Very high voltage tubes?

gearhound

gearhound

Lunatic Member
I have a 425v per leg, 350ma power transformer.
What tubes can take the very high voltage after rectification, without resorting to drastic methods (i.e. FET's), to reduce the voltage?
I'm hoping to put together a tube amp with some reasonable output.
Any/all suggestions will be greatly appreciated!

THANKS!!
Steve :scratch2: :thmbsp:
 
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with 350ma 6550 is a possibility what other secondaries does it have ? And any idea of what it came out of ?
 
It's center-tapped? 850vct? Use a choke-input supply and you can pick from LOTS of tubes!!! that's a perfectly ordinary voltage for output tubes.
 
Measure DCR and no-load voltage (be careful!!!), and then plug in the values in Duncan's free PSUD software. Use a tube rectifier and choke input, and you'll get B+ under 400 volts, with LOTS of current capability and decent regulation -- and that's a good thing!

Stacked OD3 or similar volt reg tubes can give you a reg supply too.
 
If you have a high enough current rating on the 5 and 6.3 taps you could get away with a nice KT-66 Williamson.
 
mpholland said:
If you have a high enough current rating on the 5 and 6.3 taps you could get away with a nice KT-66 Williamson.
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And if not (probably is though), it's cheap and easy to add a filament transformer just for the output tubes. Then you can switch those on first.

If it is NOT centertapped, and you want to go all out, use a fullwave bridge and choke input to get ~750 B+ for stereo SE845 drawing ~90ma each. That's a long way from full power from an 845, but it's a wonderful as a 300B, more linear, and the tubes last and last.
 
What have you built before?
What is the db rating for your speakers?

Your power supply might limit the tubes you can consider to drive your speakers?

Best from Tucson
Bob
 
becketma said:
Your power supply might limit the tubes you can consider to drive your speakers?
Click to expand...

Um, I think that was the point of the question in the first place. He thought his power transformer was going to put out too high voltage.

But from fullwave with centertap to ground and choke input (about 0.9 X 425) to full wave bridge and cap input (about 1.4 x 425 x 2), he's got a lot of leeway in target voltage, from under 400 to over 1100, and many points in between.

So... what do you want to build? Tight budget or no? Big junk box of sockets etc or no? Basic metalworking tools available or no? SE or PP? Are you open to transmitting tubes? What's your budget for output transformers?
 
I've put together smaller EL84 and 6V6 tube amps from schematics.
But I'm pretty sure I do not have to knowledge or skill to design my own tube amp.
I'd like to use some of the larger tube family.....EL34/6L6/ KT88/6550.....but am limited to 25 watts MAX, as that is the maximum wattage of my 50's University tri-axial speakers.
I'll probably go to Edcor for the OPT's, as they look like pretty good bang-for-the-buck.

The 10 pound unknown NOS PT is center taped, with 425 volts on each leg.
The 6.3 volt supply is also center taped, the 5 volt is not.
I do NOT know the current capabilities of the 6.3 and 5 volts supplies?


Steve
 
gearhound said:
I'd like to use some of the larger tube family.....EL34/6L6/ KT88/6550.....but am limited to 25 watts MAX, as that is the maximum wattage of my 50's University tri-axial speakers.
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Speaker rating doesn't need to determine maximum amplifier capability... But I think 25 honest watts is a lot (I have efficient speakers), so I wouldn't try to talk you into more. Quality is more important than quantity, or you wouldn't build a tube amp anyway.

Plenty of great schematics around. Try the free PSUD to know what to expect from that iron in different configurations. Set a load to draw what you think your tube load will be (e.g. 100ma/pair X2, + 10-30ma for drivers etc.).

Remember that SE means no phase splitter, fewer tubes to wire.. you could make an SE EL-34 or 6550 amp that sounds great. I heard one I liked a lot with James OPTs.

You can estimate the load for those fil windings by adding some tubes in parallel while measuring voltage. Watch the droop, and the load when it drops to 6.3 or 5. Back off on the real load if you want to run it cooler, but you might not be using anywhere near the 350ma capacity.
 
Tubino is on the right track here.:yes: FWIW, Heyboer wound the OPTs for my SET (strapped of course) EL34. I think they did a fantastic job, and they were very affordable. I sacrificed some power though, for less distortion and had the Pri. Z wound to 10K. I'm running just over 500v B+. It is definately one of the amps that I will NEVER sale. I'm getting around 6 watts, but if you went with a more conventional 5k Z, you could expect 9 or even 10 really nice watts of EL34 goodness.:drool:
 
It sounds like you have a good power supply for a screen-drive amplifier where the output tubes are horizontal sweep tubes with the control grids either connected to the cathodes or a small negative supply and the input going to the screens. The Berning schematic is here:

http://www.davidberning.com/support/ea230

It always looks a bit more butch for the output tubes on an amplifier to have plate caps. I got a quart fruitbasket of horizontal output tubes for $4 once, so they are plentiful and cheap and very linear when operated in screen drive.
 
Well, the 6BK4 triode takes 25KV on the plate, and has a mu of 1000. Was used to regulate very high voltage in color TV sets.
 
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