Delon voltage doubler to power relays from unused 5VAC filament tap?

[SnickSound]

I was set on powering my relays as described on this website: bridge-rectify the 6.3VAC line, massive cap then regulate down to 5VDC with an LM7805.
This works, but it has a drawback: the circuit cannot be connected to ground as that would short one side of the 6.3VAC secondaries on the PT. Not a huge deal, but a possible issue if the end user (I'm building this one for a close friend) ends up using a switching solution that shares ground.

Then while taking a peek at the Ceriatone layout for their AFD50 amp, I noticed an odd circuit for the relay supply: they send the 5VAC tap (for a rectifier tube which I won't be using) through two diodes and two caps and then regulate that down to 5VDC. If you were to bridge rectify 5VAC, you'd get at best 6VDC, not enough for regulation.

So I did a little googling and found out this is called a Delon voltage doubler. Accounting for diode voltage drop, this should still net me around 12VDC before regulation! And since I'm not using a tube rectifier, I can reference this to ground with no worries. The cost of the extra cap is partially offset by the need for only 2 diodes.

Any downsides? Current draw won't be much of an issue, my relays only pull 20mA a piece and I use two. Add a couple LEDs as channel indicators and we're still under 50mA total.
Only downside I can think of is that if I want to have DC filaments on my input tube, I still need that bridge rectifier and massive cap on the 6.3VAC line, unless it's "safe" to feed just the one tube from the Delon circuit (add an LM7086 and a cap and voilà), given that that will pull 300mA. The PT (Hammond 272DX) is good for 3A on the 5VAC line so no worries there.

What if I was to take this one step further and add a second 9VDC regulated line? I could easily add some SS components to my circuit if I wanted (was thinking of a built-in "mid-boost" à la Tubescreamer before the first stage).

[SnickSound]

Ceriatone layout for reference;

http://www.ceriatone.com/ceriatone/wp-content/uploads/2017/06/AFD-50-1-June2017.jpg

Relay supply is on the left. You'll notice another 4700uF cap after the 7805, not sure that one needs tk be that big. The 1k resistor is to feed the LED

[2deaf]

Easier to see with a schematic.

[sluckey]

I'd just keep it simple. There's no need to regulate the power supply just to energize a relay. 5VAC into a bridge with a big cap will give 7VDC. The relay is not fussy about having exactly 5V. It will work just fine with 4.5V or 6V. Just use a single series resistor with each relay coil to drop the unregulated voltage down a bit.

[SnickSound]

Easier to see with a schematic.

Nice! Thanks

Yeah that's exactly it.

There's so much about this amp that screams "a JCM800 was modified for more gain" that it's hard to know which part of it should be taken as a "good idea". Between the trim control on V2B's cathode that you're supposed to just set to a specific resistance (and I'm sure purists will argue the tone is in the trim), the odd man out 450V 47uF capacitor on the PI supply, the unused V2a triode... you know someone just tinkered around with an amp until they were happy and now people want to have an exact replica of that amp. But I digress!

Point being, maybe the relay supply is half assed and I should ignore it.

Either way, I'm gonna breadboard it and see for myself.

[SnickSound]

I'd just keep it simple. There's no need to regulate the power supply just to energize a relay. 5VAC into a bridge with a big cap will give 7VDC. The relay is not fussy about having exactly 5V. It will work just fine with 4.5V or 6V. Just use a single series resistor with each relay coil to drop the unregulated voltage down a bit.

You know, I've always wondered why some people insist on having a regulator for relays and DC filaments. For the latter, the current demand never changes, so who cares.

In the case of relays, my thinking is that as current demand changes depending on if the relays are turned on or not, the voltage would fluctuate. Not a big deal with just one relay, but if you have more than one switching options it might make sense. Either way, I have a bunch of unused LM7805s.

[SnickSound]

Breadboarded the whole thing, so far so good. Solid steady 5VDC or 6VDC or even 9VDC (just pick your regulator) off the 5VAC heater tap (assuming it's unused, do NOT do this if you have a tube rectifier)

As far as running DC filaments to one tube this way... more wasteful than just using a dropping resistor. A LM7806 will have to dissipate about 2W of heat to feed one tube (300mA), but a simple bridge rectifier on the 6.3VAC tap followed by 5-something ohm resistor will only "waste" about half a watt. Since the current demand is steady, no issue.