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traynor YBA-1A mkII OT . . . please help

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8/17/2000 5:03 AM
todd	traynor YBA-1A mkII OT . . . please help Does anyone know the primary impedance of the output transformers used in Traynor Bassmaster mkII's? I've asked many people, and nobody has answered. Please help. todd

8/17/2000 7:07 PM

Pete Traynor bought his OPTs from Hammond. Not hard to 'reverse engineer'. Depending on the Bassmaster (I've got one with 7027s, and I've had 'em with EL34s), the output tubes will want to see between 3800 and 5K ohms. Looking for the closest Hammond, which appears to be either the 1645 (5K/30 watts), the 1650K (5K/50 watts), or the 1650N (4300/60 watts). I suggest the 1645 because Hammonds are always under-rated, and I like a little transformer saturation. Some folks don't, so it's up to you. If you want it as clean as a whistle, the 1650N is for you. Match the physical size to the original and away you go. Myself personally, I would buy a Fender or Marshall OPT from New Sensor. The last price I got from Hammond on a 1650N was $103.75 Canadian. New Sensor sold me a Marshall 50 watt OPT for $59.50 US. You do the math.

8/19/2000 7:48 AM
todd	Thanks, Randy. I wasn't sure if Hammond transformers are the same as they were back then. I'm actually not looking to replace my transformer. I want to try putting 6550's or KT88's in my Bassmaster, so I've been trying to find out more about the tranny; I want to make sure the power handling and impedance will be OK. Does anyone know if this mod is do-able todd

8/19/2000 12:37 PM

I don't know the KT88 very well at all and would have to 'look it up', but the 6550 should be OK. Just like Chrysler built a few cars on the same chassis, more than one tube was built on the '807' chassis. This makes some operating parameters like plate impedance similar. Plus, remember impedances are pretty well anything goes; higher impedances yield less ouptput wattage/lower bandwidth/less distortion while lower ones give you more output wattage/more bandwidth/more distortion. The old guys bought their transformers compromising at least something. As long as you bias it up right (and there's an all day tale of neurotic preferences) you may/may not get the wattage you expect, but the 6550 should give you more headroom. With the cost of US 6550s I would use 6L6s and apply more feedback until I got the amplifier to break up where I wanted it to on the volume knob. I'll probably be told that's 'wrong', but it works for me, so there it is.

8/20/2000 4:17 AM

Todd,

It is pretty easy to venture a guess based on the output tubes and plate voltages employed.

You can also measure the transformer's ratio directly.

Simply apply a known AC voltage to one side and measure the AC voltage on the other. This will immediately reveal the transformer's turns ratio.

The impedance ratio is the square of the turns ratio.

It should be pretty easy to take a pair of clip leads and temporarily jump the filament supply to the output transformer (with the rest of the amp unpowered and disabled of course) and make your measurements.

Hope that helps.

8/20/2000 4:31 AM
Bird Dog	Todd, the schematic for all versions of the Bassmaster call for an 8 ohm load. The plate voltages differ greatly, as do the filter cap configuration, from the 1st series through the latter series. The front end configuration allows for for a couple of relatively easy mods, from the stock 4-hole 2 channel, to the cascaded pre/ master volume setup, like a JCM 800. Have fun.

8/20/2000 4:34 AM
Bird Dog	Todd, I forgot to say that I have done the mod you are contemplating on a later model high voltage Bassmaster. She's 5 years running and working like a champ-- no trouble. Email me if you have questions.

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