Tube Rectify & SS Rectify switch - what do you think about this circuit

[kagliostro]

Some days ago there was a discussion about switch between SS & Tube rectify in another forum

One of the proposed solutions seems interesting to me as with the diodes in that place you protect your amp if the recto tube fails shorting (no AC will pass, your amp still receive DC)

Which is your opinion about ? Do you see contraindications to the use of this method ?



Many Thanks for any answer about

K

[sluckey]

I see a red X...    

I don't like the idea of switching off the filament while in SS mode.

[phsyconoodler]

I like using diode rectifiers and sag resistors to simulate the tube rectifier sag and then all the issues with tube rectifiers are no more.Install a sag switch if you must to put the resistor in and out of the circuit.

[kagliostro]

Hi Sluckey & Phsyconoodler

thanks for answering

@ Sluckey

I don't like the idea of switching off the filament while in SS mode

To me seems that you never switch off the filaments ???  ???

K

[kagliostro]

I think I've understand what you mean

I was reading the schematic like this (see the added junction dot)

K

[Merlin]

That method works fine. There is also no harm in turning off the heater when not in use (except having to wait for it to warm up). In fact, you have the benefit that the valve will last longer!

But: Don't put the standby switch BEFORE the reservoir capacitor. Most recto's do not like that.

[dscottguitars]

I'm no expert but I have had good results with this, and like above it needs to warm up.  But also saves the tube's life...

[kagliostro]

Hi Merlin

thank you for answering


Dscottguitars

If  don't remember badly Merlin on his site had something like in your circuit in the past, but (and I don't want to say I'm sure about it, may be I remember badly) he get off this circuit from the page, because to switch between SS and Tube rectify disconnecting in an alternate way the HT windings of the transformer from the SS and the Tube Rectifier, will tend to hurt the tube at the insertion moment because of the inrush current

Your circuit is a bit different and you also disconnect the filaments of the Tube Rectifier ..........

Hope Merlin will chime and clarify this question (and also if I remember correctly)

K

[sluckey]

I still prefer this circuit for simplicity and functionality.

[thelonious]

Since the SS rectifier allows for a larger reservoir cap, it would be useful to have the option to switch that in. Would the following modification be safe and effective? Is there a better way to accomplish the same thing? I suppose there should be a bleeder resistor across the extra cap to discharge it when it when switching to the tube rectifier.

[Willabe]

But: Don't put the standby switch BEFORE the reservoir capacitor. Most recto's do not like that.

Too much inrush current going to fill all the filter caps when you flip the standby switch with the recto tube already warmed up.

Putting the reservoir before the standby switch allows it to charge up as the recto turns on. This is usually the largest cap value in the B+. So it takes some stress off of the recto tube if it's already charged up when you flip the standby switch.


                       Brad      

                  

[dscottguitars]

Thanks for that tip.  I'm assuming it is not the same as turning the amp on with a tube rectifier only then?  Wouldn't that have the inrush current too?  I do like sluckey's schematic and will do that but with a DPDT for the filament.

[Willabe]

I'm assuming it is not the same as turning the amp on with a tube rectifier only then?  Wouldn't that have the inrush current too? 

They both will have inrush current at turn on, but the SS diodes can take it where a tube recto can only handle so much. Look at the tube spec sheets and you will see the limit they list for each different recto tube.


                     Brad     

[DummyLoad]

was thinking; if you use kalio's plan - the inrush currents are a wash since the valve rectifier still has to warm up -UNLESS- you flip back and forth like a child with a new found button. in other words allow a few seconds of cool-down time before you switch to and fro.

i'll ave' the lot  - cut off valve power with kalio's filament kill arrangement; switch in another reservoir cap when SS is selected; use a center off 3PDT NKK switch for added sby.

--DL

[Merlin]

was thinking; if you use kalio's plan - the inrush currents are a wash since the valve rectifier still has to warm up -UNLESS- you flip back and forth like a child with a new found button.

That doesn't matter, because if you flip rapidly between the two, the cap never has time to discharge, so there is no inrush except the very first time you power up.

[DummyLoad]

That doesn't matter, because if you flip rapidly between the two, the cap never has time to discharge, so there is no inrush except the very first time you power up.

it discharges if there's a load on it.

--DL

[jeff]

Any problem with tube to the smaller cap, ss diodes to another bigger cap, On/Off/On switch for tube/standby/SS?
I'm thinking use a DPDT and the other side of the switch can be used to set correct bias for different B+?