Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => PC Express and JSchem - Schematics and Layout diagrams => Topic started by: DummyLoad on January 08, 2010, 12:03:25 am
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all, i'd like to share this amp with the forum - buttery and i are planning on a build and why i'm posting it here.
enjoy!
--ISO
edit - fixed the grounding nomenclature & the standby switch i so thoughtfully omitted. :embarrassed:
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Are you sure you want to have the two coupling caps from V1a's plate in parallel?
Just an idea: I think ECL86s are no longer in production and pretty expensive. You can use the cheaper PCL86/14GW8 instead but these need 13V filament voltage. Combining and rectifying the two low-voltage secondaries would yield about 12V which is close enough. I can draw a schematic if you're interested.
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Are you sure you want to have the two coupling caps from V1a's plate in parallel
absolutely! :smiley:
ECL86s are no longer in production
correct. i have a nice little stash... enough to last me a for quite some time... ;)
...and pretty expensive
expensive is relative - USA branded versions (still euro tubes tho) can be had for around 25 USD - certainly not on fleabay though... that's not too bad considering that you get 1/2 euro made 12AX7 as a kicker.
the PCL tubes are definitely an option in the future... if i were to do so and do things proper, i'd have a PT wound w/ 13V RMS filament secondary along w/ a 6.3V and use switch selection - or just simply do as mr. geezer did; acquire a 14V transformer.
:wink:
the 6.3V and 5V fil windings strapped in series should give ~~11.3VRMS still marginally within the +/-10% spec for 13V tubes. the 12xx tubes could also on run @ 11.3V, again marginally out of +-10% spec. the plus is that filament life is extended, the minus is there would probably be some loss in gain - but i'll defer that last statement to the experts.
I can draw a schematic if you're interested.
by all means, please do so if you're so inclined and have the time. i'm always open to new ideas.
respectfully,
ISO.
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Here's my suggestion for an alternative power supply for using PCL86/14GW8 tubes. It is on the second sheet of your schematic, the first sheet (your circuit) is unchanged. I have only simulated this circuit but haven't built it. So if you decide to use it, use some caution before you fry your tube filaments.
The filament voltage will slightly rise if a tube fails, but it will not rise above 13.8V as long as there's at least still one tube left (if all tubes are gone it won't hurt them, will it?). This should be no problem since you'll switch it off soon and even 14V should be within specs for the tubes, at least for some time.
The 7805 regulator is a universal solution for generic 5V relays. It can be replaced with a resistor that drops 7V if the relay current is known and it can be dropped completely with a 12V relay.
Best regards
Bernhard
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hienz, thank you.
i don't think the regulator needs a heat sink - with the relay on, Pdiss would be ~~350mW.