What is this for around the output tube?

GERPUD · Post by **GERPUD** » Mon Mar 02, 2015 12:32 pm

Hi
See picture.
Anybody have an idea of the purpose of theses components?
I can t find something similar anywhere....
Thanks!

Stevem · Post by **Stevem** » Mon Mar 02, 2015 12:49 pm

You need to post a better image, I can not enlarge it and keep it clear !

GERPUD · Post by **GERPUD** » Mon Mar 02, 2015 12:56 pm

https://fmic1.zendesk.com/attachments/t ... agrams.pdf
Group R33, R34, R35, C23, C24

sluckey · Post by **sluckey** » Mon Mar 02, 2015 12:57 pm

I've never seen that.

martin manning · Post by **martin manning** » Mon Mar 02, 2015 1:01 pm

Zobel network, I think.

GERPUD · Post by **GERPUD** » Mon Mar 02, 2015 1:05 pm

It take a fair amount of place on the pcb, it uses the biggest non polarized caps of the amp and i have no idea of its uses....

GERPUD · Post by **GERPUD** » Mon Mar 02, 2015 1:09 pm

martin manning wrote:Zobel network, I think.

In a tube amp?
Why?

pdf64 · Post by **pdf64** » Mon Mar 02, 2015 1:17 pm

My guess is that (being as it's SE), the network is feeding phase shifted B+ ripple to the cathode, in order for it to achieve a degree of ripple cancellation.

GERPUD · Post by **GERPUD** » Mon Mar 02, 2015 2:10 pm

Ok, that would be a kind of negative feedback of the noise signal in the power supply that would be needed when using bad power supply design?
Since i have added a filtering stage with a choke, maybe this thing is not needed anymore...

pdf64 · Post by **pdf64** » Mon Mar 02, 2015 2:26 pm

Ok, that would be a kind of negative feedback of the noise signal in the power supply that would be needed when using bad power supply design?

I can't see that it's part of a feedback loop; rather it's simply passively mixing some ripple into the signal path (at the power tube cathode), such that it will cancel itself out at the plate.

If you've amended the B+, eg such that there's a pi filter feeding the plate node, then (as it's passive) the network may be increasing the hum level!

GERPUD · Post by **GERPUD** » Mon Mar 02, 2015 3:04 pm

I've tried deconnecting C24 and R35.
No difference on the noise.
No difference in the sound.
Looks like a very useless network...

Leo_Gnardo · Post by **Leo_Gnardo** » Mon Mar 02, 2015 3:19 pm

pdf64 wrote:My guess is that (being as it's SE), the network is feeding phase shifted B+ ripple to the cathode, in order for it to achieve a degree of ripple cancellation.

Some engineer's clever solution for avoiding an expensive, heavy filter choke in the power surprise. Now you've improved the PS filtering with an extra cap & choke, the "bandaid" network has no use.

A cap 'n choke pre-filter does wonders for Champs and similar amps, IMHO well worth doing, good work GERPUD!

GERPUD · Post by **GERPUD** » Mon Mar 02, 2015 4:50 pm

You're right.
It is a cheap amp, but it seems to not be a lazy cut and paste from other simple SE tube amps.
Indonesia seems to have hard working engineers...

matt h · Post by **matt h** » Mon Mar 02, 2015 11:10 pm

(deleted)

The Amp Garage

What is this for around the output tube?

What is this for around the output tube?

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