surfsup wrote:availability, could you clarify? You are using a full wave, the rectifier at bottom left of the pdf, not a full wave bridge, right? I'm not sure what you're referring to when you use the term 'voltage doubler'
I was planning to use the FWB and tape off the centertap so I should see 250*1.4 = ~350V at B+. So I thought the Hammonds would work fine with 250VAC, but your post concerns me.
the problem is you can't just tape off the center tap because of how the transformer is constructed. the secondary is like two secondaries facing each other, wound out of phase. i've been too lazy to modify my dumblator (u see, it's in a small enclosure) for a voltage doubler so i haven't, but it still works.
surfsup wrote:If I use a FWB and tape off the CT on the hammond that will work right? I just need to be sure. If anything I can get that from AES or mouser and just use a 1k resistor instead of the 1k choke for the B1.
usual dumblators use a voltage doubler too, if you haven't seen it.
i forget which one is good for what application, but theres some difference. something about peak reverse voltage and allowable current and capacitor specs and all these crazy witchcraft.
ecisthebest wrote:...the problem is you can't just tape off the center tap because of how the transformer is constructed. the secondary is like two secondaries facing each other, wound out of phase.
The secondary is one continuous winding. The two ends will be out of phase with respect to the CT, which is referenced to ground in a FW rectifier. No problem using half or all of the scondary (taping-off the CT) with a FWB or doubler as long as the current rating of the winding is observed.
okay I'm going to get the Hammond PT, and figuring for 125VAC supply at my wall vs the 115 supply the PT expects, here's what I'm going to do to put 340V and 280V on the two supply nodes (got these values from an old schemo by structo, I think). I assumed 1.8mA for the CF since that was about what the last two CF's were pulling when I measured them in other amps. Yea, I know probably not that accurate, but most of the voltage will be dropped across the 82k anyway so it should be close enough even if I was off by 0.5mA:
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Just to let ya guys know, I've gotten the heyboer tp2-x from Allen amps before without a min order. Just send him a money order instead. It fits perfectly inside a 1u rack or on the back panel easilly.
surfsup wrote:okay I'm going to get the Hammond PT, and figuring for 125VAC supply at my wall vs the 115 supply the PT expects, here's what I'm going to do to put 340V and 280V on the two supply nodes (got these values from an old schemo by structo, I think). I assumed 1.8mA for the CF since that was about what the last two CF's were pulling when I measured them in other amps. Yea, I know probably not that accurate, but most of the voltage will be dropped across the 82k anyway so it should be close enough even if I was off by 0.5mA:
just confirming, it works. but my transformer measures 300vAC (dont ask me why) and also 7.2vAC out of the heater taps, so i have 6v DC heaters. but i can get 404vDC at the first capacitor node if i wished. just letting you know.
did voltage checks. 380vDC just after the bridge rectifier, through a 15k resistor down to about 370v, and a 68k resistor down to 300v for the cathode follower's plate. pin 3 was at 30.0vDC.
also, with the 6vDC heaters, the dumbleator is completely quiet. there is no "noise" whatsoever. i thought i did something wrong when i fired it up. turned up the controls to max and no sound. i hit my guitar strings, and it scared me. haha!
Well i bought the allen PT and itcdoesn't fit on the outside. But, glory be she fits inside! I dont think i can squeeze a piece of paper between it and the cover, but it does fit phew....
