18Watt.com

which rectifier tubes work best ? 5ar4 ? 5y3 ,5u4 ,6ca4
does any one tube stand as the best ractifier ?
better sage and compression ect.

would a 5ar4 (gz34) work well in a liteIIB

Stanb

Well that would depend on several factors; how much current your power tubes are drawing, total current draw for the amp, etc. Here's a handy chart that helps me. It also depends on your power xformer, what current rating is the 5v winding? A gz34 is big overkill in a Lite, look at the chart, it can handle 250ma. The normal rectifier tube in a lite is a ez81, it handles 150ma, all you need is 150 ma not 250ma. You could probably even use a 5y3gt in a Lite and be ok.

A lot depends on what you're aiming to achieve. A 5Y3GT will give you more sag, for example - as long as it isn't a Sovtek one. I take it you don't want to use the regular EZ81 for some reason.

awsome joebob that chart was just what I needed thank you !
I was thinking of using an octal stocket so I could try different rectifier.
with the ez81 you are limited. but it looks like the ez81 is a better match
for 18watt .
sorry about posting the wrong forum

stanb

It's ok to go down in most amps, but in some older amps going from a 5y3 to a 5ar4 may be more than the components of the amp are spec'd for. So proceed with care.

I hope no one minds me askin' this and leading the thread down another path, but as the ins and outs of amp design click in my head, and since we're already on the topic of rectifiers, I have a question.

Why, as a general rule, do most of our amps use 6v heaters for all the 'sound-production' tubes, but 5v for the rectifiers? Are there simply very few 6v rectos, or is there another reason for it? Would they (6v rectos) allow for less-complex PTs? Or would the extra current requirements just shift the burden on the PT? It occurs to me that is there were a way to make amps cheaper by using some sort of 6V rectos, Leo woulda thought of it already, but it does make me wonder.

Any thoughts?

zaphod_phil wrote:A lot depends on what you're aiming to achieve. A 5Y3GT will give you more sag, for example - as long as it isn't a Sovtek one. I take it you don't want to use the regular EZ81 for some reason.

What the heck! I just ordered a Sovtek for my lite. I got the 5y3 so it would sag!
Why does the Sovtek not sag?

Marshman wrote: Why, as a general rule, do most of our amps use 6v heaters for all the 'sound-production' tubes, but 5v for the rectifiers?

I'm not an expert, but many 5 volt rectifiers (all?) have their cathodes tied internally to heaters. This means they could not be used from the same heater winding as for example 12AX7 or EL84 tubes anyway, even if the required heater voltage would be same.

bbrunskill wrote:

zaphod_phil wrote:A lot depends on what you're aiming to achieve. A 5Y3GT will give you more sag, for example - as long as it isn't a Sovtek one. I take it you don't want to use the regular EZ81 for some reason.

What the heck! I just ordered a Sovtek for my lite. I got the 5y3 so it would sag!
Why does the Sovtek not sag?

Because it's not a real 5Y3, but some Russian tube that looks close enough to fool people. A true 5Y3 is directly heated, so the internal resistance is higher, which causes more voltage drop...

- Scott

msormune wrote:

Marshman wrote: Why, as a general rule, do most of our amps use 6v heaters for all the 'sound-production' tubes, but 5v for the rectifiers?

I'm not an expert, but many 5 volt rectifiers (all?) have their cathodes tied internally to heaters. This means they could not be used from the same heater winding as for example 12AX7 or EL84 tubes anyway, even if the required heater voltage would be same.

Probably historical too. The 5V standard is eariler, 1920s/30s? and suited the battery voltages of the time. I imagine they contued with it so later valves could be used as replacements in old equipment. The 6.3V standard came in around the 1940s I beleive, to suit the common battery voltages of that time.

msormune wrote:I'm not an expert, but many 5 volt rectifiers (all?) have their cathodes tied internally to heaters. This means they could not be used from the same heater winding as for example 12AX7 or EL84 tubes anyway, even if the required heater voltage would be same.

5V4 and 5AR4/GZ34 are indirectly heated, but these are 5v tubes and, as you note, you wouldn't use the same heater winding as the 12A?7 or EL84 tubes, as those require 6.3v. In addition to the 6CA4/EZ81, 6X4 and 6X5 are examples of indirectly heated 6.3v rectifiers that can run on the same winding as the other 6.3v tubes. The spec's of all these tubes differ somewhat, so they may not be easily interchangeable.