Bogner Shiva

[bsco]

Scoured the net for a schematic for this but came up empty..anybody out there have one by chance....I think this is pretty new.....or if anybody has any bias info......
Cheers,
Bernie

[Tone Meister]

Bogner schematics are proprietary, according to Charlie at Bogner, and good luck getting real-world technical info from them unless they have changed in the last year or two. I sold both my XTC Classic and Shiva because technical info is all but unavailable and will never own another Bogner.

Bogner's method of biasing the Shiva is uncommon. Essentially what you will end up doing is biasing it quite cold since the bias will increase substantially once the chassis is re-installed inside the cabinet. You will need to verify this for yourself, but I remember that my Shiva would draw 12-14 mA more current when the chassis was in the cabinet than on the bench. Bogner will tell you the same thing, but that's about all they'll tell you, in my experience. It's pretty much trial and error, but with the high plate voltage and assuming EL34 power tubes, you'll want to end up with about 32 mA when the amp is hot.

I hope you have lots of patience. Good luck!

[Tone Meister]

Forgot I had this hand-drawn schem that was posted here some time back. Also, here is a thread with links that may be helpful: http://music-electronics-forum.com/t33900/

[Enzo]

Or here too

http://bmamps.com/Schematics/Bogner/Shiva.pdf

[Mick Bailey]

I see a lot of stuff missing from those schematics compared to the actual amps, so wouldn't rely on them for service work.

[bsco]

Thanks guys for the info...I think I'll install a couple of 1 ohm 1W 1% resistors off the cathodes and adjust the bias to read about 15ma below the max level in accordance with the plate voltage...then I will probably enclose the amp by putting a cardboard box down over it and let it heat up and re-check the bias.....that should give me an idea as to where the bias voltage will sit...if anybody has a better suggestion I am all ears.....
Cheers,
Bernie

[Tone Meister]

...then I will probably enclose the amp by putting a cardboard box down over it and let it heat up and re-check the bias.....that should give me an idea as to where the bias voltage will sit...if anybody has a better suggestion I am all ears...

I was gonna suggest exactly the same thing. Over time, that's what I ended up doing and it'll give you a good approximation.

[J M Fahey]

d of biasing the Shiva is uncommon. Essentially what you will end up doing is biasing it quite cold since the bias will increase substantially once the chassis is re-installed inside the cabinet. You will need to verify this for yourself, but I remember that my Shiva would draw 12-14 mA more current when the chassis was in the cabinet than on the bench. Bogner will tell you the same thing,

They-must-be-kidding !!!!

[Tone Meister]

Nope, and they actually think that's normal.

[TimmyP1955]

I put 1 Ohm resistors on the cathodes, cranked it for about 5 minutes, and set the bias. Can't remember what I set it at though - thought I had notes on the subject but.... (The cranking was Bogner's idea, the resistors were mine.)

[bsco]

I put 1 Ohm resistors on the cathodes, cranked it for about 5 minutes, and set the bias. Can't remember what I set it at though - thought I had notes on the subject but.... (The cranking was Bogner's idea, the resistors were mine.)

The owner of this amp "Finally" got his set of matched tubes in.......so now I am going to try and get this sorted out......
Cheers

[bsco]

installed the tubes last night...I installed two 1ohm, 1 watt 1 percent resistors on the cathodes.....Fired it up and just took some static measurements....plate voltage at 524V.........voltage drop across the 1 ohm resistors.......7.8Mv and 9.6Mv........the bias pot was not touched...it is in the factory set position.......which when looking at the pot, it is turned all the way to the right when viewed from the front of the amp.....with the chassis upside down.......turning the pot to the left decreases the voltage drop across the cathode resistors....
I did try a Les Paul and it sounds good.......but the voltage drops are not really making any sense......Thoughts anybody??

[g1]

Hot or cold?
Did you check the bias on the old tubes, or do you still have them so you can compare?
How does it look for crossover notch?

[Jazz P Bass]

"7.8Mv and 9.6Mv........"

Not exactly "matched" now are they?

[bsco]

Hot or cold?
Did you check the bias on the old tubes, or do you still have them so you can compare?
How does it look for crossover notch?

NO....one of the tubes are blown.....milky white color inside...I was going to re-install the other original tube to see what it draws....