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Old 14th July 2011, 01:00 AM   #1
diyAudio Member
Join Date: Jul 2004
Location: Wisconsin
Default My first project. Need some help...

I've decided to start on my first tube amp project. I've had a little experience with solid state but this will be my first go with tubes. I have access to a gentleman with some experience with Tube amps who's agreed to help me with construction. He's not wanting to do the math though, and I'm not quite knowledgable enough to figure out what exactly I need.

The amp I have my eye on trying to replicate is the Audio Innovations 500 integrated amplifier. 25W per channel output, has a phono stage in it. I found the schematics here: Audio Tube Amp Schematics

The questions I have are, what kind of transformers will I need for this? I see some voltages, but I'm not sure of the exact specifications on this one.

Also what kind of capacitors and resistors would be best to use? PIO? something else? What about capacitors?

I want to try and get a parts list together so I can figure out price and a plan for purchasing parts. Any help would be much appreciated.

Thanks in advance!
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Old 14th July 2011, 12:08 PM   #2
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Join Date: Jul 2004
Location: Wisconsin
Just noticed I got my resistors and capacitors mixed up in one of those last sentences. Newbie alert.
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Old 14th July 2011, 01:10 PM   #3
Loren42 is offline Loren42  United States
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Join Date: Sep 2008
Location: "Space Coast" Florida, USA
You should post this question on the tube amp forum.
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Old 15th July 2011, 03:29 PM   #4
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Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
The schematic I saw said 400V@2 to 3 amps, had a couple of 6.3 VAC supplies, then had a 6.3DC supply out of a separate winding. You should be able to take those specs and find a modern hammond transformer at a website like that will do the high DC and one of the 6.3 AC. It will also come with a separate 5 VAC, that you use to run the heater of the 5AR4 rectifier you use to produce the 400 VDC from the 450 VAC. I still like tube rectifiers, the slow heat up provisions are proven to work well with tubes. The schematic shows a 400V 2-3A rated bridge rectifier (silicon) you can do that instead of the 5AR4 but 400V rating is a little light, I'd go for 500 or more. This schematic doesn't show a choke on the B+, they are good for saving your expensive ($18) 5AR4. I also put 33 ohm 5 W resistors between the transformer winding and the plates of the rectifier, in case the rectifier tube (5AR4) shorts out. I install them on phenolic headers, sold as "terminal strips" now, but not the ones with the screws, the ones with the solder terminals.
To get the other 6.3 VAC windings, and the 6.3 DC, you might need some separate 6.3 VAC transformers. Putting the phone stage in the amp gives it a little heavier 6.3 vAC need than a guitar amp the hammonds are marketed for. Instead of the 50 V rated silicon bridge shown on 6.3 VDC, you can also use 1n4003-4-5-6-7 for the DC heater, there is no reported problem of hitting the heater hard and fast, just you want delay on the B+ according to most (and others think not using silicon B+ rectification is stupid).
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300

Last edited by indianajo; 15th July 2011 at 03:39 PM.
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