by EWBrown » Sun Jan 25, 2009 4:35 pm
8BQ5s are especially flexible, the filaments are rated as 8V, +/- 0.7V, so there is plenty of allowable latitude.
Another source of approximately 8V for the filaments is to get ahold of one of the 1970s vintage 5V, 3A linear regulated power supplies, the power trannie and rectifiers usually deliver around 8VDC before it hits the regulator and pass transistor. I've seen these PSUs for dirt cheap, and even if the regulator is blown, the trannie is almost never bad.
FWIW, a 6K11/6Q11 can serve as a 6.3V filament 5HA7. Just use triodes #1 and #3, the pinouts are compatible, and triode #2 is not usesd (pins 5, 6, and 7). The high gain ald low gain sections are also compatible.
6U10, the low gain and high gain sections are swapped around, so that one is NOT a drop in replacement.
6AC10 is almost three 12AT7 sections, close enough for most 12AT7 VA and LTPI (as in VTA-70 driver) applications.
Another of my many incomplete or uncompleted amp projects is a PPP EL84, using the Poseidons, or posswibly a VTA-70 driver board as the drivers. Basically a rip-off of the VTL "tiny triode" 25W triode, 46W UL design, but as a single chassis "dual mono" design, rather than two monoblocks.
The related project is a stripped Hhath AA-151, retaining only the original bare chassis, traisformers, basic power spply and power amp sections, using Poseidons or equivalent P2P circuits as the drivers. That one is much closer to completion, I have 80% of it functional. Just to choose the final VA/LTPI design remains....
/ed B
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