About a year ago I got a deal on a case of NOS 8 and 10 volt BQ5 tubes from a local guy in Indiana. So I'm thinking of making the Broski 5 parallel tube SE schematic from back in 1999. Because its parallel tubes I want the heaters in series per channel so they all go out if you pull a tube out. To make the amp able to use 6, 8 or 10 volt tubes I'm thinking of getting an Antek 30 volt transformer and an Antek 10 volt transformer. These have dual secondaries. Five 6 volt tubes in series is approx 30 volts, 8 is 40 and 10 is 50. so the 30 volt transfprmer would be in circuit all the time with the secondaries in parallel. If I install 8 volt tubes then Ill add a 10 volt winding to get 40 volts, If I use 10 volt tubes then Ill add both 10 volt windings to get 50 volts. Then trim the strings with resistors experimentally. I was thinking DC heaters but that has its own set of problems with power loss. (Ill be using a one-Electron OPT UBT-1).
Does this sound like the way you would do a 6, 8 or 10 volt filament option using stock transformers?
AS-1230 - 100VA 30V Transformer - AnTek Products Corp
AN-0210 - 25VA 10V Transformer - AnTek Products Corp
Does this sound like the way you would do a 6, 8 or 10 volt filament option using stock transformers?
AS-1230 - 100VA 30V Transformer - AnTek Products Corp
AN-0210 - 25VA 10V Transformer - AnTek Products Corp
So what you're saying is if it were parallel wired, and I pull a tube, I'm still ok because each tube has its own cathode resistor? But if the string of 5 tubes had a single shared cathode resistor... bad things could happen if I pull a tube because the other 4 tubes are still conducting. Wouldn't the bias point change in that case maybe over the max power curve?
My main reason for series heating though is to keep the current low, that way I can get by with only a 25VA add-on transformer for the 40/50 volt boosts. I wish Antek sold a 50VA for the 30V transformer but their lineup jumps from 25 to 100 in the 30V.
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I have to think, 'I don't believe I would go and pull a tube whilst it is running'.
cheers,
Douglas
cheers,
Douglas
> Wouldn't the bias point change
Yeah. But at 5 or 4 tubes, not a quickly-fatal amount. Lots of home consoles had shared cathode bias and lived for decades. Even as tubes worked loose, failed, were taken out for replacement. (Not talking series-heater but good parallel heat.)
A 6.3V tube fed 10.0V will have life cut to about 1/400. Unlike incandescent lamps, tube heaters usually give over 10,000 hours life. So this is cut to 24 hours. Seriously bad, but not "Ka-Boom!" You should fix it today, doesn't have to be this very minute.
And 10BQ5 is, what? A $7 tube? (Everywhere except the place that asks $550 for 33 different 10BQ5 in 30 sad boxes.) I'd be sorry to burn $7, but not devastated.
Yeah. But at 5 or 4 tubes, not a quickly-fatal amount. Lots of home consoles had shared cathode bias and lived for decades. Even as tubes worked loose, failed, were taken out for replacement. (Not talking series-heater but good parallel heat.)
A 6.3V tube fed 10.0V will have life cut to about 1/400. Unlike incandescent lamps, tube heaters usually give over 10,000 hours life. So this is cut to 24 hours. Seriously bad, but not "Ka-Boom!" You should fix it today, doesn't have to be this very minute.
And 10BQ5 is, what? A $7 tube? (Everywhere except the place that asks $550 for 33 different 10BQ5 in 30 sad boxes.) I'd be sorry to burn $7, but not devastated.
I had a bunch of 8BQ5's. Most of them worked just fine when stuffed into a typical amp intended for 6BQ5 / EL84's (a Tubelab SPP). The typical Hammond or Edcor power transformer will put out around 7 volts or more on today's high line voltages.
You can always rectify and filter the 6.3 volt winding and get about 8 volts if you use a Schottky bridge.
You can always rectify and filter the 6.3 volt winding and get about 8 volts if you use a Schottky bridge.
Or I could use this as my opportunity to add two 10 volt windings onto a 100VA 30 volt antek. Then Id only need one transformer if the windings will fit.
30 for the 6x5 string
30 + 10 for 8x5
30 + 10 + 10 for 10x5
I've seen people do this, its only if I have a big enough donut hole left on the transformer to fit the wire.
10 6BQ5s of good quality for the stereo amp can be rather expensive nowadays...if you settle for the 8BQ5 and 10BQ5 only with 30V secondary you don't need to add anything. Can use a normal bridge rectifier + RC filter if use 5x 8BQ5 and use a voltage doubler if use 5x10BQ5 + RC filter. The RC filter can use a standard good quality (cheap) electrolytic and the amp will be dead quiet if grounding is good.
check the data sheets but I suspect filament currents are different so no series connection possible.
EDIT: forget it. Respective currents are 760-600-450 mA
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Oh I probably forgot to mention I wouldn't be mixing voltages. five 6 volt tubes or five 8, or five 10's. So equal currents on each tube in the string.
Get a 30 volt toroid and add two 10 volt tertiary windings to it. 30 -40 - 50 volts. Easy peasy.
yes 30, 10, 10 is what I described initially but by buying separate 30 and a 10 volt units. But now's probably the time to try winding on two 10 volt windings myself for the first time ever. If I fold a length in half and wind two wires at once Ill have a perfect center tap. I read up on it, wind 10 turns, measure, divide by 10 to get the volts per turn, then Ill know the total turns, add a few turns for regulation to not be under voltage. It sounds easy enough and take up less chassis space.
Run it “over” by the same % as the original secondary. For something this simple you can use bell wire instead of having to use “magnet wire”. Then taping isn’t as critical. Unless you’ve got transformer tape on hand.
I have enameled wire I would think 20 gauge should be thick enough, I have 18 gauge too. My 30 v 100 VA Transformer has an outer shield but I'll leave that in place for the first try to see if its a hindrance before I assume it needs to come off.