Re: Reducing AC Filament Hum On A 5W SE

On 27 Mar, 13:25, "Phil S." <psymo...@xxxxxxxxxxx> wrote:
"Mr. Green" <cl...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message

news:1f2e84aa-d98e-4537-9124-f596b582453e@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx





On 27 Mar, 09:51, jh <j...@xxxxxx> wrote:
Mr. Green schrieb:

I've looked at several options and have narrowed it down to four
variations on adding a DC reference voltage.

Could do the Weber mod make up a volage divider to supply 40V dc to
the heater coils centre tap.

Or, do the same mod but forget the centre tap and add a pair of 100K
resistors to produce an artificle centre (may be less risk of frying
transformer?).

Or, connect centre tap or resistors to power tube cathode supply
(19V).

I suppose I'm mainly wondering about the chances of burning out the
transformer. Would a 2W dropping resistor with a 0.6W, metal film,
load resistor be a good combination for a voltage divider straight
onto the heater centre tap?

Green

Hello Mr. Green,

you've got solutions, but what is your real problem?

propably hum. are you sure it's filament hum?

Jochen- Hide quoted text -

- Show quoted text -

Yep - I believe it is. It's nothing major. I built this little amp as
a learning project. Love to fiddle so, thought I'd see how quiet I
could get it.

Thanks for the reply, Green

Green: assuming you are correct in your assessement [note 1], look around
for an old cell phone charger.  These typically put out 5.7vdc @ 800mA - 1A,
which should be enough to power two tubes (I'm assuming a 12AX7 and a 6V6).
Use it to test your assumption rather than doing something fancy that
doesn't really work.  As an alternative, you can buy yourself a 6V lantern
battery for the test.

If it works, you can figure out how to keep that cell phone transformer
inside the amp and wire it parallel to your main PT supply.  Not fancy or
elegant, but it's quick and easy.

[Note 1]: I'm not easily convinced it is the filament supply.  See what WB
asks?  Make sure before you start soldering away.- Hide quoted text -

- Show quoted text -

Hi,

Nice ideas for testing out a dc supply on the filament circuit,
thanks. Swapping the transformer centre tap from earth to the power
tube cathode is pretty straight forward though. If it does nothing
I'll just put the wiring back to original.

Either way I'll post the results.

Thanks, Green (but not as green as I'm cabbage looking ;-)
.

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