can I use this OT?

[nosaj]

What about a 6x4 My Champ-ish home made amp uses a 6x4 rectifier, and I have spares. How difficult is it to implement dual rectifiers, switchable?

Why not make it a 5v winding? You'd have to loose the CT and float it I believe and use a 5v diode to drop the voltage. Give more options I'd think for not much more work.
nosaj

http://www.valvewizard.co.uk/heater.html

[Chuck H]

Why not make it a 5v winding? You'd have to loose the CT and float it I believe and use a 5v diode to drop the voltage. Give more options I'd think for not much more work.
nosaj

Good idea. He certainly has the necessary current to handle it. So, implementing your idea makes a lot of sense since it would also allow regulation of the 6.3V circuits rather than just suffering with high filament voltages there too.

[nosaj]

Good idea. He certainly has the necessary current to handle it. So, implementing your idea makes a lot of sense since it would also allow regulation of the 6.3V circuits rather than just suffering with high filament voltages there too.

I was thinking that since there were 2 6.3 taps on the PT is why. And more options for tube rolling the rectifiers.
nosaj

[Bloomfield]

I was thinking the other day, have you tested the output transformer to find the impedance ratio? It occurred to me that maybe the primary on the schematic might be a misprint and perhaps it might actually be 6250 ohms which would be more in line with what we'd expect to find. 625 does seem awfully low.

andy

[Helmholtz]

I was thinking the other day, have you tested the output transformer to find the impedance ratio? It occurred to me that maybe the primary on the schematic might be a misprint and perhaps it might actually be 6250 ohms which would be more in line with what we'd expect to find. 625 does seem awfully low.

andy

I assume it's the DCR. Looks high but not uncommon for small sized OTs. Will waste and dissipate up to 20% of output power (depending on actual primary impedance).

[dmartn149]

Probably another good reason to use a tube rectifier (6ca4) is that the filament winding is designed for a butt load of tubes. If you only load it with a couple of tubes your filament voltage may be grossly higher than spec.

So would I be wrong to think that the heater load from 6, 6v tubes would be equal to 3, 12v tubes? I realise that we run them at 6v, but there are two heaters ea. right?

[nosaj]

So would I be wrong to think that the heater load from 6, 6v tubes would be equal to 3, 12v tubes? I realise that we run them at 6v, but there are two heaters ea. right?

I do not think that applies here as there are 2 6.3 v taps. Your rectifier tap should ALWAYS be on a separate winding. On the tube datasheet you count the amp or milliamp draw of each tube and add that up. Use the tubes on the schematic you provided look up the tube data sheet and add up the draw and that would give you a boundry not to get near. Cause you don't want to run your PT on the edge.
nosaj

[dmartn149]

Ok now I'm confused. I thought the issue was having to few heater filaments, causing the filament voltage to be in excess of 6.3v

[Chuck H]

So would I be wrong to think that the heater load from 6, 6v tubes would be equal to 3, 12v tubes? I realise that we run them at 6v, but there are two heaters ea. right?

The filament current for most preamp tubes, including the ones in the original amp, is about the same regardless of whether they're one triode or two. About 300mA each. Plus the rectifier tube which is probably drawing about twice that (so let's just count it like two more preamp tubes worth of filament current). I didn't see where there are two filament secondaries on the schematic. Did I miss that from a post? Anyway, the schematic shows one 6.3V winding. So... A 5e3 uses two preamp tubes. The PT from the amp you have powered the equivalent of eight. Plus it has a vintage primary and you'll be plugging into a modern wall. That alone can cause problems. Without some measure to lower filament voltage you'll probably be over spec.

[nosaj]

The filament current for most preamp tubes, including the ones in the original amp, is about the same regardless of whether they're one triode or two. About 300mA each. Plus the rectifier tube which is probably drawing about twice that (so let's just count it like two more preamp tubes worth of filament current). I didn't see where there are two filament secondaries on the schematic. Did I miss that from a post? Anyway, the schematic shows one 6.3V winding. So... A 5e3 uses two preamp tubes. The PT from the amp you have powered the equivalent of eight. Plus it has a vintage primary and you'll be plugging into a modern wall. That alone can cause problems. Without some measure to lower filament voltage you'll probably be over spec.

His very first post there is a rca pdf that the transformers came from to use in the 5e3 . That's the data I'm using.

nosaj

[Chuck H]

Yep. That's the one I looked at. It shows all the tubes filaments, including the rectifier PLUS the panel, dial and pilot lamps powered from a single 6.3V winding. That secondary is a bruiser to be sure and isn't going to load much in a 5e3 design with a diode rectifier. It would take some burly parts, but I think your regulation idea should work fine since the secondary has the current capacity to spare.

[nosaj]

Yep. That's the one I looked at. It shows all the tubes filaments, including the rectifier PLUS the panel, dial and pilot lamps powered from a single 6.3V winding. That secondary is a bruiser to be sure and isn't going to load much in a 5e3 design with a diode rectifier. It would take some burly parts, but I think your regulation idea should work fine since the secondary has the current capacity to spare.

Ok my BIG mistake upon using magnification I can clearly see it now. Think it's time for some specs...

nosaj

[dmartn149]

The filament current for most preamp tubes, including the ones in the original amp, is about the same regardless of whether they're one triode or two. About 300mA each.

Ok I looked them all up, You are absolutely right, (you knew that) It's getting late for me (5:00am wake up) I'll have to revisit this in a couple of days.
Thanks All

[Helmholtz]

Tube rectifiers like 5Y3 or 5AR4 having non-isolated cathodes MUST be fed from a separate heater winding/transformer as their filaments carry HT. Also note high heater currents.

[Chuck H]

Yes! This^^^^^^^^^^^^^^^^^^^^^^^^^^^

The 6ca4 is an indirectly heated cathode tube. Plus it soaks up one amp of filament current. A good start toward getting the filament current up to load the winding as it was intended.