2 x el84PP with a voltage doubler power supply

[jbrew73]

I want to build an amp using a voltage doubler power transformer from an old hifi donor amp.  Are there any issues like hum that I may encounter using this type rectifier? The amp will be an AC15 variant .

[kagliostro]

Using a doubler the humm frequency changes, but if build correctly, as any amp must be, there are no particular reasons to aspect much more humm than with a traditional PS

only you must remember that doubling the voltages the current halves, so you must have enough current in the PT to avoid problems

Kagliostro

[jbrew73]

The donor amp was two single ended el84 so I should be fine on the current capacity .

[kagliostro]

The donor amp was two single ended el84 so I should be fine on the current capacity

OK the donor amp was a pair of el84

but if you use the doubler, anyway you halve the current

which are the voltage of the PT ?

why you want to double B+ ?

Kagliostro

[jbrew73]

Voltage doubler rectification was used in the donor amp. I don't remember the secondary voltages  but I put a note on the transformer when I removed it that said "285 vdc - voltage doubler".
I was mainly concerned about hum or other side effects since this type of rectification is not common in guitar amps.

[jjasilli]

Voltage doublers were used in older amps mostly because the filter caps and SS rectifier diodes couldn't handle the the full compliment of plate voltage.  By doubling to say 300V, ea diode and cap sees only 150V.  I'm using vintage PA amps with voltage doubling to power my home theater system.  There's no hum.

[SoundmasterG]

Lots of old organ amps used voltage doubler power supplies, and Silvertone often used them too. In the Silvertone 1484 and 1485 they stacked two doubler windings on top of each other for some generally lousy regulation but cheap results.

The key to a doubler with the cheap caps nowadays is to use large value caps. If you use a pair of 100uf caps in a doubler circuit, the effect is the same as a 50uf cap in a full wave diode bridge circuit for the first filter, so just make sure to use large caps. I used a pair of 220uf and the doubler regulates just fine and sounds fine with as low of hum as any other design.

Personally I like doublers in guitar amps....I feel like they somewhat emulate the sag of a tube rectifier, though I don't have any test results to verify it.

Greg

[jbrew73]

Thanks or all the help guys. Now I just need to decide exactly what to build . That amp will have to fit in an old tube CB base  station enclosure. Its going to be a tight fit but its a really neat chrome tube cage.