Page 1 of 1

Reducing Heater Voltage?

Posted: Wed Oct 24, 2018 1:57 pm
by revolver1
[Image][/url]

Re: Reducing Heater Voltage?

Posted: Wed Oct 24, 2018 2:13 pm
by revolver1
So I've powered it up hooked up to the 220v tap with a wall voltage of 230v and I'm getting 525Vdc out of the rectifier.

Across the heaters I'm getting 7.23Vac and 3.61Vac on either side. I did some rough calcs and rounded up a bit I went for .3 Ohms on either side of the heater wires to try get down to 6.3Vac. (Now doubting my calcs).

So I got two .14 and two .16 Ohm resistors and soldered two together in series aiming for a total of .3 Ohm I measured each set and they both came in at .6 Ohms, I then gator clipped them in to see what I'd get and to my suprise It does absolutely nothing, nada still got the same voltages.

So then I soldered together 5 resistors and clipped them in on each side and I't did a bit but not alot. I have now ordered some larger 3Watt resistors 1 Ohm and up, I'm just not sure I'm doing the right thing?

Re: Reducing Heater Voltage?

Posted: Mon Oct 29, 2018 4:31 am
by revolver1
Tubes need to be installed to see any reduction....

Re: Reducing Heater Voltage?

Posted: Tue Oct 30, 2018 7:35 pm
by danman
Yes, without a load, there is no voltage drop across the resistors.

Re: Reducing Heater Voltage?

Posted: Tue Oct 30, 2018 11:02 pm
by RockinRocket
You said in another post your were looking for head room?

I don't know if dumping more voltage in to a lowervolt tap is the way to go.. I would assume less life from the power transformer could be expected. May last a life time though :what: :what:

Re: Reducing Heater Voltage?

Posted: Wed Oct 31, 2018 3:42 am
by revolver1
I was going for a West Coast modded amp but in the 50w format. I've posted a little bit in the 6550 Experience post in the Hendrix section but now it's wrapped up I need to finnish off the build journel I started a year ago in the 50w section.

I needed high plate voltage so I went for the Classic Tone but i over looked the fact it only has 220v or 240v primary taps and I'm on 230v.

As it turns out I wired to the 240v tap, the heater voltage is about right and i have 460v to 466v on the plates. Its one hot PT....

Re: Reducing Heater Voltage?

Posted: Wed Oct 31, 2018 7:30 am
by Roe
the filter caps only handle 500v anyway, so the 240v primary is the best solution.

Re: Reducing Heater Voltage?

Posted: Wed Oct 31, 2018 7:33 am
by Roe
measure heater voltages with the tubes connected

Re: Reducing Heater Voltage?

Posted: Fri Apr 12, 2019 7:58 pm
by awangotango
if all else fails, variac it down 10%. but I seem to recall a method to strictly attack/adjust heater voltage,....

Re: Reducing Heater Voltage?

Posted: Wed Nov 13, 2019 5:32 am
by bhyatt1
I had an issue with high heater voltages on my bassman and was advised to use 2x120-150mOhm resistors on the heater wires to drop the voltage. Worked out great.

Re: Reducing Heater Voltage?

Posted: Thu Apr 02, 2020 1:05 pm
by BibbieMok
Hi...the power resistor method is definitely the easiest. With the KT88s drawing 1.6A and the 6N1P pulling 0.6A just make sure it is big enough!
As Eric said you could convert the heaters to DC and use a couple of smaller resistors and some caps to filter the current. However with this design DC heaters aren't at all necessary to have a hum-free amp.