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In Reply to: RE: Is this feasible? Rectifying 6.3v for heaters posted by Audio Pete on December 18, 2017 at 09:30:08:
Hi Pete,This is a bit of a long story, but here goes.
The Citation 4, Citation 5, and the Electro Voice 30W subwoofer were part of the audio system in my old house and are to be re-united it the system in my stereo room under construction in my present house. The 30W was initially driven by a solid-state amp of conventional (for solid state amp) design. The amp screwed up and put DC on the voice coil of the 30 W. NOT GOOD! At that time fortunately Electro Voice still supported the speaker and did recone it. It was not cheap as it cost me $500 for the job. Ouch! The stereo store (Century Music In San Jose CA) where I bought the 30 W handled the crating and shipping for the 30W. The sales man at the time said "you know, when this speaker was designed amps had tubes". He said he also had a 30W and he was also bi-amping it but he was using an old Mac tube tube amp for it while driving his main speakers with a sand amp. I thought that what he was suggesting was backwards from what most folks do, but it made me think that driving a spendy speaker like the 30W with a non transformer coupled amp is probably not prudent.
A vacuum tube amp which would be flat down to below 15 Hz would be spendy. Since I didn't care about response over several hundred Hz I designed a transformer coupled push-pull amp around a big TV power transformer. This transformer was from a old energy decadent TV and was @ 500 VA. That means it has lots of iron and can go easily down to 10 Hz at @ 40 Watts. That may not seem like much but the 30W is ~ 105 dB / Watt so not a lot of power is needed. The amp uses CMOS power transistors in the push-pull output stage.
All was fine with this amp until the fridge did its thing. All that iron in the transformer is sufficient for 10 Hz but not for 2-3 Hz. When the fridge did its thing The core saturated and popped the B+ fuse. I added a protection circuit which would shut down the amp when there was much low frequency content at its input. That stopped the fuse blowing but the sub woofer amp clicking on and off when the fridge did its thing was annoying.
I was not about to part with the Citation 4 so I regulated the B+ supply. With the new Citation 4 power supply, The fridge and my 30W could co-exist.
I still have not updated the heater supply schematic to show the new pilot light circuit. Hopefully I'll get on that tonight.
Phil
Edits: 12/21/17 12/21/17
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- RE: Is this feasible? Rectifying 6.3v for heaters - coffee-phil 15:44:30 12/18/17 (0)
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