Adding Tube Rectifier on a Switch

[Nathan]

So I decided the Blues Deville RI I am modding needs a tube rectifier. I am using the Rob Robinette method found here: https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Rectifier_Switch


*and a Hammond 167M5 (there it is in the 3rd pic! So cute).


I got to wondering about the 250V switch: isn't there more than that coming off the rectifier to feed the B+ rail?



Here are some progress pics for $#!ts & giggles:

[Nathan]

And one more

[mresistor]

It would be ok  but I'd personally never hot switch it although I guess it's assumed that would be ok too by reading some on this.   


Doesn't an ANB763 standby switch have high voltage on it? and we've been switching them for years.

[mresistor]

here's some additional ratings for a Carling standby switch in common AB763 amps.

[tubeswell]

Mr Rob Rob's suggestion only works if you have a HT winding with a center tap (that can be used for a rectifier tube or a 2-phase SS rectifier). The HT winding on the PT in a Blues Deville doesn't have a centre-tap and is FW bridge rectified.


You could have a tube rectifier as part of a hybrid SS/tube rectifier,* but making that into a switchable hybrid tube/FWB SS rectifier would be more complicated (and I can't be bothered putting my mind to that today sorry)


*half way down this page https://valvewizard.co.uk/bridge.html

[pdf64]

Well spotted!
My take is that a sag resistor makes far more sense here than attempting to add a valve rectifier.

[Nathan]

Well spotted!
My take is that a sag resistor makes far more sense here than attempting to add a valve rectifier.

While that may be true and I did consider it, those pics are mine and I've done about 90% of the work. Never said it made sense! There is a center tap too.

[mresistor]

Well spotted!
My take is that a sag resistor makes far more sense here than attempting to add a valve rectifier.

While that may be true and I did consider it, those pics are mine and I've done about 90% of the work. Never said it made sense! There is a center tap too.

No there is no center tap on the pt HV secondary   so..  maybe not so doable. 

[scstill]

could something like this Merlin approach work for the tube rectifier?
Or a second tube...
Then add the SS rectifier and switch as RobRob suggests....

https://www.valvewizard.co.uk/bridge.html
Already mentioned by Tubeswell in #4

[mresistor]

It would be interesting to try Merlins mod out and see how it works.  You won't use the center tap on the 5V transformer.

[scstill]

My take is that a sag resistor makes far more sense here than attempting to add a valve rectifier.

Although in Robs case was going from Tube to SS...

Would voltage sag  be the only difference between SS and Tube rectification?
Be a lot cheaper to build amps this way. Nice feature if really noticeable.
Is the sag resistor first component from the HV (HT) winding?

I do however still like looking at the tube glow. Never built a SS rectifier amp.

BTW - are HV (high voltage) and HT (high tension) used synonymous? Or is one preferred?
I've always used HV but just noticed that many here use HT.

[pdf64]

... Would voltage sag  be the only difference between SS and Tube rectification?
Be a lot cheaper to build amps this way. Nice feature if really noticeable.

From the time when power is applied, a valve rectifier will have a slower ramp up of rectified voltage. Much slower for indirectly heated types eg GZ34 EZ81 maybe 45 seconds.
Whereas silicon etc diodes are instant.

Is the sag resistor first component from the HV (HT) winding?

In that Merlin schematic, yes.
Current is much higher on the AC side of the rectifier.

I do however still like looking at the tube glow. Never built a SS rectifier amp.

Me too :)

are HV (high voltage) and HT (high tension) used synonymous? Or is one preferred?
I've always used HV but just noticed that many here use HT.

There's a HT fuse on the rear panel of most Marshall type amps. So despite it perhaps being anachronistic in regard of EE terminology  , I thought it might be widely understood by valve guitar amp enthusiasts.

[pdf64]

could something like this Merlin approach work for the tube rectifier?
Or a second tube...

I think all regular valve rectifier types have a 2 diodes with a shared cathode.
Due to that, for a fully thermionic FWB rectifier, at least 3 valves would be needed.

[mresistor]

trying Merlins Hybrid setup uses what he has on hand already     why wouldn't it work?

[pdf64]

trying Merlins Hybrid setup uses what he has on hand already     why wouldn't it work?

It would work, apologies if my response caused anyone to think it wouldn't.

[scstill]

Here is a interesting two tube design from the HiFi guys
They refer to the "Merlin" approach as second  choice in the link
Rectifiers look so sad.

https://www.audiodesignguide.com/my/se1.html

[Willabe]

BTW - are HV (high voltage) and HT (high tension) used synonymous? Or is one preferred?
I've always used HV but just noticed that many here use HT.

Yes, their the same, as well as B+ supply.

HT is what they use in England for HV, just like they use the term valves for vacuum tubes.

But they also drive on the wrong side of the road, sooooo.....   

[shooter]

Rectifiers look so sad.

you try and provide for an Audiophile, they're NEVER satisfied 

[mresistor]

we can blame the Romans for left side driving..     

[pdf64]

Here is a interesting two tube design from the HiFi guys
They refer to the "Merlin" approach as second  choice ...

Dunno how they have it working out that 2 x 5R4 (as half of FWB) provide the same rectified smoothed V DC as a GZ34, all else being equal   

[shooter]

all else being equal

 


see reply #17

[tubeswell]

HV (high voltage) and HT (high tension) ... synonymous?

My take on it is that when referred to in the context of the topic of electricity, 'Tension' refers to the potential energy that exerts pressure or force to produce current through a given resistance. An analogy might be a stretched rubber band which is under tension and contains potential energy that can slap you if you let go of it the wrong way. The more you stretch the rubber band, the harder it can slap you.


'Voltage' is another way of referring to the same thing, but instead of directly referring the concept electrical pressure or force, it adopts the nomenclature of the Volt as a unit of potential energy (which was derived from the guy who invented the battery).


In the antipodes, you get to pick whichever you want. Some people say high voltage, others high tension, sometimes valves, sometimes tubes. I prefer to say tubes and High Tension.  To me the concept of tension is easier to intuitively grasp than voltage, but tubes are cooler because they're made in the USA. YMMV

[mresistor]

tubeswell   we think of volts as pressure   which is like tension in the carrying conductor..  sort of a diametric tension ..

[tubeswell]

tubeswell   we think of volts as pressure   which is like tension in the carrying conductor..  sort of a diametric tension ..

I know. I'm just making click bait ;-)

[shooter]

 

which is like tension in the carrying conductor

if you've ever been bit by big-volts, every muscle in your body becomes tense  
 

[scstill]

So back to @Nathan
are you going to do the Merlin Hybrid approach (to compensate for lack of center tap on the HT)?
or just a switched sag resistor?

When done let us know how you like the difference in tone between tube and SS.

[Nathan]

So back to @Nathan
are you going to do the Merlin Hybrid approach (to compensate for lack of center tap on the HT)?
or just a switched sag resistor?

When done let us know how you like the difference in tone between tube and SS.

I will definitely follow up on the sound, but as indicated in post 1, 2 and 7 I went with the external transformer and RobRob method!

[pdf64]

So back to @Nathan
are you going to do the Merlin Hybrid approach (to compensate for lack of center tap on the HT)?
or just a switched sag resistor?

When done let us know how you like the difference in tone between tube and SS.

I will definitely follow up on the sound, but as indicated in post 1, 2 and 7 I went with the external transformer and RobRob method!

Are you quite sure that you understand the scenario here? ie if the mains transformer HT winding does indeed have a CT, and you ground the CT and use 2 phase rectification, the rectified HT voltage will be rather low, probably less than 250V DC with solid state rectification.
If it doesn’t have a CT, it just won't work, there won't be a HT supply.

[scstill]

The 167m5 transformer you added is 5vac with a center tap for the rectifier tube filament its not the HT/HV center tap being discussed.

[mresistor]

Nathan    Tubeswell in reply #4 indicated what you are attempting is not going to work
               I told you it isn't going to work in reply #7 


The two replies above this reply  PDF64 and scstill have told you it isn't going to work. 


You should have asked about this prior to doing any modificatioin.  Rob Robinettes mod is for adding a solid state rectifier to and amp that already has a TUBE rectifier, not the other way around. Why do you think Robinette used a diagram of a tube rectified 5E3 as an example? 


Your amplifier POWER TRANSFORMER's HIGH VOLTAGE SECONDARY does NOT HAVE A CENTER TAP.   That puny little 5v transformer is only for supplying 5v to a tube rectifier and nothing else in this instance.  Please listen to the people  none of us would ever do what you are attempting because IT WONT WORK!

[Nathan]

Well I'm embarrassed. I thought it looked like a thread hijack, and I just let you all discuss among yourselves...   


I can see now that HT/HV center tap is not optional for this situation (and yes, I did think you were referring to my 5V heater transformer). Thank you for recognizing that I was in error and correcting me. 


What about an artificial center tap like we do for 6.3V heaters? Would need large resistors perhaps?

[mresistor]

Hi Nathan    that's not practially feasible because it has to attach to the center of the HV winding inside the power transformer.  The transforner would have to be taken apart and rewound.  I searched a bit for a compatible center tapped pt but there is none for that amp with the different windings it has.
I suggest, since you have already drilled holes and added an octal socket for a rectifier tube, that you try Merlins hybrid mod referenced above and chalk this up to a learning experience.

[scstill]

To add the tube rectifier to a non center tap HV/HT secondary
do the Merlin Hybrid Approach discussed reply #8

Then run into your existing SS Rectifier and switch.

[Nathan]

Alright guys - THANK YOU very much - for the guidance! I am wiring up the hybrid rectifier and have given up on making it switchable.


But I do have a question: can I still use an octal plug-in SS rectifier with this setup if I don't love the extra sag? That was my plan before I found RobRob's switch method. Just wondering if the 2 added diodes will interfere with the operation?

[scstill]

Read this article
https://www.valvewizard.co.uk/bridge.html

Here is an example SS Octal rectifier.
https://www.tubedepot.com/products/solid-state-rectifier?srsltid=AfmBOoqXnd6KOOErynlMEEH5WoKYpkxFd-ShMdlBU2q7T5SDzgzZ9_sG

Since the SS Octal is replacing a tube it is intended to fit a transformer that has a HV center tap like the two phase rectifier in the article. (tube rectifiers are two diodes and need a center tap)

Merlin hybrid design adds the two forward diodes of a full wave bridge which is for HV secondary without center tap (like your amp)

So it should work for tube or for SS octal rectifier. Although I have never done this.
But might consider it in a future build if I come across an interesting transformer without CT.

I still want to hear from someone who has added tube rectification to Blues Jr or Pro Jr...

[HotBluePlates]

But I do have a question: can I still use an octal plug-in SS rectifier with this setup if I don't love the extra sag? ...

Yes.

Say you are using the tube rectifier for "the front 2 diodes" of the bridge rectifier, and solid-state for the "back 2 diodes" that connect to the filter cap Negative terminals.  If you use a plug-in rectifier replacement, it will have solid-state diodes in that "front 2 dudes" portion of the bridge where you have a tube now.  So it will reduce the sag as desired.