Installing SS Rectifiers for Tube Rectification

[mikepukmel]

You may be getting mixed up between HT and heater fusing?
I seem to remember RG Keen recommending the use of automotive blade type fusing for protecting heater windings as, unlike regular cartridge fuse systems, they are specifically designed for low voltage, high current applications.
I've not tried it out yet.

The key issue driving the inclusion of heater circuit overcurent protection is that due to the low capacity of the heater winding (relative to the PT as a whole), a fault in the heater circuit might overheat and damage the winding, without ever drawing enough primary current to blow the mains fuse.

Thankfully, as Leo points out, despite the historical absence of heater circuit protection, such a failure mode seems somewhat unusual.

Yes, definitely, mixed up HT and low V high current. SO, those car fuses work ok? I think I even remember looking up holders for those kind of fuses, but could not find a really small one with space for 2 fuses. Sorry.

[mikepukmel]

So the old Marshall circuit that fused the HV center tap is no good. Then, for similar amp, similar reasons, bad to fuse each leg of the HT, since if one blows there's still a current path on the other leg. Before I knew nothing. Now I know a little and I feel worse off.

[g1]

a Marshall amp that was sold in Denmark or Netherlands, one of those places. The amp has a board loaded with fuses. Like 6 or 8.

Like Canada? One of those places?
I think you probably saw a CSA JCM800. I'll add an interesting side note that they also did not have a 16ohm tap; as at the time, the voltage that can be developed across a 16 ohm load was considered hazardous.

[pdf64]

So the old Marshall circuit that fused the HV center tap is no good. Then, for similar amp, similar reasons, bad to fuse each leg of the HT, since if one blows there's still a current path on the other leg. Before I knew nothing. Now I know a little and I feel worse off.

I think it’s fine to fuse the 0V return of the HT winding CT, as long as a tube rectifier has adequate back up silicon diodes, and there isn’t a tap, eg for the bias supply.
If fusing each winding leg, should one fuse blow spuriously, I don’t foresee it causing an issue, other than reduced HT voltage and hence power output. Any bias supply feed (ie not from a tap) should either be taken from both legs if after the fuses, or before the fuse if, as per the traditional arrangement, it’s taken from just one leg.
Hope that makes sense?

[mikepukmel]

Like Canada? One of those places?
I think you probably saw a CSA JCM800. I'll add an interesting side note that they also did not have a 16ohm tap; as at the time, the voltage that can be developed across a 16 ohm load was considered hazardous.


[ATTACH=CONFIG]54879[/ATTACH]

There were more fuses than that on the board! I'll dig around and see if I can find the post and scrape a photo from the video.

[mikepukmel]

Or use single sufficiently rated (1250V/1A or higher) diodes like BY127/227/133/255 without the caps.

https://www.donberg.fr/catalogue/sem...bz/page_2.html

Ive been trying to find these rectifiers on Mouser (From north america), can't get any of the part numbers to come up. Is there maybe another number? I tried BY *** . Thanks.


Edit:
These were the only "through hole" I could find, with higher voltage rating:
https://www.mouser.com/ProductDetail...2SpeK5IUM1o%3D

[Gtr0]

Ive been trying to find these rectifiers on Mouser (From north america), can't get any of the part numbers to come up. Is there maybe another number? I tried BY *** . Thanks.


Edit:
These were the only "through hole" I could find, with higher voltage rating:
https://www.mouser.com/ProductDetail...2SpeK5IUM1o%3D

Well, that's a first.

I'm from good ol' Pittsburgh, PA. Moved to Belgium 10 years ago - it's ROUGH to say the least... I often dwell upon fond memories of finding everything I need at half the price, receiving it before I even get through the checkout ;-)

Try This? 625-BY255P-E3
This is the mouser part number on the EU Mouser website.

Link to the EU page - https://eu.mouser.com/ProductDetail/...FeEB70Pkf5%2FJ

If all else fails and your curiosity gets the better of you, PM me and I will send you a handful - my treat.. countrymen to countrymen ;-) or mef'er to mef'er (though that one doesn't read as well!)

[Helmholtz]

PA. Moved to Belgium 10 years ago - it's ROUGH to say the least... I often dwell upon fond memories of finding everything I need at half the price, receiving it before I even get through the checkout ;-)

Strange. I often get the impression that it's much easier to find parts at good prices over here in Europe. There are so many distributors. E.g.:
https://www.reichelt.de/rectifier-di...NGUAGE=EN&&r=1

[Gtr0]

Thanks for the tip!
It's good to know good suppliers...

I have never purchased anything from Mouser in EU - I am always seem to end up with ridiculous shipping prices. I have an issue paying 25€ shipping for the same in parts.

I suppose much of my problem boils down to not knowing what is reputable... less often is language.. I live in the french part of belgium.,.. most sites want you to load your country for the appropriate website and when I click begium, it is often available only in Dutch... and I barely know the proper terms for stuff in english, let alone french. More my fault, but that's what it is.....

Seems Reichelt has a separation between language and country! Good stuff! Shopping now... :-)

[mikepukmel]

Strange. I often get the impression that it's much easier to find parts at good prices over here in Europe. There are so many distributors. E.g.:
https://www.reichelt.de/rectifier-di...NGUAGE=EN&&r=1

I believe you on that Helmholtz. In the 25 years Ive lived around the North east, Ive seen local shop after local shop close up and go out of business. When we moved here in the mid 1990's, the area had at least 10 local electronics suppliers. I mean, not like Radio Shack, but a real warehouse type place, with a small office, you could get just about anything you needed. Lots of stuff big places wouldn't carry. There's almost nothing left anywhere within driving distance. A few really small places, not a lot of inventory. Maybe some areas of the country are luckier than tha North East, but judging by the internet searches, we only have a handful of big distributors (like Mouser and Digikey) and a handful of smaller places, that its really hard to find some parts. Thanks for the link.

[mikepukmel]

Of course, a lot of my problems could be that I don't know enough about the parts Im looking for.

[Gtr0]

I believe you on that Helmholtz. In the 25 years Ive lived around the North east, Ive seen local shop after local shop close up and go out of business. When we moved here in the mid 1990's, the area had at least 10 local electronics suppliers. I mean, not like Radio Shack, but a real warehouse type place, with a small office, you could get just about anything you needed. Lots of stuff big places wouldn't carry. There's almost nothing left anywhere within driving distance. A few really small places, not a lot of inventory. Maybe some areas of the country are luckier than tha North East, but judging by the internet searches, we only have a handful of big distributors (like Mouser and Digikey) and a handful of smaller places, that its really hard to find some parts. Thanks for the link.

Well ask my wife and she'd say that I have delusional memories of the US when it comes to prices and ease of xyz - who is, evidentially, belgian.

Of course, my taste for quality products has vastly changed over the years - back in the day I would order 98% of my parts from metro amp, so I suppose I am holding on to the memory, lacking the details. Point being that I got just about everything from one place never questioning the brands or tolerences etc. I don't just go for the run of the mill cheapo parts in most amps even though I will readily admit most times I go to Xicon resistors and capacitors, so now I have a harder time spreading out my purchases between several different suppliers.

[Gtr0]

Yes, I was looking into adding fusing for the HT winding of a Fender 75 a while back, and decided it was too complicated. The CT feeds the half voltage output used for the low 1/4 power mode.
https://el34world.com/charts/Schemat.../Fender_75.pdf
Both red HT winding legs and the red/yellow CT would seem to need fusing but would there be any deliterious consequences should one of them blow spuriously? eg might one the stacked reservoir caps potentially get reverse biased?

Regarding fusing the HT CT return to 0V of a regular biphase arrangement, my understanding is that it shouldn’t be done for HT windings with a bias supply tap, as per eg TR AB763, as when the fuse blows, large voltage can appear the bias supply, potentially damaging components there. I’ve not breadboarded it out (yet) though.

I think it’s fine to fuse the 0V return of the HT winding CT, as long as a tube rectifier has adequate back up silicon diodes, and there isn’t a tap, eg for the bias supply.
If fusing each winding leg, should one fuse blow spuriously, I don’t foresee it causing an issue, other than reduced HT voltage and hence power output. Any bias supply feed (ie not from a tap) should either be taken from both legs if after the fuses, or before the fuse if, as per the traditional arrangement, it’s taken from just one leg.
Hope that makes sense?

I must resurrect this thread and ask for clarification here...

Señor PDF64..... I wonder at the moment if I missed your first post initially, so I will ask for an expansion here to follow...

So the topic has come to have TWO objections. The first being utilizing SS rectifiers for tube diode protection,adding 1x BY255 diode per tube anode. Is there a way to wire this in a way that *if* a tube diode were to fail, the BY255s carry forward, with an albeit higher voltage? The transformer I had wound for me is 360-0-360 - and on ss rectifiers yields just over 500VDC and the 1st B+ node. And all B+ nodes are equipped to handle 1000V until we get to nodes 4 and 5 where they are able to handle 500VDC. So I would hope that would be no problem.

My initial thoughts (and sorry I am just riffing off the top of my head while I write this) tell me that it is not easily accomplished without the use of switches. But I also lack the experience to know for sure.

The second topic has evolved into secondary fusing on the power transformer. Which is also of immense importance to me at the moment as well.

I am trying to **carefully** read and absord PDF64's initial post quoted above -

my understanding is that it shouldn’t be done for HT windings with a bias supply tap

. Can anyone offer some clarity here? I currently have each leg wired to fusing (of which the value is yet to bve tested/determined with the help of YET another post :-) ) AND the bias tap does come from one leg. I am wondering if this is the referenced case in which one should NOT fuse the secondaries? Or is the reference to CT fusing only?

And while we are at it, what is the TR AB763 reference? I know what an AB763 is (as in Fender circuit), but what's the TR and .... well, I don't know (in Ronald Reagan voice)

Thank you for any additional explanations here.

Thanks!!!!!!!!!!!!!!

[pdf64]

...Is there a way to wire this in a way that *if* a tube diode were to fail, the BY255s carry forward, with an albeit higher voltage? The transformer I had wound for me is 360-0-360 - and on ss rectifiers yields just over 500VDC and the 1st B+ node. And all B+ nodes are equipped to handle 1000V until we get to nodes 4 and 5 where they are able to handle 500VDC...

Silicon back up diodes in series with the plates of a tube rectifier are fine, no switching needed, the silicon diodes automatically 'take over' if the tube has any kind of short type of fault. They won't keep the amp working with every type of tube fault, eg if the rectifier tube's heater fails, an otherwise good tube can't conduct; as the tube diode is in series, no HT current can flow. Heater failures seem to be quite rare though.
As you note, the only proviso is that the rest of the circuit must be able to accommodate the increased HT voltage; consider all conditions, including a combination of high mains and no load on the HT, eg at start up.
So is your power transformer's (PT ) 360-0-360 winding voltage at no load, idle load, or full load?
Fender have been using the silicon back up diode method, on some tube rectifier models at least https://el34world.com/charts/Schemat...57_reissue.pdf
(The standby switch arrangement, between the high tension (HT) winding centre tap (CT) and 0V, on that model is bad though, not good for the the tube and unsuitable if there's a dedicated bias tap).

...I currently have each leg wired to fusing (of which the value is yet to bve tested/determined with the help of YET another post :-) ) AND the bias tap does come from one leg. I am wondering if this is the referenced case in which one should NOT fuse the secondaries? Or is the reference to CT fusing only?

Your arrangement of a bi phase winding with its CT directly connected to 0V, and a fuse between each winding end and the rectifier, is fine, Merlin approved. The cases I raised are different arrangements to that, sorry for any confusion inadvertently caused

...what is the TR AB763 reference? I know what an AB763 is (as in Fender circuit), but what's the TR and .... well, I don't know (in Ronald Reagan voice)...

TR is a fairly common foreshortening of 'Twin Reverb'; so DR may be similarly used for Deluxe Reverb. The system falls down for the models that share the same initial, eg Princeton and Pro.
The AB763 is just a system for designating the version level and date of a drawing that Fender used; on its own, it doesn't mean anything, many Fender models share that designation, eg Twin Reverb (TR), Deluxe Reverb (DR); to specify an particular amp model, under that system, the model type AND its drawing designation must be used. So a Twin Reverb (TR) AB763 is different to a TR AA769 is different to a DR AB673.

[Gtr0]

Silicon back up diodes in series with the plates of a tube rectifier are fine, no switching needed, the silicon diodes automatically 'take over' if the tube has any kind of short type of fault. They won't keep the amp working with every type of tube fault, eg if the rectifier tube's heater fails, an otherwise good tube can't conduct; as the tube diode is in series, no HT current can flow. Heater failures seem to be quite rare though.

Awesome, and I didn't know that without heater failure that the tube would still conduct the already rectified (from ss) power.

As you note, the only proviso is that the rest of the circuit must be able to accommodate the increased HT voltage; consider all conditions, including a combination of high mains and no load on the HT, eg at start up.

All covered there. ATM the amp is setup similar to a dual rectifier - it has a switch to go between the two types of rectification - but I am digging the sound I get using the 5U4GBs so much I am prepared to just remove the possibility of switching to ss, and want to add the inline BY255 protection as well. First time startup for me is no tubes, no load... highest amount of DC possible and the amp is capable to handle no load voltages all the way down the line as far as I can tell.

So is your power transformer's (PT ) 360-0-360 winding voltage at no load, idle load, or full load?
Fender have been using the silicon back up diode method, on some tube rectifier models at least https://el34world.com/charts/Schemat...57_reissue.pdf
(The standby switch arrangement, between the high tension (HT) winding centre tap (CT) and 0V, on that model is bad though, not good for the the tube and unsuitable if there's a dedicated bias tap).

345-0-345 is datasheet AC on the secondary. I quoted the wrong tranny - I have another exact tranny that quotes 360-0-360, in reality - under load - it puts 372-372 VAC into the rectifiers. But with the proper tranny (345-0-345) Under load I get a bit over 500 VDC with a load and ss rectifiers. If I recall I get some 570VDC with no load, but I forget at this moment. Sorry about the confusion there.

Your arrangement of a bi phase winding with its CT directly connected to 0V, and a fuse between each winding end and the rectifier, is fine, Merlin approved. The cases I raised are different arrangements to that, sorry for any confusion inadvertently caused


TR is a fairly common foreshortening of 'Twin Reverb'; so DR may be similarly used for Deluxe Reverb. The system falls down for the models that share the same initial, eg Princeton and Pro.
The AB763 is just a system for designating the version level and date of a drawing that Fender used; on its own, it doesn't mean anything, many Fender models share that designation, eg Twin Reverb (TR), Deluxe Reverb (DR); to specify an particular amp model, under that system, the model type AND its drawing designation must be used. So a Twin Reverb (TR) AB763 is different to a TR AA769 is different to a DR AB673.

I should have known the TR reference. I suppose I wasn't all together this morning when I was going through all of the posts. Sorry, and thanks for pointing that out!!

Thnks for all the clarification, PDF64 - I appreciate your time!!