Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: glassesnvests on February 09, 2016, 11:38:49 am
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So I've been wanting to make a solid bass amp, and a friend of mine owned an AD200 that he loved. The 200W is a little much for my needs so I was wanting to make a 100w version, with only 2 6550's. Going off the spec sheet for the 6550, that means I need to shoot for 600V plate voltage and 300v screen voltage. A schem I found for the AD200 says that plate is 660 and screen supply is 375 before the dropping resistors at the screen pins.
The schem has the Screen supply coming off a separate secondary tap of the transformer. I can't find any transformers wired like this (other than the Mercury Mag drop ins that are for the 200W AD200 and 400$ per, yikes!)
I know it'd be a little hackish, but would it work if I used this transformer set:
OT: https://www.edcorusa.com/cxpp100-ms-5k (https://www.edcorusa.com/cxpp100-ms-5k)
PT's: https://www.edcorusa.com/xpwr173 (https://www.edcorusa.com/xpwr173)
and separate screen supply https://www.edcorusa.com/xpwr257 (https://www.edcorusa.com/xpwr257)
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Or is it necessary to have a separate screen supply? Or can it just be had off the main HT, assuming a current capable transformer? The AD200 seems like a very simple amp, just 2 Ecc83, (preamp and phase inverter) and an ECC81 as a cathode follower between the PI and power tubes? the biggest problem so far is the transformer issue, finding a suitable OT seems easy, but the PT is the toughy. Any recommendations are greatly appreciated.
http://www.prowessamplifiers.com/schematics/images/AD200BMarkIIIPI.jpg (http://www.prowessamplifiers.com/schematics/images/AD200BMarkIIIPI.jpg)
http://www.prowessamplifiers.com/schematics/images/AD200BMarkIIIPreamp.jpg (http://www.prowessamplifiers.com/schematics/images/AD200BMarkIIIPreamp.jpg)
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If your target voltages are 600 for plate and 300 for screen, then a 424VAC CT, AKA, 212-0-212VAC would easily give you both using the attached circuit. Go to Hammond's website and see if anything with 300mA to 400mA current capacity comes close.
http://www.hammondmfg.com/ (http://www.hammondmfg.com/)
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The whole point of the 600V/300V condition on the very large tubes is to use the split-voltage power supply scheme that Sluckey showed you.
Yes, 210V-230V AC each side will rectify-out to about 300V DC (that 350V transformer will give 495V or 990V DC!)
One 240V winding can be used in a voltage-doubler affair to give about 670V DC and a half-tap for screens.
The target voltage in the Suggested Conditions is 600V full-load; there will be considerable sag in any PT you would want to lift. The rated Max voltage on 6550 is 660V Ab Max; however this is routinely violated (say 700V, not 990V!).