Bogner Shiva blown flyback diode

[Zouto]

I just retubed a KT88 Bogner Shiva, it worked fine, but suddenly blew a flyback diode, D3 on Relay 3. Since there‘s no schematic available, I need Information what diode to use as replacement. Thanks for help
Zouto

[Jazz P Bass]

A 1N4007 should work fine.

[Zouto]

Thanks, the blown type is a small one. I‘ll give the 1N4007 a try.

[Zouto]

[J M Fahey]

Is it D3?
1N4007 will be fine.

[Jon Snell]

Back in the day, the most common blocking diode was the 1N914 or 1N4148.
1N4007 is a bit of an overkill but will work fine as will most diodes.
All it does is block the back EMF spike caused when removing the DC across the coil.
It can be many hundreds of volts when left unleashed but the current is measured in micro Amps so non hazardous to us just it can kill the switching transistor.

[Enzo]

Agree, it was likely a 1N4148, but 1N4007 would be fine as well.

That would be a very unusual failure, by the way.

[The Dude]

Yes, very unusual. Usually current is through the lower resistance parallel relay coil. I have to wonder if the diode was checked out of circuit.

[Enzo]

I thought that too, since in circuit the diode disappears into the coil resistance that is parallel.

[Enzo]

Sure, but I doubt there was any danger from contacts welding in the signal path of that amp. And for that matter, speed wouldn't be an issue either. But the diode is ther to protect the transistor or IC that drives the relay coil.

[Jon Snell]

The beefier diode should be tougher, but adding the flyback does slow down the contacts, check out the bottom arrangement


the added zener is supposed to help the relay open faster and with full force and decreases the chance of the contacts welding closed in some applications.
this is from a big doc on relays from Panasonic:

https://www.panasonic-electric-works...n_relay_en.pdf

The diode in question goes across the coil, not the load.

A little confusion perhaps.

[Zouto]

Agree, it was likely a 1N4148, but 1N4007 would be fine as well.

That would be a very unusual failure, by the way.

Yeah, the amp seems to have some issues with the
switched PSU for the heaters, since there was occasional multiple clicking of that relay near D3 when switching from off to standby. Also the Pilot Light is off since then, all fuses are ok. The amp came with a blown 500mA fuse, but was working fine after replacing all tubes, filter caps seem to be ok. It‘s a pity that no complete schematics are available. A Bogner replacement for the switched PSU for the heaters is also unobtainable.

[vintagekiki]

Since there‘s no schematic available

https://www.freestompboxes.org/viewtopic.php?f=2&p=38561
Bogner Shiva schematic
Bogner Shiva.pdf
Bognor_shiva.pdf

https://ampgarage.com/forum/viewtopic.php?t=26615
Bogner shiva schematic

https://elektrotanya.com/bogner_shiva_sch.pdf/download.html
https://elektrotanya.com/bogner_shiva._hand_drawn_sch.pdf/download.html

Bognor_shiva.pdf

[Zouto]

https://www.freestompboxes.org/viewtopic.php?f=2&p=38561
Bogner Shiva schematic
Bogner Shiva.pdf
Bognor_shiva.pdf

https://ampgarage.com/forum/viewtopic.php?t=26615
Bogner shiva schematic

https://elektrotanya.com/bogner_shiva_sch.pdf/download.html
https://elektrotanya.com/bogner_shiva._hand_drawn_sch.pdf/download.html

Bognor_shiva.pdf

Thanks, I also have those, but there‘s no schemo with all the power supplies and the switched PSU for the heaters. I swapped the blown diode with an UF4007, the amp’s just warming up at the moment, biasing will follow. There‘s a small trimpot on the switched heater PSU board, no Idea, what‘s it good for exactly, heater voltage probably.

[vintagekiki]

... no schemo with all the power supplies ... small trimpot on the switched heater PSU board, no Idea, what‘s it good for exactly, heater voltage probably.

As far as can be noticed, for Bogner there are only partial schematics hand-drawn without power supply schematic.

If negative voltage is on small trimpot, set the bias with it.
https://www.thegearpage.net/board/index.php?threads/bogner-shiva-bias-trim-pot-location.1879392/


http://web.archive.org/web/20140806224910/http://bognerampforum.informe.com/shiva-df4.html
_{^{Discussion of the Bogner Shiva and 20th Anniversary model}}

https://music-electronics-forum.com/forum/schematic-requests/34769-bogner-shiva-and-acstacy-service-manual-needed-and-other-scematics