram  India
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Default Re: Small Guitar Amp

Quote:
Originally posted by bournville
...can you cannibalise some of the bits from the Garrard system you dismantled? I'd have thought that the mains transformer, and possibly the output transformer, could be put to use once if they check OK.

Yeah the Garrard had a lot of good parts, it was a 20 watt amp or so. Unfortunately I lost everything from it when we moved house. I don't even know where it all actually is, and I didn't know I'd need it later...
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