I am looking for a push pull schematic to use with a pair of Edcor 10k - 8 ohm 60w OPT. I would like more power for this build than a EL84/6v6 can provide. Most of my amps are SE and I would like to build an amp for those (rare) times when nobody else is home, Ive had a few drinks, and want to listen to Metal.
My main speakers are Klipsh Forte I @ 99db sensitivity
My main speakers are Klipsh Forte I @ 99db sensitivity
That is kinda what I was thinking, but definitely more power than what I'm used to with my 45 SET amp lol
807s would work well with your 10K 60 watt output transformers. Look at page 3:
http://www.mif.pg.gda.pl/homepages/frank/sheets/084/8/807.pdf
Use a 220vac secondary transformer as a voltage doubler configuration for the 300 and 600 volts B+
http://www.mif.pg.gda.pl/homepages/frank/sheets/084/8/807.pdf
Use a 220vac secondary transformer as a voltage doubler configuration for the 300 and 600 volts B+
The zero-signal current is suggested 37mA. Doing Hi-Fi, especially with hot speakers, the average heat in the PTs will be far closer to 40mA than to 154mA.
That 37mA idle looks cold to me. I might aim nearer 30mA/tube (~~65mA per pair). That's still far under your 150mA spec.
I'd also look to 6550/KT88, being kinda a larger 6L6/807. The 6550 has a suggestion for ~600V ~5K load at 100W out. De-loading to 10K suggests a bit over half that, which is fit for your OT rating. However if these are Heaths you wonder about 0.9A vs 1.6A heater demand. OTOH to get ~~600V in the Heath PT you will be Silicon rectifier, avoiding considerable bottle-rectifier filament load.
For nearly all audio power pentodes, 600V on plates with 10K (even 5K) loading suggests running Screens WAY below full plate voltage. 6550 suggests ~300Vg2 for 5K, so even 200V will work at 10K. This means much less G1 bias and *swing*, easing the driver's work. However you see that G2 current can increase a lot on peaks, so it really wants a dedicated supply, not a saggy/hot resistor voltage divider.
Lots of good info here, much appreciated! The power transformers are Edcor 425-0-425 with bias tap and 6.3v heater taps. I purchased them off eBay a while back for a really good price, same with the OPT. I will probably make these into mono blocks on hammond steel chassis.
I appreciate everyone's advice and sorry for some of the dumb questions as I am not an engineer; most of my electronics experience is from my time in the Marine Corps, the rest I just "figure out" on my own.
I built a P-P 300B amp about 12 years ago and I liked it a lot. It keeps a good bit of the SE 300B "magic" while adding the dynamics that only a P-P amp can provide. It blew up during a thunderstorm power surge when I lived in Florida (the lightning capital of the US). I saved it, and have been waffling between repairing it and designing a new one. I have learned a lot in the years since I built that one.
The OPT's that I have are 6600 ohms, which requires class AB operation with 300B's. The old amp made 28 watts in AB1. If I were to redesign it, I would run AB2 for a little more power and better dynamics. I also have a bunch of 307A tubes which work a lot like 300B's when triode wired, and didn't cost me anything, so I may use those.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.