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previous: Ricky will the 150mA (as opposed to 100mA... -- 1/17/2000 7:01 PM

Re: 5E3 rectifier

1/18/2000 6:18 AM
Bruce	Re: 5E3 rectifier Well Ricky it's not really related. It will help your overall sag though. A vacuum tube has a forward voltage drop when it is turned on and that voltage drop is greater when there is more current flowing throuogh the tube. In a given amp, once the drop is established at idle the only real difference when playing is how much extra current the power tubes are pulling during high volume peaks. All the preamp tubes are running class A and their average current is constant. Roughly speaking: If your PT can't keep up with those peaks and the current load from the depletion of stored energy in the first main filter cap, (the main filer capacitor is like a battery too), then the PT will start to cave in a little (and maybe get pretty warm) while the B+ is going to sag even more. That's independent of the rectifier. If your PT is of decent quality and rated at 275vac@100ma, I think you'll still be OK in a little tweed Deluxe. Use a 5AR4 to experiment or (and) use a slightly larger first filter cap value to compensate a little too. I've used my share of 40uf to 50uF caps connected to 5Y3s with NO damage to the rectifier tube. I have a power supply test jig at the shop that has a single 100uF/500v E-cap and I've never blown a 5Y3 rectifer with it. It has two 50 watt 1000 ohm power resistors on it that can be shunted right across the filter cap to ground. That means with one of them switched in, your 275v@100ma PT would have to handle 275ma of current to stay at 275vac on the secondary. Most decent PTs will out do their ratings. Many PTs, that I've given their true life test, have survived this for 24 hours or more! I've had good trannies so hot, I could cook lunch on them. After they've cooled down for a day or so, they seemed exactly the same as new! Yes, I've let the smoke out of a few too. It's pretty unlikely you'll be running the amp at full clipped volume all the time anyhow so I think you're OK. Bruce

1/18/2000 6:18 AM

Bruce

Re: 5E3 rectifier

Well Ricky it's not really related.
It will help your overall sag though.
A vacuum tube has a forward voltage drop when it is turned on and that voltage drop is greater when there is more current flowing throuogh the tube.
In a given amp, once the drop is established at idle the only real difference when playing is how much extra current the power tubes are pulling during high volume peaks.
All the preamp tubes are running class A and their average current is constant.
Roughly speaking:
If your PT can't keep up with those peaks and the current load from the depletion of stored energy in the first main filter cap, (the main filer capacitor is like a battery too), then the PT will start to cave in a little (and maybe get pretty warm) while the B+ is going to sag even more.
That's independent of the rectifier.
If your PT is of decent quality and rated at 275vac@100ma, I think you'll still be OK in a little tweed Deluxe.
Use a 5AR4 to experiment or (and) use a slightly larger first filter cap value to compensate a little too.
I've used my share of 40uf to 50uF caps connected to 5Y3s with NO damage to the rectifier tube.
I have a power supply test jig at the shop that has a single 100uF/500v E-cap and I've never blown a 5Y3 rectifer with it.
It has two 50 watt 1000 ohm power resistors on it that can be shunted right across the filter cap to ground.
That means with one of them switched in, your 275v@100ma PT would have to handle 275ma of current to stay at 275vac on the secondary.
Most decent PTs will out do their ratings.
Many PTs, that I've given their true life test, have survived this for 24 hours or more!
I've had good trannies so hot, I could cook lunch on them.
After they've cooled down for a day or so, they seemed exactly the same as new!
Yes, I've let the smoke out of a few too.
It's pretty unlikely you'll be running the amp at full clipped volume all the time anyhow so I think you're OK.

Bruce