Voltage Doubler using a Recto Tube

[Jack1962]

Is this possible ?

[eleventeen]

It's absolutely possible, but the problem is that the great majority of common rectifier tubes have the cathodes of both diodes connected together internally. I am not aware of a dual-rectifier tube without this characteristic, though that doesn't mean there isn't one. In a voltage doubler, the diodes are connected in series, one "chases" the other, cathode of one to anode of the other. (Google images "voltage doubler") Since you cannot break that cathode-cathode connection, this would force you to use two tubes, requiring two heaters (BIG current, in general) and of course undergo TWO internal voltage drops across the tubes---and here you are trying to INCREASE overall voltage output. Not very efficient. Of course, there few things on earth as efficient as a silicon diode; insanely cheap for what it does.

Hey! Maybe there's a use for those 6AL5s after all? Just kidding. No current capacity to speak of.

[Jack_Hester]

Is this possible ?

Here's an older discussion on the same:

http://www.el34world.com/Forum/index.php?topic=11088.msg102066#msg102066

Jack

[kagliostro]

Here is one other example of doubler that uses a dual diode tube rectifier

instead of a pair of single diode tube rectifiers

(I've never seen this before)

http://www.vias.org/basicradio/basic_radio_12_05.html



K

[Jack1962]

Ok I see possible but not practical

[Jack_Hester]

Ok I see possible but not practical

Build it because it's fun.  Practical doesn't always apply.

Jack

[PRR]

35Z6 twin-diode voltage doubler:
http://www.mif.pg.gda.pl/homepages/frank/sheets/127/3/35Z6G.pdf

25Y5, 25Z5, 25Z6:
http://www.mif.pg.gda.pl/homepages/frank/sheets/021/2/25Z5.pdf
http://www.mif.pg.gda.pl/homepages/frank/sheets/049/2/25Y5.pdf
http://www.mif.pg.gda.pl/homepages/frank/sheets/021/2/25Z6.pdf
http://www.mif.pg.gda.pl/homepages/frank/sheets/127/2/25Z5.pdf

Only killer use is right off the 117V wall power. Maximum 350V B+ to B-, and you can get into that zone E-Z with a transformer and cheap common-cathode rectifier. The 25V/35V heater will generally be awkward.

[DummyLoad]

VT doubler will need two rectifier filament windings, or a supplementary 5V transformer, assuming of course, that you're using 5V rectifiers. you'd use use duo-diode tubes (e.g. 5Y3, 5U4GB, GZ34, etc.) wired in parallel or pair of 1/2 wave rectifiers. xenon gas, etc..

there are some rectifiers that are specifically made to be used in VT doubler service. e.g. 25Z5, 50Y6, 177Z6, etc.. output current is usually limited to under 75mA. these types require a pair of heater supply pins like the GZ34 (each diode gets it's own heater), however, each the cathodes are wired out to individual pins so you have essentially 2 INDEPENDENT diodes with a single string 2-wire heater connection.

http://tubedata.milbert.com/sheets/127/2/25Z6GT.pdf

for a 15-20W or so guitar amp, likely best results would be with two GZ34 with each bottle strapped in parallel and since the current demand with the full wave voltage doubler is at least 2x that of the full wave CT.

IMO VT Delon doubler is a waste of time and parts with the SS path would be the simplest and give best filtered performance, however, if you must...b/c you like that VT sound and sag, etc...

schematic of a concept VT delon doubler attached. PSU designer indicates ~25mV of ripple @ 100mA load. choke is a hammond 159S

--pete

EDIT: PRR beat me to finish line w/ the 25Z6 etc... :-)   

[PRR]

> e.g. 25Z5, 50Y6, 177Z6, etc..

117Z6, of course. (Probably line-noise on your teletype.)

http://www.mif.pg.gda.pl/homepages/frank/sheets/049/1/117Z6GT.pdf

[DummyLoad]

(Probably line-noise on your teletype.)

pesky 4-20mA CL... ugh! 

--pete

[kagliostro]

I think it is easier to have a SS voltage doubler and after this add a standard tube rectifier

you can connect both diodes in parallel as at the input of the tube you have DC instead AC

or use a single diode tube rectifier

Of course, the use of a Tube Rectifier add SAG feature to the PS

insofar as a bit of SAG will be present anyway in a PS based on a doubler

K

[SoundmasterG]

insofar as a bit of SAG will be present anyway in a PS based on a doubler

K

That is the best thing about a voltage doubler...solid state diodes that don't wear out and sag just like a tube rectifier. I suspect they are probably a little noisier than more typical circuits maybe, but I like to avoid tube rectifiers if I can, but still get the sag. Doublers are a good way.

Greg

[kagliostro]

That is true, but if you aren't interested on SAG

remember that the SAG in a doubler circuit depends on disposable current and the capacitance of the cap that are used

so I'm sure that if is used a PT with enough current and the electrolytic capacitors are of an adequate value

only a small SAG will happen

K

[SoundmasterG]

That is true, but if you aren't interested on SAG

remember that the SAG in a doubler circuit depends on disposable current and the capacitance of the cap that are used

so I'm sure that if is used a PT with enough current and the electrolytic capacitors are of an adequate value

only a small SAG will happen

K

Yes you are probably right there. I've got several amps that used doublers....a Bogen that I converted to my own design has wonderful sag characteristics. It uses larger caps than stock but the PT is sort of small. There is also the Silvertone 1484 which uses two doublers stacked on top of each other....I have one of these, though it doesn't sag a bunch. I also have a Conn organ power amp chassis that should prove an interesting experiment in sag. There are three output sections in the amp, each with their own PI and OT and tube pair. Formerly the sections were all cathode biased, but I made them fixed bias and added a separate preamp chassis, with three preamps in it. So I essentially have 3 amps in one head. I can stick two on standby and only use one at a time, in which case the power transformer which is already quite robust will be very robust. I used somewhat largish caps in the doubler too, so it will be interesting to see how much sag that one has....if I could ever get it done anyway. I ran into a problem with my preamp chassis design and have redesigned it into something that should work well, but need to build it still.

Greg

[kagliostro]

There is also the Silvertone 1484 which uses two doublers stacked on top of each other

That is interesting for my personal knowledge

Thanks for sharing the info

K

[SoundmasterG]

There is also the Silvertone 1484 which uses two doublers stacked on top of each other

That is interesting for my personal knowledge

Thanks for sharing the info

K

Welcome!

The Silvertone 1485 does the same thing and uses the same transformers as the 1484, however it has two output transformers. If you added the OT's together, and combined them into one, they would still be smaller than they should be for a 6L6 pair running at the voltages they do...so that tells you just how underszied the OT's are in the 1484/1485 Silvertones!

Many other Silvertone models used voltage doublers too, though not two doublers stacked like these ones. The wiring is a major rats nest on these too, and chassis layout is very poor with the PT right behind channel two's inputs! Needless to say they hum stock and if you increase the gain in the amp the hum goes up exponentially.
Greg