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In Reply to: MQ introduces a new limited series of output tranneys posted by MQracing on May 14, 2004 at 08:31:51:
This sounds really interesting to me.
Thankx
Michael
Follow Ups:
There are several posible approaches, as suggested by Mike and Douglas below. I have never heard of any results - probably someone in Japan has done it though!A related problem is to simulate a tap where one does not already exist. I have heard of an unsuccessful attempt to use a cathode follower driven by a voltage divider between plate and ground, and direct coupled to the screen grid. Apparently it would rather be an oscillator than an amplifier. So as with any new or untried circuit idea, experimentalists should budget some time and effort for debugging.
I hope someone tries and posts the results - but it probably won't be me!
HEY-Hey!!!,
The parafeed UL is an interesting proposition. SE and UL but with DC-Free primary L.There are a few options, and depend on the plate load. An inductive plate load will need a larger B+ for the screen signal than a CCS type. The goal will be to provide a low output z screen supply, modulated at the UL tap's fraction of plate signal.
A cathode follower, or source follower will do an adequate job. Set up a seperate rail, at 2x B+, and self bias a cathode follower at what ever fraction of B+ you want the screens to operate at under idle. cap couple its grid ( or gate )to the U-L tap, and you're off to the races.
For a low voltage tube like an EL84, an IRF820 might be a reasonable choice, or a 12BY7 ( relax Eli, there won't be enough folks doing this to make them any scarcer for your Brown Monster ), or maybe a 5687...
regards,
Douglas
Hello Braubeat:the UL taps are on the coil mostly for the airgapped versions wherein the power supply is in series with the primary winding of the trans...
then you just hook it up a you would any UL circuit configuration.The parafeed implementation uses the same coil.... as the RH-40, 60 and 80... and, hence, it too has the ul tap by default.
running UL with parallel feed while not technically impossible... is so cumbersome that I can't imagine anyone doing it....
you would need to have a DC screen supply and a plate supply each of which was in parallel with respect to the signal and you would need to use a blocking cap (as far as I can tell) btwn the screen and the UL tap as well as btwn the plate and the plate lead on the output transformer.
Like... I hinted at.... the ul tap was incorporated into this design to give folks more flexibility in the range of applications that this trans would be suitable for. Though, i clearly envisioned that the UL taps would be most likely used in the RH-60 model in particular.
hope I've answered your query,
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